Add segment limits

1 files changed, 25 insertions, 2 deletions

diff --git a/user_visible_state.c b/user_visible_state.c
index 58d1d88..055de34 100644
--- a/user_visible_state.c
+++ b/user_visible_state.c
@@ -2,18 +2,25 @@
 #include <stdint.h>
 #include <xmmintrin.h>
 
-static void show_gdt_and_idt(void)
+/* returns GDT limit */
+static uint16_t show_gdt_and_idt(void)
 {
 	struct {
 		unsigned short limit;
 		unsigned long base;
 	} __attribute__((packed)) val;
 
+	uint16_t ret;
+
 	__asm__ ("sgdt %0" : "=m" (val));
 	printf("GDT:    base = 0x%016lX limit = 0x%04hX\n", val.base, val.limit);
 
+	ret = val.limit;
+
 	__asm__ ("sidt %0" : "=m" (val));
 	printf("IDT:    base = 0x%016lX limit = 0x%04hX\n", val.base, val.limit);
+
+	return ret;
 }
 
 static void show_ldt(void)
@@ -54,12 +61,28 @@ static void show_rdtscp(void)
 	printf("RDTSCP: cpu %d\n", cpu);
 }
 
+static void show_seglimit(uint16_t index)
+{
+	uint32_t okay = 0, limit;
+	asm ("lsl %[index], %[limit]\n\t"
+	     "jnz 1f\n\t"
+	     "mov $1, %[okay]\n\t"
+	     "1:"
+	     : [limit] "=r" (limit), [okay] "+rm" (okay)
+	     : [index] "r" ((index << 3) + 3));
+	if (okay) {
+		printf("GDT entry %02hu limit: 0x%08X\n", index, limit);
+	}
+}
+
 int main()
 {
-	show_gdt_and_idt();
+	uint16_t gdtlimit = show_gdt_and_idt();
 	show_ldt();
 	show_tr();
 	show_msw();
 	show_flags();
 	show_rdtscp();
+	for (int i = 0; i <= gdtlimit; i++)
+		show_seglimit(i);
 }