1 files changed, 35 insertions, 9 deletions

diff --git a/arch/sh/kernel/dwarf.c b/arch/sh/kernel/dwarf.c
index 49d039f19426..83f3cc92549f 100644
--- a/arch/sh/kernel/dwarf.c
+++ b/arch/sh/kernel/dwarf.c
@@ -330,6 +330,7 @@ struct dwarf_fde *dwarf_lookup_fde(unsigned long pc)
  *	@fde: the FDE for this function
  *	@frame: the instructions calculate the CFA for this frame
  *	@pc: the program counter of the address we're interested in
+ *	@define_ra: keep executing insns until the return addr reg is defined?
  *
  *	Execute the Call Frame instruction sequence starting at
  *	@insn_start and ending at @insn_end. The instructions describe
@@ -341,17 +342,36 @@ static int dwarf_cfa_execute_insns(unsigned char *insn_start,
 				   struct dwarf_cie *cie,
 				   struct dwarf_fde *fde,
 				   struct dwarf_frame *frame,
-				   unsigned long pc)
+				   unsigned long pc,
+				   bool define_ra)
 {
 	unsigned char insn;
 	unsigned char *current_insn;
 	unsigned int count, delta, reg, expr_len, offset;
+	bool seen_ra_reg;
 
 	current_insn = insn_start;
 
-	while (current_insn < insn_end && frame->pc <= pc) {
+	/*
+	 * If we're executing instructions for the dwarf_unwind_stack()
+	 * FDE we need to keep executing instructions until the value of
+	 * DWARF_ARCH_RA_REG is defined. See the comment in
+	 * dwarf_unwind_stack() for more details.
+	 */
+	if (define_ra)
+		seen_ra_reg = false;
+	else
+		seen_ra_reg = true;
+
+	while (current_insn < insn_end && (frame->pc <= pc || !seen_ra_reg) ) {
 		insn = __raw_readb(current_insn++);
 
+		if (!seen_ra_reg) {
+			if (frame->num_regs >= DWARF_ARCH_RA_REG &&
+			    frame->regs[DWARF_ARCH_RA_REG].flags)
+				seen_ra_reg = true;
+		}
+
 		/*
 		 * Firstly, handle the opcodes that embed their operands
 		 * in the instructions.
@@ -490,20 +510,25 @@ struct dwarf_frame *dwarf_unwind_stack(unsigned long pc,
 	struct dwarf_fde *fde;
 	unsigned long addr;
 	int i, offset;
+	bool define_ra = false;
 
 	/*
 	 * If this is the first invocation of this recursive function we
 	 * need get the contents of a physical register to get the CFA
 	 * in order to begin the virtual unwinding of the stack.
 	 *
-	 * The constant DWARF_ARCH_UNWIND_OFFSET is added to the address of
-	 * this function because the return address register
-	 * (DWARF_ARCH_RA_REG) will probably not be initialised until a
-	 * few instructions into the prologue.
+	 * Setting "define_ra" to true indictates that we want
+	 * dwarf_cfa_execute_insns() to continue executing instructions
+	 * until we know how to calculate the value of DWARF_ARCH_RA_REG
+	 * (which we need in order to kick off the whole unwinding
+	 * process).
+	 *
+	 * NOTE: the return address is guaranteed to be setup by the
+	 * time this function makes its first function call.
 	 */
 	if (!pc && !prev) {
 		pc = (unsigned long)&dwarf_unwind_stack;
-		pc += DWARF_ARCH_UNWIND_OFFSET;
+		define_ra = true;
 	}
 
 	frame = kzalloc(sizeof(*frame), GFP_KERNEL);
@@ -539,11 +564,12 @@ struct dwarf_frame *dwarf_unwind_stack(unsigned long pc,
 
 	/* CIE initial instructions */
 	dwarf_cfa_execute_insns(cie->initial_instructions,
-				cie->instructions_end, cie, fde, frame, pc);
+				cie->instructions_end, cie, fde,
+				frame, pc, false);
 
 	/* FDE instructions */
 	dwarf_cfa_execute_insns(fde->instructions, fde->end, cie,
-				fde, frame, pc);
+				fde, frame, pc, define_ra);
 
 	/* Calculate the CFA */
 	switch (frame->flags) {