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tile: Fix BZ #18508 (makecontext yield infinite backtrace) 

It turns out tile suffered from the same problem as S390.  However,
disabling CFI information for the __startcontext on tile was not
sufficient to fix the problem; I think the backtracer will just
blindly try to follow the link register (lr) in that case.

Instead, the change adds a cfi_undefined directive for "lr"
and then arranges to call __startcontext directly when the new
context starts, rather than just synthesizing a return to it.
In addition to being a bit easier now to understand the control
flow, this also allows the cfi_undefined directive to be placed in
a way that causes it to be in force at the address that the "lr"
from the called function points to.
This commit is contained in:
Chris Metcalf 2015-07-21 12:04:52 -04:00
parent f30d94a74a
commit 0ac4f1dab3
3 changed files with 13 additions and 4 deletions
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7
ChangeLog
View File

@ -1,3 +1,10 @@
2015-07-21 Chris Metcalf <cmetcalf@ezchip.com>
* sysdeps/unix/sysv/linux/tile/makecontext.c (__makecontext): Call
__startcontext to initialize the new context.
* sysdeps/unix/sysv/linux/tile/setcontext.S (__startcontext): Set
up CFI directive to forbid further backtracing.
2015-07-21 Marko Myllynen <myllynen@redhat.com>
* charmaps/ANSI_X3.110-1983: Remove obsolete repertoire map

8
sysdeps/unix/sysv/linux/tile/makecontext.c
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@ -52,14 +52,14 @@ __makecontext (ucontext_t *ucp, void (*func) (void), int argc, ...)
}
va_end (ap);
/* Pass (*func) to __startcontext in pc. */
ucp->uc_mcontext.pc = (long) func;
/* Start in the trampoline. */
ucp->uc_mcontext.pc = (long) __startcontext;
/* Set stack pointer. */
ucp->uc_mcontext.sp = (long) sp;
/* Set the return address to trampoline. */
ucp->uc_mcontext.lr = (long) __startcontext;
/* Pass FUNC to __startcontext in r31. */
ucp->uc_mcontext.gregs[31] = (long) func;
/* Pass ucp->uc_link to __startcontext in r30. */
ucp->uc_mcontext.gregs[30] = (long) ucp->uc_link;

2
sysdeps/unix/sysv/linux/tile/setcontext.S
View File

@ -190,7 +190,9 @@ END (__setcontext)
weak_alias (__setcontext, setcontext)
ENTRY (__startcontext)
cfi_undefined (lr)
FEEDBACK_ENTER(__startcontext)
jalr r31
BEQZ r30, 1f
{
move r0, r30