Generated assembly doesn't correspond to the ARM processor

[Snark]

While investigating why I couldn't compile sage on the toshiba AC100 (an ARM-based netbook) -- this is report http://trac.sagemath.org/sage_trac/ticket/10285 , it appeared that some of the problems are due to the compiler, which from a C file goes to an assembly file... and then fails to build it!

Here is an example -- taken from Boehm's garbage collector's failed compilation (the full build log is attached to the sage report):

gcc -DPACKAGE_NAME=\"gc\" -DPACKAGE_TARNAME=\"gc\" -DPACKAGE_VERSION=\"7.1\" "-DPACKAGE_STRING=\"gc 7.1\"" -DPACKAGE_BUGREPORT=\"snipped\" -DGC_VERSI
ON_MAJOR=7 -DGC_VERSION_MINOR=1 -DPACKAGE=\"gc\" -DVERSION=\"7.1\" -DGC_LINUX_TH
READS=1 -D_REENTRANT=1 -DSTDC_HEADERS=1 -DHAVE_SYS_TYPES_H=1 -DHAVE_SYS_STAT_H=1
 -DHAVE_STDLIB_H=1 -DHAVE_STRING_H=1 -DHAVE_MEMORY_H=1 -DHAVE_STRINGS_H=1 -DHAVE
_INTTYPES_H=1 -DHAVE_STDINT_H=1 -DHAVE_UNISTD_H=1 -DHAVE_DLFCN_H=1 -DNO_EXECUTE_
PERMISSION=1 -DALL_INTERIOR_POINTERS=1 -DGC_GCJ_SUPPORT=1 -DJAVA_FINALIZATION=1
-DATOMIC_UNCOLLECTABLE=1 -DLARGE_CONFIG=1 -I./include -fexceptions -I libatomic_
ops/src -g -O2 -MT alloc.lo -MD -MP -MF .deps/alloc.Tpo -c alloc.c -fPIC -DPIC
-o .libs/alloc.o
/tmp/cckXY2Jn.s: Assembler messages:
/tmp/cckXY2Jn.s:1314: Error: selected processor does not support Thumb mode `swp ip,r2,[r3]'
/tmp/cckXY2Jn.s:1371: Error: selected processor does not support Thumb mode `swp ip,r0,[r2]'
/tmp/cckXY2Jn.s:2783: Error: selected processor does not support Thumb mode `swp lr,r2,[r6]'
/tmp/cckXY2Jn.s:2851: Error: selected processor does not support Thumb mode `swp r1,r0,[r3]'
/tmp/cckXY2Jn.s:3613: Error: selected processor does not support Thumb mode `swp ip,r2,[r3]'
/tmp/cckXY2Jn.s:3652: Error: selected processor does not support Thumb mode `swp ip,r1,[r3]'
make[3]: *** [alloc.lo] Error 1

[Snark (julien-puydt)]

Notice that launchpad insisted that my package number doesn't exist -- but I know it does, since the head of /usr/share/doc/gcc-4.4/changelog.Debian.gz is :
gcc-4.4 (4.4.4-14ubuntu5) maverick; urgency=low

  * Avoid include paths starting with a double slash. LP: #635840.

 -- Matthias Klose <email address hidden> Mon, 27 Sep 2010 16:00:29 +0200

and :
$ ls /var/cache/apt/archives/ | grep gcc-4.4
gcc-4.4_4.4.4-14ubuntu5_armel.deb

I say it is 4.4.4-14ubuntu5, and I have good reasons to think so!

[Dimitri John Ledkov (xnox)]

can linaro-gcc toolchain build this?

[Michael Hope (michaelh1)]

Hi there. I think the original author has a configuration problem. The code above is in sysdeps/gcc/arm.h and has two chunks: one with a #ifdef __ARMv6__ around it which uses the correct Thumb-2 instructions, and the fallback version for earlier architectures that uses the (no longer supported) 'swp' instruction. For some reason his setup is picking up the pre-v6 version.

Note that the same code in the libatomic-ops-dev compiles correctly under Ubuntu Maverick. I don't think this is a compiler problem.

I've posted more detail on the original bug at:
 http://trac.sagemath.org/sage_trac/ticket/10285

[Matthias Klose (doko)]

The thing is that there's a plethora of defines, and even GCC itself doesn't get it right all the times.

see libffi/src/arm/sysv.S. This is error prone, and maybe Linaro should push something better upstream.

/* We need a better way of testing for this, but for now, this is all
   we can do. */
@ This selects the minimum architecture level required.
#define __ARM_ARCH__ 3

#if defined(__ARM_ARCH_4__) || defined(__ARM_ARCH_4T__)
# undef __ARM_ARCH__
# define __ARM_ARCH__ 4
#endif

#if defined(__ARM_ARCH_5__) || defined(__ARM_ARCH_5T__) \
        || defined(__ARM_ARCH_5E__) || defined(__ARM_ARCH_5TE__) \
        || defined(__ARM_ARCH_5TEJ__)
# undef __ARM_ARCH__
# define __ARM_ARCH__ 5
#endif

#if defined(__ARM_ARCH_6__) || defined(__ARM_ARCH_6J__) \
        || defined(__ARM_ARCH_6K__) || defined(__ARM_ARCH_6Z__) \
        || defined(__ARM_ARCH_6ZK__) || defined(__ARM_ARCH_6T2__) \
        || defined(__ARM_ARCH_6M__)
# undef __ARM_ARCH__
# define __ARM_ARCH__ 6
#endif

#if defined(__ARM_ARCH_7__) || defined(__ARM_ARCH_7A__) \
        || defined(__ARM_ARCH_7R__) || defined(__ARM_ARCH_7M__) \
        || defined(__ARM_ARCH_7EM__)
# undef __ARM_ARCH__
# define __ARM_ARCH__ 7
#endif