diff mbox series

[2/3] fortify: cosmetic cleanups to __compiletime_strlen

Message ID 20220830205309.312864-3-ndesaulniers@google.com (mailing list archive)
State New, archived
Headers show
Series Fix FORTIFY=y UBSAN_LOCAL_BOUNDS=y | expand

Commit Message

Nick Desaulniers Aug. 30, 2022, 8:53 p.m. UTC 
Two things I noticed in __compiletime_strlen:
1. A temporary, __p, is created+used to avoid repeated side effects from
   multiple evaluation of the macro parameter, but the macro parameter
   was being used accidentally in __builtin_object_size.
2. The temporary has a curious signedness and const-less qualification.
   Just use __auto_type.
3. (size_t)-1 is perhaps more readable as -1UL.
4. __p_size == -1UL when __builtin_object_size can't evaluate the
   object size at compile time. We could just reuse __ret and use one
   less variable here.

Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
 include/linux/fortify-string.h | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

Comments

kernel test robot Aug. 31, 2022, 1:13 p.m. UTC | #1 
Hi Nick,

I love your patch! Perhaps something to improve:

[auto build test WARNING on kees/for-next/hardening]
[also build test WARNING on kees/for-next/pstore hid/for-next linus/master v6.0-rc3 next-20220831]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Nick-Desaulniers/Fix-FORTIFY-y-UBSAN_LOCAL_BOUNDS-y/20220831-045536
base:   https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git for-next/hardening
config: x86_64-randconfig-a004 (https://download.01.org/0day-ci/archive/20220831/202208312049.JxYsAiD2-lkp@intel.com/config)
compiler: gcc-11 (Debian 11.3.0-5) 11.3.0
reproduce (this is a W=1 build):
        # https://github.com/intel-lab-lkp/linux/commit/ab66e7d1d8a90f6addac0da9b3ae13d77f095f76
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Nick-Desaulniers/Fix-FORTIFY-y-UBSAN_LOCAL_BOUNDS-y/20220831-045536
        git checkout ab66e7d1d8a90f6addac0da9b3ae13d77f095f76
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash drivers/mtd/ubi/

If you fix the issue, kindly add following tag where applicable
Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

   drivers/mtd/ubi/cdev.c: In function 'rename_volumes':
>> drivers/mtd/ubi/cdev.c:710:61: warning: array subscript -1 is below array bounds of 'struct <anonymous>[32]' [-Warray-bounds]
     710 |                         if (req->ents[i].vol_id == req->ents[n].vol_id) {
         |                                                    ~~~~~~~~~^~~
   In file included from drivers/mtd/ubi/cdev.c:33:
   include/uapi/mtd/ubi-user.h:404:11: note: while referencing 'ents'
     404 |         } ents[UBI_MAX_RNVOL];
         |           ^~~~
   drivers/mtd/ubi/cdev.c:715:68: warning: array subscript -1 is below array bounds of 'struct <anonymous>[32]' [-Warray-bounds]
     715 |                         if (!strcmp(req->ents[i].name, req->ents[n].name)) {
         |                                                        ~~~~~~~~~~~~^~~~~
   In file included from drivers/mtd/ubi/cdev.c:33:
   include/uapi/mtd/ubi-user.h:404:11: note: while referencing 'ents'
     404 |         } ents[UBI_MAX_RNVOL];
         |           ^~~~


vim +710 drivers/mtd/ubi/cdev.c

801c135ce73d5d Artem B. Bityutskiy 2006-06-27  668  
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  669  /**
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  670   * rename_volumes - rename UBI volumes.
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  671   * @ubi: UBI device description object
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  672   * @req: volumes re-name request
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  673   *
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  674   * This is a helper function for the volume re-name IOCTL which validates the
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  675   * the request, opens the volume and calls corresponding volumes management
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  676   * function. Returns zero in case of success and a negative error code in case
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  677   * of failure.
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  678   */
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  679  static int rename_volumes(struct ubi_device *ubi,
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  680  			  struct ubi_rnvol_req *req)
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  681  {
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  682  	int i, n, err;
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  683  	struct list_head rename_list;
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  684  	struct ubi_rename_entry *re, *re1;
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  685  
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  686  	if (req->count < 0 || req->count > UBI_MAX_RNVOL)
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  687  		return -EINVAL;
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  688  
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  689  	if (req->count == 0)
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  690  		return 0;
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  691  
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  692  	/* Validate volume IDs and names in the request */
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  693  	for (i = 0; i < req->count; i++) {
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  694  		if (req->ents[i].vol_id < 0 ||
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  695  		    req->ents[i].vol_id >= ubi->vtbl_slots)
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  696  			return -EINVAL;
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  697  		if (req->ents[i].name_len < 0)
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  698  			return -EINVAL;
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  699  		if (req->ents[i].name_len > UBI_VOL_NAME_MAX)
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  700  			return -ENAMETOOLONG;
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  701  		req->ents[i].name[req->ents[i].name_len] = '\0';
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  702  		n = strlen(req->ents[i].name);
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  703  		if (n != req->ents[i].name_len)
7fbbd05799976c Dan Carpenter       2014-09-19  704  			return -EINVAL;
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  705  	}
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  706  
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  707  	/* Make sure volume IDs and names are unique */
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  708  	for (i = 0; i < req->count - 1; i++) {
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  709  		for (n = i + 1; n < req->count; n++) {
f40ac9cdf69912 Artem Bityutskiy    2008-07-13 @710  			if (req->ents[i].vol_id == req->ents[n].vol_id) {
326087033108e7 Tanya Brokhman      2014-10-20  711  				ubi_err(ubi, "duplicated volume id %d",
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  712  					req->ents[i].vol_id);
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  713  				return -EINVAL;
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  714  			}
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  715  			if (!strcmp(req->ents[i].name, req->ents[n].name)) {
326087033108e7 Tanya Brokhman      2014-10-20  716  				ubi_err(ubi, "duplicated volume name \"%s\"",
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  717  					req->ents[i].name);
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  718  				return -EINVAL;
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  719  			}
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  720  		}
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  721  	}
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  722  
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  723  	/* Create the re-name list */
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  724  	INIT_LIST_HEAD(&rename_list);
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  725  	for (i = 0; i < req->count; i++) {
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  726  		int vol_id = req->ents[i].vol_id;
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  727  		int name_len = req->ents[i].name_len;
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  728  		const char *name = req->ents[i].name;
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  729  
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  730  		re = kzalloc(sizeof(struct ubi_rename_entry), GFP_KERNEL);
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  731  		if (!re) {
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  732  			err = -ENOMEM;
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  733  			goto out_free;
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  734  		}
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  735  
892abde56c1c5a Richard Weinberger  2014-11-24  736  		re->desc = ubi_open_volume(ubi->ubi_num, vol_id, UBI_METAONLY);
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  737  		if (IS_ERR(re->desc)) {
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  738  			err = PTR_ERR(re->desc);
326087033108e7 Tanya Brokhman      2014-10-20  739  			ubi_err(ubi, "cannot open volume %d, error %d",
326087033108e7 Tanya Brokhman      2014-10-20  740  				vol_id, err);
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  741  			kfree(re);
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  742  			goto out_free;
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  743  		}
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  744  
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  745  		/* Skip this re-naming if the name does not really change */
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  746  		if (re->desc->vol->name_len == name_len &&
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  747  		    !memcmp(re->desc->vol->name, name, name_len)) {
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  748  			ubi_close_volume(re->desc);
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  749  			kfree(re);
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  750  			continue;
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  751  		}
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  752  
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  753  		re->new_name_len = name_len;
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  754  		memcpy(re->new_name, name, name_len);
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  755  		list_add_tail(&re->list, &rename_list);
719bb84017fcfc Artem Bityutskiy    2012-08-27  756  		dbg_gen("will rename volume %d from \"%s\" to \"%s\"",
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  757  			vol_id, re->desc->vol->name, name);
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  758  	}
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  759  
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  760  	if (list_empty(&rename_list))
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  761  		return 0;
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  762  
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  763  	/* Find out the volumes which have to be removed */
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  764  	list_for_each_entry(re, &rename_list, list) {
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  765  		struct ubi_volume_desc *desc;
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  766  		int no_remove_needed = 0;
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  767  
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  768  		/*
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  769  		 * Volume @re->vol_id is going to be re-named to
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  770  		 * @re->new_name, while its current name is @name. If a volume
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  771  		 * with name @re->new_name currently exists, it has to be
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  772  		 * removed, unless it is also re-named in the request (@req).
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  773  		 */
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  774  		list_for_each_entry(re1, &rename_list, list) {
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  775  			if (re->new_name_len == re1->desc->vol->name_len &&
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  776  			    !memcmp(re->new_name, re1->desc->vol->name,
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  777  				    re1->desc->vol->name_len)) {
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  778  				no_remove_needed = 1;
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  779  				break;
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  780  			}
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  781  		}
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  782  
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  783  		if (no_remove_needed)
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  784  			continue;
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  785  
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  786  		/*
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  787  		 * It seems we need to remove volume with name @re->new_name,
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  788  		 * if it exists.
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  789  		 */
f2863c54f30ccc Artem Bityutskiy    2008-12-28  790  		desc = ubi_open_volume_nm(ubi->ubi_num, re->new_name,
f2863c54f30ccc Artem Bityutskiy    2008-12-28  791  					  UBI_EXCLUSIVE);
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  792  		if (IS_ERR(desc)) {
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  793  			err = PTR_ERR(desc);
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  794  			if (err == -ENODEV)
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  795  				/* Re-naming into a non-existing volume name */
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  796  				continue;
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  797  
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  798  			/* The volume exists but busy, or an error occurred */
326087033108e7 Tanya Brokhman      2014-10-20  799  			ubi_err(ubi, "cannot open volume \"%s\", error %d",
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  800  				re->new_name, err);
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  801  			goto out_free;
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  802  		}
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  803  
01ebc12f5f2e88 Julia Lawall        2010-08-07  804  		re1 = kzalloc(sizeof(struct ubi_rename_entry), GFP_KERNEL);
01ebc12f5f2e88 Julia Lawall        2010-08-07  805  		if (!re1) {
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  806  			err = -ENOMEM;
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  807  			ubi_close_volume(desc);
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  808  			goto out_free;
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  809  		}
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  810  
01ebc12f5f2e88 Julia Lawall        2010-08-07  811  		re1->remove = 1;
01ebc12f5f2e88 Julia Lawall        2010-08-07  812  		re1->desc = desc;
01ebc12f5f2e88 Julia Lawall        2010-08-07  813  		list_add(&re1->list, &rename_list);
719bb84017fcfc Artem Bityutskiy    2012-08-27  814  		dbg_gen("will remove volume %d, name \"%s\"",
01ebc12f5f2e88 Julia Lawall        2010-08-07  815  			re1->desc->vol->vol_id, re1->desc->vol->name);
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  816  	}
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  817  
f089c0b28cdba1 Artem Bityutskiy    2009-05-07  818  	mutex_lock(&ubi->device_mutex);
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  819  	err = ubi_rename_volumes(ubi, &rename_list);
f089c0b28cdba1 Artem Bityutskiy    2009-05-07  820  	mutex_unlock(&ubi->device_mutex);
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  821  
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  822  out_free:
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  823  	list_for_each_entry_safe(re, re1, &rename_list, list) {
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  824  		ubi_close_volume(re->desc);
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  825  		list_del(&re->list);
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  826  		kfree(re);
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  827  	}
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  828  	return err;
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  829  }
f40ac9cdf69912 Artem Bityutskiy    2008-07-13  830
Kees Cook Aug. 31, 2022, 7:06 p.m. UTC | #2 
On Tue, Aug 30, 2022 at 01:53:08PM -0700, Nick Desaulniers wrote:
> Two things I noticed in __compiletime_strlen:

Four? :)

> 1. A temporary, __p, is created+used to avoid repeated side effects from
>    multiple evaluation of the macro parameter, but the macro parameter
>    was being used accidentally in __builtin_object_size.

__builtin_object_size(), like sizeof() but unlike __builtin_strlen(),
will not evaluate side-effects: https://godbolt.org/z/Yaa1z7YvK
And using bos on __p will sometimes mask the actual object, so p needs to
stay the argument.

> 2. The temporary has a curious signedness and const-less qualification.
>    Just use __auto_type.

__auto_type is pretty rare in the kernel, but does provide the removal
of "const". Even though the kernel builds with -Wno-pointer-sign, the
explicit case does fix a potential warnings about signedness differences,
not just const differences, for __builtin_strlen() which requires "const
char *", but many arguments are "unsigned char *", "u8 *", etc.

Is __auto_type more readable than the explicit cast? It does seem to
work fine.

> 3. (size_t)-1 is perhaps more readable as -1UL.

That's true, though I kind of prefer (size_t)-1, though yes, it appears
to be the extreme minority in the kernel.

> 4. __p_size == -1UL when __builtin_object_size can't evaluate the
>    object size at compile time. We could just reuse __ret and use one
>    less variable here.

This seems to get entire optimized away by the compiler? I think it's
more readable to keep the explicit variable.

-Kees

> 
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
> ---
>  include/linux/fortify-string.h | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h
> index c5adad596a3f..aaf73575050f 100644
> --- a/include/linux/fortify-string.h
> +++ b/include/linux/fortify-string.h
> @@ -22,11 +22,10 @@ void __write_overflow_field(size_t avail, size_t wanted) __compiletime_warning("
>  
>  #define __compiletime_strlen(p)					\
>  ({								\
> -	unsigned char *__p = (unsigned char *)(p);		\
> -	size_t __ret = (size_t)-1;				\
> -	size_t __p_size = __object_size(p, 1);			\
> -	if (__p_size != (size_t)-1) {				\
> -		size_t __p_len = __p_size - 1;			\
> +	__auto_type __p = (p);					\
> +	size_t __ret = __object_size(__p, 1);			\
> +	if (__ret != -1UL) {					\
> +		size_t __p_len = __ret - 1;			\
>  		if (__builtin_constant_p(__p[__p_len]) &&	\
>  		    __p[__p_len] == '\0')			\
>  			__ret = __builtin_strlen(__p);		\
> -- 
> 2.37.2.672.g94769d06f0-goog
>
diff mbox series

Patch

diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h
index c5adad596a3f..aaf73575050f 100644
--- a/include/linux/fortify-string.h
+++ b/include/linux/fortify-string.h
@@ -22,11 +22,10 @@  void __write_overflow_field(size_t avail, size_t wanted) __compiletime_warning("
 
 #define __compiletime_strlen(p)					\
 ({								\
-	unsigned char *__p = (unsigned char *)(p);		\
-	size_t __ret = (size_t)-1;				\
-	size_t __p_size = __object_size(p, 1);			\
-	if (__p_size != (size_t)-1) {				\
-		size_t __p_len = __p_size - 1;			\
+	__auto_type __p = (p);					\
+	size_t __ret = __object_size(__p, 1);			\
+	if (__ret != -1UL) {					\
+		size_t __p_len = __ret - 1;			\
 		if (__builtin_constant_p(__p[__p_len]) &&	\
 		    __p[__p_len] == '\0')			\
 			__ret = __builtin_strlen(__p);		\