This is the mail archive of the
libc-alpha@sourceware.org
mailing list for the glibc project.
Re: [PATCH] i386: Add _startup_sbrk and _startup_fatal [BZ #21913]
On Mon, Aug 7, 2017 at 10:39 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Mon, Aug 7, 2017 at 10:37 AM, Andreas Schwab <schwab@linux-m68k.org> wrote:
>> On Aug 07 2017, "H.J. Lu" <hjl.tools@gmail.com> wrote:
>>
>>> Given this, we need a working sbrk before TLS is initialized.
>>
>> How about making sbrk always use int $0x80?
>>
>> Andreas.
>
> We can do that in sbrk.o and will make change less complex.
> I will give it a try.
>
Here is a patch to add <startup.h>. Tested on i686. OK for master?
--
H.J.
From 99dd28489e425c6f654126871f89d514331aa69f 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 syscalls.
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.
[BZ #21913]
* config.h.in (BUILD_PIE_DEFAULT): New.
* csu/libc-tls.c: Include <startup.h>.
* elf/dl-tunables.c: Likewise.
* sysdeps/unix/sysv/linux/i386/brk.c: Likewise.
* csu/libc-tls.c: Include <startup.h>.
(__libc_setup_tls): Call _startup_fatal instead of __libc_fatal.
* sysdeps/generic/startup.h: New file.
* sysdeps/unix/sysv/linux/i386/startup.h: Likewise.
---
config.h.in | 6 ++++++
csu/libc-tls.c | 3 ++-
elf/dl-tunables.c | 1 +
sysdeps/generic/startup.h | 20 +++++++++++++++++++
sysdeps/unix/sysv/linux/i386/brk.c | 1 +
sysdeps/unix/sysv/linux/i386/startup.h | 36 ++++++++++++++++++++++++++++++++++
6 files changed, 66 insertions(+), 1 deletion(-)
create mode 100644 sysdeps/generic/startup.h
create mode 100644 sysdeps/unix/sysv/linux/i386/startup.h
diff --git a/config.h.in b/config.h.in
index 22418576a0..a00eb511f2 100644
--- a/config.h.in
+++ b/config.h.in
@@ -47,6 +47,12 @@
#undef STACK_PROTECTOR_LEVEL
#endif
+/* 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
+
/* Define if the regparm attribute shall be used for local functions
(gcc on ix86 only). */
#undef USE_REGPARMS
diff --git a/csu/libc-tls.c b/csu/libc-tls.c
index 3c897bf28b..00138eb43a 100644
--- a/csu/libc-tls.c
+++ b/csu/libc-tls.c
@@ -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. */
diff --git a/elf/dl-tunables.c b/elf/dl-tunables.c
index 231fb8ca93..b964a09413 100644
--- a/elf/dl-tunables.c
+++ b/elf/dl-tunables.c
@@ -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>
diff --git a/sysdeps/generic/startup.h b/sysdeps/generic/startup.h
new file mode 100644
index 0000000000..196f49edc3
--- /dev/null
+++ b/sysdeps/generic/startup.h
@@ -0,0 +1,20 @@
+/* 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/>. */
+
+/* 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..bb9cf7ac35 100644
--- a/sysdeps/unix/sysv/linux/i386/brk.c
+++ b/sysdeps/unix/sysv/linux/i386/brk.c
@@ -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 <unistd.h>
#include <sysdep.h>
diff --git a/sysdeps/unix/sysv/linux/i386/startup.h b/sysdeps/unix/sysv/linux/i386/startup.h
new file mode 100644
index 0000000000..a8fd3134b7
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/i386/startup.h
@@ -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/>. */
+
+#ifdef 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
--
2.13.3