On Sat, May 18, 2019 at 5:30 PM Segher Boessenkool
<segher@xxxxxxxxxxxxxxxxxxx> wrote:
> That won't help, the compiler will remove those dead stores.
>
> Add a
>
> asm("" ::: "memory");
>
> between these two lines?
>
This didn't seem to do anything:
--- cpuid.h.orig 2019-05-14 05:52:11.000000000 -0400
+++ cpuid.h 2019-05-18 18:20:02.000000000 -0400
@@ -251,6 +251,10 @@
if (__maxlevel == 0 || __maxlevel < __leaf)
return 0;
+ asm volatile("" ::: "memory");
+ *__ebx = *__ecx = *__edx = 0;
+ asm volatile("" ::: "memory");
+
__cpuid (__leaf, *__eax, *__ebx, *__ecx, *__edx);
return 1;
}
The code looks unchanged to me:
0xb7e21491 <+81>: test $0x200000,%eax
0xb7e21496 <+86>: je 0xb7e214c0 <rdrand+128>
0xb7e21498 <+88>: xor %eax,%eax
0xb7e2149a <+90>: cpuid
0xb7e2149c <+92>: test %eax,%eax
0xb7e2149e <+94>: je 0xb7e214c0 <rdrand+128>
0xb7e214a0 <+96>: mov $0x1,%eax
0xb7e214a5 <+101>: cpuid
0xb7e214a7 <+103>: shr $0x1e,%ecx
0xb7e214aa <+106>: and $0x1,%ecx
0xb7e214ad <+109>: mov %ecx,0x35a0(%esi)
0xb7e214b3 <+115>: jmp 0xb7e21457 <rdrand+23>
Other ideas?
- Matthew
