GCC 4.6.x miscompiling arm-linux?

On Tue, Sep 11, 2012 at 12:42:26PM +0200, David Jander wrote:

On Tue, 11 Sep 2012 12:29:05 +0200
Michael Olbrich [off-list ref] wrote:

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On Tue, Sep 11, 2012 at 11:31:39AM +0200, David Jander wrote:

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On Tue, 11 Sep 2012 10:48:53 +0200
Sascha Hauer [off-list ref] wrote:

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On Tue, Sep 11, 2012 at 09:27:53AM +0200, David Jander wrote:

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Hi Matt,

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        @ Function supports interworking.
        @ args = 0, pretend = 0, frame = 0
        @ frame_needed = 0, uses_anonymous_args = 0
        @ link register save eliminated.
        cmp     r0, #9
        mov     r3, #0
        str     r3, [r1, #0]
        mov     r0, #0
        strgt   r3, [r1, #4]
        bx      lr
        .size   flexcan_chip_start, .-flexcan_chip_start
        .ident  "GCC: (GNU) 4.3.3"
        .section        .note.GNU-stack,"",%progbits

I think this looks correct. Perhaps you could try the angstrom arm5te
toolchain and see if it's a toolchain issue?

Yes, this looks a lot better, and is exactly what I get when I compile this
code with CodeSourcery GCC-4.4.1

I have tries building gcc-4.6.3 also with OSELAS/PTXdist, and it gives the
same (wrong) result as with gcc-4.6.2

AFAIK our OSELAS/PTXdist Toolchains use Linaro patches, this would
explain why both have the same result.

No, OSELAS Toolchains only uses the Linaro GCC for Cortex-A8/-A9

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It would indeed, if I had just used OSELAS as-is, but I didn't ;-)
I made a copy of
arm-v5te-linux-gnueabi_gcc-4.6.2_glibc-2.14.1_binutils-2.21.1a_kernel-2.6.39-sanitized.ptxconfig
and replaced the version string 4.6.2 with 4.6.3. AFAIK, this way PTXdist will
download pristine gcc-4.6.3 sources and not apply any patches, since there is
no directory named patches/gcc-4.6.3, right? Can I assume that I have an
unpatched version of gcc-4.6.3 then?

Correct. This way you'll get gcc-4.6.3 without any patches.

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Btw, Here's what I get from it:

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

How can I reproduce this output? I'd like to test this with different
toolchain versions.

I basically do this:

$ /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;
}

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Wrong code.
See the version string? It is clearly not an existing OSELAS version.

Hmmm, so far it seems all tested gcc-4.6.x versions produce wrong code,
correct?

Looks like that, yes.

Including the Linaro gcc releases it seems. I rebuilt the toolchain with
Linaro GCC 4.6-2012.08 and the result is the same.

Regards,
Michael

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