Re: [PATCH RFC 2/4] include/linux/compiler.h: allow memory operands
From: Will Deacon <hidden>
Date: 2019-01-07 17:54:40
Also in:
linux-arch, lkml, virtualization
On Wed, Jan 02, 2019 at 03:57:54PM -0500, Michael S. Tsirkin wrote:
quoted hunk ↗ jump to hunk
We don't really care whether the variable is in-register or in-memory. Relax the constraint accordingly. Signed-off-by: Michael S. Tsirkin <mst@redhat.com> --- include/linux/compiler.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 1ad367b4cd8d..6601d39e8c48 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h@@ -154,7 +154,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, #ifndef OPTIMIZER_HIDE_VAR /* Make the optimizer believe the variable can be manipulated arbitrarily. */ #define OPTIMIZER_HIDE_VAR(var) \ - __asm__ ("" : "=r" (var) : "0" (var)) + __asm__ ("" : "=rm" (var) : "0" (var)) #endif
I think this can break for architectures with write-back addressing modes such as arm, where the "m" constraint is assumed to be evaluated precisely once in the asm block. Will