i386: Add _startup_sbrk and _startup_fatal [BZ #21913]
Commit Message
On Tue, Aug 8, 2017 at 5:43 AM, Carlos O'Donell <carlos@redhat.com> wrote:
> On 08/07/2017 05:17 PM, H.J. Lu wrote:
>> From 58d4201ae107eab72478a366a24135246236f060 Mon Sep 17 00:00:00 2001
>> From: "H.J. Lu" <hjl.tools@gmail.com>
>> Date: Wed, 19 Jul 2017 14:32:42 -0700
>> Subject: [PATCH] i386: Add <startup.h> [BZ #21913]
>>
>> 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.
>
> Overall I don't have any objections except that you have a typo-prone
> macro API that needs fixing.
>
>> [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]
>> (I386_USE_SYSENTER): New. Defined to 0.
>
>
>>
>> +/* When PIC is defined and SHARED isn't defined, we are building PIE
>> + by default. */
>> +#if defined PIC && !defined SHARED
>> +# define BUILD_PIE_DEFAULT
>> +#endif
>
> This is typo-prone.
>
> We should define BUILD_PIE_DEFAULT to 1 or 0, and always defined.
Done.
>
>> +/* Use macro instead of inline function to avoid including <stdio.h>. */
>> +#define _startup_fatal(message) __libc_fatal ((message))
>> diff --git a/sysdeps/unix/sysv/linux/i386/brk.c b/sysdeps/unix/sysv/linux/i386/brk.c
>> index 25ab1015d3..b55f0236d1 100644
>> --- a/sysdeps/unix/sysv/linux/i386/brk.c
>> +++ b/sysdeps/unix/sysv/linux/i386/brk.c
>> @@ -16,6 +16,11 @@
>> License along with the GNU C Library; if not, see
>> <http://www.gnu.org/licenses/>. */
>>
>> +#ifdef BUILD_PIE_DEFAULT
>
> This is a typo-prone macro-api and should use #if to allow -Wunused
> checking.
Done.
>> +
>> +#ifdef BUILD_PIE_DEFAULT
>
> Likewise.
Done.
>> +# include <abort-instr.h>
>> +
>
Here is the patch I am checking in.
From a5eb29646bbc64530b4133c08061079ae3450633 Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Wed, 19 Jul 2017 14:32:42 -0700
Subject: [PATCH] i386: Add <startup.h> [BZ #21913]
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.
---
csu/libc-tls.c | 3 ++-
elf/dl-tunables.c | 1 +
include/libc-symbols.h | 8 ++++++++
sysdeps/generic/startup.h | 23 ++++++++++++++++++++++
sysdeps/unix/sysv/linux/i386/brk.c | 5 +++++
sysdeps/unix/sysv/linux/i386/startup.h | 36 ++++++++++++++++++++++++++++++++++
6 files changed, 75 insertions(+), 1 deletion(-)
create mode 100644 sysdeps/generic/startup.h
create mode 100644 sysdeps/unix/sysv/linux/i386/startup.h
@@ -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. */
@@ -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>
@@ -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,
new file mode 100644
@@ -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))
@@ -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>
new file mode 100644
@@ -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
--
2.13.4