From 4d1ae634e6b4a1ea65c4ab10f2988ffde7476e55 Mon Sep 17 00:00:00 2001 From: Aurelien Jarno Date: Fri, 9 Mar 2018 00:14:27 +0100 Subject: [PATCH] sparc32: Add nop before __startcontext to stop unwinding [BZ #22919] 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 494f98b51b..3ae0ecd07a 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,9 @@ +2018-03-09 Aurelien Jarno + + [BZ #22919] + * sysdeps/unix/sysv/linux/sparc/sparc32/setcontext.S (__startcontext): + Add nop before __startcontext, add explaining comments. + 2018-03-07 Adhemerval Zanella [BZ #22926] 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