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sparc32: Add nop before __startcontext to stop unwinding [BZ #22919]

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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.
This commit is contained in:
Aurelien Jarno
2018-03-09 00:14:27 +01:00
parent e921c89e01
commit 9aa5c222b9
2 changed files with 19 additions and 0 deletions
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13
sysdeps/unix/sysv/linux/sparc/sparc32/setcontext.S
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@ -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