[Bug c/60158] New: powerpc: usage of the .data.rel.ro.local section

[Bug c/60158] New: powerpc: usage of the .data.rel.ro.local section

[jal2 at gmx dot de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60158

            Bug ID: 60158
           Summary: powerpc: usage of the .data.rel.ro.local section
           Product: gcc
           Version: 4.8.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jal2 at gmx dot de

This bug may concern the gcc documentation on section usage only.

Crosscompiling "Das U-Boot" with gcc 4.8.2 for powerpc with
-fpic -mrelocatable, some addresses are put into a section .data.rel.ro.local,
e.g. the address of "qwerty" from

printf("%p\n", "qwerty");

There is no corresponding entry in the .fixup section.
As "Das U-Boot" relocates itself to RAM using .got2/.got and .fixup sections
only, how shall the section .data.rel.ro.local be handled?

Currently it contains addresses only, but this may depend on the source code.
I put .data.rel.ro.local into the GOT which solved my problem, but I'm not sure
if this is the intention of the gcc developers.

I've tried gcc 4.7.3 which put the address of "qwerty" into the GOT directly,
i.e. there was no .data.rel.ro.local section and the string address was
accessed with one redirection less.

details:
- gcc version: powerpc-softfloat-linux-gnuspe-gcc (Gentoo 4.8.2 p1.3r1,
pie-0.5.8r1) 4.8.2
- gcc command line (some -I removed):
  -g -gdwarf-2  -Os   -fpic -mrelocatable \
  -meabi \
  -D__KERNEL__ -DCONFIG_SYS_TEXT_BASE=0xef770000 \
  -fno-builtin  -ffreestanding \
  -isystem /usr/lib/gcc/powerpc-softfloat-linux-gnuspe/4.8.1/include \
  -nostdinc -pipe  -DCONFIG_PPC -D__powerpc__ -ffixed-r2 -Wa,-me500 \
  -msoft-float -mno-string -mspe=yes -mno-spe -Wall -Wstrict-prototypes \
  -fno-stack-protector -Wno-format-nonliteral -Wno-format-security \
  -fstack-usage"

[Bug other/60158] powerpc: usage of the .data.rel.ro.local section

[joakim.tjernlund at transmode dot se]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60158

joakim.tjernlund at transmode dot se <joakim.tjernlund at transmode dot se> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |joakim.tjernlund@transmode.
                   |                            |se

--- Comment #1 from joakim.tjernlund at transmode dot se <joakim.tjernlund at transmode dot se> ---
There is a patch at http://patchwork.ozlabs.org/patch/342888/
to address this issue and I THINK it is included in gcc-4.9.3

However, when I build the test case I do not get any .fixup section
I cross building from amd64 to ppc32 if that is important

[Bug other/60158] powerpc: usage of the .data.rel.ro.local section

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60158

Segher Boessenkool <segher at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |segher at gcc dot gnu.org
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |WONTFIX

--- Comment #6 from Segher Boessenkool <segher at gcc dot gnu.org> ---
The powerpcspe backend has been deprecated in GCC 8 and removed during GCC 9
development. See corresponding mailing list threads[1,2,3] for details.

[1] https://gcc.gnu.org/legacy-ml/gcc/2018-04/msg00102.html
[2] https://gcc.gnu.org/legacy-ml/gcc-patches/2018-12/msg00123.html
[3] https://gcc.gnu.org/pipermail/gcc/2020-May/232342.html

[Bug other/60158] powerpc: usage of the .data.rel.ro.local section

[joakim.tjernlund at infinera dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60158

--- Comment #7 from Joakim Tjernlund <joakim.tjernlund at infinera dot com> ---
(In reply to Segher Boessenkool from comment #6)
> The powerpcspe backend has been deprecated in GCC 8 and removed during GCC 9
> development. See corresponding mailing list threads[1,2,3] for details.
> 
> [1] https://gcc.gnu.org/legacy-ml/gcc/2018-04/msg00102.html
> [2] https://gcc.gnu.org/legacy-ml/gcc-patches/2018-12/msg00123.html
> [3] https://gcc.gnu.org/pipermail/gcc/2020-May/232342.html

This is not SPE specific.
More like powerpc or gcc

[Bug other/60158] powerpc: usage of the .data.rel.ro.local section

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60158

--- Comment #8 from Segher Boessenkool <segher at gcc dot gnu.org> ---
It does not happen on any target currently, and it has never happened
on non-SPE targets before.

[Bug other/60158] powerpc: usage of the .data.rel.ro.local section

[joakim.tjernlund at infinera dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60158

--- Comment #9 from Joakim Tjernlund <joakim.tjernlund at infinera dot com> ---
(In reply to Segher Boessenkool from comment #8)
> It does not happen on any target currently, and it has never happened
> on non-SPE targets before.

The main user, u-boot, added the workaround with -fno-ira-hoist-pressure 
to avoid the bug:

    arch/powerpc/config.mk: Pass -fno-ira-hoist-pressure when possible

    There are various toolchain issues that cause us to produce invalid
    binaries with certain gcc 4.8.x and 4.9.x versions when we don't pass
    this flag in.

    Tested-by: Joakim Tjernlund <joakim.tjernlund@transmode.se>
    Signed-off-by: Tom Rini <trini@konsulko.com>

The bug is still there as far as I known, the one-line patch hasn't been
applied
I think.

[Bug other/60158] powerpc: usage of the .data.rel.ro.local section

[joakim.tjernlund at infinera dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60158

--- Comment #10 from Joakim Tjernlund <joakim.tjernlund at infinera dot com> ---
To be clear, this is still a bug for powerpc(SPE or no SPE) and possibly any
other arch using fixup tables like ppc.

One can workaround this bug by using the -fno-ira-hoist-pressure, I am not
sure why this option work and if there is a chance it will stop working in the
future.

[Bug other/60158] powerpc: usage of the .data.rel.ro.local section

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60158

--- Comment #11 from Segher Boessenkool <segher at gcc dot gnu.org> ---
Do you have a reproducer you can share?

I'll happily reopen the PR then, of course!

[Bug other/60158] powerpc: usage of the .data.rel.ro.local section

[joakim.tjernlund at infinera dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60158

--- Comment #12 from Joakim Tjernlund <joakim.tjernlund at infinera dot com> ---
(In reply to Segher Boessenkool from comment #11)
> Do you have a reproducer you can share?
> 
> I'll happily reopen the PR then, of course!

After 6 years, no I don't.
You could use the test case included in the the patch I think.