On Wed, Oct 09, 2013 at 04:07:34PM +0200, Peter Zijlstra wrote:
> Once I force a x86_64 build using the 'same' config it goes away and
> generates 'sensible' code again (although I don't see why L9 isn't
> merged with L2):
i386-SMP also generates correct code afaict; a tad stupid but not wrong.
If I remove ftrace from the .config its still broken..
If I also remove the likely/unlikely tracer its still broken and lots
smaller:
.p2align 4,,15
.globl task_work_add
.type task_work_add, @function
task_work_add:
pushl %ebp #
movl %esp, %ebp #,
pushl %edi #
pushl %esi #
pushl %ebx #
movl %eax, %esi # task, task
.p2align 4,,15
.L4:
movl 904(%esi), %ebx # task_5(D)->task_works, __old
cmpl $work_exited, %ebx #, __old
je .L5 #,
movl %ebx, (%edx) # __old, work_10(D)->next
movl %ebx, %eax # __old, __ret
#APP
# 34 "/usr/src/linux-2.6/kernel/task_work.c" 1
cmpxchgl %edx,904(%esi) # work, *__ptr_12
# 0 "" 2
#NO_APP
cmpl %eax, %ebx # __ret, __old
jne .L4 #,
testb %cl, %cl # notify
je .L6 #,
movl 4(%esi), %eax # task_5(D)->stack, task_5(D)->stack
#APP
# 208 "/usr/src/linux-2.6/arch/x86/include/asm/bitops.h" 1
bts $1, 8(%eax); jc .L2 #, MEM[(volatile long unsigned int *)_18],
# 0 "" 2
#NO_APP
.L6:
xorl %edi, %edi # D.14172
.L2:
movl %edi, %eax # D.14172,
popl %ebx #
popl %esi #
popl %edi #
popl %ebp #
ret
.L5:
movl $-3, %edi #, D.14172
jmp .L2 #
.size task_work_add, .-task_work_add
That "jc .L2" needs to be .L6 ! It looks like it fails to deal with the
empty branch.
Why this thing needs to use EDI is anybodies guess I suppose. Would've
made much more sense to have:
.L6:
xorl %eax, %eax
.L2:
popl %ebx
popl %esi
popl %ebp
ret
.L5:
movl, $-3, %eax
jmp .L2
At least its not duplicating the popl+ret bits 3 times anymore.
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