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signal: Add comment on why we don't use the restorer.

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* lib/linux/signal.c: Add comment on why we don't use the restorer.
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Danny Milosavljevic 2019-07-04 13:22:42 +02:00 committed by Jan Nieuwenhuizen
parent 4a183fa1cf
commit 23d857c834
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lib/linux/signal.c
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@ -44,6 +44,16 @@ signal (int signum, sighandler_t action)
unsigned short itembitcount;
setup_action.sa_handler = action;
/* The sa_restorer is not used. Reason:
* The kernel uses its own restorer anyway by pretending we gave one on
our side (no, really).
glibc still has a custom restorer because they want to be able to
backtrace. gdb has a second part that detects a specific instruction
sequence and then fixes up the backtrace. Since we don't use that
specific instruction sequence and also the non-siginfo restorer
is complicated (pops foreign item off the stack--so needs inline
assembly) and we don't support great debuggability in other places,
I've decided to take the easy way out for now. */
/*setup_action.sa_restorer = _restorer_for_siginfo;*/
bitindex = signum - 1;
itembitcount = 8 * sizeof(setup_action.sa_mask.items[0]);