Messages in this thread | | | Subject | Re: [PATCH v4 7/7] x86/speculation: Add basic IBPB (Indirect Branch Prediction Barrier) support | From | David Woodhouse <> | Date | Thu, 25 Jan 2018 11:58:20 +0000 |
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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 [unhandled content-type:application/x-pkcs7-signature] | |