[PATCH] powerpc64[le]: Fix CFI for assembly templated syscalls [BZ #28532]
Paul E Murphy
murphyp@linux.ibm.com
Wed Nov 3 15:46:17 GMT 2021
On 11/3/21 9:22 AM, Matheus Castanho via Libc-alpha wrote:
> Syscalls based on the assembly templates are missing CFI for r31, which gets
> clobbered when scv is used, and info for LR is inaccurate, placed in the wrong
> LOC and not using the proper offset. These are fixed by this commit.
>
> After this change:
>
> $ readelf -wF libc.so.6 | grep 0004b9d4.. -A 7 && objdump --disassemble=kill libc.so.6
> 00004a48 0000000000000020 00004a4c FDE cie=00000000 pc=000000000004b9d4..000000000004ba3c
> LOC CFA r31 ra
> 000000000004b9d4 r1+0 u u
> 000000000004b9e4 r1+48 u u
> 000000000004b9e8 r1+48 c-16 u
> 000000000004b9fc r1+48 c-16 c-32
> 000000000004ba08 r1+48 c-16
> 000000000004ba18 r1+48 u
> 000000000004ba1c r1+0 u
>
> libc.so.6: file format elf64-powerpcle
>
> Disassembly of section .text:
>
> 000000000004b9d4 <kill>:
> 4b9d4: 1f 00 4c 3c addis r2,r12,31
> 4b9d8: 2c c3 42 38 addi r2,r2,-15572
> 4b9dc: 25 00 00 38 li r0,37
> 4b9e0: d1 ff 21 f8 stdu r1,-48(r1)
> 4b9e4: 20 00 e1 fb std r31,32(r1)
> 4b9e8: 98 8f ed eb ld r31,-28776(r13)
> 4b9ec: 10 00 ff 77 andis. r31,r31,16
> 4b9f0: 1c 00 82 41 beq 4ba0c <kill+0x38>
> 4b9f4: a6 02 28 7d mflr r9
> 4b9f8: 10 00 21 f9 std r9,16(r1)
> 4b9fc: 01 00 00 44 scv 0
> 4ba00: 10 00 21 e9 ld r9,16(r1)
> 4ba04: a6 03 28 7d mtlr r9
> 4ba08: 08 00 00 48 b 4ba10 <kill+0x3c>
> 4ba0c: 02 00 00 44 sc
> 4ba10: 00 00 bf 2e cmpdi cr5,r31,0
> 4ba14: 20 00 e1 eb ld r31,32(r1)
> 4ba18: 30 00 21 38 addi r1,r1,48
> 4ba1c: 18 00 96 41 beq cr5,4ba34 <kill+0x60>
> 4ba20: 01 f0 20 39 li r9,-4095
> 4ba24: 40 48 23 7c cmpld r3,r9
> 4ba28: 20 00 e0 4d bltlr+
> 4ba2c: d0 00 63 7c neg r3,r3
> 4ba30: 08 00 00 48 b 4ba38 <kill+0x64>
> 4ba34: 20 00 e3 4c bnslr+
> 4ba38: c8 32 fe 4b b 2ed00 <__syscall_error>
> ...
> 4ba44: 40 20 0c 00 .long 0xc2040
> 4ba48: 68 00 00 00 .long 0x68
> 4ba4c: 06 00 5f 5f rlwnm r31,r26,r0,0,3
> 4ba50: 6b 69 6c 6c xoris r12,r3,26987
> ---
> sysdeps/powerpc/powerpc64/sysdep.h | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/sysdeps/powerpc/powerpc64/sysdep.h b/sysdeps/powerpc/powerpc64/sysdep.h
> index 589f7c8d18..beb477d57b 100644
> --- a/sysdeps/powerpc/powerpc64/sysdep.h
> +++ b/sysdeps/powerpc/powerpc64/sysdep.h
> @@ -275,12 +275,14 @@ LT_LABELSUFFIX(name,_name_end): ; \
> /* Allocate frame and save register */
> #define NVOLREG_SAVE \
> stdu r1,-SCV_FRAME_SIZE(r1); \
> + cfi_adjust_cfa_offset(SCV_FRAME_SIZE); \
> std r31,SCV_FRAME_NVOLREG_SAVE(r1); \
> - cfi_adjust_cfa_offset(SCV_FRAME_SIZE);
> + cfi_offset(r31,-(SCV_FRAME_SIZE-SCV_FRAME_NVOLREG_SAVE));
>OK. This (and similarly the case below) seem a little obfuscated for
computing stack save slots. I wonder if a distinct macro like
SCV_FRAME_R31_SAVE_SLOT (and similar SCV_FRAME_CALLER_LR_SAVE_SLOT
below) would make this code more approachable for those less familiar
with ppc64 abis.
> /* Restore register and destroy frame */
> #define NVOLREG_RESTORE \
> ld r31,SCV_FRAME_NVOLREG_SAVE(r1); \
> + cfi_restore(r31); \
> addi r1,r1,SCV_FRAME_SIZE; \
> cfi_adjust_cfa_offset(-SCV_FRAME_SIZE);
>
> @@ -332,7 +334,7 @@ LT_LABELSUFFIX(name,_name_end): ; \
> #define DO_CALL_SCV \
> mflr r9; \
> std r9,FRAME_LR_SAVE(r1); \
> - cfi_offset(lr,FRAME_LR_SAVE); \
> + cfi_offset(lr,-(SCV_FRAME_SIZE-FRAME_LR_SAVE)) > .machine "push"; \
> .machine "power9"; \
> scv 0; \
>
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