GCC 4.6.x miscompiling arm-linux?

[David Jander]

Hi all,

On Tue, 11 Sep 2012 09:27:53 +0200
David Jander <david.jander at protonic.nl> wrote:
> Hi Matt,
> 
> On Mon, 10 Sep 2012 18:11:19 +0100
> Matthew Leach <matthew at mattleach.net> wrote:
> > David Jander <david.jander at protonic.nl> writes:
> > > ...
> > > 	.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) 4.6.2"
> > > 	.section	.note.GNU-stack,"",%progbits
> > >
> > 
> > This does indeed look wrong. I had a go at compile your code snippet the
> > following assembly was produced:
> > 
> >         .text
> >         .align  2
> >         .global flexcan_chip_start
> >         .type   flexcan_chip_start, %function
> > flexcan_chip_start:
> >         @ 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
> 
> > I think this looks correct. Perhaps you could try the angstrom arm5te
> > toolchain and see if it's a toolchain issue?
> >
> > http://www.angstrom-distribution.org/toolchains/angstrom-2011.03-i686-linux-armv5te-linux-gnueabi-toolchain-qte-4.6.3.tar.bz2
> 
> This toolchain is a lot older:
> 
> $ ./usr/local/angstrom/arm/bin/arm-angstrom-linux-gnueabi-gcc --version
> arm-angstrom-linux-gnueabi-gcc (GCC) 4.3.3
> Copyright (C) 2008 Free Software Foundation, Inc.
> This is free software; see the source for copying conditions.  There is NO
> warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
> 
> The tar-ball says 4.6.3, but that is probably the version number of the qte
> library, not that of gcc, which is 4.3.3, It does indeed produce
> the same (correct) output as in your case.
> 
> The newest angstrom (next) toolchain has gcc version 4.5.3, and it produces
> this (correct) output:
> 
> flexcan_chip_start:
>         @ Function supports interworking.
>         @ 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]
>         mov     r0, #0
>         strgt   r3, [r1, #4]
>         bx      lr
>         .size   flexcan_chip_start, .-flexcan_chip_start
>         .ident  "GCC: (GNU) 4.5.3 20110311 (prerelease)"
>         .section        .note.GNU-stack,"",%progbits
> 
> Anyone knows where I can download a pre-built toolchain for 32-bit linux that
> is based on gcc-4.6 and/or gcc-4.7 to try out?
> 
> I have quite a hard time believing this issue is a yet unknown bug in GCC...
> I'd rather believe that I lack sufficient GCC knowledge to know how to
> correctly tell the compiler that this is a memory-IO operation. Anyone knows
> how to do this correctly? Or to explain why the output of gcc-4.6 looks less
> optimal than the output of older versions of GCC?

I finally found two linaro toolchains that I could download and try. The
results are rather interesting though:

1.- Ubuntu package gcc-4.6-arm-linux-gnueabi 4.6.3-1ubuntu5cross1.62:

flexcan_chip_start:
        .fnstart
        @ 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
        .fnend
        .size   flexcan_chip_start, .-flexcan_chip_start
        .ident  "GCC: (Ubuntu/Linaro 4.6.3-1ubuntu5) 4.6.3"
        .section        .note.GNU-stack,"",%progbits

Wrong code.

2. Linaro gcc-linaro-arm-linux-gnueabihf-2012.08-20120827_linux gcc 4.7.2:

flexcan_chip_start:
        .fnstart
        @ 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
        .fnend
        .size   flexcan_chip_start, .-flexcan_chip_start
        .ident  "GCC: (crosstool-NG linaro-1.13.1-2012.08-20120827 - Linaro GCC 2012.08) 4.7.2 20120731 (prerelease)"
        .section        .note.GNU-stack,"",%progbits

This looks correct again! Could it be that all versions 4.6.x of gcc are
broken for ARM??

Best regards,

-- 
David Jander
Protonic Holland.