GCC 4.6.x miscompiling arm-linux?

[Mikael Pettersson]

David Jander writes:
 > On Tue, 11 Sep 2012 13:35:40 +0200
 > Mikael Pettersson <mikpe at it.uu.se> wrote:
 > 
 > > David Jander writes:
 > >  > > I can make the patches available if there's confirmation that a vanilla
 > >  > > upstream gcc-4.6.3 doesn't work.
 > >  > 
 > >  > I am pretty sure this is the case... do you have a patch series that you can
 > >  > easily tar and mail to me? I'd like to try those patches with OSELAS, to see
 > >  > if I can indeed build a gcc-4.6.3 toolchain that generates correct code.... I
 > >  > already know that I can generate one that doesn't ;-)
 > >  > 
 > > ...
 > >  > > If you're sure no add-on patches were applied, then yes please do.
 > >  > 
 > >  > Pretty sure, but not 100%, so I'd like to try your patches first if you don't
 > >  > mind....
 > > 
 > > And I'd like to confirm first. Please tell us the following:
 > > 
 > >  > >  > > 2: include the output of gcc -v which tells how that gcc was configured,
 > 
 > Using built-in specs.
 > COLLECT_GCC=/opt/OSELAS.Toolchain-2011.11.1/arm-v5te-linux-gnueabi/gcc-4.6.3-glibc-2.14.1-binutils-2.21.1a-kernel-2.6.39-sanitized/bin/arm-v5te-linux-gnueabi-gcc-4.6.3
 > COLLECT_LTO_WRAPPER=/opt/OSELAS.Toolchain-2011.11.1/arm-v5te-linux-gnueabi/gcc-4.6.3-glibc-2.14.1-binutils-2.21.1a-kernel-2.6.39-sanitized/libexec/gcc/arm-v5te-linux-gnueabi/4.6.3/lto-wrapper
 > Target: arm-v5te-linux-gnueabi
 > Configured with: /home/djander/ptxdist/OSELAS.Toolchain-2011.11.1/platform-arm-v5te-linux-gnueabi-gcc-4.6.3-glibc-2.14.1-binutils-2.21.1a-kernel-2.6.39-sanitized/build-cross/gcc-4.6.3/configure --target=arm-v5te-linux-gnueabi --with-sysroot=/opt/OSELAS.Toolchain-2011.11.1/arm-v5te-linux-gnueabi/gcc-4.6.3
 > -glibc-2.14.1-binutils-2.21.1a-kernel-2.6.39-sanitized/sysroot-arm-v5te-linux-gnueabi --disable-multilib --with-float=soft --with-fpu=vfp --with-cpu=arm926ej-s --enable-__cxa_atexit --disable-sjlj-exceptions --disable-nls --disable-decimal-float --disable-fixed-point --disable-win32-registry --enable-symvers=gnu --with-pkgversion=OSELAS.Toolchain-2011.11.1 --with-system-zlib --with-gmp=/home/djander/ptxdist/OSELAS.Toolchain-2011.11.1/platform-arm-v5te
 > -linux-gnueabi-gcc-4.6.3-glibc-2.14.1-binutils-2.21.1a-kernel-2.6.39-sanitized/sysroot-host --with-mpfr=/home/djander/ptxdist/OSELAS.Toolchain-2011.11.1/platform-arm-v5te-linux-gnueabi-gcc-4.6.3-glibc-2.14.1-binutils-2.21.1a-kernel-2.6.39-sanitized/sysroot-host --prefix=/opt/OSELAS.Toolchain-2011.11.1/arm-v5te-linux-gnueabi/gcc-4.6.3-glibc-2.14.1-binutils-2.21.1a-kernel-2.6.39-sanitized --enable-languages=c,c++ --enable-threads=posix --enable-c99 --enable-long-long --enable-libstdcxx-debug --enable-profile --enable-shared --disable-libssp --enable-checking=release
 > Thread model: posix
 > gcc version 4.6.3 (OSELAS.Toolchain-2011.11.1)
 > 
 > >  > >  > > 3: give the exact set of gcc options used then compiling the test case.
 > 
 > If I type this in a terminal:
 > 
 > 
 > $ /opt/OSELAS.Toolchain-2011.11.1/arm-v5te-linux-gnueabi/gcc-4.6.3-glibc-2.14.1-binutils-2.21.1a-kernel-2.6.39-sanitized/bin/arm-v5te-linux-gnueabi-gcc-4.6.3 -Os -S -o - -x c -
 > 
 > struct flexcan_regs {
 >         unsigned int mcr;
 >         unsigned int rxfgmask;
 > };
 > 
 > #define flexcan_read(a) (*(volatile unsigned int *)(a))
 > #define flexcan_write(v,a)      (*(volatile unsigned int *)(a) = (v))
 > 
 > int flexcan_chip_start(int ver, struct flexcan_regs *regs)
 > {
 >         flexcan_write(0, &regs->mcr);
 > 
 >         if (ver >= 10)
 >                 flexcan_write(0, &regs->rxfgmask);
 > 
 >         return 0;
 > }
 > 
 > 
 > I get this output after hitting <CTRL-D>:
 > 
 >         .cpu arm926ej-s
 >         .fpu softvfp
 >         .eabi_attribute 20, 1
 >         .eabi_attribute 21, 1
 >         .eabi_attribute 23, 3
 >         .eabi_attribute 24, 1
 >         .eabi_attribute 25, 1
 >         .eabi_attribute 26, 2
 >         .eabi_attribute 30, 4
 >         .eabi_attribute 18, 4
 >         .file   ""
 >         .text
 >         .align  2
 >         .global flexcan_chip_start
 >         .type   flexcan_chip_start, %function
 > flexcan_chip_start:
 >         @ args = 0, pretend = 0, frame = 0
 >         @ frame_needed = 0, uses_anonymous_args = 0
 >         @ link register save eliminated.
 >         mov     r3, #0
 >         cmp     r0, #9
 >         str     r3, [r1, #0]
 >         ldrle   r3, [r1, #4]
 >         mov     r0, #0
 >         str     r3, [r1, #4]
 >         bx      lr
 >         .size   flexcan_chip_start, .-flexcan_chip_start
 >         .ident  "GCC: (OSELAS.Toolchain-2011.11.1) 4.6.3"
 >         .section        .note.GNU-stack,"",%progbits
 > 
 > 
 > Do you need more information?

No, I can reproduce the bug with vanilla gcc-4.6.3; vanilla 4.7.1 and 4.5.4 are Ok.

I'll bisect my 4.6.3 patch series to see which patch fixes it.