On Tue, 30 Oct 2018 at 20:07, Jeff Law <l...@redhat.com> wrote: > > On 10/29/18 3:59 PM, Martin Sebor wrote: > > PR 87041 - -Wformat "reading through null pointer" on unreachable > > code is a complaint about -Wformat false positives due to null > > arguments to %s directives in unreachable printf calls. The warning > > is issued by the front end, too early to know whether or not the call > > is ever made. > > > > The -Wformat-overflow has had the ability to detect null pointers > > in %s and similar directives to sprintf calls since GCC 7 without > > these false positives, but the warning doesn't consider stream or > > file I/O functions like printf/fprintf. To resolve the bug report > > I have enhanced -Wformat-overflow to consider all printf-like > > functions, including user-defined ones declared attribute format > > (printf). > > > > Besides null pointers the enhancement also makes it possible to > > detect other problems (like out-of-range arguments and output in > > excess of INT_MAX bytes). It also lays the groundwork for > > checking user-defined printf-like functions for buffer overflow > > (once a suitable attribute is added to indicate which arguments > > are the destination buffer pointer and the buffer size). > > > > With that, I have removed the null checking from -Wformat (again, > > only for printf-like functions). > > > > Martin > > > > gcc-87041.diff > > > > PR middle-end/87041 - -Wformat reading through null pointer on unreachable > > code > > > > gcc/ChangeLog: > > > > PR middle-end/87041 > > * gimple-ssa-sprintf.c (format_directive): Use %G to include > > inlining context. > > (sprintf_dom_walker::compute_format_length): > > Avoid setting POSUNDER4K here. > > (get_destination_size): Handle null argument values. > > (get_user_idx_format): New function. > > (sprintf_dom_walker::handle_gimple_call): Handle all printf-like > > functions, including user-defined with attribute format printf. > > Use %G to include inlining context. > > Set POSUNDER4K here. > > > > gcc/c-family/ChangeLog: > > > > PR middle-end/87041 > > * c-format.c (check_format_types): Avoid diagnosing null pointer > > arguments to printf-family of functions. > > > > gcc/testsuite/ChangeLog: > > > > PR middle-end/87041 > > * gcc.c-torture/execute/fprintf-2.c: New test. > > * gcc.c-torture/execute/printf-2.c: Same. > > * gcc.c-torture/execute/user-printf.c: Same. > > * gcc.dg/tree-ssa/builtin-fprintf-warn-1.c: Same. > > * gcc.dg/tree-ssa/builtin-printf-2.c: Same. > > * gcc.dg/tree-ssa/builtin-printf-warn-1.c: Same. > > * gcc.dg/tree-ssa/user-printf-warn-1.c: Same. > OK. >
Hi, I've noticed failure on targets using newlib (aarch64-elf and arm-eabi): FAIL: gcc.c-torture/execute/printf-2.c FAIL: gcc.c-torture/execute/user-printf.c my gcc.log contains: gcc.c-torture/execute/user-printf.c -O0 execution test (reason: TCL LOOKUP CHANNEL exp5) which is not very helpful > Note some folks might complain about dropping the warning from the > front-end. Their (largely reasonable) argument is that warning out of > the front-end is stable across releases and doesn't depend on > optimizations. Of course the downside of warning out of the front-end > is false positives like we see in this PR. > > jeff
