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SubjectRe: [PATCH] x86/cpu/vmware: use the full form of inl in VMWARE_PORT
On Mon, Oct 7, 2019 at 12:21 PM 'Sami Tolvanen' via Clang Built Linux
<clang-built-linux@googlegroups.com> wrote:
>
> LLVM's assembler doesn't accept the short form inl (%%dx) instruction,
> but instead insists on the output register to be explicitly specified:
>
> <inline asm>:1:7: error: invalid operand for instruction
> inl (%dx)
> ^
> LLVM ERROR: Error parsing inline asm
>
> Use the full form of the instruction to fix the build.
>
> Signed-off-by: Sami Tolvanen <samitolvanen@google.com>

Thanks Sami, this looks like it addresses:
Link: https://github.com/ClangBuiltLinux/linux/issues/734
Looks like GAS' testsuite has some cases where the second operand is
indeed implicitly %eax if unspecified. (This should still be fixed in
Clang).
Just to triple check that they're equivalent:
$ cat inl.s
inl (%dx)
inl (%dx), %eax
$ as inl.s
$ objdump -d a.out

a.out: file format elf64-x86-64


Disassembly of section .text:

0000000000000000 <.text>:
0: ed in (%dx),%eax
1: ed in (%dx),%eax

Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

> ---
> arch/x86/kernel/cpu/vmware.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/cpu/vmware.c b/arch/x86/kernel/cpu/vmware.c
> index 9735139cfdf8..46d732696c1c 100644
> --- a/arch/x86/kernel/cpu/vmware.c
> +++ b/arch/x86/kernel/cpu/vmware.c
> @@ -49,7 +49,7 @@
> #define VMWARE_CMD_VCPU_RESERVED 31
>
> #define VMWARE_PORT(cmd, eax, ebx, ecx, edx) \
> - __asm__("inl (%%dx)" : \
> + __asm__("inl (%%dx), %%eax" : \
> "=a"(eax), "=c"(ecx), "=d"(edx), "=b"(ebx) : \
> "a"(VMWARE_HYPERVISOR_MAGIC), \
> "c"(VMWARE_CMD_##cmd), \

--
Thanks,
~Nick Desaulniers

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