From 0ac4f1dab3e5778c79994a89111b4eb1d247ab12 Mon Sep 17 00:00:00 2001 From: Chris Metcalf Date: Tue, 21 Jul 2015 12:04:52 -0400 Subject: 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. --- sysdeps/unix/sysv/linux/tile/makecontext.c | 8 ++++---- sysdeps/unix/sysv/linux/tile/setcontext.S | 2 ++ 2 files changed, 6 insertions(+), 4 deletions(-) (limited to 'sysdeps') diff --git a/sysdeps/unix/sysv/linux/tile/makecontext.c b/sysdeps/unix/sysv/linux/tile/makecontext.c index b14b8d5cc9..c77d005672 100644 --- a/sysdeps/unix/sysv/linux/tile/makecontext.c +++ b/sysdeps/unix/sysv/linux/tile/makecontext.c @@ -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; diff --git a/sysdeps/unix/sysv/linux/tile/setcontext.S b/sysdeps/unix/sysv/linux/tile/setcontext.S index ee9edbefe1..02d6a1578c 100644 --- a/sysdeps/unix/sysv/linux/tile/setcontext.S +++ b/sysdeps/unix/sysv/linux/tile/setcontext.S @@ -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 -- cgit 1.4.1