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On Thu, 2016-21-01 at 00:55:41 UTC, Cyril Bur wrote:
> Test that the non volatile floating point and Altivec registers get
> correctly preserved across the fork() syscall.
>
> fork() works nicely for this purpose, the registers should be the same for
> both parent and child
...
> diff --git a/tools/testing/selftests/powerpc/basic_asm.h
> b/tools/testing/selftests/powerpc/basic_asm.h
> new file mode 100644
> index 0000000..27aca79
> --- /dev/null
> +++ b/tools/testing/selftests/powerpc/basic_asm.h
> @@ -0,0 +1,26 @@
> +#include <ppc-asm.h>
> +#include <asm/unistd.h>
> +
> +#define LOAD_REG_IMMEDIATE(reg,expr) \
> + lis reg,(expr)@highest; \
> + ori reg,reg,(expr)@higher; \
> + rldicr reg,reg,32,31; \
> + oris reg,reg,(expr)@high; \
> + ori reg,reg,(expr)@l;
> +
> +#define PUSH_BASIC_STACK(size) \
> + std 2,24(sp); \
> + mflr r0; \
> + std r0,16(sp); \
> + mfcr r0; \
> + stw r0,8(sp); \
> + stdu sp,-size(sp);
Unless I'm completely misreading this, that's not ABI compliant.
You are supposed to save LR into your caller's stack frame, but the TOC and CR
go into *your* stack frame.
I know that's not super obvious from the ABI doc.
See for example this code generated by GCC:
extern int global_thing;
int foo(int x, int (*fp)(int x))
{
int a, b, c;
a = x;
b = a + global_thing;
c = b + 2;
a = fp(x);
printf("%d %d %d\n", a, b, c);
return a;
}
0000000000000000 <foo>:
0: 00 00 4c 3c addis r2,r12,0
0: R_PPC64_REL16_HA .TOC.
4: 00 00 42 38 addi r2,r2,0
4: R_PPC64_REL16_LO .TOC.+0x4
8: a6 02 08 7c mflr r0
c: f0 ff c1 fb std r30,-16(r1) <- save r30 into (what will be)
our stack frame
10: f8 ff e1 fb std r31,-8(r1) <- save r31 into (what will be)
our stack frame
14: 78 23 8c 7c mr r12,r4 <- put fp into r12 because
we'll be calling its global entry point
18: a6 03 89 7c mtctr r4 <- put fp into CTR
1c: 00 00 22 3d addis r9,r2,0
1c: R_PPC64_TOC16_HA .toc
20: 00 00 29 e9 ld r9,0(r9)
20: R_PPC64_TOC16_LO_DS .toc
24: 10 00 01 f8 std r0,16(r1) <- save r0 (LR) into *our
caller's* stack frame
28: 91 ff 21 f8 stdu r1,-112(r1) <- create our stack frame &
store the backchain pointer
2c: 18 00 41 f8 std r2,24(r1) <- save r2 (TOC) into *our*
stack frame
30: 00 00 e9 83 lwz r31,0(r9)
34: 14 1a ff 7f add r31,r31,r3
38: 21 04 80 4e bctrl <- call fp, it will get it's
TOC pointer using r12
3c: 18 00 41 e8 ld r2,24(r1) <- restore our r2 (TOC) from
*our* stack frame
40: 02 00 ff 38 addi r7,r31,2
44: b4 07 e6 7f extsw r6,r31
48: b4 07 e7 7c extsw r7,r7
4c: 78 1b 7e 7c mr r30,r3
50: 00 00 82 3c addis r4,r2,0
50: R_PPC64_TOC16_HA .rodata.str1.8
54: 78 f3 c5 7f mr r5,r30
58: 00 00 84 38 addi r4,r4,0
58: R_PPC64_TOC16_LO .rodata.str1.8
5c: 01 00 60 38 li r3,1
60: 01 00 00 48 bl 60 <foo+0x60>
60: R_PPC64_REL24 __printf_chk
64: 00 00 00 60 nop
68: 70 00 21 38 addi r1,r1,112 <- pop our stack frame
6c: 78 f3 c3 7f mr r3,r30
70: 10 00 01 e8 ld r0,16(r1) <- restore r0 (LR) from our
caller's stack frame
74: f0 ff c1 eb ld r30,-16(r1) <- restore r30 from (what was)
our stack frame
78: f8 ff e1 eb ld r31,-8(r1) <- restore r31 from (what was)
our stack frame
7c: a6 03 08 7c mtlr r0 <- restore LR
80: 20 00 80 4e blr <- return
So your macro wants to be more like:
#define PUSH_BASIC_STACK(_size) \
mflr r0; \
std r0,16(r1); \
stdu r1,-_size(r1); \
mfcr r0; \
stw r0,8(r1); \
std r2,24(r1);
Though untested.
Also you're relying on the caller to ensure size is big enough. So maybe it'd
be better if you ensured that, making the size parameter the *extra* size above
the minimum stack frame. eg:
#define PUSH_BASIC_STACK(_extra) \
mflr r0; \
std r0,16(r1); \
stdu r1,-(_extra + 32)(r1); \
mfcr r0; \
stw r0,8(r1); \
std r2,24(r1);
cheers
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