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