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) {