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[HURD, PATCH] Fix stack switching at initialization time
- From: ludo at gnu dot org (Ludovic Courtès)
- To: libc-alpha at sourceware dot org
- Cc: bug-hurd at gnu dot org
- Date: Fri, 22 Jul 2011 15:48:29 +0200
- Subject: [HURD, PATCH] Fix stack switching at initialization time
Hello,
The attached patch fixes stack switching in init-first.c when cthreads
are used (this is for code compiled with a cross-GCC 4.5.1 for
i586-pc-gnu; Debian GNU/Hurd uses an older GCC and is not affected.)
With this compiler, âdata[-1]â does not point to the return address.
Thus, âswitch_stacksâ would never be called, which breaks TLS.
It seems to me that using âdata[-1]â here was fragile in the presence of
nested functions, inlining, and tail-call optimizations.
Thanks,
Ludoâ.
>From efa6d7e310b1d8918054222483f100d43525ba66 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ludovic=20Court=C3=A8s?= <ludo@gnu.org>
Date: Fri, 22 Jul 2011 15:46:11 +0200
Subject: [PATCH] Hurd: Fix stack switching at initialization time when using
cthreads.
---
ChangeLog | 7 +++++++
sysdeps/mach/hurd/i386/init-first.c | 4 ++--
2 files changed, 9 insertions(+), 2 deletions(-)
diff --git a/ChangeLog b/ChangeLog
index 606bc22..6239986 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2011-07-22 Ludovic Courtès <ludo@gnu.org>
+
+ * sysdeps/mach/hurd/i386/init-first.c (init): Use
+ `__builtin_return_address' and `__builtin_frame_address' instead
+ of making assumptions about the location of the return address
+ relative to DATA.
+
2010-04-09 Ulrich Drepper <drepper@redhat.com>
* nscd/aicache.c (addhstaiX): Correct passing memory to address
diff --git a/sysdeps/mach/hurd/i386/init-first.c b/sysdeps/mach/hurd/i386/init-first.c
index 7d93638..09af037 100644
--- a/sysdeps/mach/hurd/i386/init-first.c
+++ b/sysdeps/mach/hurd/i386/init-first.c
@@ -257,8 +257,8 @@ init (int *data)
/* Push the user code address on the top of the new stack. It will
be the return address for `init1'; we will jump there with NEWSP
as the stack pointer. */
- *--newsp = data[-1];
- data[-1] = (int) &switch_stacks;
+ *--newsp = __builtin_return_address (0);
+ * ((void **) __builtin_frame_address (0) + 1) = &switch_stacks;
/* Force NEWSP into %eax and &init1 into %ecx, which are not restored
by function return. */
asm volatile ("# a %0 c %1" : : "a" (newsp), "c" (&init1));
--
1.7.6