[committed] MIPS: Make the extracted stack offset signed in the prologue scanner

[committed] MIPS: Make the extracted stack offset signed in the prologue scanner

[Maciej W. Rozycki]

Hi,

 I have committed this change to clean up the handling of the stack offset 
in the standard MIPS prologue scanner.  It is now treated as signed 
similarly to how the microMIPS version prologue scanner handles it.  This 
simplifies handling and makes register offsets correct in all cases, 
especially where $fp is the virtual frame pointer.

2015-01-02  Maciej W. Rozycki  <macro@codesourcery.com>

	gdb/
	* mips-tdep.c (mips32_scan_prologue): Make the extracted stack
	offset signed.

  Maciej

gdb-mips-scan-prologue-offset.diff
Index: gdb-fsf-trunk-quilt/gdb/mips-tdep.c
===================================================================
--- gdb-fsf-trunk-quilt.orig/gdb/mips-tdep.c	2014-10-13 13:40:57.657712716 +0100
+++ gdb-fsf-trunk-quilt/gdb/mips-tdep.c	2014-10-13 13:42:23.167881635 +0100
@@ -3394,7 +3394,8 @@ mips32_scan_prologue (struct gdbarch *gd
   frame_offset = 0;
   for (cur_pc = start_pc; cur_pc < limit_pc; cur_pc += MIPS_INSN32_SIZE)
     {
-      unsigned long inst, high_word, low_word;
+      unsigned long inst, high_word;
+      long offset;
       int reg;
 
       this_non_prologue_insn = 0;
@@ -3406,15 +3407,15 @@ mips32_scan_prologue (struct gdbarch *gd
 
       /* Save some code by pre-extracting some useful fields.  */
       high_word = (inst >> 16) & 0xffff;
-      low_word = inst & 0xffff;
+      offset = ((inst & 0xffff) ^ 0x8000) - 0x8000;
       reg = high_word & 0x1f;
 
       if (high_word == 0x27bd		/* addiu $sp,$sp,-i */
 	  || high_word == 0x23bd	/* addi $sp,$sp,-i */
 	  || high_word == 0x67bd)	/* daddiu $sp,$sp,-i */
 	{
-	  if (low_word & 0x8000)	/* Negative stack adjustment?  */
-            frame_offset += 0x10000 - low_word;
+	  if (offset < 0)		/* Negative stack adjustment?  */
+            frame_offset -= offset;
 	  else
 	    /* Exit loop if a positive stack adjustment is found, which
 	       usually means that the stack cleanup code in the function
@@ -3425,19 +3426,19 @@ mips32_scan_prologue (struct gdbarch *gd
       else if (((high_word & 0xFFE0) == 0xafa0) /* sw reg,offset($sp) */
                && !regsize_is_64_bits)
 	{
-	  set_reg_offset (gdbarch, this_cache, reg, sp + low_word);
+	  set_reg_offset (gdbarch, this_cache, reg, sp + offset);
 	}
       else if (((high_word & 0xFFE0) == 0xffa0)	/* sd reg,offset($sp) */
                && regsize_is_64_bits)
 	{
 	  /* Irix 6.2 N32 ABI uses sd instructions for saving $gp and $ra.  */
-	  set_reg_offset (gdbarch, this_cache, reg, sp + low_word);
+	  set_reg_offset (gdbarch, this_cache, reg, sp + offset);
 	}
       else if (high_word == 0x27be)	/* addiu $30,$sp,size */
 	{
 	  /* Old gcc frame, r30 is virtual frame pointer.  */
-	  if ((long) low_word != frame_offset)
-	    frame_addr = sp + low_word;
+	  if (offset != frame_offset)
+	    frame_addr = sp + offset;
 	  else if (this_frame && frame_reg == MIPS_SP_REGNUM)
 	    {
 	      unsigned alloca_adjust;
@@ -3447,7 +3448,7 @@ mips32_scan_prologue (struct gdbarch *gd
 		(this_frame, gdbarch_num_regs (gdbarch) + 30);
 	      frame_offset = 0;
 
-	      alloca_adjust = (unsigned) (frame_addr - (sp + low_word));
+	      alloca_adjust = (unsigned) (frame_addr - (sp + offset));
 	      if (alloca_adjust > 0)
 		{
                   /* FP > SP + frame_size.  This may be because of
@@ -3496,7 +3497,7 @@ mips32_scan_prologue (struct gdbarch *gd
       else if ((high_word & 0xFFE0) == 0xafc0 	/* sw reg,offset($30) */
                && !regsize_is_64_bits)
 	{
-	  set_reg_offset (gdbarch, this_cache, reg, frame_addr + low_word);
+	  set_reg_offset (gdbarch, this_cache, reg, frame_addr + offset);
 	}
       else if ((high_word & 0xFFE0) == 0xE7A0 /* swc1 freg,n($sp) */
                || (high_word & 0xF3E0) == 0xA3C0 /* sx reg,n($s8) */