| Message ID | 20190102205715.14054-3-mst@redhat.com |
|---|---|
| State | RFC |
| Delegated to: | David Miller |
| Headers | show |
| Series | barriers using data dependency | expand |
On Wed, Jan 02, 2019 at 03:57:54PM -0500, Michael S. Tsirkin wrote: > 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
On Mon, Jan 07, 2019 at 05:54:27PM +0000, Will Deacon wrote: > On Wed, Jan 02, 2019 at 03:57:54PM -0500, Michael S. Tsirkin wrote: > > 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 Thanks, I'll drop this patch.
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 /* Not-quite-unique ID. */
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(-)