€•¯Ó      Œsphinx.addnodes”Œdocument”“”)”}”(Œ	rawsource”Œ ”Œchildren”]”(Œtranslations”ŒLanguagesNode”“”)”}”(hhh]”(h Œpending_xref”“”)”}”(hhh]”Œdocutils.nodes”ŒText”“”ŒChinese (Simplified)”…””}”Œparent”hsbaŒ
attributes”}”(Œids”]”Œclasses”]”Œnames”]”Œdupnames”]”Œbackrefs”]”Œ	refdomain”Œstd”Œreftype”Œdoc”Œ	reftarget”Œ'/translations/zh_CN/dev-tools/checkuapi”Œmodname”NŒ	classname”NŒrefexplicit”ˆuŒtagname”hhhubh)”}”(hhh]”hŒChinese (Traditional)”…””}”hh2sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ'/translations/zh_TW/dev-tools/checkuapi”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒItalian”…””}”hhFsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ'/translations/it_IT/dev-tools/checkuapi”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒJapanese”…””}”hhZsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ'/translations/ja_JP/dev-tools/checkuapi”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒKorean”…””}”hhnsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ'/translations/ko_KR/dev-tools/checkuapi”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒSpanish”…””}”hh‚sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ'/translations/sp_SP/dev-tools/checkuapi”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubeh}”(h]”h ]”h"]”h$]”h&]”Œcurrent_language”ŒEnglish”uh1h
hhŒ	_document”hŒsource”NŒline”NubhŒcomment”“”)”}”(hŒ%SPDX-License-Identifier: GPL-2.0-only”h]”hŒ%SPDX-License-Identifier: GPL-2.0-only”…””}”hh£sbah}”(h]”h ]”h"]”h$]”h&]”Œ	xml:space”Œpreserve”uh1h¡hhhžhhŸŒA/var/lib/git/docbuild/linux/Documentation/dev-tools/checkuapi.rst”h KubhŒsection”“”)”}”(hhh]”(hŒtitle”“”)”}”(hŒUAPI Checker”h]”hŒUAPI Checker”…””}”(hh»hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hh¶hžhhŸh³h KubhŒ	paragraph”“”)”}”(hŒ˜The UAPI checker (``scripts/check-uapi.sh``) is a shell script which
checks UAPI header files for userspace backwards-compatibility across
the git tree.”h]”(hŒThe UAPI checker (”…””}”(hhËhžhhŸNh NubhŒliteral”“”)”}”(hŒ``scripts/check-uapi.sh``”h]”hŒscripts/check-uapi.sh”…””}”(hhÕhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÓhhËubhŒm) is a shell script which
checks UAPI header files for userspace backwards-compatibility across
the git tree.”…””}”(hhËhžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h Khh¶hžhubhµ)”}”(hhh]”(hº)”}”(hŒOptions”h]”hŒOptions”…””}”(hhðhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hhíhžhhŸh³h KubhÊ)”}”(hŒOThis section will describe the options with which ``check-uapi.sh``
can be run.”h]”(hŒ2This section will describe the options with which ”…””}”(hhþhžhhŸNh NubhÔ)”}”(hŒ``check-uapi.sh``”h]”hŒcheck-uapi.sh”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÓhhþubhŒ
can be run.”…””}”(hhþhžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h KhhíhžhubhÊ)”}”(hŒUsage::”h]”hŒUsage:”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h KhhíhžhubhŒliteral_block”“”)”}”(hŒNcheck-uapi.sh [-b BASE_REF] [-p PAST_REF] [-j N] [-l ERROR_LOG] [-i] [-q] [-v]”h]”hŒNcheck-uapi.sh [-b BASE_REF] [-p PAST_REF] [-j N] [-l ERROR_LOG] [-i] [-q] [-v]”…””}”hj.  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j,  hŸh³h KhhíhžhubhÊ)”}”(hŒAvailable options::”h]”hŒAvailable options:”…””}”(hj<  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h Khhíhžhubj-  )”}”(hX4  -b BASE_REF    Base git reference to use for comparison. If unspecified or empty,
               will use any dirty changes in tree to UAPI files. If there are no
               dirty changes, HEAD will be used.
-p PAST_REF    Compare BASE_REF to PAST_REF (e.g. -p v6.1). If unspecified or empty,
               will use BASE_REF^1. Must be an ancestor of BASE_REF. Only headers
               that exist on PAST_REF will be checked for compatibility.
-j JOBS        Number of checks to run in parallel (default: number of CPU cores).
-l ERROR_LOG   Write error log to file (default: no error log is generated).
-i             Ignore ambiguous changes that may or may not break UAPI compatibility.
-q             Quiet operation.
-v             Verbose operation (print more information about each header being checked).”h]”hX4  -b BASE_REF    Base git reference to use for comparison. If unspecified or empty,
               will use any dirty changes in tree to UAPI files. If there are no
               dirty changes, HEAD will be used.
-p PAST_REF    Compare BASE_REF to PAST_REF (e.g. -p v6.1). If unspecified or empty,
               will use BASE_REF^1. Must be an ancestor of BASE_REF. Only headers
               that exist on PAST_REF will be checked for compatibility.
-j JOBS        Number of checks to run in parallel (default: number of CPU cores).
-l ERROR_LOG   Write error log to file (default: no error log is generated).
-i             Ignore ambiguous changes that may or may not break UAPI compatibility.
-q             Quiet operation.
-v             Verbose operation (print more information about each header being checked).”…””}”hjJ  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j,  hŸh³h KhhíhžhubhÊ)”}”(hŒEnvironmental args::”h]”hŒEnvironmental args:”…””}”(hjX  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h K#hhíhžhubj-  )”}”(hŒABIDIFF  Custom path to abidiff binary
CC       C compiler (default is "gcc")
ARCH     Target architecture of C compiler (default is host arch)”h]”hŒABIDIFF  Custom path to abidiff binary
CC       C compiler (default is "gcc")
ARCH     Target architecture of C compiler (default is host arch)”…””}”hjf  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j,  hŸh³h K%hhíhžhubhÊ)”}”(hŒExit codes::”h]”hŒExit codes:”…””}”(hjt  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h K)hhíhžhubj-  )”}”(hŒ=0) Success
1) ABI difference detected
2) Prerequisite not met”h]”hŒ=0) Success
1) ABI difference detected
2) Prerequisite not met”…””}”hj‚  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j,  hŸh³h K+hhíhžhubeh}”(h]”Œoptions”ah ]”h"]”Œoptions”ah$]”h&]”uh1h´hh¶hžhhŸh³h Kubhµ)”}”(hhh]”(hº)”}”(hŒExamples”h]”hŒExamples”…””}”(hj›  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hj˜  hžhhŸh³h K0ubhµ)”}”(hhh]”(hº)”}”(hŒBasic Usage”h]”hŒBasic Usage”…””}”(hj¬  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hj©  hžhhŸh³h K3ubhÊ)”}”(hŒ]First, let's try making a change to a UAPI header file that obviously
won't break userspace::”h]”hŒ`First, letâ€™s try making a change to a UAPI header file that obviously
wonâ€™t break userspace:”…””}”(hjº  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h K5hj©  hžhubj-  )”}”(hX­  cat << 'EOF' | patch -l -p1
--- a/include/uapi/linux/acct.h
+++ b/include/uapi/linux/acct.h
@@ -21,7 +21,9 @@
 #include <asm/param.h>
 #include <asm/byteorder.h>

-/*
+#define FOO
+
+/*
  *  comp_t is a 16-bit "floating" point number with a 3-bit base 8
  *  exponent and a 13-bit fraction.
  *  comp2_t is 24-bit with 5-bit base 2 exponent and 20 bit fraction
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
EOF”h]”hX­  cat << 'EOF' | patch -l -p1
--- a/include/uapi/linux/acct.h
+++ b/include/uapi/linux/acct.h
@@ -21,7 +21,9 @@
 #include <asm/param.h>
 #include <asm/byteorder.h>

-/*
+#define FOO
+
+/*
  *  comp_t is a 16-bit "floating" point number with a 3-bit base 8
  *  exponent and a 13-bit fraction.
  *  comp2_t is 24-bit with 5-bit base 2 exponent and 20 bit fraction
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
EOF”…””}”hjÈ  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j,  hŸh³h K8hj©  hžhubhÊ)”}”(hŒ'Now, let's use the script to validate::”h]”hŒ(Now, letâ€™s use the script to validate:”…””}”(hjÖ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h KIhj©  hžhubj-  )”}”(hX  % ./scripts/check-uapi.sh
Installing user-facing UAPI headers from dirty tree... OK
Installing user-facing UAPI headers from HEAD... OK
Checking changes to UAPI headers between HEAD and dirty tree...
All 912 UAPI headers compatible with x86 appear to be backwards compatible”h]”hX  % ./scripts/check-uapi.sh
Installing user-facing UAPI headers from dirty tree... OK
Installing user-facing UAPI headers from HEAD... OK
Checking changes to UAPI headers between HEAD and dirty tree...
All 912 UAPI headers compatible with x86 appear to be backwards compatible”…””}”hjä  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j,  hŸh³h KKhj©  hžhubhÊ)”}”(hŒ7Let's add another change that *might* break userspace::”h]”(hŒ Letâ€™s add another change that ”…””}”(hjò  hžhhŸNh NubhŒemphasis”“”)”}”(hŒ*might*”h]”hŒmight”…””}”(hjü  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jú  hjò  ubhŒ break userspace:”…””}”(hjò  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h KQhj©  hžhubj-  )”}”(hXÕ  cat << 'EOF' | patch -l -p1
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -74,7 +74,7 @@ struct bpf_insn {
        __u8    dst_reg:4;      /* dest register */
        __u8    src_reg:4;      /* source register */
        __s16   off;            /* signed offset */
-       __s32   imm;            /* signed immediate constant */
+       __u32   imm;            /* unsigned immediate constant */
 };

 /* Key of an a BPF_MAP_TYPE_LPM_TRIE entry */
EOF”h]”hXÕ  cat << 'EOF' | patch -l -p1
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -74,7 +74,7 @@ struct bpf_insn {
        __u8    dst_reg:4;      /* dest register */
        __u8    src_reg:4;      /* source register */
        __s16   off;            /* signed offset */
-       __s32   imm;            /* signed immediate constant */
+       __u32   imm;            /* unsigned immediate constant */
 };

 /* Key of an a BPF_MAP_TYPE_LPM_TRIE entry */
EOF”…””}”hj  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j,  hŸh³h KShj©  hžhubhÊ)”}”(hŒThe script will catch this::”h]”hŒThe script will catch this:”…””}”(hj"  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h Kahj©  hžhubj-  )”}”(hX  % ./scripts/check-uapi.sh
Installing user-facing UAPI headers from dirty tree... OK
Installing user-facing UAPI headers from HEAD... OK
Checking changes to UAPI headers between HEAD and dirty tree...
==== ABI differences detected in include/linux/bpf.h from HEAD -> dirty tree ====
    [C] 'struct bpf_insn' changed:
      type size hasn't changed
      1 data member change:
        type of '__s32 imm' changed:
          typedef name changed from __s32 to __u32 at int-ll64.h:27:1
          underlying type 'int' changed:
            type name changed from 'int' to 'unsigned int'
            type size hasn't changed
==================================================================================

error - 1/912 UAPI headers compatible with x86 appear _not_ to be backwards compatible”h]”hX  % ./scripts/check-uapi.sh
Installing user-facing UAPI headers from dirty tree... OK
Installing user-facing UAPI headers from HEAD... OK
Checking changes to UAPI headers between HEAD and dirty tree...
==== ABI differences detected in include/linux/bpf.h from HEAD -> dirty tree ====
    [C] 'struct bpf_insn' changed:
      type size hasn't changed
      1 data member change:
        type of '__s32 imm' changed:
          typedef name changed from __s32 to __u32 at int-ll64.h:27:1
          underlying type 'int' changed:
            type name changed from 'int' to 'unsigned int'
            type size hasn't changed
==================================================================================

error - 1/912 UAPI headers compatible with x86 appear _not_ to be backwards compatible”…””}”hj0  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j,  hŸh³h Kchj©  hžhubhÊ)”}”(hX£  In this case, the script is reporting the type change because it could
break a userspace program that passes in a negative number. Now, let's
say you know that no userspace program could possibly be using a negative
value in ``imm``, so changing to an unsigned type there shouldn't hurt
anything. You can pass the ``-i`` flag to the script to ignore changes
in which the userspace backwards compatibility is ambiguous::”h]”(hŒãIn this case, the script is reporting the type change because it could
break a userspace program that passes in a negative number. Now, letâ€™s
say you know that no userspace program could possibly be using a negative
value in ”…””}”(hj>  hžhhŸNh NubhÔ)”}”(hŒ``imm``”h]”hŒimm”…””}”(hjF  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÓhj>  ubhŒT, so changing to an unsigned type there shouldnâ€™t hurt
anything. You can pass the ”…””}”(hj>  hžhhŸNh NubhÔ)”}”(hŒ``-i``”h]”hŒ-i”…””}”(hjX  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÓhj>  ubhŒb flag to the script to ignore changes
in which the userspace backwards compatibility is ambiguous:”…””}”(hj>  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h Kthj©  hžhubj-  )”}”(hX  % ./scripts/check-uapi.sh -i
Installing user-facing UAPI headers from dirty tree... OK
Installing user-facing UAPI headers from HEAD... OK
Checking changes to UAPI headers between HEAD and dirty tree...
All 912 UAPI headers compatible with x86 appear to be backwards compatible”h]”hX  % ./scripts/check-uapi.sh -i
Installing user-facing UAPI headers from dirty tree... OK
Installing user-facing UAPI headers from HEAD... OK
Checking changes to UAPI headers between HEAD and dirty tree...
All 912 UAPI headers compatible with x86 appear to be backwards compatible”…””}”hjp  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j,  hŸh³h K{hj©  hžhubhÊ)”}”(hŒ>Now, let's make a similar change that *will* break userspace::”h]”(hŒ(Now, letâ€™s make a similar change that ”…””}”(hj~  hžhhŸNh Nubjû  )”}”(hŒ*will*”h]”hŒwill”…””}”(hj†  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jú  hj~  ubhŒ break userspace:”…””}”(hj~  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h Khj©  hžhubj-  )”}”(hXÍ  cat << 'EOF' | patch -l -p1
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -71,8 +71,8 @@ enum {

 struct bpf_insn {
        __u8    code;           /* opcode */
-       __u8    dst_reg:4;      /* dest register */
        __u8    src_reg:4;      /* source register */
+       __u8    dst_reg:4;      /* dest register */
        __s16   off;            /* signed offset */
        __s32   imm;            /* signed immediate constant */
 };
EOF”h]”hXÍ  cat << 'EOF' | patch -l -p1
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -71,8 +71,8 @@ enum {

 struct bpf_insn {
        __u8    code;           /* opcode */
-       __u8    dst_reg:4;      /* dest register */
        __u8    src_reg:4;      /* source register */
+       __u8    dst_reg:4;      /* dest register */
        __s16   off;            /* signed offset */
        __s32   imm;            /* signed immediate constant */
 };
EOF”…””}”hjž  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j,  hŸh³h Kƒhj©  hžhubhÊ)”}”(hŒŠSince we're re-ordering an existing struct member, there's no ambiguity,
and the script will report the breakage even if you pass ``-i``::”h]”(hŒ†Since weâ€™re re-ordering an existing struct member, thereâ€™s no ambiguity,
and the script will report the breakage even if you pass ”…””}”(hj¬  hžhhŸNh NubhÔ)”}”(hŒ``-i``”h]”hŒ-i”…””}”(hj´  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÓhj¬  ubhŒ:”…””}”(hj¬  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h K’hj©  hžhubj-  )”}”(hXº  % ./scripts/check-uapi.sh -i
Installing user-facing UAPI headers from dirty tree... OK
Installing user-facing UAPI headers from HEAD... OK
Checking changes to UAPI headers between HEAD and dirty tree...
==== ABI differences detected in include/linux/bpf.h from HEAD -> dirty tree ====
    [C] 'struct bpf_insn' changed:
      type size hasn't changed
      2 data member changes:
        '__u8 dst_reg' offset changed from 8 to 12 (in bits) (by +4 bits)
        '__u8 src_reg' offset changed from 12 to 8 (in bits) (by -4 bits)
==================================================================================

error - 1/912 UAPI headers compatible with x86 appear _not_ to be backwards compatible”h]”hXº  % ./scripts/check-uapi.sh -i
Installing user-facing UAPI headers from dirty tree... OK
Installing user-facing UAPI headers from HEAD... OK
Checking changes to UAPI headers between HEAD and dirty tree...
==== ABI differences detected in include/linux/bpf.h from HEAD -> dirty tree ====
    [C] 'struct bpf_insn' changed:
      type size hasn't changed
      2 data member changes:
        '__u8 dst_reg' offset changed from 8 to 12 (in bits) (by +4 bits)
        '__u8 src_reg' offset changed from 12 to 8 (in bits) (by -4 bits)
==================================================================================

error - 1/912 UAPI headers compatible with x86 appear _not_ to be backwards compatible”…””}”hjÌ  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j,  hŸh³h K•hj©  hžhubhÊ)”}”(hŒDLet's commit the breaking change, then commit the innocuous change::”h]”hŒELetâ€™s commit the breaking change, then commit the innocuous change:”…””}”(hjÚ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h K£hj©  hžhubj-  )”}”(hXE  % git commit -m 'Breaking UAPI change' include/uapi/linux/bpf.h
[detached HEAD f758e574663a] Breaking UAPI change
 1 file changed, 1 insertion(+), 1 deletion(-)
% git commit -m 'Innocuous UAPI change' include/uapi/linux/acct.h
[detached HEAD 2e87df769081] Innocuous UAPI change
 1 file changed, 3 insertions(+), 1 deletion(-)”h]”hXE  % git commit -m 'Breaking UAPI change' include/uapi/linux/bpf.h
[detached HEAD f758e574663a] Breaking UAPI change
 1 file changed, 1 insertion(+), 1 deletion(-)
% git commit -m 'Innocuous UAPI change' include/uapi/linux/acct.h
[detached HEAD 2e87df769081] Innocuous UAPI change
 1 file changed, 3 insertions(+), 1 deletion(-)”…””}”hjè  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j,  hŸh³h K¥hj©  hžhubhÊ)”}”(hŒ3Now, let's run the script again with no arguments::”h]”hŒ4Now, letâ€™s run the script again with no arguments:”…””}”(hjö  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h K¬hj©  hžhubj-  )”}”(hX
  % ./scripts/check-uapi.sh
Installing user-facing UAPI headers from HEAD... OK
Installing user-facing UAPI headers from HEAD^1... OK
Checking changes to UAPI headers between HEAD^1 and HEAD...
All 912 UAPI headers compatible with x86 appear to be backwards compatible”h]”hX
  % ./scripts/check-uapi.sh
Installing user-facing UAPI headers from HEAD... OK
Installing user-facing UAPI headers from HEAD^1... OK
Checking changes to UAPI headers between HEAD^1 and HEAD...
All 912 UAPI headers compatible with x86 appear to be backwards compatible”…””}”hj  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j,  hŸh³h K®hj©  hžhubhÊ)”}”(hX}  It doesn't catch any breaking change because, by default, it only
compares ``HEAD`` to ``HEAD^1``. The breaking change was committed on
``HEAD~2``. If we wanted the search scope to go back further, we'd have to
use the ``-p`` option to pass a different past reference. In this case,
let's pass ``-p HEAD~2`` to the script so it checks UAPI changes between
``HEAD~2`` and ``HEAD``::”h]”(hŒMIt doesnâ€™t catch any breaking change because, by default, it only
compares ”…””}”(hj  hžhhŸNh NubhÔ)”}”(hŒ``HEAD``”h]”hŒHEAD”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÓhj  ubhŒ to ”…””}”(hj  hžhhŸNh NubhÔ)”}”(hŒ
``HEAD^1``”h]”hŒHEAD^1”…””}”(hj,  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÓhj  ubhŒ'. The breaking change was committed on
”…””}”(hj  hžhhŸNh NubhÔ)”}”(hŒ
``HEAD~2``”h]”hŒHEAD~2”…””}”(hj>  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÓhj  ubhŒK. If we wanted the search scope to go back further, weâ€™d have to
use the ”…””}”(hj  hžhhŸNh NubhÔ)”}”(hŒ``-p``”h]”hŒ-p”…””}”(hjP  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÓhj  ubhŒG option to pass a different past reference. In this case,
letâ€™s pass ”…””}”(hj  hžhhŸNh NubhÔ)”}”(hŒ``-p HEAD~2``”h]”hŒ	-p HEAD~2”…””}”(hjb  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÓhj  ubhŒ1 to the script so it checks UAPI changes between
”…””}”(hj  hžhhŸNh NubhÔ)”}”(hŒ
``HEAD~2``”h]”hŒHEAD~2”…””}”(hjt  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÓhj  ubhŒ and ”…””}”(hj  hžhhŸNh NubhÔ)”}”(hŒ``HEAD``”h]”hŒHEAD”…””}”(hj†  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÓhj  ubhŒ:”…””}”(hj  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h K´hj©  hžhubj-  )”}”(hX±  % ./scripts/check-uapi.sh -p HEAD~2
Installing user-facing UAPI headers from HEAD... OK
Installing user-facing UAPI headers from HEAD~2... OK
Checking changes to UAPI headers between HEAD~2 and HEAD...
==== ABI differences detected in include/linux/bpf.h from HEAD~2 -> HEAD ====
    [C] 'struct bpf_insn' changed:
      type size hasn't changed
      2 data member changes:
        '__u8 dst_reg' offset changed from 8 to 12 (in bits) (by +4 bits)
        '__u8 src_reg' offset changed from 12 to 8 (in bits) (by -4 bits)
==============================================================================

error - 1/912 UAPI headers compatible with x86 appear _not_ to be backwards compatible”h]”hX±  % ./scripts/check-uapi.sh -p HEAD~2
Installing user-facing UAPI headers from HEAD... OK
Installing user-facing UAPI headers from HEAD~2... OK
Checking changes to UAPI headers between HEAD~2 and HEAD...
==== ABI differences detected in include/linux/bpf.h from HEAD~2 -> HEAD ====
    [C] 'struct bpf_insn' changed:
      type size hasn't changed
      2 data member changes:
        '__u8 dst_reg' offset changed from 8 to 12 (in bits) (by +4 bits)
        '__u8 src_reg' offset changed from 12 to 8 (in bits) (by -4 bits)
==============================================================================

error - 1/912 UAPI headers compatible with x86 appear _not_ to be backwards compatible”…””}”hjž  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j,  hŸh³h K»hj©  hžhubhÊ)”}”(hŒ›Alternatively, we could have also run with ``-b HEAD~``. This would set the
base reference to ``HEAD~`` so then the script would compare it to ``HEAD~^1``.”h]”(hŒ+Alternatively, we could have also run with ”…””}”(hj¬  hžhhŸNh NubhÔ)”}”(hŒ``-b HEAD~``”h]”hŒ-b HEAD~”…””}”(hj´  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÓhj¬  ubhŒ'. This would set the
base reference to ”…””}”(hj¬  hžhhŸNh NubhÔ)”}”(hŒ	``HEAD~``”h]”hŒHEAD~”…””}”(hjÆ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÓhj¬  ubhŒ( so then the script would compare it to ”…””}”(hj¬  hžhhŸNh NubhÔ)”}”(hŒ``HEAD~^1``”h]”hŒHEAD~^1”…””}”(hjØ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÓhj¬  ubhŒ.”…””}”(hj¬  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h KÉhj©  hžhubeh}”(h]”Œbasic-usage”ah ]”h"]”Œbasic usage”ah$]”h&]”uh1h´hj˜  hžhhŸh³h K3ubhµ)”}”(hhh]”(hº)”}”(hŒArchitecture-specific Headers”h]”hŒArchitecture-specific Headers”…””}”(hjû  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hjø  hžhhŸh³h KÍubhÊ)”}”(hŒConsider this change::”h]”hŒConsider this change:”…””}”(hj	  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h KÏhjø  hžhubj-  )”}”(hX"  cat << 'EOF' | patch -l -p1
--- a/arch/arm64/include/uapi/asm/sigcontext.h
+++ b/arch/arm64/include/uapi/asm/sigcontext.h
@@ -70,6 +70,7 @@ struct sigcontext {
 struct _aarch64_ctx {
        __u32 magic;
        __u32 size;
+       __u32 new_var;
 };

 #define FPSIMD_MAGIC   0x46508001
EOF”h]”hX"  cat << 'EOF' | patch -l -p1
--- a/arch/arm64/include/uapi/asm/sigcontext.h
+++ b/arch/arm64/include/uapi/asm/sigcontext.h
@@ -70,6 +70,7 @@ struct sigcontext {
 struct _aarch64_ctx {
        __u32 magic;
        __u32 size;
+       __u32 new_var;
 };

 #define FPSIMD_MAGIC   0x46508001
EOF”…””}”hj  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j,  hŸh³h KÑhjø  hžhubhÊ)”}”(hŒÓThis is a change to an arm64-specific UAPI header file. In this example, I'm
running the script from an x86 machine with an x86 compiler, so, by default,
the script only checks x86-compatible UAPI header files::”h]”hŒÔThis is a change to an arm64-specific UAPI header file. In this example, Iâ€™m
running the script from an x86 machine with an x86 compiler, so, by default,
the script only checks x86-compatible UAPI header files:”…””}”(hj%  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h KÞhjø  hžhubj-  )”}”(hŒË% ./scripts/check-uapi.sh
Installing user-facing UAPI headers from dirty tree... OK
Installing user-facing UAPI headers from HEAD... OK
No changes to UAPI headers were applied between HEAD and dirty tree”h]”hŒË% ./scripts/check-uapi.sh
Installing user-facing UAPI headers from dirty tree... OK
Installing user-facing UAPI headers from HEAD... OK
No changes to UAPI headers were applied between HEAD and dirty tree”…””}”hj3  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j,  hŸh³h Kâhjø  hžhubhÊ)”}”(hŒdWith an x86 compiler, we can't check header files in ``arch/arm64``, so the
script doesn't even try.”h]”(hŒ7With an x86 compiler, we canâ€™t check header files in ”…””}”(hjA  hžhhŸNh NubhÔ)”}”(hŒ``arch/arm64``”h]”hŒ
arch/arm64”…””}”(hjI  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÓhjA  ubhŒ#, so the
script doesnâ€™t even try.”…””}”(hjA  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h Kçhjø  hžhubhÊ)”}”(hŒgIf we want to check the header file, we'll have to use an arm64 compiler and
set ``ARCH`` accordingly::”h]”(hŒSIf we want to check the header file, weâ€™ll have to use an arm64 compiler and
set ”…””}”(hja  hžhhŸNh NubhÔ)”}”(hŒ``ARCH``”h]”hŒARCH”…””}”(hji  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÓhja  ubhŒ accordingly:”…””}”(hja  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h Kêhjø  hžhubj-  )”}”(hXÞ  % CC=aarch64-linux-gnu-gcc ARCH=arm64 ./scripts/check-uapi.sh
Installing user-facing UAPI headers from dirty tree... OK
Installing user-facing UAPI headers from HEAD... OK
Checking changes to UAPI headers between HEAD and dirty tree...
==== ABI differences detected in include/asm/sigcontext.h from HEAD -> dirty tree ====
    [C] 'struct _aarch64_ctx' changed:
      type size changed from 64 to 96 (in bits)
      1 data member insertion:
        '__u32 new_var', at offset 64 (in bits) at sigcontext.h:73:1
    -- snip --
    [C] 'struct zt_context' changed:
      type size changed from 128 to 160 (in bits)
      2 data member changes (1 filtered):
        '__u16 nregs' offset changed from 64 to 96 (in bits) (by +32 bits)
        '__u16 __reserved[3]' offset changed from 80 to 112 (in bits) (by +32 bits)
=======================================================================================

error - 1/884 UAPI headers compatible with arm64 appear _not_ to be backwards compatible”h]”hXÞ  % CC=aarch64-linux-gnu-gcc ARCH=arm64 ./scripts/check-uapi.sh
Installing user-facing UAPI headers from dirty tree... OK
Installing user-facing UAPI headers from HEAD... OK
Checking changes to UAPI headers between HEAD and dirty tree...
==== ABI differences detected in include/asm/sigcontext.h from HEAD -> dirty tree ====
    [C] 'struct _aarch64_ctx' changed:
      type size changed from 64 to 96 (in bits)
      1 data member insertion:
        '__u32 new_var', at offset 64 (in bits) at sigcontext.h:73:1
    -- snip --
    [C] 'struct zt_context' changed:
      type size changed from 128 to 160 (in bits)
      2 data member changes (1 filtered):
        '__u16 nregs' offset changed from 64 to 96 (in bits) (by +32 bits)
        '__u16 __reserved[3]' offset changed from 80 to 112 (in bits) (by +32 bits)
=======================================================================================

error - 1/884 UAPI headers compatible with arm64 appear _not_ to be backwards compatible”…””}”hj  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j,  hŸh³h Kíhjø  hžhubhÊ)”}”(hX  We can see with ``ARCH`` and ``CC`` set properly for the file, the ABI
change is reported properly. Also notice that the total number of UAPI
header files checked by the script changes. This is because the number
of headers installed for arm64 platforms is different than x86.”h]”(hŒWe can see with ”…””}”(hj  hžhhŸNh NubhÔ)”}”(hŒ``ARCH``”h]”hŒARCH”…””}”(hj—  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÓhj  ubhŒ and ”…””}”(hj  hžhhŸNh NubhÔ)”}”(hŒ``CC``”h]”hŒCC”…””}”(hj©  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÓhj  ubhŒñ set properly for the file, the ABI
change is reported properly. Also notice that the total number of UAPI
header files checked by the script changes. This is because the number
of headers installed for arm64 platforms is different than x86.”…””}”(hj  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h M hjø  hžhubeh}”(h]”Œarchitecture-specific-headers”ah ]”h"]”Œarchitecture-specific headers”ah$]”h&]”uh1h´hj˜  hžhhŸh³h KÍubhµ)”}”(hhh]”(hº)”}”(hŒCross-Dependency Breakages”h]”hŒCross-Dependency Breakages”…””}”(hjÌ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hjÉ  hžhhŸh³h MubhÊ)”}”(hŒConsider this change::”h]”hŒConsider this change:”…””}”(hjÚ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h MhjÉ  hžhubj-  )”}”(hX›  cat << 'EOF' | patch -l -p1
--- a/include/uapi/linux/types.h
+++ b/include/uapi/linux/types.h
@@ -52,7 +52,7 @@ typedef __u32 __bitwise __wsum;
 #define __aligned_be64 __be64 __attribute__((aligned(8)))
 #define __aligned_le64 __le64 __attribute__((aligned(8)))

-typedef unsigned __bitwise __poll_t;
+typedef unsigned short __bitwise __poll_t;

 #endif /*  __ASSEMBLY__ */
 #endif /* _UAPI_LINUX_TYPES_H */
EOF”h]”hX›  cat << 'EOF' | patch -l -p1
--- a/include/uapi/linux/types.h
+++ b/include/uapi/linux/types.h
@@ -52,7 +52,7 @@ typedef __u32 __bitwise __wsum;
 #define __aligned_be64 __be64 __attribute__((aligned(8)))
 #define __aligned_le64 __le64 __attribute__((aligned(8)))

-typedef unsigned __bitwise __poll_t;
+typedef unsigned short __bitwise __poll_t;

 #endif /*  __ASSEMBLY__ */
 #endif /* _UAPI_LINUX_TYPES_H */
EOF”…””}”hjè  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j,  hŸh³h M
hjÉ  hžhubhÊ)”}”(hŒ—Here, we're changing a ``typedef`` in ``types.h``. This doesn't break
a UAPI in ``types.h``, but other UAPIs in the tree may break due to
this change::”h]”(hŒHere, weâ€™re changing a ”…””}”(hjö  hžhhŸNh NubhÔ)”}”(hŒ``typedef``”h]”hŒtypedef”…””}”(hjþ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÓhjö  ubhŒ in ”…””}”(hjö  hžhhŸNh NubhÔ)”}”(hŒ``types.h``”h]”hŒtypes.h”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÓhjö  ubhŒ!. This doesnâ€™t break
a UAPI in ”…””}”(hjö  hžhhŸNh NubhÔ)”}”(hŒ``types.h``”h]”hŒtypes.h”…””}”(hj"  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÓhjö  ubhŒ;, but other UAPIs in the tree may break due to
this change:”…””}”(hjö  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h MhjÉ  hžhubj-  )”}”(hXØ  % ./scripts/check-uapi.sh
Installing user-facing UAPI headers from dirty tree... OK
Installing user-facing UAPI headers from HEAD... OK
Checking changes to UAPI headers between HEAD and dirty tree...
==== ABI differences detected in include/linux/eventpoll.h from HEAD -> dirty tree ====
    [C] 'struct epoll_event' changed:
      type size changed from 96 to 80 (in bits)
      2 data member changes:
        type of '__poll_t events' changed:
          underlying type 'unsigned int' changed:
            type name changed from 'unsigned int' to 'unsigned short int'
            type size changed from 32 to 16 (in bits)
        '__u64 data' offset changed from 32 to 16 (in bits) (by -16 bits)
========================================================================================
include/linux/eventpoll.h did not change between HEAD and dirty tree...
It's possible a change to one of the headers it includes caused this error:
#include <linux/fcntl.h>
#include <linux/types.h>”h]”hXØ  % ./scripts/check-uapi.sh
Installing user-facing UAPI headers from dirty tree... OK
Installing user-facing UAPI headers from HEAD... OK
Checking changes to UAPI headers between HEAD and dirty tree...
==== ABI differences detected in include/linux/eventpoll.h from HEAD -> dirty tree ====
    [C] 'struct epoll_event' changed:
      type size changed from 96 to 80 (in bits)
      2 data member changes:
        type of '__poll_t events' changed:
          underlying type 'unsigned int' changed:
            type name changed from 'unsigned int' to 'unsigned short int'
            type size changed from 32 to 16 (in bits)
        '__u64 data' offset changed from 32 to 16 (in bits) (by -16 bits)
========================================================================================
include/linux/eventpoll.h did not change between HEAD and dirty tree...
It's possible a change to one of the headers it includes caused this error:
#include <linux/fcntl.h>
#include <linux/types.h>”…””}”hj:  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j,  hŸh³h MhjÉ  hžhubhÊ)”}”(hŒÈNote that the script noticed the failing header file did not change,
so it assumes one of its includes must have caused the breakage. Indeed,
we can see ``linux/types.h`` is used from ``eventpoll.h``.”h]”(hŒ™Note that the script noticed the failing header file did not change,
so it assumes one of its includes must have caused the breakage. Indeed,
we can see ”…””}”(hjH  hžhhŸNh NubhÔ)”}”(hŒ``linux/types.h``”h]”hŒlinux/types.h”…””}”(hjP  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÓhjH  ubhŒ is used from ”…””}”(hjH  hžhhŸNh NubhÔ)”}”(hŒ``eventpoll.h``”h]”hŒeventpoll.h”…””}”(hjb  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÓhjH  ubhŒ.”…””}”(hjH  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h M/hjÉ  hžhubeh}”(h]”Œcross-dependency-breakages”ah ]”h"]”Œcross-dependency breakages”ah$]”h&]”uh1h´hj˜  hžhhŸh³h Mubhµ)”}”(hhh]”(hº)”}”(hŒUAPI Header Removals”h]”hŒUAPI Header Removals”…””}”(hj…  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hj‚  hžhhŸh³h M4ubhÊ)”}”(hŒConsider this change::”h]”hŒConsider this change:”…””}”(hj“  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h M6hj‚  hžhubj-  )”}”(hX»  cat << 'EOF' | patch -l -p1
diff --git a/include/uapi/asm-generic/Kbuild b/include/uapi/asm-generic/Kbuild
index ebb180aac74e..a9c88b0a8b3b 100644
--- a/include/uapi/asm-generic/Kbuild
+++ b/include/uapi/asm-generic/Kbuild
@@ -31,6 +31,6 @@ mandatory-y += stat.h
 mandatory-y += statfs.h
 mandatory-y += swab.h
 mandatory-y += termbits.h
-mandatory-y += termios.h
+#mandatory-y += termios.h
 mandatory-y += types.h
 mandatory-y += unistd.h
EOF”h]”hX»  cat << 'EOF' | patch -l -p1
diff --git a/include/uapi/asm-generic/Kbuild b/include/uapi/asm-generic/Kbuild
index ebb180aac74e..a9c88b0a8b3b 100644
--- a/include/uapi/asm-generic/Kbuild
+++ b/include/uapi/asm-generic/Kbuild
@@ -31,6 +31,6 @@ mandatory-y += stat.h
 mandatory-y += statfs.h
 mandatory-y += swab.h
 mandatory-y += termbits.h
-mandatory-y += termios.h
+#mandatory-y += termios.h
 mandatory-y += types.h
 mandatory-y += unistd.h
EOF”…””}”hj¡  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j,  hŸh³h M8hj‚  hžhubhÊ)”}”(hŒTThis script removes a UAPI header file from the install list. Let's run
the script::”h]”hŒUThis script removes a UAPI header file from the install list. Letâ€™s run
the script:”…””}”(hj¯  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h MGhj‚  hžhubj-  )”}”(hXs  % ./scripts/check-uapi.sh
Installing user-facing UAPI headers from dirty tree... OK
Installing user-facing UAPI headers from HEAD... OK
Checking changes to UAPI headers between HEAD and dirty tree...
==== UAPI header include/asm/termios.h was removed between HEAD and dirty tree ====

error - 1/912 UAPI headers compatible with x86 appear _not_ to be backwards compatible”h]”hXs  % ./scripts/check-uapi.sh
Installing user-facing UAPI headers from dirty tree... OK
Installing user-facing UAPI headers from HEAD... OK
Checking changes to UAPI headers between HEAD and dirty tree...
==== UAPI header include/asm/termios.h was removed between HEAD and dirty tree ====

error - 1/912 UAPI headers compatible with x86 appear _not_ to be backwards compatible”…””}”hj½  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j,  hŸh³h MJhj‚  hžhubhÊ)”}”(hŒ\Removing a UAPI header is considered a breaking change, and the script
will flag it as such.”h]”hŒ\Removing a UAPI header is considered a breaking change, and the script
will flag it as such.”…””}”(hjË  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h MRhj‚  hžhubeh}”(h]”Œuapi-header-removals”ah ]”h"]”Œuapi header removals”ah$]”h&]”uh1h´hj˜  hžhhŸh³h M4ubhµ)”}”(hhh]”(hº)”}”(hŒ$Checking Historic UAPI Compatibility”h]”hŒ$Checking Historic UAPI Compatibility”…””}”(hjä  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hjá  hžhhŸh³h MVubhÊ)”}”(hŒ³You can use the ``-b`` and ``-p`` options to examine different chunks of your
git tree. For example, to check all changed UAPI header files between tags
v6.0 and v6.1, you'd run::”h]”(hŒYou can use the ”…””}”(hjò  hžhhŸNh NubhÔ)”}”(hŒ``-b``”h]”hŒ-b”…””}”(hjú  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÓhjò  ubhŒ and ”…””}”(hjò  hžhhŸNh NubhÔ)”}”(hŒ``-p``”h]”hŒ-p”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÓhjò  ubhŒ“ options to examine different chunks of your
git tree. For example, to check all changed UAPI header files between tags
v6.0 and v6.1, youâ€™d run:”…””}”(hjò  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h MXhjá  hžhubj-  )”}”(hX1  % ./scripts/check-uapi.sh -b v6.1 -p v6.0
Installing user-facing UAPI headers from v6.1... OK
Installing user-facing UAPI headers from v6.0... OK
Checking changes to UAPI headers between v6.0 and v6.1...

--- snip ---
error - 37/907 UAPI headers compatible with x86 appear _not_ to be backwards compatible”h]”hX1  % ./scripts/check-uapi.sh -b v6.1 -p v6.0
Installing user-facing UAPI headers from v6.1... OK
Installing user-facing UAPI headers from v6.0... OK
Checking changes to UAPI headers between v6.0 and v6.1...

--- snip ---
error - 37/907 UAPI headers compatible with x86 appear _not_ to be backwards compatible”…””}”hj$  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j,  hŸh³h M\hjá  hžhubhÊ)”}”(hŒ{Note: Before v5.3, a header file needed by the script is not present,
so the script is unable to check changes before then.”h]”hŒ{Note: Before v5.3, a header file needed by the script is not present,
so the script is unable to check changes before then.”…””}”(hj2  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h Mdhjá  hžhubhÊ)”}”(hŒáYou'll notice that the script detected many UAPI changes that are not
backwards compatible. Knowing that kernel UAPIs are supposed to be stable
forever, this is an alarming result. This brings us to the next section:
caveats.”h]”hŒãYouâ€™ll notice that the script detected many UAPI changes that are not
backwards compatible. Knowing that kernel UAPIs are supposed to be stable
forever, this is an alarming result. This brings us to the next section:
caveats.”…””}”(hj@  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h Mghjá  hžhubeh}”(h]”Œ$checking-historic-uapi-compatibility”ah ]”h"]”Œ$checking historic uapi compatibility”ah$]”h&]”uh1h´hj˜  hžhhŸh³h MVubeh}”(h]”Œexamples”ah ]”h"]”Œexamples”ah$]”h&]”uh1h´hh¶hžhhŸh³h K0ubhµ)”}”(hhh]”(hº)”}”(hŒCaveats”h]”hŒCaveats”…””}”(hja  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hj^  hžhhŸh³h MmubhÊ)”}”(hŒ–The UAPI checker makes no assumptions about the author's intention, so some
types of changes may be flagged even though they intentionally break UAPI.”h]”hŒ˜The UAPI checker makes no assumptions about the authorâ€™s intention, so some
types of changes may be flagged even though they intentionally break UAPI.”…””}”(hjo  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h Mohj^  hžhubhµ)”}”(hhh]”(hº)”}”(hŒ'Removals For Refactoring or Deprecation”h]”hŒ'Removals For Refactoring or Deprecation”…””}”(hj€  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hj}  hžhhŸh³h MsubhÊ)”}”(hŒNSometimes drivers for very old hardware are removed, such as in this example::”h]”hŒMSometimes drivers for very old hardware are removed, such as in this example:”…””}”(hjŽ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h Muhj}  hžhubj-  )”}”(hX¦  % ./scripts/check-uapi.sh -b ba47652ba655
Installing user-facing UAPI headers from ba47652ba655... OK
Installing user-facing UAPI headers from ba47652ba655^1... OK
Checking changes to UAPI headers between ba47652ba655^1 and ba47652ba655...
==== UAPI header include/linux/meye.h was removed between ba47652ba655^1 and ba47652ba655 ====

error - 1/910 UAPI headers compatible with x86 appear _not_ to be backwards compatible”h]”hX¦  % ./scripts/check-uapi.sh -b ba47652ba655
Installing user-facing UAPI headers from ba47652ba655... OK
Installing user-facing UAPI headers from ba47652ba655^1... OK
Checking changes to UAPI headers between ba47652ba655^1 and ba47652ba655...
==== UAPI header include/linux/meye.h was removed between ba47652ba655^1 and ba47652ba655 ====

error - 1/910 UAPI headers compatible with x86 appear _not_ to be backwards compatible”…””}”hjœ  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j,  hŸh³h Mwhj}  hžhubhÊ)”}”(hŒCThe script will always flag removals (even if they're intentional).”h]”hŒEThe script will always flag removals (even if theyâ€™re intentional).”…””}”(hjª  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h Mhj}  hžhubeh}”(h]”Œ'removals-for-refactoring-or-deprecation”ah ]”h"]”Œ'removals for refactoring or deprecation”ah$]”h&]”uh1h´hj^  hžhhŸh³h Msubhµ)”}”(hhh]”(hº)”}”(hŒStruct Expansions”h]”hŒStruct Expansions”…””}”(hjÃ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hjÀ  hžhhŸh³h M‚ubhÊ)”}”(hŒnDepending on how a structure is handled in kernelspace, a change which
expands a struct could be non-breaking.”h]”hŒnDepending on how a structure is handled in kernelspace, a change which
expands a struct could be non-breaking.”…””}”(hjÑ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h M„hjÀ  hžhubhÊ)”}”(hŒüIf a struct is used as the argument to an ioctl, then the kernel driver
must be able to handle ioctl commands of any size. Beyond that, you need
to be careful when copying data from the user. Say, for example, that
``struct foo`` is changed like this::”h]”(hŒ×If a struct is used as the argument to an ioctl, then the kernel driver
must be able to handle ioctl commands of any size. Beyond that, you need
to be careful when copying data from the user. Say, for example, that
”…””}”(hjß  hžhhŸNh NubhÔ)”}”(hŒ``struct foo``”h]”hŒ
struct foo”…””}”(hjç  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÓhjß  ubhŒ is changed like this:”…””}”(hjß  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h M‡hjÀ  hžhubj-  )”}”(hŒ€struct foo {
    __u64 a; /* added in version 1 */
+   __u32 b; /* added in version 2 */
+   __u32 c; /* added in version 2 */
}”h]”hŒ€struct foo {
    __u64 a; /* added in version 1 */
+   __u32 b; /* added in version 2 */
+   __u32 c; /* added in version 2 */
}”…””}”hjÿ  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j,  hŸh³h MŒhjÀ  hžhubhÊ)”}”(hŒIBy default, the script will flag this kind of change for further review::”h]”hŒHBy default, the script will flag this kind of change for further review:”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h M’hjÀ  hžhubj-  )”}”(hŒ®[C] 'struct foo' changed:
  type size changed from 64 to 128 (in bits)
  2 data member insertions:
    '__u32 b', at offset 64 (in bits)
    '__u32 c', at offset 96 (in bits)”h]”hŒ®[C] 'struct foo' changed:
  type size changed from 64 to 128 (in bits)
  2 data member insertions:
    '__u32 b', at offset 64 (in bits)
    '__u32 c', at offset 96 (in bits)”…””}”hj  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j,  hŸh³h M”hjÀ  hžhubhÊ)”}”(hŒ9However, it is possible that this change was made safely.”h]”hŒ9However, it is possible that this change was made safely.”…””}”(hj)  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h MšhjÀ  hžhubhÊ)”}”(hŒýIf a userspace program was built with version 1, it will think
``sizeof(struct foo)`` is 8. That size will be encoded in the
ioctl value that gets sent to the kernel. If the kernel is built
with version 2, it will think the ``sizeof(struct foo)`` is 16.”h]”(hŒ?If a userspace program was built with version 1, it will think
”…””}”(hj7  hžhhŸNh NubhÔ)”}”(hŒ``sizeof(struct foo)``”h]”hŒsizeof(struct foo)”…””}”(hj?  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÓhj7  ubhŒ‹ is 8. That size will be encoded in the
ioctl value that gets sent to the kernel. If the kernel is built
with version 2, it will think the ”…””}”(hj7  hžhhŸNh NubhÔ)”}”(hŒ``sizeof(struct foo)``”h]”hŒsizeof(struct foo)”…””}”(hjQ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÓhj7  ubhŒ is 16.”…””}”(hj7  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h MœhjÀ  hžhubhÊ)”}”(hŒ°The kernel can use the ``_IOC_SIZE`` macro to get the size encoded
in the ioctl code that the user passed in and then use
``copy_struct_from_user()`` to safely copy the value::”h]”(hŒThe kernel can use the ”…””}”(hji  hžhhŸNh NubhÔ)”}”(hŒ``_IOC_SIZE``”h]”hŒ	_IOC_SIZE”…””}”(hjq  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÓhji  ubhŒV macro to get the size encoded
in the ioctl code that the user passed in and then use
”…””}”(hji  hžhhŸNh NubhÔ)”}”(hŒ``copy_struct_from_user()``”h]”hŒcopy_struct_from_user()”…””}”(hjƒ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÓhji  ubhŒ to safely copy the value:”…””}”(hji  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h M¡hjÀ  hžhubj-  )”}”(hŒúint handle_ioctl(unsigned long cmd, unsigned long arg)
{
    switch _IOC_NR(cmd) {
    0x01: {
        struct foo my_cmd;  /* size 16 in the kernel */

        ret = copy_struct_from_user(&my_cmd, arg, sizeof(struct foo), _IOC_SIZE(cmd));
        ...”h]”hŒúint handle_ioctl(unsigned long cmd, unsigned long arg)
{
    switch _IOC_NR(cmd) {
    0x01: {
        struct foo my_cmd;  /* size 16 in the kernel */

        ret = copy_struct_from_user(&my_cmd, arg, sizeof(struct foo), _IOC_SIZE(cmd));
        ...”…””}”hj›  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j,  hŸh³h M¥hjÀ  hžhubhÊ)”}”(hŒ×``copy_struct_from_user`` will zero the struct in the kernel and then copy
only the bytes passed in from the user (leaving new members zeroized).
If the user passed in a larger struct, the extra members are ignored.”h]”(hÔ)”}”(hŒ``copy_struct_from_user``”h]”hŒcopy_struct_from_user”…””}”(hj­  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÓhj©  ubhŒ¾ will zero the struct in the kernel and then copy
only the bytes passed in from the user (leaving new members zeroized).
If the user passed in a larger struct, the extra members are ignored.”…””}”(hj©  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h M®hjÀ  hžhubhÊ)”}”(hŒ“If you know this situation is accounted for in the kernel code, you can
pass ``-i`` to the script, and struct expansions like this will be ignored.”h]”(hŒMIf you know this situation is accounted for in the kernel code, you can
pass ”…””}”(hjÅ  hžhhŸNh NubhÔ)”}”(hŒ``-i``”h]”hŒ-i”…””}”(hjÍ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÓhjÅ  ubhŒ@ to the script, and struct expansions like this will be ignored.”…””}”(hjÅ  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h M²hjÀ  hžhubeh}”(h]”Œstruct-expansions”ah ]”h"]”Œstruct expansions”ah$]”h&]”uh1h´hj^  hžhhŸh³h M‚ubhµ)”}”(hhh]”(hº)”}”(hŒFlex Array Migration”h]”hŒFlex Array Migration”…””}”(hjð  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hjí  hžhhŸh³h M¶ubhÊ)”}”(hŒ¢While the script handles expansion into an existing flex array, it does
still flag initial migration to flex arrays from 1-element fake flex
arrays. For example::”h]”hŒ¡While the script handles expansion into an existing flex array, it does
still flag initial migration to flex arrays from 1-element fake flex
arrays. For example:”…””}”(hjþ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h M¸hjí  hžhubj-  )”}”(hŒhstruct foo {
      __u32 x;
-     __u32 flex[1]; /* fake flex */
+     __u32 flex[];  /* real flex */
};”h]”hŒhstruct foo {
      __u32 x;
-     __u32 flex[1]; /* fake flex */
+     __u32 flex[];  /* real flex */
};”…””}”hj  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j,  hŸh³h M¼hjí  hžhubhÊ)”}”(hŒ,This change would be flagged by the script::”h]”hŒ+This change would be flagged by the script:”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h MÂhjí  hžhubj-  )”}”(hX)  [C] 'struct foo' changed:
  type size changed from 64 to 32 (in bits)
  1 data member change:
    type of '__u32 flex[1]' changed:
      type name changed from '__u32[1]' to '__u32[]'
      array type size changed from 32 to 'unknown'
      array type subrange 1 changed length from 1 to 'unknown'”h]”hX)  [C] 'struct foo' changed:
  type size changed from 64 to 32 (in bits)
  1 data member change:
    type of '__u32 flex[1]' changed:
      type name changed from '__u32[1]' to '__u32[]'
      array type size changed from 32 to 'unknown'
      array type subrange 1 changed length from 1 to 'unknown'”…””}”hj(  sbah}”(h]”h ]”h"]”h$]”h&]”h±h²uh1j,  hŸh³h MÄhjí  hžhubhÊ)”}”(hŒkAt this time, there's no way to filter these types of changes, so be
aware of this possible false positive.”h]”hŒmAt this time, thereâ€™s no way to filter these types of changes, so be
aware of this possible false positive.”…””}”(hj6  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h MÌhjí  hžhubeh}”(h]”Œflex-array-migration”ah ]”h"]”Œflex array migration”ah$]”h&]”uh1h´hj^  hžhhŸh³h M¶ubhµ)”}”(hhh]”(hº)”}”(hŒSummary”h]”hŒSummary”…””}”(hjO  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¹hjL  hžhhŸh³h MÐubhÊ)”}”(hXz  While many types of false positives are filtered out by the script,
it's possible there are some cases where the script flags a change
which does not break UAPI. It's also possible a change which *does*
break userspace would not be flagged by this script. While the script
has been run on much of the kernel history, there could still be corner
cases that are not accounted for.”h]”(hŒÈWhile many types of false positives are filtered out by the script,
itâ€™s possible there are some cases where the script flags a change
which does not break UAPI. Itâ€™s also possible a change which ”…””}”(hj]  hžhhŸNh Nubjû  )”}”(hŒ*does*”h]”hŒdoes”…””}”(hje  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jú  hj]  ubhŒ°
break userspace would not be flagged by this script. While the script
has been run on much of the kernel history, there could still be corner
cases that are not accounted for.”…””}”(hj]  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÉhŸh³h MÒhjL  hžhubhÊ)”}”(hX%  The intention is for this script to be used as a quick check for
maintainers or automated tooling, not as the end-all authority on
patch compatibility. It's best to remember: use your best judgment
(and ideally a unit test in userspace) to make sure your UAPI changes
are backwards-compatible!”h]”hX'  The intention is for this script to be used as a quick check for
maintainers or automated tooling, not as the end-all authority on
patch compatibility. Itâ€™s best to remember: use your best judgment
(and ideally a unit test in userspace) to make sure your UAPI changes
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