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SubjectRe: memcpy(a,b,CONST) is not inlined by gcc 3.4.1 in Linux kernel
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> >         childregs = ((struct pt_regs *) (THREAD_SIZE + (unsigned long) p->thread_info)) - 1;
> > *childregs = *regs;
> > ^^^^^^^^^^^^^^^^^^^
> > childregs->eax = 0;
> > childregs->esp = esp;
> >
> > # make arch/i386/kernel/process.s
> >
> > copy_thread:
> > pushl %ebp
> > movl %esp, %ebp
> > pushl %edi
> > pushl %esi
> > pushl %ebx
> > subl $20, %esp
> > movl 24(%ebp), %eax
> > movl 4(%eax), %esi
> > pushl $60
> > leal 8132(%esi), %ebx
> > pushl 28(%ebp)
> > pushl %ebx
> > call memcpy <=================
> > movl $0, 24(%ebx)
> >
> > Jakub, is there a way to instruct gcc to inine this copy, or better yet,
> > to use user-supplied inline version of memcpy?
>
> You can't inline struct copy as it is not function call at first place.
> You can experiment with -minline-all-stringops where GCC will use it's
> own memcpy implementation for this.

No luck. Actually, memcpy calls are produced with -Os. Adding
-minline-all-stringops changes nothing.

-O2 compile does inline copying, however, suboptimally.
Pushing/popping esi/edi on the stack is not needed.
Also "mov $1,ecx; rep; movsl" is rather silly.

Here what did I test:

t.c:
#define STRUCT1(n) struct s##n { char c[n]; } v##n, w##n; void f##n(void) { v##n = w##n; }
#define STRUCT(n) STRUCT1(n)
STRUCT(1)
STRUCT(2)
STRUCT(3)
STRUCT(4)
STRUCT(5)
STRUCT(6)
STRUCT(7)
STRUCT(8)
STRUCT(9)
STRUCT(10)
STRUCT(11)
STRUCT(12)
STRUCT(13)
STRUCT(14)
STRUCT(15)
STRUCT(16)
STRUCT(17)
STRUCT(18)
STRUCT(19)
STRUCT(20)

mk.sh:
#!/bin/sh

# yeah yeah. push/pop + 1 repetition 'rep movsl'
# 88: 55 push %ebp
# 89: 89 e5 mov %esp,%ebp
# 8b: 57 push %edi
# 8c: 56 push %esi
# 8d: fc cld
# 8e: bf 00 00 00 00 mov $0x0,%edi
# 8f: R_386_32 v7
# 93: be 00 00 00 00 mov $0x0,%esi
# 94: R_386_32 w7
# 98: b9 01 00 00 00 mov $0x1,%ecx
# 9d: f3 a5 repz movsl %ds:(%esi),%es:(%edi)
# 9f: 66 a5 movsw %ds:(%esi),%es:(%edi)
# a1: a4 movsb %ds:(%esi),%es:(%edi)
# a2: 5e pop %esi
# a3: 5f pop %edi
# a4: c9 leave
# a5: c3 ret
# a6: 89 f6 mov %esi,%esi
if false; then
gcc -O2 \
falign-functions=1 -falign-labels=1 -falign-loops=1 -falign-jumps=1 \
-c t.c
echo Done; read junk
objdump -d -r t.o | $PAGER
exit
fi
# -Os: emits memcpy
if false; then
gcc -nostdinc -isystem /.share/usr/app/gcc-3.4.1/bin/../lib/gcc/i386-pc-linux-gnu/3.4.1/include \
-Wall -Wstrict-prototypes -Wno-trigraphs -fno-strict-aliasing \
-fno-common -ffreestanding -Os -falign-functions=1 -falign-labels=1 \
-falign-loops=1 -falign-jumps=1 -fno-omit-frame-pointer -pipe -msoft-float \
-mpreferred-stack-boundary=2 -fno-unit-at-a-time -march=i486 \
-Wdeclaration-after-statement -c t.c
echo Done; read junk
objdump -d -r t.o | $PAGER
exit
fi
# -march=486: emits horrible tail:
# 271: f3 a5 repz movsl %ds:(%esi),%es:(%edi)
# 273: 5e pop %esi
# 274: 66 a1 10 00 00 00 mov 0x10,%ax
# 276: R_386_32 w19
# 27a: 5f pop %edi
# 27b: 66 a3 10 00 00 00 mov %ax,0x10
# 27d: R_386_32 v19
# 281: 5d pop %ebp
# 282: a0 12 00 00 00 mov 0x12,%al
# 283: R_386_32 w19
# 287: a2 12 00 00 00 mov %al,0x12
# 288: R_386_32 v19
# 28c: c3 ret
if false; then
gcc \
-fno-common -ffreestanding -O2 -falign-functions=1 -falign-labels=1 \
-falign-loops=1 -falign-jumps=1 -fno-omit-frame-pointer -pipe -msoft-float \
-mpreferred-stack-boundary=2 -fno-unit-at-a-time -march=i486 \
-Wdeclaration-after-statement \
-c t.c
echo Done; read junk
objdump -d -r t.o | $PAGER
exit
fi
# -Os -minline-all-stringops: still emits memcpy
if true; then
gcc -nostdinc -isystem /.share/usr/app/gcc-3.4.1/bin/../lib/gcc/i386-pc-linux-gnu/3.4.1/include \
-Wall -Wstrict-prototypes -Wno-trigraphs -fno-strict-aliasing \
-fno-common -ffreestanding -Os -minline-all-stringops -falign-functions=1 -falign-labels=1 \
-falign-loops=1 -falign-jumps=1 -fno-omit-frame-pointer -pipe -msoft-float \
-mpreferred-stack-boundary=2 -fno-unit-at-a-time -march=i486 \
-Wdeclaration-after-statement -c t.c
echo Done; read junk
objdump -d -r t.o | $PAGER
exit
fi
--
vda

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