On Mon, Aug 12, 2024 at 6:57 AM Alan Maguire <alan.maguire@xxxxxxxxxx> wrote: > > 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 - yes, I don't like that each caller has to remember to initialize the struct that is clearly initialized by elf_open() itself, so see below. pw-bot: cr > I suppose another option would perhaps be to > > - have elf_open() to init int fd = -1, Elf *elf = NULL. I'd do just elf_fd->elf = NULL; elf_fd->fd = -1; and do nothing else. This should be enough for compiler to not trigger this. > - 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 > Let's not touch anything else, this should be enough. > 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);
