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i386: Add <startup.h> [BZ #21913]

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On Linux/i386, there are 3 ways to make a system call:

1. call *%gs:SYSINFO_OFFSET.  This requires TLS initialization.
2. call *_dl_sysinfo.  This requires relocation of _dl_sysinfo.
3. int $0x80.  This is slower than #2 and #3, but works everywhere.

When an object file is compiled with PIC, #1 is prefered since it is
faster than #3 and doesn't require relocation of _dl_sysinfo.  For
dynamic executables, ld.so initializes TLS.  However, for static
executables, before TLS is initialized by __libc_setup_tls, #3 should
be used for system calls.

This patch adds <startup.h> which defines _startup_fatal and defaults
it to __libc_fatal.  It replaces __libc_fatal with _startup_fatal in
static executables where it is called before __libc_setup_tls is called.
This header file is included in all files containing functions which are
called before __libc_setup_tls is called.  On Linux/i386, when PIE is
enabled by default, _startup_fatal is turned into ABORT_INSTRUCTION and
I386_USE_SYSENTER is defined to 0 so that "int $0x80" is used for system
calls before __libc_setup_tls is called.

Tested on i686 and x86-64.  Without this patch, all statically-linked
tests will fail on i686 when the compiler defaults to -fPIE.

	[BZ #21913]
	* csu/libc-tls.c: Include <startup.h> first.
	(__libc_setup_tls): Call _startup_fatal instead of __libc_fatal.
	* elf/dl-tunables.c: Include <startup.h> first.
	* include/libc-symbols.h (BUILD_PIE_DEFAULT): New.
	* sysdeps/generic/startup.h: New file.
	* sysdeps/unix/sysv/linux/i386/startup.h: Likewise.
	* sysdeps/unix/sysv/linux/i386/brk.c [BUILD_PIE_DEFAULT != 0]
	(I386_USE_SYSENTER): New.  Defined to 0.
This commit is contained in:
H.J. Lu 2017-08-08 08:41:08 -07:00
parent fc5ad7024c
commit 086df229ee
7 changed files with 87 additions and 1 deletions
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12
ChangeLog
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@ -1,3 +1,15 @@
2017-08-08 H.J. Lu <hongjiu.lu@intel.com>
[BZ #21913]
* csu/libc-tls.c: Include <startup.h> first.
(__libc_setup_tls): Call _startup_fatal instead of __libc_fatal.
* elf/dl-tunables.c: Include <startup.h> first.
* include/libc-symbols.h (BUILD_PIE_DEFAULT): New.
* sysdeps/generic/startup.h: New file.
* sysdeps/unix/sysv/linux/i386/startup.h: Likewise.
* sysdeps/unix/sysv/linux/i386/brk.c [BUILD_PIE_DEFAULT != 0]
(I386_USE_SYSENTER): New. Defined to 0.
2017-08-08 Andreas Schwab <schwab@suse.de>
[BZ #21041]

3
csu/libc-tls.c
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@ -16,6 +16,7 @@
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
#include <startup.h>
#include <errno.h>
#include <ldsodefs.h>
#include <tls.h>
@ -193,7 +194,7 @@ __libc_setup_tls (void)
# error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
#endif
if (__builtin_expect (lossage != NULL, 0))
__libc_fatal (lossage);
_startup_fatal (lossage);
/* Update the executable's link map with enough information to make
the TLS routines happy. */

1
elf/dl-tunables.c
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@ -18,6 +18,7 @@
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
#include <startup.h>
#include <stdint.h>
#include <stdbool.h>
#include <unistd.h>

8
include/libc-symbols.h
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@ -84,6 +84,14 @@
#include <config.h>
/* When PIC is defined and SHARED isn't defined, we are building PIE
by default. */
#if defined PIC && !defined SHARED
# define BUILD_PIE_DEFAULT 1
#else
# define BUILD_PIE_DEFAULT 0
#endif
/* Define this for the benefit of portable GNU code that wants to check it.
Code that checks with #if will not #include <config.h> again, since we've
already done it (and this file is implicitly included in every compile,

23
sysdeps/generic/startup.h Normal file
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@ -0,0 +1,23 @@
/* Generic definitions of functions used by static libc main startup.
Copyright (C) 2017 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/>. */
/* Targets should override this file if the default definitions below
will not work correctly very early before TLS is initialized. */
/* Use macro instead of inline function to avoid including <stdio.h>. */
#define _startup_fatal(message) __libc_fatal ((message))

5
sysdeps/unix/sysv/linux/i386/brk.c
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@ -16,6 +16,11 @@
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
#if BUILD_PIE_DEFAULT
/* Can't use "call *%gs:SYSINFO_OFFSET" during statup in static PIE. */
# define I386_USE_SYSENTER 0
#endif
#include <errno.h>
#include <unistd.h>
#include <sysdep.h>

36
sysdeps/unix/sysv/linux/i386/startup.h Normal file
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@ -0,0 +1,36 @@
/* Linux/i386 definitions of functions used by static libc main startup.
Copyright (C) 2017 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/>. */
#if BUILD_PIE_DEFAULT
# include <abort-instr.h>
/* Can't use "call *%gs:SYSINFO_OFFSET" during statup in static PIE. */
# define I386_USE_SYSENTER 0
__attribute__ ((__noreturn__))
static inline void
_startup_fatal (const char *message __attribute__ ((unused)))
{
/* This is only called very early during startup in static PIE.
FIXME: How can it be improved? */
ABORT_INSTRUCTION;
__builtin_unreachable ();
}
#else
# include_next <startup.h>
#endif