Re: [PATCH v2 1/4] compiler.h: Introduce absolute_pointer macro

[Guenter Roeck]

On 9/15/21 12:13 AM, Geert Uytterhoeven wrote:
> Hi Günter,
>
> On Wed, Sep 15, 2021 at 5:52 AM Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> > absolute_pointer() disassociates a pointer from its originating symbol
> > type and context. Use it to prevent compiler warnings/errors such as
> >
> > drivers/net/ethernet/i825xx/82596.c: In function 'i82596_probe':
> > ./arch/m68k/include/asm/string.h:72:25: error:
> >          '__builtin_memcpy' reading 6 bytes from a region of size 0
> >                  [-Werror=stringop-overread]
> >
> > Such warnings may be reported by gcc 11.x for string and memory operations
> > on fixed addresses.
> >
> > Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> > ---
> > v2: No change
> >
> >   include/linux/compiler.h | 2 ++
> >   1 file changed, 2 insertions(+)
> >
> > diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> > index b67261a1e3e9..3d5af56337bd 100644
> > --- a/include/linux/compiler.h
> > +++ b/include/linux/compiler.h
> > @@ -188,6 +188,8 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
> >       (typeof(ptr)) (__ptr + (off)); })
> >   #endif
> >
> > +#define absolute_pointer(val)  RELOC_HIDE((void *)(val), 0)
>
> I guess we're not worried about "val" being evaluated multiple
> times inside RELOC_HIDE(), as this is mainly intended for constants?

No, we are not. It is quite similar to RELOC_HIDE() in that regard.

Guenter