Hi Bruno, On 4/27/24 2:02 AM, Bruno Haible wrote: > At this point of the investigations, it's too early for a patch. > First, one needs to determine whether it's a bug in Gnulib or a > bug in some package we rely on (typically gcc or glibc). In the > latter case, we report the bug and wait for the answer. Depending > on the answer, we may fix the test (if they say that our test is > wrong), or we may put in an officially recommended workaround, > or a workaround of our liking, or disable that part of the unit test.
Sounds like a lot of things to learn. > If some glibc-optimized expansions are active, you would also see some > *_chk symbols in the 'nm' output. Interesting, I didn't know that is how you could tell. Thanks! > So, at this point it looks like a gcc problem. The next step is to prepare > a trimmed-down test case <https://gcc.gnu.org/bugs/#need>: > 1. Concentrate on the simpler test case. In this case, I would say, it's > sprintf, since it takes one argument less than snprintf. > 2. Eliminate the -I, -L, -l options specific to gnulib. So that you have > a program that succeeds without -O2 and fails with -O2. This implies > inlining include files from gnulib (test-sprintf-posix.h, macros.h, > etc.). > 3. Work on minimizing the compilation unit that succeeds without -O2 and > fails with -O2. Always keep -Wall enabled, to guard against mistakes. > Remove the test cases that pass, remove unnecessary includes, and so on. > 4. When you can't minimize that further, preprocess it: > $ gcc OPTIONS -E foo.c > foo-pre.c > Verify that it still succeeds without -O2 and fails with -O2. > 5. Continue minimizing, with -Wall enabled. Typically the end result will > be a small file, 10-20 lines of code. > > If you got that far and can argue (by the standards) that it is a GCC bug, > open a bug report. The GCC shipped by Fedora is not an upstream release; > nevertheless Paul opens his bug reports about Fedora's gcc directly in the > upstream bug tracker, e.g. > <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114870?>. You can do the same. Thanks for the information! I did a little expirementing with this program: ==================================================================== #include <stdio.h> #include <wchar.h> int main (void) { char buffer[5000]; wint_t ch = (wint_t) L'\0'; int result = sprintf (buffer, "%lc%lc%lc%lc", ch, ch, ch, ch); printf ("%d\n", result); return 0; } ==================================================================== I think I did decent at narrowing it down: $ make gcc -Wall -g -O2 -fprintf-return-value -o a.out main.c ./a.out 0 $ make gcc -Wall -g -O0 -o a.out main.c ./a.out 4 $ make gcc -Wall -g -O1 -o a.out main.c ./a.out 0 $ make gcc -Wall -g -O1 -fprintf-return-value -o a.out main.c ./a.out 0 $ make gcc -Wall -g -O1 -fno-printf-return-value -o a.out main.c ./a.out 4 If I understand correctly, sprintf should return 4 here correct? And the buffer should have 5 NUL bytes. 4 from the arguments and 1 trailing, which is excluded from the return value. Collin
