Re: [PATCH] improve out-of-bounds checking with GCC 10 attribute access [BZ #25219]

[Joseph Myers <joseph@codesourcery.com>]

How exactly was this patch tested?  I'm seeing glibc testsuite build 
failures with GCC 10 on what looks like every configuration supported by 
build-many-glibcs.py, with errors referencing these attributes.  (I 
haven't bisected to confirm the responsible commit; this is with the first 
run of my bot for GCC 10, and my GCC mainline bot had the build fail 
earlier because of GCC bugs at the relevant time.)

test-errno.c: In function 'do_test':
test-errno.c:122:30: error: argument 1 value -1 is negative [-Werror=stringop-overflow=]
  122 |   fails |= test_wrp (EINVAL, getgroups, -1, 0);
      |                              ^
test-errno.c:65:17: note: in definition of macro 'test_wrp_rv'
   65 |     rtype ret = syscall (__VA_ARGS__);    \
      |                 ^~~~~~~
test-errno.c:122:12: note: in expansion of macro 'test_wrp'
  122 |   fails |= test_wrp (EINVAL, getgroups, -1, 0);
      |            ^~~~~~~~
In file included from ../include/unistd.h:2,
                 from test-errno.c:35:
../posix/unistd.h:701:12: note: in a call to function 'getgroups' declared with attribute 'write_only (2, 1)'
  701 | extern int getgroups (int __size, __gid_t __list[]) __THROW __wur
      |            ^~~~~~~~~
test-errno.c:137:30: error: 'readlink' specified size 18446744073709551615 exceeds maximum object size 9223372036854775807 [-Werror=stringop-overflow=]
  137 |   fails |= test_wrp (EINVAL, readlink, "/", buf, -1);
      |                              ^
test-errno.c:65:17: note: in definition of macro 'test_wrp_rv'
   65 |     rtype ret = syscall (__VA_ARGS__);    \
      |                 ^~~~~~~
test-errno.c:137:12: note: in expansion of macro 'test_wrp'
  137 |   fails |= test_wrp (EINVAL, readlink, "/", buf, -1);
      |            ^~~~~~~~
In file included from ../include/unistd.h:2,
                 from test-errno.c:35:
../posix/unistd.h:820:16: note: in a call to function 'readlink' declared with attribute 'write_only (2, 3)'
  820 | extern ssize_t readlink (const char *__restrict __path,
      |                ^~~~~~~~


-- 
Joseph S. Myers
joseph@codesourcery.com