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Re: [PATCH v2 7/9] aarch64: Rely on syscalls preserving registers
- From: Will Newton <will dot newton at linaro dot org>
- To: Richard Henderson <rth at twiddle dot net>
- Cc: libc-alpha <libc-alpha at sourceware dot org>, Marcus Shawcroft <marcus dot shawcroft at gmail dot com>, Richard Henderson <rth at redhat dot com>
- Date: Tue, 27 May 2014 09:16:06 +0100
- Subject: Re: [PATCH v2 7/9] aarch64: Rely on syscalls preserving registers
- Authentication-results: sourceware.org; auth=none
- References: <1400890309-16710-1-git-send-email-rth at twiddle dot net> <1400890309-16710-8-git-send-email-rth at twiddle dot net>
On 24 May 2014 01:11, Richard Henderson <rth@twiddle.net> wrote:
> From: Richard Henderson <rth@redhat.com>
>
> In several cases we've had asm routines rely on syscalls not clobbering
> call-clobbered registers, and that's now deemed ABI. So take advantage
> of this in the INLINE_SYSCALL path as well.
I wonder if this ABI deserves a comment somewhere? I suppose sysdep.h
would be as good a place as any.
> Shrinks libc.so by about 1k.
> ---
> sysdeps/unix/sysv/linux/aarch64/sysdep.h | 36 +++++++++++---------------------
> 1 file changed, 12 insertions(+), 24 deletions(-)
>
> diff --git a/sysdeps/unix/sysv/linux/aarch64/sysdep.h b/sysdeps/unix/sysv/linux/aarch64/sysdep.h
> index 8cce986..4686599 100644
> --- a/sysdeps/unix/sysv/linux/aarch64/sysdep.h
> +++ b/sysdeps/unix/sysv/linux/aarch64/sysdep.h
> @@ -231,7 +231,7 @@
> LOAD_ARGS_##nr (args) \
> asm volatile ("blr %1" \
> : "=r" (_x0) \
> - : "r" (funcptr), ASM_ARGS_##nr \
> + : "r" (funcptr) ASM_ARGS_##nr \
> : "x30", "memory"); \
> (long) _x0; \
> })
> @@ -254,17 +254,15 @@
>
> # undef INTERNAL_SYSCALL_RAW
> # define INTERNAL_SYSCALL_RAW(name, err, nr, args...) \
> - ({ unsigned long _sys_result; \
> + ({ long _sys_result; \
> { \
> LOAD_ARGS_##nr (args) \
> register long _x8 asm ("x8") = (name); \
> asm volatile ("svc 0 // syscall " # name \
> - : "+r" (_x0), "+r" (_x8) \
> - : ASM_ARGS_##nr \
> - : "memory", CLOBBER_ARGS_##nr); \
> + : "=r" (_x0) : "r"(_x8) ASM_ARGS_##nr : "memory"); \
> _sys_result = _x0; \
> } \
> - (long) _sys_result; })
> + _sys_result; })
>
> # undef INTERNAL_SYSCALL
> # define INTERNAL_SYSCALL(name, err, nr, args...) \
> @@ -281,54 +279,44 @@
> # undef INTERNAL_SYSCALL_ERRNO
> # define INTERNAL_SYSCALL_ERRNO(val, err) (-(val))
>
> -# define CLOBBER_ARGS_0 CLOBBER_ARGS_1
> -# define CLOBBER_ARGS_1 "x1", CLOBBER_ARGS_2
> -# define CLOBBER_ARGS_2 "x2", CLOBBER_ARGS_3
> -# define CLOBBER_ARGS_3 "x3", CLOBBER_ARGS_4
> -# define CLOBBER_ARGS_4 "x4", CLOBBER_ARGS_5
> -# define CLOBBER_ARGS_5 "x5", CLOBBER_ARGS_6
> -# define CLOBBER_ARGS_6 "x6", CLOBBER_ARGS_7
> -# define CLOBBER_ARGS_7 \
> - "x7", "x9", "x10", "x11", "x12", "x13", "x14", "x15", "x16", "x17", "x18"
> -
> # define LOAD_ARGS_0() \
> register long _x0 asm ("x0");
> -
> -# define ASM_ARGS_0
> # define LOAD_ARGS_1(x0) \
> long _x0tmp = (long) (x0); \
> LOAD_ARGS_0 () \
> _x0 = _x0tmp;
> -# define ASM_ARGS_1 "r" (_x0)
> # define LOAD_ARGS_2(x0, x1) \
> long _x1tmp = (long) (x1); \
> LOAD_ARGS_1 (x0) \
> register long _x1 asm ("x1") = _x1tmp;
> -# define ASM_ARGS_2 ASM_ARGS_1, "r" (_x1)
> # define LOAD_ARGS_3(x0, x1, x2) \
> long _x2tmp = (long) (x2); \
> LOAD_ARGS_2 (x0, x1) \
> register long _x2 asm ("x2") = _x2tmp;
> -# define ASM_ARGS_3 ASM_ARGS_2, "r" (_x2)
> # define LOAD_ARGS_4(x0, x1, x2, x3) \
> long _x3tmp = (long) (x3); \
> LOAD_ARGS_3 (x0, x1, x2) \
> register long _x3 asm ("x3") = _x3tmp;
> -# define ASM_ARGS_4 ASM_ARGS_3, "r" (_x3)
> # define LOAD_ARGS_5(x0, x1, x2, x3, x4) \
> long _x4tmp = (long) (x4); \
> LOAD_ARGS_4 (x0, x1, x2, x3) \
> register long _x4 asm ("x4") = _x4tmp;
> -# define ASM_ARGS_5 ASM_ARGS_4, "r" (_x4)
> # define LOAD_ARGS_6(x0, x1, x2, x3, x4, x5) \
> long _x5tmp = (long) (x5); \
> LOAD_ARGS_5 (x0, x1, x2, x3, x4) \
> register long _x5 asm ("x5") = _x5tmp;
> -# define ASM_ARGS_6 ASM_ARGS_5, "r" (_x5)
> # define LOAD_ARGS_7(x0, x1, x2, x3, x4, x5, x6)\
> long _x6tmp = (long) (x6); \
> LOAD_ARGS_6 (x0, x1, x2, x3, x4, x5) \
> register long _x6 asm ("x6") = _x6tmp;
> +
> +# define ASM_ARGS_0
> +# define ASM_ARGS_1 , "r" (_x0)
> +# define ASM_ARGS_2 ASM_ARGS_1, "r" (_x1)
> +# define ASM_ARGS_3 ASM_ARGS_2, "r" (_x2)
> +# define ASM_ARGS_4 ASM_ARGS_3, "r" (_x3)
> +# define ASM_ARGS_5 ASM_ARGS_4, "r" (_x4)
> +# define ASM_ARGS_6 ASM_ARGS_5, "r" (_x5)
> # define ASM_ARGS_7 ASM_ARGS_6, "r" (_x6)
>
> # undef INTERNAL_SYSCALL_NCS
> --
> 1.9.0
>
--
Will Newton
Toolchain Working Group, Linaro