Re: Support six-argument syscalls from C for 32-bit x86, use generic lowlevellock-futex.h (bug 18138)

["Carlos O'Donell" <carlos at redhat dot com>]

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.