Re: [PATCH 1/3] lib: early_string: allow early usage of some string functions

[Christophe Leroy]

Le 30/04/2021 à 10:47, Christophe Leroy a écrit :
> Le 30/04/2021 à 06:22, Daniel Walker a écrit :
> > This systems allows some string functions to be moved into
> > lib/early_string.c and they will be prepended with "early_" and compiled
> > without debugging like KASAN.
> >
> > This is already done on x86 for,
> > "AMD Secure Memory Encryption (SME) support"
> >
> > and on powerpc prom_init.c , and EFI's libstub.
> >
> > The AMD memory feature disabled KASAN for all string functions, and
> > prom_init.c and efi libstub implement their own versions of the
> > functions.
> >
> > This implementation allows sharing of the string functions without
> > removing the debugging features for the whole system.
>
> This looks good. I prefer that rather than the way you proposed to do it two years ago.
>
> Only one problem, see below.
>
> > +size_t strlcat(char *dest, const char *src, size_t count)
> > +{
> > +    size_t dsize = strlen(dest);
> > +    size_t len = strlen(src);
> > +    size_t res = dsize + len;
> > +
> > +    /* This would be a bug */
> > +    BUG_ON(dsize >= count);
>
> powerpc is not ready to handle BUG_ON() in when in prom_init.
>
> Can you do:
>
> #ifndef __EARLY_STRING_ENABLED
>      BUG_ON(dsize >= count);
> #endif

In fact, should be like in prom_init today:

#ifdef __EARLY_STRING_ENABLED
	if (dsize >= count)
		return count;
#else
	BUG_ON(dsize >= count);
#endif

> > +
> > +    dest += dsize;
> > +    count -= dsize;
> > +    if (len >= count)
> > +        len = count-1;
> > +    memcpy(dest, src, len);
> > +    dest[len] = 0;
> > +    return res;
> > +}
> > +EXPORT_SYMBOL(strlcat);
> > +#endif
> > +