On 12/08/2024 11:37, Sam James wrote: > In `elf_close`, we get this with GCC 15 -O3 (at least): > ``` > In function ‘elf_close’, > inlined from ‘elf_close’ at elf.c:53:6, > inlined from ‘elf_find_func_offset_from_file’ at elf.c:384:2: > elf.c:57:9: warning: ‘elf_fd.elf’ may be used uninitialized [-Wmaybe-uninitialized] > 57 | elf_end(elf_fd->elf); > | ^~~~~~~~~~~~~~~~~~~~ > elf.c: In function ‘elf_find_func_offset_from_file’: > elf.c:377:23: note: ‘elf_fd.elf’ was declared here > 377 | struct elf_fd elf_fd; > | ^~~~~~ > In function ‘elf_close’, > inlined from ‘elf_close’ at elf.c:53:6, > inlined from ‘elf_find_func_offset_from_file’ at elf.c:384:2: > elf.c:58:9: warning: ‘elf_fd.fd’ may be used uninitialized [-Wmaybe-uninitialized] > 58 | close(elf_fd->fd); > | ^~~~~~~~~~~~~~~~~ > elf.c: In function ‘elf_find_func_offset_from_file’: > elf.c:377:23: note: ‘elf_fd.fd’ was declared here > 377 | struct elf_fd elf_fd; > | ^~~~~~ > ``` > > In reality, our use is fine, it's just that GCC doesn't model errno > here (see linked GCC bug). Suppress -Wmaybe-uninitialized accordingly > by initializing elf_fd.elf to -1. > > I've done this in two other functions as well given it could easily > occur there too (same access/use pattern). > hmm, looking at this again - given that there are multiple consumers - I suppose another option would perhaps be to - have elf_open() to init int fd = -1, Elf *elf = NULL. - have error paths in elf_open() "goto out"; at out: we set elf_fd->fd, elf_fd->elf to fd, elf - have elf_close() exit it elf_fd < 0 (since 0 is a valid fd), as it will for the error cases Might all be bit excessive, and might not even fix the false positive issue here, so > Link: https://gcc.gnu.org/PR114952 > Signed-off-by: Sam James <sam@xxxxxxxxxx> Reviewed-by: Alan Maguire <alan.maguire@xxxxxxxxxx> > --- > v3: Initialize to -1 instead of using a pragma. > > Range-diff against v2: > 1: 8f5c3b173e4cb < -: ------------- libbpf: workaround -Wmaybe-uninitialized false positive > -: ------------- > 1: 12cec1262be71 libbpf: workaround -Wmaybe-uninitialized false positive > > tools/lib/bpf/elf.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/tools/lib/bpf/elf.c b/tools/lib/bpf/elf.c > index c92e02394159e..00ea3f867bbc8 100644 > --- a/tools/lib/bpf/elf.c > +++ b/tools/lib/bpf/elf.c > @@ -374,7 +374,7 @@ long elf_find_func_offset(Elf *elf, const char *binary_path, const char *name) > */ > long elf_find_func_offset_from_file(const char *binary_path, const char *name) > { > - struct elf_fd elf_fd; > + struct elf_fd elf_fd = { .fd = -1 }; > long ret = -ENOENT; > > ret = elf_open(binary_path, &elf_fd); > @@ -412,7 +412,7 @@ int elf_resolve_syms_offsets(const char *binary_path, int cnt, > int err = 0, i, cnt_done = 0; > unsigned long *offsets; > struct symbol *symbols; > - struct elf_fd elf_fd; > + struct elf_fd elf_fd = { .fd = -1 }; > > err = elf_open(binary_path, &elf_fd); > if (err) > @@ -507,7 +507,7 @@ int elf_resolve_pattern_offsets(const char *binary_path, const char *pattern, > int sh_types[2] = { SHT_SYMTAB, SHT_DYNSYM }; > unsigned long *offsets = NULL; > size_t cap = 0, cnt = 0; > - struct elf_fd elf_fd; > + struct elf_fd elf_fd = { .fd = -1 }; > int err = 0, i; > > err = elf_open(binary_path, &elf_fd);
