[PATCH] microMIPS/GAS: Avoid relocation overflow with forced 16-bit branches

[Maciej W. Rozycki]

Hi,

 The change below fixes a relocation overflow triggered by forced 16-bit 
branches:

$ cat b16.s
	.text
test1:
	.space	65536
test2:
	b16	1f
1:
$ mips-linux-gnu-as -mmicromips -o b16.o b16.s
b16.s: Assembler messages:
b16.s:5: Error: value of fffffffffffefffe too large for field of 2 bytes at 0000000000010000
$

Overall it looks to me the whole idea of using fixp->fx_size to check for 
relocatable field overflows is missing the point, at least for the MIPS 
target and relocations in text, where the size of the fixup reflects the 
width of the instruction a relocation is applied to and has little to do 
with the range supported.

 Anyway, to fix this immediate problem I have gladly accepted Chao-ying's 
proposal.

 No regressions in testing across the usual MIPS targets.  OK to apply?

2012-10-24  Chao-ying Fu  <fu@mips.com>

	gas/
	* config/tc-mips.c (append_insn): Set fx_no_overflow for 16-bit
	microMIPS branch relocations.

	gas/testsuite/
	* gas/mips/micromips-b16.d: New test.
	* gas/mips/micromips-b16.s: New test source.
	* gas/mips/mips.exp: Run the new test.

  Maciej

binutils-mips-gas-b16-overflow.diff
Index: binutils-fsf-trunk-quilt/gas/config/tc-mips.c
===================================================================
--- binutils-fsf-trunk-quilt.orig/gas/config/tc-mips.c	2012-10-23 16:01:36.000000000 +0100
+++ binutils-fsf-trunk-quilt/gas/config/tc-mips.c	2012-10-23 16:50:29.421771475 +0100
@@ -4464,6 +4464,11 @@ append_insn (struct mips_cl_insn *ip, ex
 	      || lo16_reloc_p (reloc_type[0])))
 	ip->fixp[0]->fx_no_overflow = 1;
 
+      /* These relocations can have an addend that won't fit in 2 octets.  */
+      if (reloc_type[0] == BFD_RELOC_MICROMIPS_7_PCREL_S1
+	  || reloc_type[0] == BFD_RELOC_MICROMIPS_10_PCREL_S1)
+	ip->fixp[0]->fx_no_overflow = 1;
+
       if (mips_relax.sequence)
 	{
 	  if (mips_relax.first_fixup == 0)
Index: binutils-fsf-trunk-quilt/gas/testsuite/gas/mips/micromips-b16.d
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ binutils-fsf-trunk-quilt/gas/testsuite/gas/mips/micromips-b16.d	2012-10-23 16:06:13.491781218 +0100
@@ -0,0 +1,45 @@
+#objdump: -dr --show-raw-insn
+#name: microMIPS b16, bnez16, beqz16
+#as: -32 -mmicromips
+#source: micromips-b16.s
+
+.*: +file format .*mips.*
+
+Disassembly of section \.text:
+
+[0-9a-f]+ <test1>:
+	\.\.\.
+
+[0-9a-f]+ <test2>:
+[ 0-9a-f]+:	cfff      	b	[0-9a-f]+ <.*>
+[ 	]*[0-9a-f]+: R_MICROMIPS_PC10_S1	.*
+[ 0-9a-f]+:	0c00      	nop
+
+[0-9a-f]+ <.*>:
+[ 0-9a-f]+:	ad7f      	bnez	v0,[0-9a-f]+ <.*>
+[ 	]*[0-9a-f]+: R_MICROMIPS_PC7_S1	.*
+[ 0-9a-f]+:	0c00      	nop
+
+[0-9a-f]+ <.*>:
+[ 0-9a-f]+:	8d7f      	beqz	v0,[0-9a-f]+ <.*>
+[ 	]*[0-9a-f]+: R_MICROMIPS_PC7_S1	.*
+[ 0-9a-f]+:	0c00      	nop
+
+[0-9a-f]+ <.*>:
+[ 0-9a-f]+:	cfff      	b	[0-9a-f]+ <.*>
+[ 	]*[0-9a-f]+: R_MICROMIPS_PC10_S1	.*
+[ 0-9a-f]+:	0c00      	nop
+
+[0-9a-f]+ <.*>:
+[ 0-9a-f]+:	ad7f      	bnez	v0,[0-9a-f]+ <.*>
+[ 	]*[0-9a-f]+: R_MICROMIPS_PC7_S1	.*
+[ 0-9a-f]+:	0c00      	nop
+
+[0-9a-f]+ <.*>:
+[ 0-9a-f]+:	8d7f      	beqz	v0,[0-9a-f]+ <.*>
+[ 	]*[0-9a-f]+: R_MICROMIPS_PC7_S1	.*
+[ 0-9a-f]+:	0c00      	nop
+
+[0-9a-f]+ <.*>:
+[ 0-9a-f]+:	0c00      	nop
+#pass
Index: binutils-fsf-trunk-quilt/gas/testsuite/gas/mips/micromips-b16.s
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ binutils-fsf-trunk-quilt/gas/testsuite/gas/mips/micromips-b16.s	2012-10-23 16:06:13.491781218 +0100
@@ -0,0 +1,17 @@
+	.text
+test1:
+	.space	65536
+test2:
+	b16	1f
+1:
+	bnez16	$2,1f
+1:
+	beqz16	$2,1f
+1:
+	b	1f
+1:
+	bnez	$2,1f
+1:
+	beqz	$2,1f
+1:
+	nop
Index: binutils-fsf-trunk-quilt/gas/testsuite/gas/mips/mips.exp
===================================================================
--- binutils-fsf-trunk-quilt.orig/gas/testsuite/gas/mips/mips.exp	2012-10-23 16:05:48.000000000 +0100
+++ binutils-fsf-trunk-quilt/gas/testsuite/gas/mips/mips.exp	2012-10-23 16:06:13.491781218 +0100
@@ -1115,6 +1115,7 @@ if { [istarget mips*-*-vxworks*] } {
 	run_dump_test "micromips-branch-delay"
 	run_dump_test "micromips-warn-branch-delay"
 	run_dump_test "micromips-warn-branch-delay-1"
+	run_dump_test "micromips-b16"
     }
 
     run_dump_test_arches "mcu"		[mips_arch_list_matching mips32r2 \