glibc/stdlib/bits/stdlib.h
Siddhesh Poyarekar a643f60c53 Make sure that the fortified function conditionals are constant
In _FORTIFY_SOURCE=3, the size expression may be non-constant,
resulting in branches in the inline functions remaining intact and
causing a tiny overhead.  Clang (and in future, gcc) make sure that
the -1 case is always safe, i.e. any comparison of the generated
expression with (size_t)-1 is always false so that bit is taken care
of.  The rest is avoidable since we want the _chk variant whenever we
have a size expression and it's not -1.

Rework the conditionals in a uniform way to clearly indicate two
conditions at compile time:

- Either the size is unknown (-1) or we know at compile time that the
  operation length is less than the object size.  We can call the
  original function in this case.  It could be that either the length,
  object size or both are non-constant, but the compiler, through
  range analysis, is able to fold the *comparison* to a constant.

- The size and length are known and the compiler can see at compile
  time that operation length > object size.  This is valid grounds for
  a warning at compile time, followed by emitting the _chk variant.

For everything else, emit the _chk variant.

This simplifies most of the fortified function implementations and at
the same time, ensures that only one call from _chk or the regular
function is emitted.

Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
2021-10-20 18:12:41 +05:30

144 lines
5.3 KiB
C

/* Checking macros for stdlib functions.
Copyright (C) 2005-2021 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#ifndef _STDLIB_H
# error "Never include <bits/stdlib.h> directly; use <stdlib.h> instead."
#endif
extern char *__realpath_chk (const char *__restrict __name,
char *__restrict __resolved,
size_t __resolvedlen) __THROW __wur;
extern char *__REDIRECT_NTH (__realpath_alias,
(const char *__restrict __name,
char *__restrict __resolved), realpath) __wur;
extern char *__REDIRECT_NTH (__realpath_chk_warn,
(const char *__restrict __name,
char *__restrict __resolved,
size_t __resolvedlen), __realpath_chk) __wur
__warnattr ("second argument of realpath must be either NULL or at "
"least PATH_MAX bytes long buffer");
__fortify_function __wur char *
__NTH (realpath (const char *__restrict __name, char *__restrict __resolved))
{
size_t sz = __glibc_objsize (__resolved);
if (sz == (size_t) -1)
return __realpath_alias (__name, __resolved);
#if defined _LIBC_LIMITS_H_ && defined PATH_MAX
if (__glibc_unsafe_len (sz, sizeof (char), PATH_MAX))
return __realpath_chk_warn (__name, __resolved, sz);
#endif
return __realpath_chk (__name, __resolved, sz);
}
extern int __ptsname_r_chk (int __fd, char *__buf, size_t __buflen,
size_t __nreal) __THROW __nonnull ((2))
__attr_access ((__write_only__, 2, 3));
extern int __REDIRECT_NTH (__ptsname_r_alias, (int __fd, char *__buf,
size_t __buflen), ptsname_r)
__nonnull ((2)) __attr_access ((__write_only__, 2, 3));
extern int __REDIRECT_NTH (__ptsname_r_chk_warn,
(int __fd, char *__buf, size_t __buflen,
size_t __nreal), __ptsname_r_chk)
__nonnull ((2)) __warnattr ("ptsname_r called with buflen bigger than "
"size of buf");
__fortify_function int
__NTH (ptsname_r (int __fd, char *__buf, size_t __buflen))
{
return __glibc_fortify (ptsname_r, __buflen, sizeof (char),
__glibc_objsize (__buf),
__fd, __buf, __buflen);
}
extern int __wctomb_chk (char *__s, wchar_t __wchar, size_t __buflen)
__THROW __wur;
extern int __REDIRECT_NTH (__wctomb_alias, (char *__s, wchar_t __wchar),
wctomb) __wur;
__fortify_function __wur int
__NTH (wctomb (char *__s, wchar_t __wchar))
{
/* We would have to include <limits.h> to get a definition of MB_LEN_MAX.
But this would only disturb the namespace. So we define our own
version here. */
#define __STDLIB_MB_LEN_MAX 16
#if defined MB_LEN_MAX && MB_LEN_MAX != __STDLIB_MB_LEN_MAX
# error "Assumed value of MB_LEN_MAX wrong"
#endif
if (__glibc_objsize (__s) != (size_t) -1
&& __STDLIB_MB_LEN_MAX > __glibc_objsize (__s))
return __wctomb_chk (__s, __wchar, __glibc_objsize (__s));
return __wctomb_alias (__s, __wchar);
}
extern size_t __mbstowcs_chk (wchar_t *__restrict __dst,
const char *__restrict __src,
size_t __len, size_t __dstlen) __THROW
__attr_access ((__write_only__, 1, 3)) __attr_access ((__read_only__, 2));
extern size_t __REDIRECT_NTH (__mbstowcs_alias,
(wchar_t *__restrict __dst,
const char *__restrict __src,
size_t __len), mbstowcs)
__attr_access ((__write_only__, 1, 3)) __attr_access ((__read_only__, 2));
extern size_t __REDIRECT_NTH (__mbstowcs_chk_warn,
(wchar_t *__restrict __dst,
const char *__restrict __src,
size_t __len, size_t __dstlen), __mbstowcs_chk)
__warnattr ("mbstowcs called with dst buffer smaller than len "
"* sizeof (wchar_t)");
__fortify_function size_t
__NTH (mbstowcs (wchar_t *__restrict __dst, const char *__restrict __src,
size_t __len))
{
return __glibc_fortify_n (mbstowcs, __len, sizeof (wchar_t),
__glibc_objsize (__dst),
__dst, __src, __len);
}
extern size_t __wcstombs_chk (char *__restrict __dst,
const wchar_t *__restrict __src,
size_t __len, size_t __dstlen) __THROW
__attr_access ((__write_only__, 1, 3)) __attr_access ((__read_only__, 2));
extern size_t __REDIRECT_NTH (__wcstombs_alias,
(char *__restrict __dst,
const wchar_t *__restrict __src,
size_t __len), wcstombs)
__attr_access ((__write_only__, 1, 3)) __attr_access ((__read_only__, 2));
extern size_t __REDIRECT_NTH (__wcstombs_chk_warn,
(char *__restrict __dst,
const wchar_t *__restrict __src,
size_t __len, size_t __dstlen), __wcstombs_chk)
__warnattr ("wcstombs called with dst buffer smaller than len");
__fortify_function size_t
__NTH (wcstombs (char *__restrict __dst, const wchar_t *__restrict __src,
size_t __len))
{
return __glibc_fortify (wcstombs, __len, sizeof (char),
__glibc_objsize (__dst),
__dst, __src, __len);
}