[ARM/FDPIC v6 13/24] [ARM] FDPIC: Force LSB bit for PC in Cortex-M architecture

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.

2019-09-10  Christophe Lyon  <christophe.lyon@st.com>
	Mickaël Guêné <mickael.guene@st.com>

	libgcc/
	* config/arm/unwind-arm.c (_Unwind_VRS_Set): Handle thumb-only
	architecture.


Co-Authored-By: Mickaël Guêné <mickael.guene@st.com>

From-SVN: r275575

libgcc/ChangeLog

 2019-09-10  Christophe Lyon  <christophe.lyon@st.com>
 	Mickaël Guêné <mickael.guene@st.com>
 
-	libgcc/
+	* config/arm/unwind-arm.c (_Unwind_VRS_Set): Handle thumb-only
+	architecture.
+
+2019-09-10  Christophe Lyon  <christophe.lyon@st.com>
+	Mickaël Guêné <mickael.guene@st.com>
+
 	* unwind-arm-common.inc (ARM_SET_R7_RT_SIGRETURN)
 	(THUMB2_SET_R7_RT_SIGRETURN, FDPIC_LDR_R12_WITH_FUNCDESC)
 	(FDPIC_LDR_R9_WITH_GOT, FDPIC_LDR_PC_WITH_RESTORER)

libgcc/config/arm/unwind-arm.c

@@ -199,6 +199,11 @@ _Unwind_VRS_Result _Unwind_VRS_Set (_Unwind_Context *context,
 	return _UVRSR_FAILED;
 
       vrs->core.r[regno] = *(_uw *) valuep;
+#if defined(__thumb__)
+      /* Force LSB bit since we always run thumb code.  */
+      if (regno == R_PC)
+	vrs->core.r[regno] |= 1;
+#endif
       return _UVRSR_OK;
 
     case _UVRSC_VFP: