Value:Copyright (C) 2016-2025 Free Software Foundation, Inc.
Contributed by Martin Sebor <msebor@redhat.com>.
This file is part of GCC.
GCC is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free
Software Foundation; either version 3, or (at your option) any later
version.
GCC 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 General Public License
for more details.
You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING3. If not see
<http://www.gnu.org/licenses/>.
This file implements the printf-return-value pass. The pass does
two things: 1) it analyzes calls to formatted output functions like
sprintf looking for possible buffer overflows and calls to bounded
functions like snprintf for early truncation (and under the control
of the -Wformat-length option issues warnings), and 2) under the
control of the -fprintf-return-value option it folds the return
value of safe calls into constants, making it possible to eliminate
code that depends on the value of those constants.
For all functions (bounded or not) the pass uses the size of the
destination object. That means that it will diagnose calls to
snprintf not on the basis of the size specified by the function's
second argument but rather on the basis of the size the first
argument points to (if possible). For bound-checking built-ins
like __builtin___snprintf_chk the pass uses the size typically
determined by __builtin_object_size and passed to the built-in
by the Glibc inline wrapper.
The pass handles all forms standard sprintf format directives,
including character, integer, floating point, pointer, and strings,
with the standard C flags, widths, and precisions. For integers
and strings it computes the length of output itself. For floating
point it uses MPFR to format known constants with up and down
rounding and uses the resulting range of output lengths. For
strings it uses the length of string literals and the sizes of
character arrays that a character pointer may point to as a bound
on the longest string.
The likely worst case value of MB_LEN_MAX for the target, large enough
for UTF-8. Ideally, this would be obtained by a target hook if it were
to be used for optimization but it's good enough as is for warnings.
1.13.2