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Re: Support six-argument syscalls from C for 32-bit x86, use generic lowlevellock-futex.h (bug 18138)
- From: "Carlos O'Donell" <carlos at redhat dot com>
- To: Joseph Myers <joseph at codesourcery dot com>, libc-alpha at sourceware dot org
- Cc: roland at hack dot frob dot com, triegel at redhat dot com
- Date: Mon, 23 Mar 2015 11:46:15 -0400
- Subject: Re: Support six-argument syscalls from C for 32-bit x86, use generic lowlevellock-futex.h (bug 18138)
- Authentication-results: sourceware.org; auth=none
- References: <alpine dot DEB dot 2 dot 10 dot 1503210026500 dot 5144 at digraph dot polyomino dot org dot uk>
On 03/20/2015 08:28 PM, Joseph Myers wrote:
> This patch follows the approach outlined in
> <https://sourceware.org/ml/libc-alpha/2015-03/msg00656.html> to
> support six-argument syscalls from INTERNAL_SYSCALL for 32-bit x86,
> making them call a function __libc_do_syscall that takes the syscall
> number and three syscall arguments in the registers in which the
> kernel expects them, along with a pointer to a structure containing
> the other three arguments.
>
> In turn, this allows the generic lowlevellock-futex.h to be used on
> 32-bit x86, so supporting lll_futex_timed_wait_bitset (and so allowing
> FUTEX_CLOCK_REALTIME to be used in various cases, so fixing bug 18138
> for 32-bit x86 and leaving hppa as the only architecture missing
> lll_futex_timed_wait_bitset). The change to lowlevellock.h's
> definition of SYS_futex is because the generic lowlevelloc-futex.h
> ends up bringing in bits/syscall.h which defines SYS_futex to
> __NR_futex, so resulting in redefinition errors. The revised
> definition in lowlevellock.h is in line with what the x86_64 version
> does.
>
> __libc_do_syscall is only needed in libpthread at present (meaning
> nothing special needs to be done to make it shared-only in most
> libraries containing it, static in libc only, as on ARM).
>
> Tested for 32-bit x86, with the glibc testsuite and with the test in
> bug 18138. The failures seen
>
> FAIL: nptl/tst-cleanupx4
> FAIL: rt/tst-cpuclock2
>
> are pre-existing.
The last time I changed the 6-argument syscall code for hppa, I didn't
notice I'd gotten it wrong until I reran more userspace tests like
running firefox with the new glibc.
What kind of confidence do we have here without a test that exercises
the 6-argument syscall?
> 2015-03-21 Joseph Myers <joseph@codesourcery.com>
>
> [BZ #18138]
> * sysdeps/unix/sysv/linux/i386/sysdep.h (struct
> libc_do_syscall_args): New structure.
> (INTERNAL_SYSCALL_MAIN_0): New macro.
> (INTERNAL_SYSCALL_MAIN_1): Likewise.
> (INTERNAL_SYSCALL_MAIN_2): Likewise.
> (INTERNAL_SYSCALL_MAIN_3): Likewise.
> (INTERNAL_SYSCALL_MAIN_4): Likewise.
> (INTERNAL_SYSCALL_MAIN_5): Likewise.
> (INTERNAL_SYSCALL_MAIN_6): Likewise. Call __libc_do_syscall.
> (INTERNAL_SYSCALL): Define to use INTERNAL_SYSCALL_MAIN_##nr.
> Replace conditional definitions by conditional definitions of ....
> (INTERNAL_SYSCALL_MAIN_INLINE): ... this. New macro.
> * sysdeps/unix/sysv/linux/i386/libc-do-syscall.S: New file.
> * sysdeps/unix/sysv/linux/i386/Makefile [$(subdir) = nptl]
> (libpthread-sysdep_routines): Add libc-do-syscall.
> * sysdeps/unix/sysv/linux/i386/lowlevellock-futex.h: Remove file.
> * sysdeps/unix/sysv/linux/i386/lowlevellock.h (SYS_futex): Define
> to __NR_futex not 240.
Is it possible to add an x86-specific test to show this is working
as intended?
> diff --git a/sysdeps/unix/sysv/linux/i386/Makefile b/sysdeps/unix/sysv/linux/i386/Makefile
> index acc3021..d7a59d3 100644
> --- a/sysdeps/unix/sysv/linux/i386/Makefile
> +++ b/sysdeps/unix/sysv/linux/i386/Makefile
> @@ -14,6 +14,11 @@ ifeq ($(subdir),io)
> sysdep_routines += call_sync_file_range
> endif
>
> +# libpthread uses six-argument inline syscalls.
> +ifeq ($(subdir),nptl)
> +libpthread-sysdep_routines += libc-do-syscall
> +endif
> +
OK.
> ifeq ($(subdir),resource)
> sysdep_routines += oldgetrlimit64
> endif
> diff --git a/sysdeps/unix/sysv/linux/i386/libc-do-syscall.S b/sysdeps/unix/sysv/linux/i386/libc-do-syscall.S
> new file mode 100644
> index 0000000..af5c6f0
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/i386/libc-do-syscall.S
> @@ -0,0 +1,50 @@
> +/* Out-of-line syscall stub for six-argument syscalls from C.
> + Copyright (C) 2015 Free Software Foundation, Inc.
> + This file is part of the GNU C Library.
> +
> + The GNU C Library is free software; you can redistribute it and/or
> + modify it under the terms of the GNU Lesser General Public
> + License as published by the Free Software Foundation; either
> + version 2.1 of the License, or (at your option) any later version.
> +
> + The GNU C Library is distributed in the hope that it will be useful,
> + but WITHOUT ANY WARRANTY; without even the implied warranty of
> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + Lesser General Public License for more details.
> +
> + You should have received a copy of the GNU Lesser General Public
> + License along with the GNU C Library; if not, see
> + <http://www.gnu.org/licenses/>. */
> +
> +#include <sysdep.h>
> +
> +/* %eax, %ecx, %edx and %esi contain the values expected by the kernel.
> + %edi points to a structure with the values of %ebx, %edi and %ebp. */
> +
> + .hidden __libc_do_syscall
> +
> +ENTRY (__libc_do_syscall)
> + pushl %ebx
> + cfi_adjust_cfa_offset (4)
> + cfi_rel_offset (ebx, 0)
> + pushl %edi
> + cfi_adjust_cfa_offset (4)
> + cfi_rel_offset (edi, 0)
> + pushl %ebp
> + cfi_adjust_cfa_offset (4)
> + cfi_rel_offset (ebp, 0)
> + movl 0(%edi), %ebx
> + movl 8(%edi), %ebp
> + movl 4(%edi), %edi
> + ENTER_KERNEL
OK. Defined in sysdep.h.
> + popl %ebp
> + cfi_adjust_cfa_offset (-4)
> + cfi_restore (ebp)
> + popl %edi
> + cfi_adjust_cfa_offset (-4)
> + cfi_restore (edi)
> + popl %ebx
> + cfi_adjust_cfa_offset (-4)
> + cfi_restore (ebx)
> + ret
OK.
> +END (__libc_do_syscall)
> diff --git a/sysdeps/unix/sysv/linux/i386/lowlevellock-futex.h b/sysdeps/unix/sysv/linux/i386/lowlevellock-futex.h
> deleted file mode 100644
> index f08b5b8..0000000
> --- a/sysdeps/unix/sysv/linux/i386/lowlevellock-futex.h
> +++ /dev/null
> @@ -1,137 +0,0 @@
> -/* Low-level locking access to futex facilities. Linux/i386 version.
> - Copyright (C) 2014-2015 Free Software Foundation, Inc.
> - This file is part of the GNU C Library.
> -
> - The GNU C Library is free software; you can redistribute it and/or
> - modify it under the terms of the GNU Lesser General Public
> - License as published by the Free Software Foundation; either
> - version 2.1 of the License, or (at your option) any later version.
> -
> - The GNU C Library is distributed in the hope that it will be useful,
> - but WITHOUT ANY WARRANTY; without even the implied warranty of
> - MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> - Lesser General Public License for more details.
> -
> - You should have received a copy of the GNU Lesser General Public
> - License along with the GNU C Library; if not, see
> - <http://www.gnu.org/licenses/>. */
> -
> -#ifndef _LOWLEVELLOCK_FUTEX_H
> -#define _LOWLEVELLOCK_FUTEX_H 1
> -
> -#define FUTEX_WAIT 0
> -#define FUTEX_WAKE 1
> -#define FUTEX_CMP_REQUEUE 4
> -#define FUTEX_WAKE_OP 5
> -#define FUTEX_LOCK_PI 6
> -#define FUTEX_UNLOCK_PI 7
> -#define FUTEX_TRYLOCK_PI 8
> -#define FUTEX_WAIT_BITSET 9
> -#define FUTEX_WAKE_BITSET 10
> -#define FUTEX_WAIT_REQUEUE_PI 11
> -#define FUTEX_CMP_REQUEUE_PI 12
> -#define FUTEX_PRIVATE_FLAG 128
> -#define FUTEX_CLOCK_REALTIME 256
> -
> -#define FUTEX_BITSET_MATCH_ANY 0xffffffff
> -
> -#define FUTEX_OP_CLEAR_WAKE_IF_GT_ONE ((4 << 24) | 1)
> -
> -/* Values for 'private' parameter of locking macros. Yes, the
> - definition seems to be backwards. But it is not. The bit will be
> - reversed before passing to the system call. */
> -#define LLL_PRIVATE 0
> -#define LLL_SHARED FUTEX_PRIVATE_FLAG
> -
> -
> -#if IS_IN (libc) || IS_IN (rtld)
> -/* In libc.so or ld.so all futexes are private. */
> -# ifdef __ASSUME_PRIVATE_FUTEX
> -# define __lll_private_flag(fl, private) \
> - ((fl) | FUTEX_PRIVATE_FLAG)
> -# else
> -# define __lll_private_flag(fl, private) \
> - ((fl) | THREAD_GETMEM (THREAD_SELF, header.private_futex))
> -# endif
> -#else
> -# ifdef __ASSUME_PRIVATE_FUTEX
> -# define __lll_private_flag(fl, private) \
> - (((fl) | FUTEX_PRIVATE_FLAG) ^ (private))
> -# else
> -# define __lll_private_flag(fl, private) \
> - (__builtin_constant_p (private) \
> - ? ((private) == 0 \
> - ? ((fl) | THREAD_GETMEM (THREAD_SELF, header.private_futex)) \
> - : (fl)) \
> - : ({ unsigned int __fl = ((private) ^ FUTEX_PRIVATE_FLAG); \
> - asm ("andl %%gs:%P1, %0" : "+r" (__fl) \
> - : "i" (offsetof (struct pthread, header.private_futex))); \
> - __fl | (fl); }))
> -# endif
> -#endif
> -
> -
> -#ifndef __ASSEMBLER__
> -
> -/* To avoid naming conflicts with lowlevellock.h, use a different prefix
> - here. */
> -#ifdef PIC
> -# define LLLF_EBX_LOAD "xchgl %2, %%ebx\n"
> -# define LLLF_EBX_REG "D"
> -#else
> -# define LLLF_EBX_LOAD
> -# define LLLF_EBX_REG "b"
> -#endif
> -
> -#ifdef I386_USE_SYSENTER
> -# ifdef SHARED
> -# define LLLF_ENTER_KERNEL "call *%%gs:%P6\n\t"
> -# else
> -# define LLLF_ENTER_KERNEL "call *_dl_sysinfo\n\t"
> -# endif
> -#else
> -# define LLLF_ENTER_KERNEL "int $0x80\n\t"
> -#endif
> -
> -
> -#define lll_futex_wait(futex, val, private) \
> - lll_futex_timed_wait (futex, val, NULL, private)
> -
> -
> -#define lll_futex_timed_wait(futex, val, timeout, private) \
> - ({ \
> - int __status; \
> - register __typeof (val) _val asm ("edx") = (val); \
> - __asm __volatile (LLLF_EBX_LOAD \
> - LLLF_ENTER_KERNEL \
> - LLLF_EBX_LOAD \
> - : "=a" (__status) \
> - : "0" (SYS_futex), LLLF_EBX_REG (futex), "S" (timeout), \
> - "c" (__lll_private_flag (FUTEX_WAIT, private)), \
> - "d" (_val), "i" (offsetof (tcbhead_t, sysinfo)) \
> - : "memory"); \
> - __status; \
> - })
> -
> -
> -#define lll_futex_wake(futex, nr, private) \
> - ({ \
> - int __status; \
> - register __typeof (nr) _nr asm ("edx") = (nr); \
> - LIBC_PROBE (lll_futex_wake, 3, futex, nr, private); \
> - __asm __volatile (LLLF_EBX_LOAD \
> - LLLF_ENTER_KERNEL \
> - LLLF_EBX_LOAD \
> - : "=a" (__status) \
> - : "0" (SYS_futex), LLLF_EBX_REG (futex), \
> - "c" (__lll_private_flag (FUTEX_WAKE, private)), \
> - "d" (_nr), \
> - "i" (0) /* phony, to align next arg's number */, \
> - "i" (offsetof (tcbhead_t, sysinfo))); \
> - __status; \
> - })
> -
> -
> -#endif /* !__ASSEMBLER__ */
> -
> -#endif /* lowlevellock-futex.h */
OK.
> diff --git a/sysdeps/unix/sysv/linux/i386/lowlevellock.h b/sysdeps/unix/sysv/linux/i386/lowlevellock.h
> index 1132124..2bf251f 100644
> --- a/sysdeps/unix/sysv/linux/i386/lowlevellock.h
> +++ b/sysdeps/unix/sysv/linux/i386/lowlevellock.h
> @@ -48,7 +48,7 @@
> #include <lowlevellock-futex.h>
>
> /* XXX Remove when no assembler code uses futexes anymore. */
> -#define SYS_futex 240
> +#define SYS_futex __NR_futex
OK. Verified against upstream kernel.
>
> #ifndef __ASSEMBLER__
>
> diff --git a/sysdeps/unix/sysv/linux/i386/sysdep.h b/sysdeps/unix/sysv/linux/i386/sysdep.h
> index 180f334..7f6fcf3 100644
> --- a/sysdeps/unix/sysv/linux/i386/sysdep.h
> +++ b/sysdeps/unix/sysv/linux/i386/sysdep.h
> @@ -304,6 +304,17 @@ asm (".L__X'%ebx = 1\n\t"
> ".endif\n\t"
> ".endm\n\t");
>
> +/* Six-argument syscalls use an out-of-line helper, because an inline
> + asm using all registers apart from %esp cannot work reliably and
> + the assembler does not support describing an asm that saves and
> + restores %ebp itself as a separate stack frame. This structure
> + stores the arguments not passed in registers; %edi is passed with a
> + pointer to this structure. */
> +struct libc_do_syscall_args
> +{
> + int ebx, edi, ebp;
> +};
OK.
> +
> /* Define a macro which expands inline into the wrapper code for a system
> call. */
> #undef INLINE_SYSCALL
> @@ -325,11 +336,42 @@ asm (".L__X'%ebx = 1\n\t"
> The _NCS variant allows non-constant syscall numbers but it is not
> possible to use more than four parameters. */
> #undef INTERNAL_SYSCALL
> -#ifdef I386_USE_SYSENTER
> -# ifdef SHARED
> -# define INTERNAL_SYSCALL(name, err, nr, args...) \
> +#define INTERNAL_SYSCALL_MAIN_0(name, err, args...) \
> + INTERNAL_SYSCALL_MAIN_INLINE(name, err, 0, args)
> +#define INTERNAL_SYSCALL_MAIN_1(name, err, args...) \
> + INTERNAL_SYSCALL_MAIN_INLINE(name, err, 1, args)
> +#define INTERNAL_SYSCALL_MAIN_2(name, err, args...) \
> + INTERNAL_SYSCALL_MAIN_INLINE(name, err, 2, args)
> +#define INTERNAL_SYSCALL_MAIN_3(name, err, args...) \
> + INTERNAL_SYSCALL_MAIN_INLINE(name, err, 3, args)
> +#define INTERNAL_SYSCALL_MAIN_4(name, err, args...) \
> + INTERNAL_SYSCALL_MAIN_INLINE(name, err, 4, args)
> +#define INTERNAL_SYSCALL_MAIN_5(name, err, args...) \
> + INTERNAL_SYSCALL_MAIN_INLINE(name, err, 5, args)
> +/* Each object using 6-argument inline syscalls must include a
> + definition of __libc_do_syscall. */
OK.
> +#define INTERNAL_SYSCALL_MAIN_6(name, err, arg1, arg2, arg3, \
> + arg4, arg5, arg6) \
> + struct libc_do_syscall_args _xv = \
> + { \
> + (int) (arg1), \
> + (int) (arg5), \
> + (int) (arg6) \
> + }; \
> + asm volatile ( \
> + "movl %1, %%eax\n\t" \
> + "call __libc_do_syscall" \
> + : "=a" (resultvar) \
> + : "i" (__NR_##name), "c" (arg2), "d" (arg3), "S" (arg4), "D" (&_xv) \
> + : "memory", "cc")
> +#define INTERNAL_SYSCALL(name, err, nr, args...) \
> ({ \
> register unsigned int resultvar; \
> + INTERNAL_SYSCALL_MAIN_##nr (name, err, args); \
> + (int) resultvar; })
> +#ifdef I386_USE_SYSENTER
> +# ifdef SHARED
> +# define INTERNAL_SYSCALL_MAIN_INLINE(name, err, nr, args...) \
OK.
> EXTRAVAR_##nr \
> asm volatile ( \
> LOADARGS_##nr \
> @@ -338,8 +380,7 @@ asm (".L__X'%ebx = 1\n\t"
> RESTOREARGS_##nr \
> : "=a" (resultvar) \
> : "i" (__NR_##name), "i" (offsetof (tcbhead_t, sysinfo)) \
> - ASMFMT_##nr(args) : "memory", "cc"); \
> - (int) resultvar; })
> + ASMFMT_##nr(args) : "memory", "cc")
OK.
> # define INTERNAL_SYSCALL_NCS(name, err, nr, args...) \
> ({ \
> register unsigned int resultvar; \
> @@ -353,9 +394,7 @@ asm (".L__X'%ebx = 1\n\t"
> ASMFMT_##nr(args) : "memory", "cc"); \
> (int) resultvar; })
> # else
> -# define INTERNAL_SYSCALL(name, err, nr, args...) \
> - ({ \
> - register unsigned int resultvar; \
> +# define INTERNAL_SYSCALL_MAIN_INLINE(name, err, nr, args...) \
> EXTRAVAR_##nr \
> asm volatile ( \
> LOADARGS_##nr \
> @@ -363,8 +402,7 @@ asm (".L__X'%ebx = 1\n\t"
> "call *_dl_sysinfo\n\t" \
> RESTOREARGS_##nr \
> : "=a" (resultvar) \
> - : "i" (__NR_##name) ASMFMT_##nr(args) : "memory", "cc"); \
> - (int) resultvar; })
> + : "i" (__NR_##name) ASMFMT_##nr(args) : "memory", "cc")
OK.
> # define INTERNAL_SYSCALL_NCS(name, err, nr, args...) \
> ({ \
> register unsigned int resultvar; \
> @@ -378,9 +416,7 @@ asm (".L__X'%ebx = 1\n\t"
> (int) resultvar; })
> # endif
> #else
> -# define INTERNAL_SYSCALL(name, err, nr, args...) \
> - ({ \
> - register unsigned int resultvar; \
> +# define INTERNAL_SYSCALL_MAIN_INLINE(name, err, nr, args...) \
OK.
> EXTRAVAR_##nr \
> asm volatile ( \
> LOADARGS_##nr \
> @@ -388,8 +424,7 @@ asm (".L__X'%ebx = 1\n\t"
> "int $0x80\n\t" \
> RESTOREARGS_##nr \
> : "=a" (resultvar) \
> - : "i" (__NR_##name) ASMFMT_##nr(args) : "memory", "cc"); \
> - (int) resultvar; })
> + : "i" (__NR_##name) ASMFMT_##nr(args) : "memory", "cc")
OK.
> # define INTERNAL_SYSCALL_NCS(name, err, nr, args...) \
> ({ \
> register unsigned int resultvar; \
>
Cheers,
Carlos.