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Subject[RFC HACK] Make clang hate percpu.h less in 32-bit mode
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Neither clang nor GCC like this very much with -m32:

long long ret;
asm ("movb $5, %0" : "=q" (ret));

However, GCC can tolerate this variant:

long long ret;
switch (sizeof(ret)) {
case 1:
asm ("movb $5, %0" : "=q" (ret));
case 8:
;
}

Clang, on the other hand, won't accept that because it validates the
inline asm for the '1' case *before* the optimisation phase where it
realises that it wouldn't have to emit it anyway.

This patch puts some casts in to make clang less unhappy. I don't like
it very much.

Note that we don't have the same problem for the "=r" case, where a
64-bit value *also* doesn't fit. This is because even if it *does* have
to emit it, clang will happily and silently do so even though it's
clearly bogus:

long long ret;
asm ("movl $5, %0" : "=r" (ret));

$ clang -c -o q.o q.c -m32
$ gcc -c -o q.o q.c -m32
q.c: In function ‘foo’:
q.c:6:1: warning: unsupported size for integer register


---

arch/x86/include/asm/percpu.h | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
index ba3c523aaf16..3b0e413670e4 100644
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -99,7 +99,7 @@ do { \
case 1: \
asm(op "b %1,"__percpu_arg(0) \
: "+m" (var) \
- : "qi" ((pto_T__)(val))); \
+ : "qi" ((unsigned char)(unsigned long)(val))); \
break; \
case 2: \
asm(op "w %1,"__percpu_arg(0) \
@@ -144,7 +144,7 @@ do { \
else \
asm("addb %1, "__percpu_arg(0) \
: "+m" (var) \
- : "qi" ((pao_T__)(val))); \
+ : "qi" ((unsigned char)(unsigned long)(val))); \
break; \
case 2: \
if (pao_ID__ == 1) \
@@ -182,12 +182,14 @@ do { \

#define percpu_from_op(op, var) \
({ \
+ unsigned char pfo_u8__; \
typeof(var) pfo_ret__; \
switch (sizeof(var)) { \
case 1: \
asm(op "b "__percpu_arg(1)",%0" \
- : "=q" (pfo_ret__) \
+ : "=q" (pfo_u8__) \
: "m" (var)); \
+ pfo_ret__ = (typeof(var))(unsigned long)pfo_u8__; \
break; \
case 2: \
asm(op "w "__percpu_arg(1)",%0" \
@@ -211,12 +213,14 @@ do { \

#define percpu_stable_op(op, var) \
({ \
+ unsigned char pfo_u8__; \
typeof(var) pfo_ret__; \
switch (sizeof(var)) { \
case 1: \
asm(op "b "__percpu_arg(P1)",%0" \
- : "=q" (pfo_ret__) \
+ : "=q" (pfo_u8__) \
: "p" (&(var))); \
+ pfo_ret__ = (typeof(var))(unsigned long)pfo_u8__; \
break; \
case 2: \
asm(op "w "__percpu_arg(P1)",%0" \
--
2.14.3
\
 
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