https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108661
Bug ID: 108661 Summary: -Wanalyzer-use-of-uninitialized-value false positive seen in haproxy's sink_rotate_file_backed_ring Product: gcc Version: 13.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: analyzer Assignee: dmalcolm at gcc dot gnu.org Reporter: dmalcolm at gcc dot gnu.org Target Milestone: --- Consider: #include <sys/stat.h> #include <fcntl.h> #include <unistd.h> struct ring { char buf[1024]; }; int test (const char *name) { struct ring ring; int fd; int ret; fd = open(name, O_RDONLY); if (fd < 0) return 0; ret = read(fd, &ring, sizeof(ring)); close(fd); if (ret != sizeof(ring)) return 1; if (ring.buf[0] > 1) return 2; return 3; } Currently trunk emits this false positive: <source>: In function 'test': <source>:26:21: warning: use of uninitialized value 'ring.buf[0]' [CWE-457] [-Wanalyzer-use-of-uninitialized-value] 26 | if (ring.buf[0] > 1) | ~~~~~~~~^~~ 'test': events 1-6 | | 12 | struct ring ring; | | ^~~~ | | | | | (1) region created on stack here |...... | 17 | if (fd < 0) | | ~ | | | | | (2) following 'false' branch (when 'fd >= 0')... |...... | 20 | ret = read(fd, &ring, sizeof(ring)); | | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | | | | | (3) ...to here |...... | 23 | if (ret != sizeof(ring)) | | ~ | | | | | (4) following 'false' branch (when 'ret == 1024')... |...... | 26 | if (ring.buf[0] > 1) | | ~~~~~~~~~~~ | | | | | (5) ...to here | | (6) use of uninitialized value 'ring.buf[0]' here | Compiler returned: 0 https://godbolt.org/z/3sMhxej6P Looks like the analyzer might not "know" that when "read" returns the input size, that the buffer is fully populated.