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author | Yang Weijiang <weijiang.yang@intel.com> | 2020-08-14 16:21:05 +0300 |
---|---|---|
committer | Paolo Bonzini <pbonzini@redhat.com> | 2020-08-17 20:45:22 +0300 |
commit | 98b0bf02738004829d7e26d6cb47b2e469aaba86 (patch) | |
tree | a4758c1841192d94ac12704a772b2879ab326e22 /tools | |
parent | e792415c5d3e0eb52527cce228a72e4392f8cae2 (diff) | |
download | linux-98b0bf02738004829d7e26d6cb47b2e469aaba86.tar.xz |
selftests: kvm: Use a shorter encoding to clear RAX
If debug_regs.c is built with newer binutils, the resulting binary is "optimized"
by the assembler:
asm volatile("ss_start: "
"xor %%rax,%%rax\n\t"
"cpuid\n\t"
"movl $0x1a0,%%ecx\n\t"
"rdmsr\n\t"
: : : "rax", "ecx");
is translated to :
000000000040194e <ss_start>:
40194e: 31 c0 xor %eax,%eax <----- rax->eax?
401950: 0f a2 cpuid
401952: b9 a0 01 00 00 mov $0x1a0,%ecx
401957: 0f 32 rdmsr
As you can see rax is replaced with eax in target binary code.
This causes a difference is the length of xor instruction (2 Byte vs 3 Byte),
and makes the hard-coded instruction length check fail:
/* Instruction lengths starting at ss_start */
int ss_size[4] = {
3, /* xor */ <-------- 2 or 3?
2, /* cpuid */
5, /* mov */
2, /* rdmsr */
};
Encode the shorter version directly and, while at it, fix the "clobbers"
of the asm.
Cc: stable@vger.kernel.org
Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'tools')
-rw-r--r-- | tools/testing/selftests/kvm/x86_64/debug_regs.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/tools/testing/selftests/kvm/x86_64/debug_regs.c b/tools/testing/selftests/kvm/x86_64/debug_regs.c index 8162c58a1234..b8d14f9db5f9 100644 --- a/tools/testing/selftests/kvm/x86_64/debug_regs.c +++ b/tools/testing/selftests/kvm/x86_64/debug_regs.c @@ -40,11 +40,11 @@ static void guest_code(void) /* Single step test, covers 2 basic instructions and 2 emulated */ asm volatile("ss_start: " - "xor %%rax,%%rax\n\t" + "xor %%eax,%%eax\n\t" "cpuid\n\t" "movl $0x1a0,%%ecx\n\t" "rdmsr\n\t" - : : : "rax", "ecx"); + : : : "eax", "ebx", "ecx", "edx"); /* DR6.BD test */ asm volatile("bd_start: mov %%dr0, %%rax" : : : "rax"); |