Message ID | 20180303091018.32019-1-aurelien@aurel32.net |
---|---|
State | New |
Headers | show |
Series | sparc32: Add nop before __startcontext to stop unwinding [BZ #xxxxx] | expand |
From: Aurelien Jarno <aurelien@aurel32.net> Date: Sat, 3 Mar 2018 10:10:18 +0100 > 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. Yeah this stuff is really tricky, thanks for fixing this.
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