Update trap/break handling in nios2 prologue analyzer.

2015-07-30  Sandra Loosemore  <sandra@codesourcery.com>

	gdb/
	* nios2-tdep.c (nios2_analyze_prologue): Update comments to
	reflect how current GCC emits stack overflow checks.  Match
	both trap and break instructions for backward compatibility.
	Disallow other trap and break instructions in the prologue.

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 64fbe8e55b914ea6101a4571e9fc554a91aff1f4..120148a24412a69a2d1d9d3efbd81e32906e4f71 100644 (file)
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,10 @@
+2015-07-30  Sandra Loosemore  <sandra@codesourcery.com>
+
+       * nios2-tdep.c (nios2_analyze_prologue): Update comments to
+       reflect how current GCC emits stack overflow checks.  Match
+       both trap and break instructions for backward compatbility.
+       Disallow other trap and break instructions in the prologue.
+
 2015-07-30  Pedro Alves  <palves@redhat.com>
 
        PR threads/18600

diff --git a/gdb/nios2-tdep.c b/gdb/nios2-tdep.c
index 1968a88a9f65f7b4ea502cf5ef19d6a244dd6b53..1c5dcdebfba396623d077e6c42cfbcdfb8e3180e 100644 (file)
--- a/gdb/nios2-tdep.c
+++ b/gdb/nios2-tdep.c
@@ -697,22 +697,29 @@ nios2_stack_frame_destroyed_p (struct gdbarch *gdbarch, CORE_ADDR pc)
          stw    sp, constant(rx)
          mov    sp, rx
 
-     5) A frame pointer save, which can be either a MOV or ADDI.
+     4) A frame pointer save, which can be either a MOV or ADDI.
 
-     6) A further stack pointer adjustment.  This is normally included
-        adjustment in step 4 unless the total adjustment is too large
+     5) A further stack pointer adjustment.  This is normally included
+        adjustment in step 3 unless the total adjustment is too large
        to be done in one step.
 
      7) A stack overflow check, which can take either of these forms:
          bgeu   sp, rx, +8
-         break  3
+         trap  3
        or
          bltu   sp, rx, .Lstack_overflow
          ...
        .Lstack_overflow:
-         break  3
-        If present, this is inserted after the stack pointer adjustments
-       for steps 3, 4, and 6.
+         trap  3
+         
+       Older versions of GCC emitted "break 3" instead of "trap 3" here,
+       so we check for both cases.
+
+       Older GCC versions emitted stack overflow checks after the SP
+       adjustments in both steps 3 and 4.  Starting with GCC 6, there is
+       at most one overflow check, which is placed before the first
+       stack adjustment for R2 CDX and after the first stack adjustment
+       otherwise.
 
     The prologue instructions may be combined or interleaved with other
     instructions.
@@ -995,14 +1002,15 @@ nios2_analyze_prologue (struct gdbarch *gdbarch, const CORE_ADDR start_pc,
          else if (cond == branch_geu)
            {
              /* BGEU sp, rx, +8
-                BREAK 3
+                TRAP 3  (or BREAK 3)
                 This instruction sequence is used in stack checking;
                 we can ignore it.  */
              unsigned int next_insn;
              const struct nios2_opcode *next_op
                = nios2_fetch_insn (gdbarch, pc, &next_insn);
              if (next_op != NULL
-                 && nios2_match_break (next_insn, op, mach, &uimm))
+                 && (nios2_match_trap (next_insn, op, mach, &uimm)
+                     || nios2_match_break (next_insn, op, mach, &uimm)))
                pc += next_op->size;
              else
                break;
@@ -1010,13 +1018,14 @@ nios2_analyze_prologue (struct gdbarch *gdbarch, const CORE_ADDR start_pc,
          else if (cond == branch_ltu)
            {
              /* BLTU sp, rx, .Lstackoverflow
-                If the location branched to holds a BREAK 3 instruction
-                then this is also stack overflow detection.  */
+                If the location branched to holds a TRAP or BREAK
+                instruction then this is also stack overflow detection.  */
              unsigned int next_insn;
              const struct nios2_opcode *next_op
                = nios2_fetch_insn (gdbarch, pc + imm, &next_insn);
              if (next_op != NULL
-                 && nios2_match_break (next_insn, op, mach, &uimm))
+                 && (nios2_match_trap (next_insn, op, mach, &uimm)
+                     || nios2_match_break (next_insn, op, mach, &uimm)))
                ;
              else
                break;
@@ -1025,11 +1034,13 @@ nios2_analyze_prologue (struct gdbarch *gdbarch, const CORE_ADDR start_pc,
            break;
        }
 
-      /* All other calls or jumps (including returns) terminate 
+      /* All other calls, jumps, returns, TRAPs, or BREAKs terminate
         the prologue.  */
       else if (nios2_match_callr (insn, op, mach, &ra)
               || nios2_match_jmpr (insn, op, mach, &ra)
-              || nios2_match_jmpi (insn, op, mach, &uimm))
+              || nios2_match_jmpi (insn, op, mach, &uimm)
+              || nios2_match_trap (insn, op, mach, &uimm)
+              || nios2_match_break (insn, op, mach, &uimm))
        break;
     }