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[PATCH] sparc32: Add nop before __startcontext to stop unwinding [BZ #xxxxx]
- From: Aurelien Jarno <aurelien at aurel32 dot net>
- To: libc-alpha at sourceware dot org
- Cc: Aurelien Jarno <aurelien at aurel32 dot net>
- Date: Sat, 3 Mar 2018 10:10:18 +0100
- Subject: [PATCH] sparc32: Add nop before __startcontext to stop unwinding [BZ #xxxxx]
- Authentication-results: sourceware.org; auth=none
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.
---
ChangeLog | 6 ++++++
sysdeps/unix/sysv/linux/sparc/sparc32/setcontext.S | 13 +++++++++++++
2 files changed, 19 insertions(+)
diff --git a/ChangeLog b/ChangeLog
index 4b7e0a0261..6216817498 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2018-03-03 Aurelien Jarno <aurelien@aurel32.net>
+
+ [BZ #22919]
+ * sysdeps/unix/sysv/linux/sparc/sparc32/setcontext.S (__startcontext):
+ Add nop before __startcontext, add explaining comments.
+
2018-03-01 Maciej W. Rozycki <macro@mips.com>
* nptl_db/td_ta_thr_iter.c (iterate_thread_list): Remove
diff --git a/sysdeps/unix/sysv/linux/sparc/sparc32/setcontext.S b/sysdeps/unix/sysv/linux/sparc/sparc32/setcontext.S
index 695f172c63..283aef1b30 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