user_visible_state: Add LDT decoding (useless without other changes)

1 files changed, 13 insertions, 7 deletions

diff --git a/user_visible_state.c b/user_visible_state.c
index d878e1a..0d61de6 100644
--- a/user_visible_state.c
+++ b/user_visible_state.c
@@ -7,6 +7,7 @@
 #include <xmmintrin.h>
 #include <asm/prctl.h>
 #include <sys/prctl.h>
+#include <asm/ldt.h>
 
 extern int arch_prctl(int, unsigned long);
 
@@ -174,26 +175,28 @@ static const char *user_seg_types[] = {
 	"XR code, confirming",
 };
 
-static void show_segment(uint16_t index)
+static void show_segment(uint16_t index, int ldt)
 {
 	uint32_t has_limit = 0, has_ar = 0, limit, ar;
-	asm ("lsl %[index], %[limit]\n\t"
+	uint32_t selector = (index << 3) | (ldt << 2) | 3;
+
+	asm ("lsl %[selector], %[limit]\n\t"
 	     "jnz 1f\n\t"
 	     "mov $1, %[has_limit]\n\t"
 	     "1:"
 	     : [limit] "=r" (limit), [has_limit] "+rm" (has_limit)
-	     : [index] "r" ((index << 3) + 3));
-	asm ("larl %[index], %[ar]\n\t"
+	     : [selector] "r" (selector));
+	asm ("larl %[selector], %[ar]\n\t"
 	     "jnz 1f\n\t"
 	     "mov $1, %[has_ar]\n\t"
 	     "1:"
 	     : [ar] "=r" (ar), [has_ar] "+rm" (has_ar)
-	     : [index] "r" ((index << 3) + 3));
+	     : [selector] "r" (selector));
 
 	if (!has_limit && !has_ar)
 		return;
 
-	printf("GDT entry %02hu: ", index);
+	printf("%s entry %02hu: ", (ldt ? "LDT" : "GDT"), index);
 
 	if (has_limit)
 		printf(" limit = 0x%08X", limit);
@@ -221,6 +224,7 @@ int main()
 	// Optional: gives some visibility into how TLS works.
 	arch_prctl(ARCH_SET_GS, 500);
 
+	set_ldt();
 	uint16_t gdtlimit = show_gdt_and_idt();
 	show_ldt();
 	show_tr();
@@ -228,5 +232,7 @@ int main()
 	show_flags();
 	show_rdtscp();
 	for (int i = 0; i <= gdtlimit; i++)
-		show_segment(i);
+		show_segment(i, 0);
+	for (int i = 0; i < 10; i++)
+		show_segment(i, 1);
 }