On Thu, 2018-01-25 at 12:50 +0100, Borislav Petkov wrote: > On Thu, Jan 25, 2018 at 11:47:35AM +0000, David Woodhouse wrote: > > I did already do the explicit clobbers now you reminded me how to do > > them, but I elected not to use ASM_NO_INPUT_CLOBBER() because on > > balance, losing the MSR_IA32_PRED_CMD / PRED_CMD_IBPB definitions and > > having to hard-code the numbers was not so much of a win. > > and I'm thinking exactly the opposite: if an alternative can lose a > bunch of inputs which don't change, then that's a good thing.
They're immediates, not registers. So it's like the first example in...
void foo(void)
{
asm volatile ("alternative me away; my numbers are %0 and %1\n"
:: "i" (3456), "i" (1234));
asm volatile ("alternative me away; GCC already loaded regs %0 and %1\n"
:: "c" (3456), "a" (1234));
}
... which gives you...
foo:
.LFB0:
.cfi_startproc
#APP
# 4 "foo.c" 1
alternative me away; my numbers are $3456 and $1234
# 0 "" 2
#NO_APP
movl $1234, %eax
movl $3456, %ecx
#APP
# 7 "foo.c" 1
alternative me away; GCC already loaded regs %ecx and %eax
# 0 "" 2
#NO_APP
ret
.cfi_endproc
smime.p7s
Description: S/MIME cryptographic signature
