Re: [PATCH v6 02/19] string: Add strprefix()

[Alejandro Colomar <alx+linux-hardening@kernel.org>]

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Hi Joe,

> Date: 2026-11-14 10:24:26-0800
> From: Joe Perches <joe@perches.com>
>
> On Sat, 2026-11-14 at 17:59 +0100, Alejandro Colomar wrote:
> > > A negative of this is that it implies the return should
> > > always be tested even though it can be known that the
> > > return is effectively bool.
> > 
> > I'm not sure I follow.  The attribute is about the arguments, not the
> > return value.  Perhaps I don't understand what you mean by "this".
> 
> 'this' is the return of the strprefix function itself.
> 
> It returns either a const char * or a char * or NULL.
> 
> Because it can return NULL, then the return value
> could/should be tested.

Yes, it must be tested, when not used as a boolean.
The usual replacement of
	s += str_has_prefix(s, prefix);
would be
	s = strprefix(s, prefix) ?: s;

The boolean use remains trivial:

	-       return strstarts(name, ".init") ||
	-               strstarts(name, ".ARM.extab.init") ||
	-               strstarts(name, ".ARM.exidx.init");
	+       return strprefix(name, ".init") ||
	+               strprefix(name, ".ARM.extab.init") ||
	+               strprefix(name, ".ARM.exidx.init");
and
	-       if (!str_has_prefix(p, "console=") && !strstr(p, " console=")) {
	+       if (!strprefix(p, "console=") && !strstr(p, " console=")) {

The non-boolean use would look like this (actual diffs from the patch
set):

	-       prefix_len = str_has_prefix(name, PDSC_FW_COMPONENT_PREFIX);
	-       if (prefix_len)
	-               name += prefix_len;
	+       name = strprefix(name, PDSC_FW_COMPONENT_PREFIX) ?: name;

(the old code, actually, didn't need that test, and could have been
 simply 'name += str_has_prefix(name, PDSC_FW_COMPONENT_PREFIX);')

and
	-       len = str_has_prefix(*str, "brl,");
	-       if (len) {
	+       p = strprefix(*str, "brl,");
	+       if (p) {
			*brl_options = "";
	-               *str += len;
	+               *str = p;
			return 0;
		}

and
		cmp = strstrip(option);
	 
	-       len = str_has_prefix(cmp, "no");
	-       if (len)
	+       p = strprefix(cmp, "no");
	+       if (p) {
			neg = 1;
	-
	-       cmp += len;
	+               cmp = p;
	+       }


Have a lovely night!
Alex

-- 
<https://www.alejandro-colomar.es>

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