When compiled with -fno-omit-frame-pointer, test_lldt causes a triple
fault, which insta-reboots the guest. I couldn't figure out why the
triple-fault was happening, so I disabled the test outright. Knowing
that the other emulator.c tests pass is more useful than a VM stuck in
a reboot loop.
On x86-64, this test was adding little value since it was broken to
begin with: an LDT descriptor is 16 bytes on x86-64. The GDT limit
was also bogus. I've fixed these problems for posterity.
N.B. I only tested this on Linux 4.3.5. Perhaps lldt emulation has
been fixed since then.
Signed-off-by: Peter Feiner <pfeiner@xxxxxxxxxx>
---
x86/emulator.c | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)
diff --git a/x86/emulator.c b/x86/emulator.c
index d990961..3730721 100644
--- a/x86/emulator.c
+++ b/x86/emulator.c
@@ -1006,10 +1006,17 @@ static void test_sreg(volatile uint16_t *mem)
write_ss(ss);
}
+/* Broken emulation causes triple fault, which skips the other tests. */
+#if 0
static void test_lldt(volatile uint16_t *mem)
{
- u64 gdt[] = { 0, 0x0000f82000000ffffull /* ldt descriptor */ };
- struct descriptor_table_ptr gdt_ptr = { .limit = 0xffff, .base = (ulong)&gdt };
+ u64 gdt[] = { 0, /* null descriptor */
+#ifdef __X86_64__
+ 0, /* ldt descriptor is 16 bytes in long mode */
+#endif
+ 0x0000f82000000ffffull /* ldt descriptor */ };
+ struct descriptor_table_ptr gdt_ptr = { .limit = sizeof(gdt) - 1,
+ .base = (ulong)&gdt };
struct descriptor_table_ptr orig_gdt;
cli();
@@ -1021,6 +1028,7 @@ static void test_lldt(volatile uint16_t *mem)
sti();
report("lldt", sldt() == *mem);
}
+#endif
static void test_ltr(volatile uint16_t *mem)
{
@@ -1139,7 +1147,7 @@ int main()
test_shld_shrd(mem);
//test_lgdt_lidt(mem);
test_sreg(mem);
- test_lldt(mem);
+ //test_lldt(mem);
test_ltr(mem);
test_cmov(mem);
--
2.7.0.rc3.207.g0ac5344
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