linux-kernel - Re: [m68k:master 1174/1174] arch/m68k/include/asm/string.h:72:25: warning: '__builtin_memcpy' forming offset 8 is out of the bounds [0, 7]

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Date:   Fri, 8 Mar 2019 08:43:04 +1100 (AEDT)
From:   Finn Thain <fthain@...egraphics.com.au>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
cc:     Andreas Schwab <schwab@...ux-m68k.org>,
        kbuild test robot <lkp@...el.com>, kbuild-all@...org,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Arnd Bergmann <arnd@...db.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [m68k:master 1174/1174] arch/m68k/include/asm/string.h:72:25:
 warning: '__builtin_memcpy' forming offset 8 is out of the bounds [0, 7]

On Thu, 7 Mar 2019, Geert Uytterhoeven wrote:

> On Thu, Mar 7, 2019 at 3:59 AM Finn Thain <fthain@...egraphics.com.au> wrote:
> > On Tue, 5 Mar 2019, Andreas Schwab wrote:
> > > On Mar 05 2019, Finn Thain <fthain@...egraphics.com.au> wrote:
> > >
> > > > interesting that the kernel's strlen implementation in
> > > > include/linux/string.h can't achieve this.
> > >
> > > This implementation is only available if ARCH_HAS_FORTIFY_SOURCE.
> > >
> >
> > I see. Perhaps we could add another definition to that file:
> >
> > #if !defined(__NO_FORTIFY) && defined(__OPTIMIZE__) && defined(CONFIG_FORTIFY_SOURCE)
> > ...
> > #else
> > __FORTIFY_INLINE __kernel_size_t strlen(const char *p)
> > {
> >         return __builtin_strlen(p);
> > }
> > #endif
> >
> > I didn't test that.

I've tested it now, it works too. This may be a better solution than 
defining a strlen macro.

diff --git a/include/linux/string.h b/include/linux/string.h
index 7927b875f80c..ec9c0a206bd3 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -436,6 +436,13 @@ __FORTIFY_INLINE char *strcpy(char *p, const char *q)
 	return p;
 }
 
+#else
+
+__FORTIFY_INLINE __kernel_size_t strlen(const char *p)
+{
+	return __builtin_strlen(p);
+}
+
 #endif
 
 /**

> But the following patch seems to work...
> >
> > diff --git a/arch/m68k/include/asm/string.h b/arch/m68k/include/asm/string.h
> > index f759d944c449..3cff6b128ed3 100644
> > --- a/arch/m68k/include/asm/string.h
> > +++ b/arch/m68k/include/asm/string.h
> > @@ -71,4 +71,6 @@ extern void *memset(void *, int, __kernel_size_t);
> >  extern void *memcpy(void *, const void *, __kernel_size_t);
> >  #define memcpy(d, s, n) __builtin_memcpy(d, s, n)
> >
> > +#define strlen(s) __builtin_strlen(s)
> 
> Shouldn't you add
> 
>     #define __HAVE_ARCH_STRLEN
> 
> here...
> 

No, the link fails because the compiler still emits some references to 
strlen().

-- 

> > +
> >  #endif /* _M68K_STRING_H_ */
> > diff --git a/lib/string.c b/lib/string.c
> > index 38e4ca08e757..fe970f2160e5 100644
> > --- a/lib/string.c
> > +++ b/lib/string.c
> > @@ -472,6 +472,7 @@ char *strim(char *s)
> >  EXPORT_SYMBOL(strim);
> >
> >  #ifndef __HAVE_ARCH_STRLEN
> > +#undef strlen
> 
> ... so you can drop this change?
> 
> >  /**
> >   * strlen - Find the length of a string
> >   * @s: The string to be sized
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
>