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Both syscall declarations and _start code definition are added for
powerpc to nolibc.
Like mips, powerpc uses a register (exactly, the summary overflow bit)
to record the error occurred, and uses another register to return the
value [1]. So, the return value of every syscall declaration must be
normalized to match the __sysret() helper, return -value when there is
an error, otheriwse, return value directly.
Glibc and musl use different methods to check the summary overflow bit,
glibc (sysdeps/unix/sysv/linux/powerpc/sysdep.h) saves the cr register
to r0 at first, and then check the summary overflow bit in cr0:
mfcr r0
r0 & (1 << 28) ? -r3 : r3
-->
10003c14: 7c 00 00 26 mfcr r0
10003c18: 74 09 10 00 andis. r9,r0,4096
10003c1c: 41 82 00 08 beq 0x10003c24
10003c20: 7c 63 00 d0 neg r3,r3
Musl (arch/powerpc/syscall_arch.h) directly checks the summary overflow
bit with the 'bns' instruction, it is smaller:
/* no summary overflow bit means no error, return value directly */
bns+ 1f
/* otherwise, return negated value */
neg r3, r3
1:
-->
10000418: 40 a3 00 08 bns 0x10000420
1000041c: 7c 63 00 d0 neg r3,r3
Like musl, Linux (arch/powerpc/include/asm/vdso/gettimeofday.h) uses the
same method for do_syscall_2() too.
Here applies the second method to get smaller size.
[1]: https://man7.org/linux/man-pages/man2/syscall.2.html
Reviewed-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Zhangjin Wu <falcon@tinylab.org>
Signed-off-by: Willy Tarreau <w@1wt.eu>
38 lines
1.2 KiB
C
38 lines
1.2 KiB
C
/* SPDX-License-Identifier: LGPL-2.1 OR MIT */
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/*
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* Copyright (C) 2017-2022 Willy Tarreau <w@1wt.eu>
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*/
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/* Below comes the architecture-specific code. For each architecture, we have
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* the syscall declarations and the _start code definition. This is the only
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* global part. On all architectures the kernel puts everything in the stack
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* before jumping to _start just above us, without any return address (_start
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* is not a function but an entry point). So at the stack pointer we find argc.
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* Then argv[] begins, and ends at the first NULL. Then we have envp which
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* starts and ends with a NULL as well. So envp=argv+argc+1.
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*/
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#ifndef _NOLIBC_ARCH_H
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#define _NOLIBC_ARCH_H
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#if defined(__x86_64__)
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#include "arch-x86_64.h"
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#elif defined(__i386__) || defined(__i486__) || defined(__i586__) || defined(__i686__)
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#include "arch-i386.h"
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#elif defined(__ARM_EABI__)
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#include "arch-arm.h"
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#elif defined(__aarch64__)
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#include "arch-aarch64.h"
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#elif defined(__mips__) && defined(_ABIO32)
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#include "arch-mips.h"
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#elif defined(__powerpc__)
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#include "arch-powerpc.h"
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#elif defined(__riscv)
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#include "arch-riscv.h"
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#elif defined(__s390x__)
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#include "arch-s390.h"
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#elif defined(__loongarch__)
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#include "arch-loongarch.h"
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#endif
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#endif /* _NOLIBC_ARCH_H */
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