Messages in this thread | | | Date | Mon, 30 Nov 2015 13:00:46 +0800 | From | "Wangnan (F)" <> | Subject | Re: [PATCH v2 02/13] bpf tools: Extract and collect map names from BPF object file |
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On 2015/11/30 0:14, Namhyung Kim wrote: > Hi Wang, > > On Fri, Nov 27, 2015 at 08:47:36AM +0000, Wang Nan wrote: >> This patch collects name of maps in BPF object files and saves them into >> 'maps' field in 'struct bpf_object'. 'bpf_object__get_map_by_name' is >> introduced to retrive fd and definitions of a map through its name. >> >> Signed-off-by: Wang Nan <wangnan0@huawei.com> >> Signed-off-by: He Kuang <hekuang@huawei.com> >> Cc: Alexei Starovoitov <ast@kernel.org> >> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> >> Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> >> Cc: Namhyung Kim <namhyung@kernel.org> >> Cc: Zefan Li <lizefan@huawei.com> >> Cc: pi3orama@163.com >> --- >> tools/lib/bpf/libbpf.c | 65 +++++++++++++++++++++++++++++++++++++++++++++++--- >> tools/lib/bpf/libbpf.h | 3 +++ >> 2 files changed, 65 insertions(+), 3 deletions(-) >> >> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c >> index f509825..a298614 100644 >> --- a/tools/lib/bpf/libbpf.c >> +++ b/tools/lib/bpf/libbpf.c >> @@ -165,6 +165,7 @@ struct bpf_program { >> >> struct bpf_map { >> int fd; >> + char *name; >> struct bpf_map_def def; >> void *priv; >> bpf_map_clear_priv_t clear_priv; >> @@ -526,12 +527,46 @@ bpf_object__init_maps(struct bpf_object *obj, void *data, >> return 0; >> } >> >> +static void >> +bpf_object__init_maps_name(struct bpf_object *obj, int maps_shndx) >> +{ >> + int i; >> + Elf_Data *symbols = obj->efile.symbols; >> + >> + if (!symbols || maps_shndx < 0) >> + return; >> + >> + for (i = 0; i < symbols->d_size / sizeof(GElf_Sym); i++) { >> + GElf_Sym sym; >> + size_t map_idx; >> + const char *map_name; >> + >> + if (!gelf_getsym(symbols, i, &sym)) >> + continue; >> + if (sym.st_shndx != maps_shndx) >> + continue; >> + >> + map_name = elf_strptr(obj->efile.elf, >> + obj->efile.ehdr.e_shstrndx, >> + sym.st_name); > It means that each map name is saved in section header string table?
According to elf format specification:
For an symbol table entry, the st_name field "holds an index into the object file’s symbol string table, which holds the character representations of the symbol names. If the value is non-zero, it represents a string table index that gives the symbol name. Otherwise, the symbol table entry has no name."
And so called "object file’s symbol string table" is a section in the object file which index is stored into ehdr and be loaded during gelf_getehdr(), and its index would be set to ehdr->e_shstrndx. So I think for each map its name should be saved in that string table.
> >> + map_idx = sym.st_value / sizeof(struct bpf_map_def); >> + if (map_idx >= obj->nr_maps) { >> + pr_warning("index of map \"%s\" is buggy: %zu > %zu\n", >> + map_name, map_idx, obj->nr_maps); >> + continue; >> + } >> + obj->maps[map_idx].name = strdup(map_name); > You need to check the return value.
Will send a patch for it.
Thank you.
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