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[ARM/FDPIC v2 13/21] [ARM] FDPIC: Force LSB bit for PC in Cortex-M architecture

From: Christophe Lyon <>

Without this, when we are unwinding across a signal frame we can jump
to an even address which leads to an exception.

This is needed in __gnu_persnality_sigframe_fdpic() when restoring the
PC from the signal frame since the PC saved by the kernel has the LSB
bit set to zero.

2018-XX-XX  Christophe Lyon  <>
	Mickaël Guêné <>

	* config/arm/unwind-arm.c (_Unwind_VRS_Set): Handle v7m

Change-Id: Ie84de548226bcf1751e19a09e8f091fb3013ccea

diff --git a/libgcc/config/arm/unwind-arm.c b/libgcc/config/arm/unwind-arm.c
index 564e4f13..6da6e3d 100644
--- a/libgcc/config/arm/unwind-arm.c
+++ b/libgcc/config/arm/unwind-arm.c
@@ -198,6 +198,11 @@ _Unwind_VRS_Result _Unwind_VRS_Set (_Unwind_Context *context,
 	return _UVRSR_FAILED;
       vrs->core.r[regno] = *(_uw *) valuep;
+#if defined(__ARM_ARCH_7M__)
+      /* Force LSB bit since we always run thumb code.  */
+      if (regno == 15)
+	vrs->core.r[regno] |= 1;
       return _UVRSR_OK;
     case _UVRSC_VFP:

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