[Bug libgcc/60464] New: [arm] ARM -mthumb version of libgcc contains ARM (non-thumb) code; not safe for thumb-only architectures

["jeremygccb at baymoo dot org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60464

            Bug ID: 60464
           Summary: [arm] ARM -mthumb version of libgcc contains ARM
                    (non-thumb) code; not safe for thumb-only
                    architectures
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: critical
          Priority: P3
         Component: libgcc
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jeremygccb at baymoo dot org

SUMMARY

Configuring and building gcc 4.8.2 for the target 'arm-none-eabi' results in a
thumb version of libgcc.a that is not entirely suitable for thumb-only
processors. This bug is also present in 4.8.1.

DETAILS

I have built GCC 4.8.2 using the following configuration:

----- config.log snippet -----
  $ /Users/build/Downloads/gcc-4.8.2/configure --target=arm-none-eabi
--enable-languages=c --disable-libssp --disable-libstcdxx

  ## --------- ##
  ## Platform. ##
  ## --------- ##

  hostname = not-relevant.local
  uname -m = x86_64
  uname -r = 12.4.0
  uname -s = Darwin
  uname -v = Darwin Kernel Version 12.4.0: Wed May  1 17:57:12 PDT 2013;
root:xnu-2050.24.15~1/RELEASE_X86_64
-----------

When using this compiler to compile code targeted for '-mcpu=cortex-m3 -mthumb'
I noticed that some of the routines in the resulting binary still seem to
expect the processor to support ARM (non-thumb) mode. On further inspection I
found that these routines came from '_clzsi2.o' and '_divsi3.o' from libgcc.a.
I double-checked that the correct version of libgcc.a was being used:

-----
$ /usr/local/bin/arm-none-eabi-gcc -mcpu=cortex-m3 -mthumb
-print-libgcc-file-name

/usr/local/lib/gcc/arm-none-eabi/4.8.2/thumb/libgcc.a
-----

TO REPRODUCE

1. Configure: --target=arm-none-eabi --enable-languages=c --disable-libssp
--disable-libstcdxx

2. Compile a short test program:

  $ arm-none-eabi-gcc -mcpu=cortex-m3 -mthumb -S test.c

  ----- test.c
  unsigned int
  test1(unsigned long long a)
  {
          return a % 100000;
  }
  -----

3. Notice that the resultant 'test.s' generates a call to __aeabi_uldivmod:

  -----
          .global test1
          .thumb
          .thumb_func
          .type   test1, %function
  test1:
  ...
  movw    r2, #34464
  movt    r2, 1
  mov     r3, #0
  bl      __aeabi_uldivmod
  mov     r3, r2
  mov     r0, r3
  -----

4. Notice that __aeabi_uldivmod in
/usr/local/lib/gcc/arm-none-eabi/4.8.2/thumb/libgcc.a is a non-thumb function.

  $ arm-none-eabi-objdump -d
/usr/local/lib/gcc/arm-none-eabi/4.8.2/thumb/libgcc.a

  -----
  _aeabi_uldivmod.o:     file format elf32-littlearm


  Disassembly of section .text:

  00000000 <__aeabi_uldivmod>:
     0:   e3530000        cmp     r3, #0
     4:   03520000        cmpeq   r2, #0
     8:   1a000004        bne     20 <__aeabi_uldivmod+0x20>
     c:   e3510000        cmp     r1, #0
    10:   03500000        cmpeq   r0, #0
    14:   13e01000        mvnne   r1, #0
    18:   13e00000        mvnne   r0, #0
    1c:   eafffffe        b       0 <__aeabi_ldiv0>
    20:   e24dd008        sub     sp, sp, #8
    24:   e92d6000        push    {sp, lr}
    28:   ebfffffe        bl      0 <__gnu_uldivmod_helper>
    2c:   e59de004        ldr     lr, [sp, #4]
    30:   e28dd008        add     sp, sp, #8
    34:   e8bd000c        pop     {r2, r3}
    38:   e12fff1e        bx      lr
    -----

5. Notice that this occurred even though the build process for
thumb/libgcc.a(_aeabi_uldivmod.o) correctly asserted its intent by passing the
'-mthumb' to the compiler driver by inspecting the GCC build log:

  -----
  /Users/build/builds/gcc-4.8.2-arm-none-eabi/./gcc/xgcc
-B/Users/build/builds/gcc-4.8.2-arm-none-eabi/./gcc/
-B/usr/local/arm-none-eabi/bin/ -B/usr/local/arm-none-eabi/lib/ -isystem
/usr/local/arm-none-eabi/include -isystem /usr/local/arm-none-eabi/sys-include 
  -g -O2 -mthumb -O2  -g -O2 -DIN_GCC -DCROSS_DIRECTORY_STRUCTURE  -W -Wall
-Wwrite-strings -Wcast-qual -Wstrict-prototypes -Wmissing-prototypes
-Wold-style-definition  -isystem ./include   -fno-inline -g -DIN_LIBGCC2
-fbuilding-libgcc -fno-stack-protector -Dinhibit_libc  -fno-inline -I. -I.
-I../../.././gcc -I/Users/build/Downloads/gcc-4.8.2/libgcc
-I/Users/build/Downloads/gcc-4.8.2/libgcc/.
-I/Users/build/Downloads/gcc-4.8.2/libgcc/../gcc
-I/Users/build/Downloads/gcc-4.8.2/libgcc/../include  -DHAVE_CC_TLS  -o
_aeabi_uldivmod.o -MT _aeabi_uldivmod.o -MD -MP -MF _aeabi_uldivmod.dep
-DL_aeabi_uldivmod -xassembler-with-cpp -c
/Users/build/Downloads/gcc-4.8.2/libgcc/config/arm/lib1funcs.S -include
_aeabi_uldivmod.vis
  -----