gcc-12: build errors: arch/arm64/kernel/setup.c:225:56: warning: array subscript -1 is outside array bounds of 'char[]' [-Warray-bounds]

gcc-12: build errors: arch/arm64/kernel/setup.c:225:56: warning: array subscript -1 is outside array bounds of 'char[]' [-Warray-bounds]

[Naresh Kamboju]

While building Linux kernel with gcc-12 for arm64 the following warnings/errors
noticed. These are specific to gcc-12 builds.

Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>

make --silent --keep-going --jobs=8
O=/home/tuxbuild/.cache/tuxmake/builds/2/build
CROSS_COMPILE_COMPAT=arm-linux-gnueabihf- ARCH=arm64
CROSS_COMPILE=aarch64-linux-gnu- 'CC=sccache aarch64-linux-gnu-gcc'
'HOSTCC=sccache gcc'
In file included from arch/arm64/include/asm/thread_info.h:17,
                 from include/linux/thread_info.h:60,
                 from arch/arm64/include/asm/preempt.h:6,
                 from include/linux/preempt.h:78,
                 from include/linux/smp.h:110,
                 from include/linux/lockdep.h:14,
                 from include/linux/mutex.h:17,
                 from include/linux/kernfs.h:11,
                 from include/linux/sysfs.h:16,
                 from include/linux/kobject.h:20,
                 from include/linux/of.h:17,
                 from include/linux/irqdomain.h:35,
                 from include/linux/acpi.h:13,
                 from arch/arm64/kernel/setup.c:9:
In function 'request_standard_resources',
    inlined from 'setup_arch' at arch/arm64/kernel/setup.c:350:2:
arch/arm64/kernel/setup.c:225:56: warning: array subscript -1 is
outside array bounds of 'char[]' [-Warray-bounds]
  225 |         kernel_code.end     = __pa_symbol(__init_begin - 1);

steps to reproduce:
# To install tuxmake on your system globally:
# sudo pip3 install -U tuxmake

tuxmake --runtime podman --target-arch arm64 --toolchain gcc-12
--kconfig tinyconfig CROSS_COMPILE_COMPAT=arm-linux-gnueabihf-

Build link:
https://builds.tuxbuild.com/2A2iyFqotDfgkLynaKzmpf8H7Nf/

--
Linaro LKFT
https://lkft.linaro.org

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Re: gcc-12: build errors: arch/arm64/kernel/setup.c:225:56: warning: array subscript -1 is outside array bounds of 'char[]' [-Warray-bounds]

[Arnd Bergmann]

On Fri, Jun 3, 2022 at 4:03 AM Naresh Kamboju <naresh.kamboju@linaro.org> wrote:
>     inlined from 'setup_arch' at arch/arm64/kernel/setup.c:350:2:
> arch/arm64/kernel/setup.c:225:56: warning: array subscript -1 is
> outside array bounds of 'char[]' [-Warray-bounds]
>   225 |         kernel_code.end     = __pa_symbol(__init_begin - 1);
>

Is this the only warning of this type that you get for arm64?

I think the easy fix would be to reword this line to

       kernel_code.end     = __pa_symbol(__init_begin) - 1;


        Arnd

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Re: gcc-12: build errors: arch/arm64/kernel/setup.c:225:56: warning: array subscript -1 is outside array bounds of 'char[]' [-Warray-bounds]

[Maxime Ripard]

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Hi,

On Fri, Jun 03, 2022 at 09:40:07AM +0200, Arnd Bergmann wrote:
> On Fri, Jun 3, 2022 at 4:03 AM Naresh Kamboju <naresh.kamboju@linaro.org> wrote:
> >     inlined from 'setup_arch' at arch/arm64/kernel/setup.c:350:2:
> > arch/arm64/kernel/setup.c:225:56: warning: array subscript -1 is
> > outside array bounds of 'char[]' [-Warray-bounds]
> >   225 |         kernel_code.end     = __pa_symbol(__init_begin - 1);
> >
> 
> Is this the only warning of this type that you get for arm64?

In that function, both kernel_code.end and kernel_data_end show a
similar warning in 5.19-rc1

> I think the easy fix would be to reword this line to
> 
>        kernel_code.end     = __pa_symbol(__init_begin) - 1;

Doing this for both fix the warnings.

Maxime

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Re: gcc-12: build errors: arch/arm64/kernel/setup.c:225:56: warning: array subscript -1 is outside array bounds of 'char[]' [-Warray-bounds]

[Mark Rutland]

On Fri, Jun 03, 2022 at 09:40:07AM +0200, Arnd Bergmann wrote:
> On Fri, Jun 3, 2022 at 4:03 AM Naresh Kamboju <naresh.kamboju@linaro.org> wrote:
> >     inlined from 'setup_arch' at arch/arm64/kernel/setup.c:350:2:
> > arch/arm64/kernel/setup.c:225:56: warning: array subscript -1 is
> > outside array bounds of 'char[]' [-Warray-bounds]
> >   225 |         kernel_code.end     = __pa_symbol(__init_begin - 1);
> >
> 
> Is this the only warning of this type that you get for arm64?

There are a handful of those subscript warnings. Looking at v5.19-rc1
defconfig, using the kernel.org GCC 12.1.0 cross toolchain:

| [mark@lakrids:~/src/linux]% usekorg 12.1.0 make ARCH=arm64 CROSS_COMPILE=aarch64-linux- -j50 2>&1 | grep -A1 subscript
| arch/arm64/kernel/setup.c:225:56: warning: array subscript -1 is outside array bounds of 'char[]' [-Warray-bounds]
|   225 |         kernel_code.end     = __pa_symbol(__init_begin - 1);
| --
| arch/arm64/kernel/setup.c:227:48: warning: array subscript -1 is outside array bounds of 'char[]' [-Warray-bounds]
|   227 |         kernel_data.end     = __pa_symbol(_end - 1);
| --
| arch/arm64/kernel/hibernate.c:94:65: warning: array subscript -1 is outside array bounds of 'const void[]' [-Warray-bounds]
|    94 |         unsigned long nosave_end_pfn = sym_to_pfn(&__nosave_end - 1);

The last of those can't have the `- 1` pulled out, but we could stuff a
RELOC_HIDE() in there, as __pa_symbol() has internally.

Ideally we'd rework the section markers to not have this problem, either
rethinking the way we mark them as flexible arrays, or giving them accessors,
e.g.

	#define va_init_begin()	RELOC_HIDE((unsigned long)__init_begin)

... which'd be a pain, but at least it'd solve this generally.

> I think the easy fix would be to reword this line to
> 
>        kernel_code.end     = __pa_symbol(__init_begin) - 1;
> 

I agree that'd work for the __pa_symbol() cases.

For consistency it might be worth using RELOC_HIDE(), e.g.

	kernel_code.end     = __pa_symbol(RELOC_HIDE(__init_begin)) - 1);

... which IIUC should do the trick.

Thanks,
Mark.

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Re: gcc-12: build errors: arch/arm64/kernel/setup.c:225:56: warning: array subscript -1 is outside array bounds of 'char[]' [-Warray-bounds]

[Arnd Bergmann]

On Mon, Jun 6, 2022 at 11:41 AM Mark Rutland <mark.rutland@arm.com> wrote:
> On Fri, Jun 03, 2022 at 09:40:07AM +0200, Arnd Bergmann wrote:
>
>         #define va_init_begin() RELOC_HIDE((unsigned long)__init_begin)
>
> ... which'd be a pain, but at least it'd solve this generally.
>
> > I think the easy fix would be to reword this line to
> >
> >        kernel_code.end     = __pa_symbol(__init_begin) - 1;
> >
>
> I agree that'd work for the __pa_symbol() cases.
>
> For consistency it might be worth using RELOC_HIDE(), e.g.
>
>         kernel_code.end     = __pa_symbol(RELOC_HIDE(__init_begin)) - 1);
>asm-gener
> ... which IIUC should do the trick.
>

I see we have similar logic on each architecture, and they probably
all have the same
issue now, so maybe we can just do a helper function in include/linux/ioport.h
(which has all the struct resource logic) that can be called like

resource_set_pa(&kernel_code, _stext, __init_begin);
resource_set_pa(&kernel_data, _sdata, _end);

      Arnd

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