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Date: Sat, 15 Jun 2019 13:25:54 -0700
From: Song Liu <liu.song.a23@...il.com>
To: Andrii Nakryiko <andriin@...com>
Cc: Andrii Nakryiko <andrii.nakryiko@...il.com>,
bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
Alexei Starovoitov <ast@...com>,
Daniel Borkmann <daniel@...earbox.net>,
Kernel Team <kernel-team@...com>
Subject: Re: [PATCH bpf-next 2/8] libbpf: extract BTF loading and simplify ELF
parsing logic
On Mon, Jun 10, 2019 at 9:49 PM Andrii Nakryiko <andriin@...com> wrote:
>
> As a preparation for adding BTF-based BPF map loading, extract .BTF and
> .BTF.ext loading logic. Also simplify error handling in
> bpf_object__elf_collect() by returning early, as there is no common
> clean up to be done.
>
> Signed-off-by: Andrii Nakryiko <andriin@...com>
> ---
> tools/lib/bpf/libbpf.c | 137 ++++++++++++++++++++++-------------------
> 1 file changed, 75 insertions(+), 62 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index ba89d9727137..9e39a0a33aeb 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -1078,6 +1078,58 @@ static void bpf_object__sanitize_btf_ext(struct bpf_object *obj)
> }
> }
>
> +static int bpf_object__load_btf(struct bpf_object *obj,
> + Elf_Data *btf_data,
> + Elf_Data *btf_ext_data)
> +{
> + int err = 0;
> +
> + if (btf_data) {
> + obj->btf = btf__new(btf_data->d_buf, btf_data->d_size);
> + if (IS_ERR(obj->btf)) {
> + pr_warning("Error loading ELF section %s: %d.\n",
> + BTF_ELF_SEC, err);
> + goto out;
If we goto out here, we will return 0.
> + }
> + err = btf__finalize_data(obj, obj->btf);
> + if (err) {
> + pr_warning("Error finalizing %s: %d.\n",
> + BTF_ELF_SEC, err);
> + goto out;
> + }
> + bpf_object__sanitize_btf(obj);
> + err = btf__load(obj->btf);
> + if (err) {
> + pr_warning("Error loading %s into kernel: %d.\n",
> + BTF_ELF_SEC, err);
> + goto out;
> + }
> + }
> + if (btf_ext_data) {
> + if (!obj->btf) {
> + pr_debug("Ignore ELF section %s because its depending ELF section %s is not found.\n",
> + BTF_EXT_ELF_SEC, BTF_ELF_SEC);
> + goto out;
We will also return 0 when goto out here.
> + }
> + obj->btf_ext = btf_ext__new(btf_ext_data->d_buf,
> + btf_ext_data->d_size);
> + if (IS_ERR(obj->btf_ext)) {
> + pr_warning("Error loading ELF section %s: %ld. Ignored and continue.\n",
> + BTF_EXT_ELF_SEC, PTR_ERR(obj->btf_ext));
> + obj->btf_ext = NULL;
> + goto out;
And, here. And we will not free obj->btf.
> + }
> + bpf_object__sanitize_btf_ext(obj);
> + }
> +out:
> + if (err || IS_ERR(obj->btf)) {
> + if (!IS_ERR_OR_NULL(obj->btf))
> + btf__free(obj->btf);
> + obj->btf = NULL;
> + }
> + return 0;
> +}
> +
> static int bpf_object__elf_collect(struct bpf_object *obj, int flags)
> {
> Elf *elf = obj->efile.elf;
> @@ -1102,24 +1154,21 @@ static int bpf_object__elf_collect(struct bpf_object *obj, int flags)
> if (gelf_getshdr(scn, &sh) != &sh) {
> pr_warning("failed to get section(%d) header from %s\n",
> idx, obj->path);
> - err = -LIBBPF_ERRNO__FORMAT;
> - goto out;
> + return -LIBBPF_ERRNO__FORMAT;
> }
>
> name = elf_strptr(elf, ep->e_shstrndx, sh.sh_name);
> if (!name) {
> pr_warning("failed to get section(%d) name from %s\n",
> idx, obj->path);
> - err = -LIBBPF_ERRNO__FORMAT;
> - goto out;
> + return -LIBBPF_ERRNO__FORMAT;
> }
>
> data = elf_getdata(scn, 0);
> if (!data) {
> pr_warning("failed to get section(%d) data from %s(%s)\n",
> idx, name, obj->path);
> - err = -LIBBPF_ERRNO__FORMAT;
> - goto out;
> + return -LIBBPF_ERRNO__FORMAT;
> }
> pr_debug("section(%d) %s, size %ld, link %d, flags %lx, type=%d\n",
> idx, name, (unsigned long)data->d_size,
> @@ -1130,10 +1179,14 @@ static int bpf_object__elf_collect(struct bpf_object *obj, int flags)
> err = bpf_object__init_license(obj,
> data->d_buf,
> data->d_size);
> + if (err)
> + return err;
> } else if (strcmp(name, "version") == 0) {
> err = bpf_object__init_kversion(obj,
> data->d_buf,
> data->d_size);
> + if (err)
> + return err;
> } else if (strcmp(name, "maps") == 0) {
> obj->efile.maps_shndx = idx;
> } else if (strcmp(name, BTF_ELF_SEC) == 0) {
> @@ -1144,11 +1197,10 @@ static int bpf_object__elf_collect(struct bpf_object *obj, int flags)
> if (obj->efile.symbols) {
> pr_warning("bpf: multiple SYMTAB in %s\n",
> obj->path);
> - err = -LIBBPF_ERRNO__FORMAT;
> - } else {
> - obj->efile.symbols = data;
> - obj->efile.strtabidx = sh.sh_link;
> + return -LIBBPF_ERRNO__FORMAT;
> }
> + obj->efile.symbols = data;
> + obj->efile.strtabidx = sh.sh_link;
> } else if (sh.sh_type == SHT_PROGBITS && data->d_size > 0) {
> if (sh.sh_flags & SHF_EXECINSTR) {
> if (strcmp(name, ".text") == 0)
> @@ -1162,6 +1214,7 @@ static int bpf_object__elf_collect(struct bpf_object *obj, int flags)
>
> pr_warning("failed to alloc program %s (%s): %s",
> name, obj->path, cp);
> + return err;
> }
> } else if (strcmp(name, ".data") == 0) {
> obj->efile.data = data;
> @@ -1173,8 +1226,8 @@ static int bpf_object__elf_collect(struct bpf_object *obj, int flags)
> pr_debug("skip section(%d) %s\n", idx, name);
> }
> } else if (sh.sh_type == SHT_REL) {
> + int nr_reloc = obj->efile.nr_reloc;
> void *reloc = obj->efile.reloc;
> - int nr_reloc = obj->efile.nr_reloc + 1;
> int sec = sh.sh_info; /* points to other section */
>
> /* Only do relo for section with exec instructions */
> @@ -1184,79 +1237,39 @@ static int bpf_object__elf_collect(struct bpf_object *obj, int flags)
> continue;
> }
>
> - reloc = reallocarray(reloc, nr_reloc,
> + reloc = reallocarray(reloc, nr_reloc + 1,
> sizeof(*obj->efile.reloc));
> if (!reloc) {
> pr_warning("realloc failed\n");
> - err = -ENOMEM;
> - } else {
> - int n = nr_reloc - 1;
> + return -ENOMEM;
> + }
>
> - obj->efile.reloc = reloc;
> - obj->efile.nr_reloc = nr_reloc;
> + obj->efile.reloc = reloc;
> + obj->efile.nr_reloc++;
>
> - obj->efile.reloc[n].shdr = sh;
> - obj->efile.reloc[n].data = data;
> - }
> + obj->efile.reloc[nr_reloc].shdr = sh;
> + obj->efile.reloc[nr_reloc].data = data;
> } else if (sh.sh_type == SHT_NOBITS && strcmp(name, ".bss") == 0) {
> obj->efile.bss = data;
> obj->efile.bss_shndx = idx;
> } else {
> pr_debug("skip section(%d) %s\n", idx, name);
> }
> - if (err)
> - goto out;
> }
>
> if (!obj->efile.strtabidx || obj->efile.strtabidx >= idx) {
> pr_warning("Corrupted ELF file: index of strtab invalid\n");
> return -LIBBPF_ERRNO__FORMAT;
> }
> - if (btf_data) {
> - obj->btf = btf__new(btf_data->d_buf, btf_data->d_size);
> - if (IS_ERR(obj->btf)) {
> - pr_warning("Error loading ELF section %s: %ld. Ignored and continue.\n",
> - BTF_ELF_SEC, PTR_ERR(obj->btf));
> - obj->btf = NULL;
> - } else {
> - err = btf__finalize_data(obj, obj->btf);
> - if (!err) {
> - bpf_object__sanitize_btf(obj);
> - err = btf__load(obj->btf);
> - }
> - if (err) {
> - pr_warning("Error finalizing and loading %s into kernel: %d. Ignored and continue.\n",
> - BTF_ELF_SEC, err);
> - btf__free(obj->btf);
> - obj->btf = NULL;
> - err = 0;
> - }
> - }
> - }
> - if (btf_ext_data) {
> - if (!obj->btf) {
> - pr_debug("Ignore ELF section %s because its depending ELF section %s is not found.\n",
> - BTF_EXT_ELF_SEC, BTF_ELF_SEC);
> - } else {
> - obj->btf_ext = btf_ext__new(btf_ext_data->d_buf,
> - btf_ext_data->d_size);
> - if (IS_ERR(obj->btf_ext)) {
> - pr_warning("Error loading ELF section %s: %ld. Ignored and continue.\n",
> - BTF_EXT_ELF_SEC,
> - PTR_ERR(obj->btf_ext));
> - obj->btf_ext = NULL;
> - } else {
> - bpf_object__sanitize_btf_ext(obj);
> - }
> - }
> - }
> + err = bpf_object__load_btf(obj, btf_data, btf_ext_data);
> + if (err)
> + return err;
> if (bpf_object__has_maps(obj)) {
> err = bpf_object__init_maps(obj, flags);
> if (err)
> - goto out;
> + return err;
> }
> err = bpf_object__init_prog_names(obj);
> -out:
> return err;
> }
>
> --
> 2.17.1
>
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