[PATCH] MIPS/GAS: Correct ISA bit handling in backreferences

["Maciej W. Rozycki" <macro at codesourcery dot com>]

Hi,

 While working on a test case for a bug fix I am going to send next I 
noticed he ISA bit is not set correctly in references to labels applied to 
the instruction being assembled, for example in this calculation:

	.set	micromips
0:
	nop
1:
	li	$2, 1b - 0b

the value loaded to $2 will be 1 rather than expected 2.  This is because 
at the point the subtraction is evaluated the internal symbol associated 
with the 0 label has the ISA bit set and the symbol used for 1 has the ISA 
bit clear.  This happens because the ISA bit is only calculated for labels 
once the respective instructions they have been applied to have been 
completely assembled each.  This affects both MIPS16 and microMIPS code 
and looks like a long-standing bug.

 The change below adds a call to mips_mark_labels at the beginning of 
instruction processing so that the ISA bit is updated on the internal 
symbol straight away.  The function is called in several places already 
and further auditing may be desirable to move or remove some of the other 
ones that may have become redundant with this change.  This is however not 
strictly necessary.

 An update to a test case source complements the change -- it inadvertenly 
relied on the bug and escaped the case where the argument to the first ORI 
is 0x3fffffff owing to the difference calculated coming out as -1.  This 
is fixed by ensuring the ISA bit is clear on the label used for the 
subtraction.  No other test regressions were observed.

 I made no separate test case for this change, it is covered by the test 
case referred above that I'll be sending shortly.

 OK to apply?

2012-09-21  Maciej W. Rozycki  <macro@codesourcery.com>

	gas/
	* config/tc-mips.c (md_assemble): Add a call to mips_mark_labels.

	gas/testsuite/
	* gas/mips/branch-swap-2.s: Make sure the ISA bit is clear in
	the label used for calculation.

  Maciej

binutils-gas-mips-mark-labels.diff
Index: binutils-fsf-trunk-quilt/gas/config/tc-mips.c
===================================================================
--- binutils-fsf-trunk-quilt.orig/gas/config/tc-mips.c	2012-09-18 17:46:57.251764230 +0100
+++ binutils-fsf-trunk-quilt/gas/config/tc-mips.c	2012-09-18 17:47:14.691764019 +0100
@@ -2555,6 +2555,8 @@ md_assemble (char *str)
   offset_reloc[1] = BFD_RELOC_UNUSED;
   offset_reloc[2] = BFD_RELOC_UNUSED;
 
+  mips_mark_labels ();
+
   if (mips_opts.mips16)
     mips16_ip (str, &insn);
   else
Index: binutils-fsf-trunk-quilt/gas/testsuite/gas/mips/branch-swap-2.s
===================================================================
--- binutils-fsf-trunk-quilt.orig/gas/testsuite/gas/mips/branch-swap-2.s	2012-09-18 17:46:57.251764230 +0100
+++ binutils-fsf-trunk-quilt/gas/testsuite/gas/mips/branch-swap-2.s	2012-09-18 17:47:14.691764019 +0100
@@ -1,8 +1,11 @@
 	.set	micromips
 	.text
 foo:
+	.insn				# Keep the ISA bit set on foo.
+bar:
+	.fill	0			# Keep the ISA bit clear on bar.
 	.rept	count
-	ori	$2, $3, (. - foo) >> 2
+	ori	$2, $3, (. - bar) >> 2
 	.endr
 	addu	$2, $3, $4
 	j	ext