From: Aurelien Jarno <aurelien@aurel32.net>
To: libc-stable@sourceware.org
Cc: Aurelien Jarno <aurelien@aurel32.net>
Subject: [2.27 COMMITTED] sparc32: Add nop before __startcontext to stop unwinding [BZ #22919]
Date: Mon, 01 Jan 2018 00:00:00 -0000 [thread overview]
Message-ID: <20180308233149.20477-1-aurelien@aurel32.net> (raw)
On sparc32 tst-makecontext fails, as backtrace called within a context
created by makecontext to yield infinite backtrace.
Fix that the same way than nios2 by adding a nop just before
__startcontext. This is needed as otherwise FDE lookup just repeatedly
finds __setcontext's FDE in an infinite loop, due to the convention of
using 'address - 1' for FDE lookup.
Changelog:
[BZ #22919]
* sysdeps/unix/sysv/linux/sparc/sparc32/setcontext.S (__startcontext):
Add nop before __startcontext, add explaining comments.
(cherry picked from commit 9aa5c222b9e0409143410a02b6364a3b25dbf028)
---
ChangeLog | 6 ++++++
sysdeps/unix/sysv/linux/sparc/sparc32/setcontext.S | 13 +++++++++++++
2 files changed, 19 insertions(+)
diff --git a/ChangeLog b/ChangeLog
index 494f98b51b3..3ae0ecd07a3 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2018-03-09 Aurelien Jarno <aurelien@aurel32.net>
+
+ [BZ #22919]
+ * sysdeps/unix/sysv/linux/sparc/sparc32/setcontext.S (__startcontext):
+ Add nop before __startcontext, add explaining comments.
+
2018-03-07 Adhemerval Zanella <adhemerval.zanella@linaro.org>
[BZ #22926]
diff --git a/sysdeps/unix/sysv/linux/sparc/sparc32/setcontext.S b/sysdeps/unix/sysv/linux/sparc/sparc32/setcontext.S
index 695f172c634..283aef1b304 100644
--- a/sysdeps/unix/sysv/linux/sparc/sparc32/setcontext.S
+++ b/sysdeps/unix/sysv/linux/sparc/sparc32/setcontext.S
@@ -95,6 +95,19 @@ END(__setcontext)
weak_alias (__setcontext, setcontext)
+/* We add an NOP here to separate between __setcontext/__startcontext. The
+ wanted behavior that happens is: when unwinding from a function called
+ inside a makecontext() context, FDE lookup will use '&__startcontext - 1',
+ then returns NULL for no FDE found, and immediately ends the unwind, in
+ a normal fashion.
+
+ If this NOP word does not exist, FDE lookup just repeatedly finds
+ __setcontext's FDE in an infinite loop, due to the convention of using
+ 'address - 1' for FDE lookup. Modifiying/deleting the below
+ __startcontext's FDE has no help on this. */
+
+ nop
+
/* This is the helper code which gets called if a function which is
registered with 'makecontext' returns. In this case we have to
install the context listed in the uc_link element of the context
--
2.16.1
reply other threads:[~2018-03-08 23:33 UTC|newest]
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