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fix bugs in cancellable syscall asm

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x86_64 was just plain wrong in the cancel-flag-already-set path, and
crashing.

the more subtle error was not clearing the saved stack pointer before
returning to c code. this could result in the signal handler
misidentifying c code as the pre-syscall part of the asm, and acting
on cancellation at the wrong time, and thus resource leak race
conditions.

also, now __cancel (in the c code) is responsible for clearing the
saved sp in the already-cancelled branch. this means we have to use
call rather than jmp to ensure the stack pointer in the c will never
match what the asm saved.
This commit is contained in:
Rich Felker
2011-04-17 15:30:08 -04:00
parent ebf82447be
commit 09dae2b7b6
3 changed files with 12 additions and 11 deletions
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3
src/thread/cancel_impl.c
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@ -3,6 +3,7 @@
void __cancel()
{
pthread_t self = __pthread_self();
self->cp_sp = 0;
self->canceldisable = 1;
self->cancelasync = 0;
pthread_exit(PTHREAD_CANCELED);
@ -24,8 +25,8 @@ long (__syscall_cp)(long nr, long u, long v, long w, long x, long y, long z)
self->cp_sp = 0;
self->cp_ip = 0;
r = __syscall_cp_asm(&self->cp_sp, nr, u, v, w, x, y, z);
self->cp_sp = old_sp;
self->cp_ip = old_ip;
self->cp_sp = old_sp;
if (r == -EINTR && self->cancel) __cancel();
return r;
}