[Bug driver/47535] New: -mno-thumb option does not work on ARM compiler configured --with-mode=thumb

[lennox at cs dot columbia.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47535

           Summary: -mno-thumb option does not work on ARM compiler
                    configured --with-mode=thumb
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: driver
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: lennox@cs.columbia.edu


I have a GCC 4.6.0 (SVN trunk) compiler configured targeting arm-linux,
configured with the --with-mode=thumb option to generate Thumb code by default.

When I pass the compiler the -mno-thumb option, it ignores the option, and
generates Thumb code anyway.

The -marm option works as expected, and is usable as a workaround; however,
this option is only mentioned in one place in the gcc documentation, in
passing, with no description, and is displayed by gcc --help as "This option
lacks documentation".

It looks like what's happening is that when I pass -mno-thumb to the driver,
the driver passes it to cc1, but appends an additional -mthumb option as well.

(The file arm-sad.c contains arm-specific inline assembly.  I can provide it if
needed, but its contents are not relevant.)

$ ~/GCC/FSF/bin/arm-linux-gnueabi-gcc -v -mno-thumb -c arm-sad.c
Using built-in specs.
COLLECT_GCC=/home/jonathan/GCC/FSF/bin/arm-linux-gnueabi-gcc
COLLECT_LTO_WRAPPER=/home/jonathan/GCC/FSF/libexec/gcc/arm-linux-gnueabi/4.6.0/lto-wrapper
Target: arm-linux-gnueabi
Configured with: ../svn/Trunk/configure -v --prefix=/home/jonathan/GCC/FSF/
--enable-shared --enable-multiarch --enable-linker-build-id --with-system-zlib
--without-included-gettext --enable-threads=posix --enable-nls
--enable-clocale=gnu --enable-libstdcxx-debug --enable-plugin --enable-objc-gc
--disable-sjlj-exceptions --with-arch=armv7-a --with-float=softfp
--with-fpu=vfpv3-d16 --with-mode=thumb --disable-werror
--enable-checking=release --program-prefix=arm-linux-gnueabi-
--includedir=/usr/arm-linux-gnueabi/include
--with-headers=/usr/arm-linux-gnueabi/include
--with-libs=/usr/arm-linux-gnueabi/lib --build=i486-linux-gnu
--host=i486-linux-gnu --target=arm-linux-gnueabi CC=gcc
build_alias=i486-linux-gnu host_alias=i486-linux-gnu
target_alias=arm-linux-gnueabi --enable-languages=c,c++,fortran,objc,obj-c++
Thread model: posix
gcc version 4.6.0 20110129 (experimental) (GCC) 
COLLECT_GCC_OPTIONS='-v' '-mno-thumb' '-c' '-march=armv7-a'
'-mfloat-abi=softfp' '-mfpu=vfpv3-d16' '-mthumb'
 /home/jonathan/GCC/FSF/libexec/gcc/arm-linux-gnueabi/4.6.0/cc1 -quiet -v
arm-sad.c -quiet -dumpbase arm-sad.c -mno-thumb -march=armv7-a
-mfloat-abi=softfp -mfpu=vfpv3-d16 -mthumb -auxbase arm-sad -version -o
/tmp/ccplOMN0.s
GNU C (GCC) version 4.6.0 20110129 (experimental) (arm-linux-gnueabi)
    compiled by GNU C version 4.4.3, GMP version 4.3.2, MPFR version 2.4.2-p1,
MPC version 0.8.1
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
#include "..." search starts here:
#include <...> search starts here:
 /home/jonathan/GCC/FSF/lib/gcc/arm-linux-gnueabi/4.6.0/include
 /home/jonathan/GCC/FSF/lib/gcc/arm-linux-gnueabi/4.6.0/include-fixed

/home/jonathan/GCC/FSF/lib/gcc/arm-linux-gnueabi/4.6.0/../../../../arm-linux-gnueabi/sys-include

/home/jonathan/GCC/FSF/lib/gcc/arm-linux-gnueabi/4.6.0/../../../../arm-linux-gnueabi/include
End of search list.
GNU C (GCC) version 4.6.0 20110129 (experimental) (arm-linux-gnueabi)
    compiled by GNU C version 4.4.3, GMP version 4.3.2, MPFR version 2.4.2-p1,
MPC version 0.8.1
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: b9b1ff16910c968c736abbcf1f0e1a41
COLLECT_GCC_OPTIONS='-v' '-mno-thumb' '-c' '-march=armv7-a'
'-mfloat-abi=softfp' '-mfpu=vfpv3-d16' '-mthumb'
 /home/jonathan/GCC/FSF/libexec/gcc/arm-linux-gnueabi/4.6.0/as -march=armv7-a
-mfloat-abi=softfp -mfpu=vfpv3-d16 -meabi=5 -o arm-sad.o /tmp/ccplOMN0.s
/tmp/ccplOMN0.s: Assembler messages:
/tmp/ccplOMN0.s:38: Error: Thumb does not support register post-indexing --
`ldr r4,[r0],r1'
/tmp/ccplOMN0.s:38: Error: Thumb does not support register post-indexing --
`ldr r5,[r2],ip'
/tmp/ccplOMN0.s:38: Error: Thumb does not support register post-indexing --
`ldr r4,[r0],r1'
/tmp/ccplOMN0.s:38: Error: Thumb does not support register post-indexing --
`ldr r5,[r2],ip'
/tmp/ccplOMN0.s:38: Error: Thumb does not support register post-indexing --
`ldr r4,[r0],r1'
/tmp/ccplOMN0.s:38: Error: Thumb does not support register post-indexing --
`ldr r5,[r2],ip'