[PATCH] Fix immediate asm constraint for gcc 3 x86_64

* Jeremy Fitzhardinge (jeremy@xxxxxxxx) wrote:
I'm getting this when I build for x86-64 with

jeremy@cosworth:~/hg/xen/paravirt/linux-x86_64$ gcc -v
Reading specs from /usr/lib/gcc/x86_64-linux/3.4.4/specs
Configured with: ../src/configure -v
--enable-languages=c,c++,java,f77,pascal,objc,ada,treelang --prefix=/usr
--libexecdir=/usr/lib --with-gxx-include-dir=/usr/include/c++/3.4
--enable-shared --with-system-zlib --enable-nls --without-included-gettext
--program-suffix=-3.4 --enable-__cxa_atexit --enable-libstdcxx-allocator=mt
--enable-clocale=gnu --enable-libstdcxx-debug --enable-java-gc=boehm
--enable-java-awt=gtk --disable-werror x86_64-linux
Thread model: posix
gcc version 3.4.4 20050314 (prerelease) (Debian 3.4.3-13)


CC kernel/sched.o
/home/jeremy/hg/xen/paravirt/linux/kernel/sched_trace.h: In function
`wait_task_inactive':
/home/jeremy/hg/xen/paravirt/linux/kernel/sched_trace.h:5: warning: asm
operand 1 probably doesn't match constraints
/home/jeremy/hg/xen/paravirt/linux/kernel/sched_trace.h:5: error:
impossible constraint in `asm'
/home/jeremy/hg/xen/paravirt/linux/kernel/sched_trace.h:5: warning: 'value'
might be used uninitialized in this function
/home/jeremy/hg/xen/paravirt/linux/kernel/sched.c: At top level:
/home/jeremy/hg/xen/paravirt/linux/kernel/sched_fair.c:1167: warning:
'wakeup_preempt_entity' defined but not used
make[3]: *** [kernel/sched.o] Error 1



It seems that include/asm-x86/immediate.h in sched-devel.git causes
this. gcc-3.4 does not seem to like the "i" (&name##__imv) constraint. I
have seen no such problem with gcc-4.1. This is weird. It seems that
relaxing the constraint helps fixing this, but it's not clear whether
fixing the code or gcc-3.4 is the correct solution... here is the fix :

Fix immediate asm constraint for gcc 3 x86_64

make CC=gcc-3.4 HOSTCC=gcc-3.4 causes this problem with immediate values on
x86_64 :

kernel/sched_trace.h: In function `wait_task_inactive':
kernel/sched_trace.h:5: warning: asm operand 1 probably doesn't match constraints
kernel/sched_trace.h:5: error: impossible constraint in `asm'
kernel/sched_trace.h:5: warning: 'value' might be used uninitialized in this function
make[1]: *** [kernel/sched.o] Error 1
make: *** [kernel/] Error 2

gcc-4.1 does not have this problem.

Fix this by changing the "i" (&name##__imv) for a "g" (&name##__imv) constraint.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>
CC: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
CC: Ingo Molnar <mingo@xxxxxxx>
CC: "H. Peter Anvin" <hpa@xxxxxxxxx>
---
include/asm-x86/immediate.h | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

Index: linux-2.6-sched-devel/include/asm-x86/immediate.h
===================================================================
--- linux-2.6-sched-devel.orig/include/asm-x86/immediate.h 2008-05-16 05:07:55.000000000 -0400
+++ linux-2.6-sched-devel/include/asm-x86/immediate.h 2008-05-16 05:08:29.000000000 -0400
@@ -63,7 +63,7 @@
"mov $0,%0\n\t" \
"3:\n\t" \
: "=q" (value) \
- : "i" (&name##__imv), \
+ : "g" (&name##__imv), \
"i" (sizeof(value))); \
break; \
case 2: \
@@ -81,7 +81,7 @@
"mov $0,%0\n\t" \
"3:\n\t" \
: "=r" (value) \
- : "i" (&name##__imv), \
+ : "g" (&name##__imv), \
"i" (sizeof(value))); \
break; \
case 8: \
@@ -102,7 +102,7 @@
"mov $0xFEFEFEFE01010101,%0\n\t" \
"3:\n\t" \
: "=r" (value) \
- : "i" (&name##__imv), \
+ : "g" (&name##__imv), \
"i" (sizeof(value))); \
break; \
}; \
@@ -143,7 +143,7 @@
"mov $0,%0\n\t" \
"3:\n\t" \
: "=a" (value) \
- : "i" (&name##__imv), \
+ : "g" (&name##__imv), \
"i" (sizeof(value)), \
"i" (sizeof(__typeof__(name##__imv)))); \
value; \




Turning CONFIG_MARKER off avoids the problem.

J

--
Mathieu Desnoyers
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