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# commit 5162e7dd96efcd9b45c1dc1471a964d45278b1e1
# Author: Ulrich Weigand <Ulrich.Weigand@de.ibm.com>
# Date: Wed Dec 4 06:41:52 2013 -0600
#
# PowerPC64: Fix incorrect CFI in *context routines
#
# The context established by "makecontext" has a link register pointing
# back to an error path within the makecontext routine. This is currently
# covered by the CFI FDE for makecontext itself, which is simply wrong
# for the stack frame *inside* the context. When trying to unwind (e.g.
# doing a backtrace) in a routine inside a context created by makecontext,
# this can lead to uninitialized stack slots being accessed, causing the
# unwinder to crash in the worst case.
#
# Similarly, during parts of the "setcontext" routine, when the stack
# pointer has already been switched to point to the new context, the
# address range is still covered by the CFI FDE for setcontext. When
# trying to unwind in that situation (e.g. backtrace from an async
# signal handler for profiling), it is again possible that the unwinder
# crashes.
#
# Theses are all problems in existing code, but the changes in stack
# frame layout appear to make the "worst case" much more likely in
# the ELFv2 ABI context. This causes regressions e.g. in the libgo
# testsuite on ELFv2.
#
# This patch fixes this by ending the makecontext/setcontext FDEs
# before those problematic parts of the assembler, similar to what
# is already done on other platforms. This fixes the libgo
# regression on ELFv2.
#
diff -urN glibc-2.17-c758a686/sysdeps/unix/sysv/linux/powerpc/powerpc64/makecontext.S glibc-2.17-c758a686/sysdeps/unix/sysv/linux/powerpc/powerpc64/makecontext.S
--- glibc-2.17-c758a686/sysdeps/unix/sysv/linux/powerpc/powerpc64/makecontext.S 2014-05-29 13:16:16.000000000 -0500
+++ glibc-2.17-c758a686/sysdeps/unix/sysv/linux/powerpc/powerpc64/makecontext.S 2014-05-29 13:16:17.000000000 -0500
@@ -129,6 +129,10 @@
the cpu link stack used to predict blr return addresses. */
bcl 20,31,L(gotexitcodeaddr);
+ /* End FDE now, because while executing on the context's stack
+ the unwind info would be wrong otherwise. */
+ cfi_endproc
+
/* 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
@@ -157,6 +161,11 @@
#endif
b L(do_exit)
+ /* Re-establish FDE for the rest of the actual makecontext routine. */
+ cfi_startproc
+ cfi_offset (lr, FRAME_LR_SAVE)
+ cfi_adjust_cfa_offset (128)
+
/* The address of the exit code is in the link register. Store the lr
in the ucontext as LNK so the target function will return to our
exit code. */
diff -urN glibc-2.17-c758a686/sysdeps/unix/sysv/linux/powerpc/powerpc64/setcontext.S glibc-2.17-c758a686/sysdeps/unix/sysv/linux/powerpc/powerpc64/setcontext.S
--- glibc-2.17-c758a686/sysdeps/unix/sysv/linux/powerpc/powerpc64/setcontext.S 2014-05-29 13:16:16.000000000 -0500
+++ glibc-2.17-c758a686/sysdeps/unix/sysv/linux/powerpc/powerpc64/setcontext.S 2014-05-29 13:16:17.000000000 -0500
@@ -129,6 +129,10 @@
lfd fp1,(SIGCONTEXT_FP_REGS+(PT_R1*8))(r31)
lfd fp0,(SIGCONTEXT_FP_REGS+(PT_R0*8))(r31)
+ /* End FDE now, because the unwind info would be wrong while
+ we're reloading registers to switch to the new context. */
+ cfi_endproc
+
ld r0,(SIGCONTEXT_GP_REGS+(PT_LNK*8))(r31)
ld r1,(SIGCONTEXT_GP_REGS+(PT_R1*8))(r31)
mtlr r0
@@ -177,6 +181,11 @@
ld r31,(SIGCONTEXT_GP_REGS+(PT_R31*8))(r31)
bctr
+ /* Re-establish FDE for the rest of the actual setcontext routine. */
+ cfi_startproc
+ cfi_offset (lr, FRAME_LR_SAVE)
+ cfi_adjust_cfa_offset (128)
+
L(nv_error_exit):
ld r0,128+FRAME_LR_SAVE(r1)
addi r1,r1,128
@@ -403,6 +412,10 @@
lfd fp1,(SIGCONTEXT_FP_REGS+(PT_R1*8))(r31)
lfd fp0,(SIGCONTEXT_FP_REGS+(PT_R0*8))(r31)
+ /* End FDE now, because the unwind info would be wrong while
+ we're reloading registers to switch to the new context. */
+ cfi_endproc
+
ld r0,(SIGCONTEXT_GP_REGS+(PT_LNK*8))(r31)
ld r1,(SIGCONTEXT_GP_REGS+(PT_R1*8))(r31)
mtlr r0
@@ -451,6 +464,11 @@
ld r31,(SIGCONTEXT_GP_REGS+(PT_R31*8))(r31)
bctr
+ /* Re-establish FDE for the rest of the actual setcontext routine. */
+ cfi_startproc
+ cfi_offset (lr, FRAME_LR_SAVE)
+ cfi_adjust_cfa_offset (128)
+
L(error_exit):
ld r0,128+FRAME_LR_SAVE(r1)
addi r1,r1,128