Bug#517875: gcc-4.3: [arm] bad assembly for blx from thumb mode

[John Reiser <jreiser@BitWagon.com>]

Package: gcc-4.3
Version: 4.3.2-1.1
Severity: normal

*** Please type your report below this line ***
When assembling a 'blx' from thumb to arm mode, the assembler can generate an
offset which is odd, such as when the address of the blx itself is (2 mod 4).
An odd offset is explicitly forbidden by the ARM Architecture Reference Manual,
ARM DDI 0100E (1996-2000), p.A7-28, Notes: Bit[0] for BLX, "If H==01, then
bit[0] of the instruction must be zero, or the intsruction is UNDEFINED."
When executed on armv5tel, then the CPU gives SIGILL for the odd offset.
Instead, the assembler should clear the low-order bit always.

Testcase:
----- blxbug.S;   compile: gcc -o blxbug -nostartfiles -nostdlib blxbug.S
	.globl _start
_start:
	nop
	nop
	blx  tmode
	nop

	.code 16
	.thumb_func
tmode:
	nop
	blx amode
	nop

	.balign 4
	.code 32
amode:
	nop
-----

Example execution:
(gdb) run
Starting program: blxbug

Program received signal SIGILL, Illegal instruction.
0x00008068 in tmode ()   ## the middle of the blx instruction at tmode
(gdb) x/i _start
0x8054 <_start>:	nop			(mov r0,r0)
(gdb)
0x8058 <_start+4>:	nop			(mov r0,r0)
(gdb)
0x805c <_start+8>:	blx	0x8064 <tmode>
(gdb)
0x8060 <_start+12>:	nop			(mov r0,r0)
(gdb)
0x8064 <tmode>:	nop			(mov r8, r8)
(gdb)
0x8066 <tmode+2>:	blx	0x806c <amode>
(gdb)
0x806a <tmode+6>:	nop			(mov r8, r8)
(gdb)
0x806c <amode>:	nop			(mov r0,r0)

(gdb) x/x 0x8066
0x8066 <tmode+2>:	0xe801f000
Should be               0xe800f000
 (difference is         0x00010000)

-- System Information:
Debian Release: 5.0
  APT prefers stable
  APT policy: (500, 'stable')
Architecture: armel (armv5tel)

Kernel: Linux 2.6.26-1-ixp4xx
Locale: LANG=C, LC_CTYPE=C (charmap=ANSI_X3.4-1968)
Shell: /bin/sh linked to /bin/bash

Versions of packages gcc-4.3 depends on:
ii  binutils            2.18.1~cvs20080103-7 The GNU assembler, linker and bina
ii  cpp-4.3             4.3.2-1.1            The GNU C preprocessor
ii  gcc-4.3-base        4.3.2-1.1            The GNU Compiler Collection (base
ii  libc6               2.7-18               GNU C Library: Shared libraries
ii  libgcc1             1:4.3.2-1.1          GCC support library
ii  libgomp1            4.3.2-1.1            GCC OpenMP (GOMP) support library

Versions of packages gcc-4.3 recommends:
ii  libc6-dev                     2.7-18     GNU C Library: Development Librari

Versions of packages gcc-4.3 suggests:
pn  gcc-4.3-doc                   <none>     (no description available)
pn  gcc-4.3-locales               <none>     (no description available)
pn  libgcc1-dbg                   <none>     (no description available)
pn  libgomp1-dbg                  <none>     (no description available)
pn  libmudflap0-4.3-dev           <none>     (no description available)
pn  libmudflap0-dbg               <none>     (no description available)

-- no debconf information

-- 
John Reiser, jreiser@BitWagon.com