GCC 4.6.x miscompiling arm-linux?

Hi all,

On Tue, 11 Sep 2012 09:27:53 +0200
David Jander [off-list ref] wrote:

Hi Matt,

On Mon, 10 Sep 2012 18:11:19 +0100
Matthew Leach [off-list ref] wrote:

quoted

David Jander [off-list ref] writes:

quoted

...
	.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

quoted

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.