On Sun, 2024-02-04 at 11:40 -0700, Daniel Xu wrote:
[...]
> +static int btf_encoder__tag_kfuncs(struct btf_encoder *encoder)
> +{
> + const char *filename = encoder->filename;
> + struct gobuffer btf_kfunc_ranges = {};
> + struct gobuffer btf_funcs = {};
> + Elf_Scn *symscn = NULL;
> + int symbols_shndx = -1;
> + int fd = -1, err = -1;
> + int idlist_shndx = -1;
> + Elf_Scn *scn = NULL;
> + size_t idlist_addr;
> + Elf_Data *symbols;
> + Elf_Data *idlist;
> + size_t strtabidx;
> + Elf *elf = NULL;
> + GElf_Shdr shdr;
> + size_t strndx;
> + char *secname;
> + int nr_syms;
> + int i = 0;
Note: when compiled in Release mode (e.g. using buildcmd.sh from the repo)
there is a number of false-positive warnings reported by GCC 13.2.1:
$ ./buildcmd.sh
...
In function ‘is_sym_kfunc_set’,
inlined from ‘btf_encoder__tag_kfuncs’ at /home/eddy/work/dwarves-fork/btf_encoder.c:1639:8,
inlined from ‘btf_encoder__encode’ at /home/eddy/work/dwarves-fork/btf_encoder.c:1724:29:
/home/eddy/work/dwarves-fork/btf_encoder.c:1395:29: warning: ‘idlist_addr’ may be used uninitialized [-Wmaybe-uninitialized]
1395 | off = sym->st_value - idlist_addr;
| ~~~~~~~~~~~~~~^~~~~~~~~~~~~
/home/eddy/work/dwarves-fork/btf_encoder.c: In function ‘btf_encoder__encode’:
/home/eddy/work/dwarves-fork/btf_encoder.c:1538:16: note: ‘idlist_addr’ was declared here
1538 | size_t idlist_addr;
| ^~~~~~~~~~~
In function ‘btf_encoder__tag_kfuncs’,
inlined from ‘btf_encoder__encode’ at /home/eddy/work/dwarves-fork/btf_encoder.c:1724:29:
Same thing is reported for:
- btf_encoder.c:1630:22: warning: ‘symbols’ may be used uninitialized
- btf_encoder.c:1385:15: warning: ‘idlist’ may be used uninitialized
- btf_encoder.c:1638:24: warning: ‘strtabidx’ may be used uninitialized
GCC does not figure out that the variables above are guarded by -1 checks below.
[...]
> + while ((scn = elf_nextscn(elf, scn)) != NULL) {
[...]
> + if (shdr.sh_type == SHT_SYMTAB) {
> + symbols_shndx = i;
> + symscn = scn;
> + symbols = data;
> + strtabidx = shdr.sh_link;
> + } else if (!strcmp(secname, BTF_IDS_SECTION)) {
> + idlist_shndx = i;
> + idlist_addr = shdr.sh_addr;
> + idlist = data;
> + }
> + }
> +
> + /* Cannot resolve symbol or .BTF_ids sections. Nothing to do. */
> + if (symbols_shndx == -1 || idlist_shndx == -1) {
> + err = 0;
> + goto out;
> + }
[...]
