Re: [PATCH 1/5] bpf tools: Improve libbpf error reporting

From: Arnaldo Carvalho de Melo
Date: Thu Nov 05 2015 - 10:26:17 EST

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In reply to: Wang Nan: "[PATCH 1/5] bpf tools: Improve libbpf error reporting"
Next in thread: Arnaldo Carvalho de Melo: "Re: [PATCH 1/5] bpf tools: Improve libbpf error reporting"
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Em Thu, Nov 05, 2015 at 04:26:58AM +0000, Wang Nan escreveu:
> In this patch, a series libbpf specific error numbers and
> libbpf_strerror() are created to help reporting error to caller.
> Functions are updated to pass correct error number through macro
> CHECK_ERR().
>
> All users of bpf_object__open{_buffer}() and bpf_program__title()
> in perf are modified accordingly. In addition, due to error code
> changing, bpf__strerror_load() also modified to use new error code.
>
> bpf__strerror_head() is also changed accordingly so it can parse
> libbpf error. bpf_loader_strerror() is introduced for it, and will
> be improved by following patch.

I am applying this, test shows a improvement in error reporting, but
please look below for some suggestions:

[root@zoo ~]# perf record -e /tmp/foo.o sleep 1
event syntax error: '/tmp/foo.o'
\___ Failed to load program: Validate your program and check 'license'/'version' sections in your object

Now this is a long error message, maybe:

event syntax error: '/tmp/foo.o'
\___ Failed to load: Check 'license'/'version' sections

And then, here we _know_ the problem is in the license, so why not use
that knowledge to help the user further and show instead:

event syntax error: '/tmp/foo.o'
\___ Failed to load: 'version'(4.2.0) doesn't match running kernel (4.3.0)

More below

> Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
> Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
> ---
> tools/lib/bpf/libbpf.c | 149 ++++++++++++++++++++++++++++-------------
> tools/lib/bpf/libbpf.h | 12 ++++
> tools/perf/tests/llvm.c | 2 +-
> tools/perf/util/bpf-loader.c | 36 ++++++++--
> tools/perf/util/parse-events.c | 4 +-
> 5 files changed, 145 insertions(+), 58 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 9f3c8cf..c4dcee0 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -61,6 +61,62 @@ void libbpf_set_print(libbpf_print_fn_t warn,
> __pr_debug = debug;
> }
>
> +#define ARRAY_SIZE(x) (sizeof(x)/sizeof(x[0]))
> +#define STRERR_BUFSIZE 128
> +
> +struct {
> + int code;
> + const char *msg;
> +} libbpf_strerror_table[] = {
> + {LIBBPF_ERRNO__ELIBELF, "Something wrong in libelf"},
> + {LIBBPF_ERRNO__EFORMAT, "BPF object format invalid"},
> + {LIBBPF_ERRNO__EKVERSION, "'version' section incorrect or lost"},
> + {LIBBPF_ERRNO__EENDIAN, "Endian missmatch"},
> + {LIBBPF_ERRNO__EINTERNAL, "Internal error in libbpf"},
> + {LIBBPF_ERRNO__ERELOC, "Relocation failed"},
> + {LIBBPF_ERRNO__ELOAD, "Failed to load program"},
> +};
> +
> +int libbpf_strerror(int err, char *buf, size_t size)
> +{
> + unsigned int i;
> +
> + if (!buf || !size)
> + return -1;
> +
> + err = err > 0 ? err : -err;
> +
> + if (err < LIBBPF_ERRNO__START) {
> + int ret;
> +
> + ret = strerror_r(err, buf, size);
> + buf[size - 1] = '\0';
> + return ret;
> + }

Since all those errors are in sequence, why not introduce a
LIBBPF_ERRNO__END and test against it, and then index the
libbpf_strerror_table directly using (err - LIBBPF_ERRNO__START)?

When introducing a function, take a look at similar functions and reuse
code, for instance: target__strerror() does this pretty well, I think.

> +
> + for (i = 0; i < ARRAY_SIZE(libbpf_strerror_table); i++) {
> + if (libbpf_strerror_table[i].code == err) {
> + const char *msg;
> +
> + msg = libbpf_strerror_table[i].msg;
> + snprintf(buf, size, "%s", msg);
> + buf[size - 1] = '\0';
> + return 0;
> + }
> + }
> +
> + snprintf(buf, size, "Unknown libbpf error %d", err);
> + buf[size - 1] = '\0';
> + return -1;
> +}
> +
> +#define CHECK_ERR(action, err, out) do { \
> + err = action; \
> + if (err) \
> + goto out; \
> +} while(0)
> +
> +
> /* Copied from tools/perf/util/util.h */
> #ifndef zfree
> # define zfree(ptr) ({ free(*ptr); *ptr = NULL; })
> @@ -258,7 +314,7 @@ static struct bpf_object *bpf_object__new(const char *path,
> obj = calloc(1, sizeof(struct bpf_object) + strlen(path) + 1);
> if (!obj) {
> pr_warning("alloc memory failed for %s\n", path);
> - return NULL;
> + return ERR_PTR(-ENOMEM);
> }
>
> strcpy(obj->path, path);
> @@ -305,7 +361,7 @@ static int bpf_object__elf_init(struct bpf_object *obj)
>
> if (obj_elf_valid(obj)) {
> pr_warning("elf init: internal error\n");
> - return -EEXIST;
> + return -LIBBPF_ERRNO__ELIBELF;
> }
>
> if (obj->efile.obj_buf_sz > 0) {
> @@ -331,14 +387,14 @@ static int bpf_object__elf_init(struct bpf_object *obj)
> if (!obj->efile.elf) {
> pr_warning("failed to open %s as ELF file\n",
> obj->path);
> - err = -EINVAL;
> + err = -LIBBPF_ERRNO__ELIBELF;
> goto errout;
> }
>
> if (!gelf_getehdr(obj->efile.elf, &obj->efile.ehdr)) {
> pr_warning("failed to get EHDR from %s\n",
> obj->path);
> - err = -EINVAL;
> + err = -LIBBPF_ERRNO__EFORMAT;
> goto errout;
> }
> ep = &obj->efile.ehdr;
> @@ -346,7 +402,7 @@ static int bpf_object__elf_init(struct bpf_object *obj)
> if ((ep->e_type != ET_REL) || (ep->e_machine != 0)) {
> pr_warning("%s is not an eBPF object file\n",
> obj->path);
> - err = -EINVAL;
> + err = -LIBBPF_ERRNO__EFORMAT;
> goto errout;
> }
>
> @@ -374,14 +430,14 @@ bpf_object__check_endianness(struct bpf_object *obj)
> goto mismatch;
> break;
> default:
> - return -EINVAL;
> + return -LIBBPF_ERRNO__EENDIAN;
> }
>
> return 0;
>
> mismatch:
> pr_warning("Error: endianness mismatch.\n");
> - return -EINVAL;
> + return -LIBBPF_ERRNO__EENDIAN;
> }
>
> static int
> @@ -402,7 +458,7 @@ bpf_object__init_kversion(struct bpf_object *obj,
>
> if (size != sizeof(kver)) {
> pr_warning("invalid kver section in %s\n", obj->path);
> - return -EINVAL;
> + return -LIBBPF_ERRNO__EFORMAT;
> }
> memcpy(&kver, data, sizeof(kver));
> obj->kern_version = kver;
> @@ -444,7 +500,7 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
> if (!elf_rawdata(elf_getscn(elf, ep->e_shstrndx), NULL)) {
> pr_warning("failed to get e_shstrndx from %s\n",
> obj->path);
> - return -EINVAL;
> + return -LIBBPF_ERRNO__EFORMAT;
> }
>
> while ((scn = elf_nextscn(elf, scn)) != NULL) {
> @@ -456,7 +512,7 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
> if (gelf_getshdr(scn, &sh) != &sh) {
> pr_warning("failed to get section header from %s\n",
> obj->path);
> - err = -EINVAL;
> + err = -LIBBPF_ERRNO__EFORMAT;
> goto out;
> }
>
> @@ -464,7 +520,7 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
> if (!name) {
> pr_warning("failed to get section name from %s\n",
> obj->path);
> - err = -EINVAL;
> + err = -LIBBPF_ERRNO__EFORMAT;
> goto out;
> }
>
> @@ -472,7 +528,7 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
> if (!data) {
> pr_warning("failed to get section data from %s(%s)\n",
> name, obj->path);
> - err = -EINVAL;
> + err = -LIBBPF_ERRNO__EFORMAT;
> goto out;
> }
> pr_debug("section %s, size %ld, link %d, flags %lx, type=%d\n",
> @@ -495,7 +551,7 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
> if (obj->efile.symbols) {
> pr_warning("bpf: multiple SYMTAB in %s\n",
> obj->path);
> - err = -EEXIST;
> + err = -LIBBPF_ERRNO__EFORMAT;
> } else
> obj->efile.symbols = data;
> } else if ((sh.sh_type == SHT_PROGBITS) &&
> @@ -504,7 +560,8 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
> err = bpf_object__add_program(obj, data->d_buf,
> data->d_size, name, idx);
> if (err) {
> - char errmsg[128];
> + char errmsg[STRERR_BUFSIZE];
> +
> strerror_r(-err, errmsg, sizeof(errmsg));
> pr_warning("failed to alloc program %s (%s): %s",
> name, obj->path, errmsg);
> @@ -576,7 +633,7 @@ bpf_program__collect_reloc(struct bpf_program *prog,
>
> if (!gelf_getrel(data, i, &rel)) {
> pr_warning("relocation: failed to get %d reloc\n", i);
> - return -EINVAL;
> + return -LIBBPF_ERRNO__EFORMAT;
> }
>
> insn_idx = rel.r_offset / sizeof(struct bpf_insn);
> @@ -587,20 +644,20 @@ bpf_program__collect_reloc(struct bpf_program *prog,
> &sym)) {
> pr_warning("relocation: symbol %"PRIx64" not found\n",
> GELF_R_SYM(rel.r_info));
> - return -EINVAL;
> + return -LIBBPF_ERRNO__EFORMAT;
> }
>
> if (insns[insn_idx].code != (BPF_LD | BPF_IMM | BPF_DW)) {
> pr_warning("bpf: relocation: invalid relo for insns[%d].code 0x%x\n",
> insn_idx, insns[insn_idx].code);
> - return -EINVAL;
> + return -LIBBPF_ERRNO__ERELOC;
> }
>
> map_idx = sym.st_value / sizeof(struct bpf_map_def);
> if (map_idx >= nr_maps) {
> pr_warning("bpf relocation: map_idx %d large than %d\n",
> (int)map_idx, (int)nr_maps - 1);
> - return -EINVAL;
> + return -LIBBPF_ERRNO__ERELOC;
> }
>
> prog->reloc_desc[i].insn_idx = insn_idx;
> @@ -683,7 +740,7 @@ bpf_program__relocate(struct bpf_program *prog, int *map_fds)
> if (insn_idx >= (int)prog->insns_cnt) {
> pr_warning("relocation out of range: '%s'\n",
> prog->section_name);
> - return -ERANGE;
> + return -LIBBPF_ERRNO__ERELOC;
> }
> insns[insn_idx].src_reg = BPF_PSEUDO_MAP_FD;
> insns[insn_idx].imm = map_fds[map_idx];
> @@ -721,7 +778,7 @@ static int bpf_object__collect_reloc(struct bpf_object *obj)
>
> if (!obj_elf_valid(obj)) {
> pr_warning("Internal error: elf object is closed\n");
> - return -EINVAL;
> + return -LIBBPF_ERRNO__EINTERNAL;
> }
>
> for (i = 0; i < obj->efile.nr_reloc; i++) {
> @@ -734,21 +791,21 @@ static int bpf_object__collect_reloc(struct bpf_object *obj)
>
> if (shdr->sh_type != SHT_REL) {
> pr_warning("internal error at %d\n", __LINE__);
> - return -EINVAL;
> + return -LIBBPF_ERRNO__EINTERNAL;
> }
>
> prog = bpf_object__find_prog_by_idx(obj, idx);
> if (!prog) {
> pr_warning("relocation failed: no %d section\n",
> idx);
> - return -ENOENT;
> + return -LIBBPF_ERRNO__ERELOC;
> }
>
> err = bpf_program__collect_reloc(prog, nr_maps,
> shdr, data,
> obj->efile.symbols);
> if (err)
> - return -EINVAL;
> + return err;
> }
> return 0;
> }
> @@ -777,7 +834,7 @@ load_program(struct bpf_insn *insns, int insns_cnt,
> goto out;
> }
>
> - ret = -EINVAL;
> + ret = -LIBBPF_ERRNO__ELOAD;
> pr_warning("load bpf program failed: %s\n", strerror(errno));
>
> if (log_buf) {
> @@ -831,7 +888,7 @@ static int bpf_object__validate(struct bpf_object *obj)
> if (obj->kern_version == 0) {
> pr_warning("%s doesn't provide kernel version\n",
> obj->path);
> - return -EINVAL;
> + return -LIBBPF_ERRNO__EKVERSION;
> }
> return 0;
> }
> @@ -840,32 +897,28 @@ static struct bpf_object *
> __bpf_object__open(const char *path, void *obj_buf, size_t obj_buf_sz)
> {
> struct bpf_object *obj;
> + int err;
>
> if (elf_version(EV_CURRENT) == EV_NONE) {
> pr_warning("failed to init libelf for %s\n", path);
> - return NULL;
> + return ERR_PTR(-LIBBPF_ERRNO__ELIBELF);
> }
>
> obj = bpf_object__new(path, obj_buf, obj_buf_sz);
> - if (!obj)
> - return NULL;
> + if (IS_ERR(obj))
> + return obj;
>
> - if (bpf_object__elf_init(obj))
> - goto out;
> - if (bpf_object__check_endianness(obj))
> - goto out;
> - if (bpf_object__elf_collect(obj))
> - goto out;
> - if (bpf_object__collect_reloc(obj))
> - goto out;
> - if (bpf_object__validate(obj))
> - goto out;
> + CHECK_ERR(bpf_object__elf_init(obj), err, out);
> + CHECK_ERR(bpf_object__check_endianness(obj), err, out);
> + CHECK_ERR(bpf_object__elf_collect(obj), err, out);
> + CHECK_ERR(bpf_object__collect_reloc(obj), err, out);
> + CHECK_ERR(bpf_object__validate(obj), err, out);
>
> bpf_object__elf_finish(obj);
> return obj;
> out:
> bpf_object__close(obj);
> - return NULL;
> + return ERR_PTR(err);
> }
>
> struct bpf_object *bpf_object__open(const char *path)
> @@ -922,6 +975,8 @@ int bpf_object__unload(struct bpf_object *obj)
>
> int bpf_object__load(struct bpf_object *obj)
> {
> + int err;
> +
> if (!obj)
> return -EINVAL;
>
> @@ -931,18 +986,16 @@ int bpf_object__load(struct bpf_object *obj)
> }
>
> obj->loaded = true;
> - if (bpf_object__create_maps(obj))
> - goto out;
> - if (bpf_object__relocate(obj))
> - goto out;
> - if (bpf_object__load_progs(obj))
> - goto out;
> +
> + CHECK_ERR(bpf_object__create_maps(obj), err, out);
> + CHECK_ERR(bpf_object__relocate(obj), err, out);
> + CHECK_ERR(bpf_object__load_progs(obj), err, out);
>
> return 0;
> out:
> bpf_object__unload(obj);
> pr_warning("failed to load object '%s'\n", obj->path);
> - return -EINVAL;
> + return err;
> }
>
> void bpf_object__close(struct bpf_object *obj)
> @@ -990,7 +1043,7 @@ const char *
> bpf_object__get_name(struct bpf_object *obj)
> {
> if (!obj)
> - return NULL;
> + return ERR_PTR(-EINVAL);
> return obj->path;
> }
>
> @@ -1043,7 +1096,7 @@ const char *bpf_program__title(struct bpf_program *prog, bool needs_copy)
> title = strdup(title);
> if (!title) {
> pr_warning("failed to strdup program title\n");
> - return NULL;
> + return ERR_PTR(-ENOMEM);
> }
> }
>
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index bc80af0..6491be6 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -10,6 +10,18 @@
>
> #include <stdio.h>
> #include <stdbool.h>
> +#include <linux/err.h>
> +
> +#define LIBBPF_ERRNO__START 4000
> +#define LIBBPF_ERRNO__ELIBELF 4000 /* Something wrong in libelf */
> +#define LIBBPF_ERRNO__EFORMAT 4001 /* BPF object format invalid */
> +#define LIBBPF_ERRNO__EKVERSION 4002 /* Incorrect or no 'version' section */
> +#define LIBBPF_ERRNO__EENDIAN 4003 /* Endian missmatch */
> +#define LIBBPF_ERRNO__EINTERNAL 4004 /* Internal error in libbpf */
> +#define LIBBPF_ERRNO__ERELOC 4005 /* Relocation failed */
> +#define LIBBPF_ERRNO__ELOAD 4006 /* Failed to load program */
> +
> +int libbpf_strerror(int err, char *buf, size_t size);
>
> /*
> * In include/linux/compiler-gcc.h, __printf is defined. However
> diff --git a/tools/perf/tests/llvm.c b/tools/perf/tests/llvm.c
> index 512d362..8f713f6 100644
> --- a/tools/perf/tests/llvm.c
> +++ b/tools/perf/tests/llvm.c
> @@ -27,7 +27,7 @@ static int test__bpf_parsing(void *obj_buf, size_t obj_buf_sz)
> struct bpf_object *obj;
>
> obj = bpf_object__open_buffer(obj_buf, obj_buf_sz, NULL);
> - if (!obj)
> + if (IS_ERR(obj))
> return -1;
> bpf_object__close(obj);
> return 0;
> diff --git a/tools/perf/util/bpf-loader.c b/tools/perf/util/bpf-loader.c
> index 0c5d174..72ad3dc 100644
> --- a/tools/perf/util/bpf-loader.c
> +++ b/tools/perf/util/bpf-loader.c
> @@ -59,9 +59,9 @@ struct bpf_object *bpf__prepare_load(const char *filename, bool source)
> } else
> obj = bpf_object__open(filename);
>
> - if (!obj) {
> + if (IS_ERR(obj)) {
> pr_debug("bpf: failed to load %s\n", filename);
> - return ERR_PTR(-EINVAL);
> + return obj;
> }
>
> return obj;
> @@ -96,9 +96,9 @@ config_bpf_program(struct bpf_program *prog)
> int err;
>
> config_str = bpf_program__title(prog, false);
> - if (!config_str) {
> + if (IS_ERR(config_str)) {
> pr_debug("bpf: unable to get title for program\n");
> - return -EINVAL;
> + return PTR_ERR(config_str);
> }
>
> priv = calloc(sizeof(*priv), 1);
> @@ -308,13 +308,34 @@ int bpf__foreach_tev(struct bpf_object *obj,
> return 0;
> }
>
> +static int
> +bpf_loader_strerror(int err, char *buf, size_t size)
> +{
> + char sbuf[STRERR_BUFSIZE];
> + const char *msg;
> +
> + if (!buf || !size)
> + return -1;
> +
> + err = err > 0 ? err : -err;
> +
> + if (err >= LIBBPF_ERRNO__START)
> + return libbpf_strerror(err, buf, size);
> +
> + msg = strerror_r(err, sbuf, sizeof(sbuf));
> + snprintf(buf, size, "%s", msg);
> + buf[size - 1] = '\0';
> + return 0;
> +}
> +
> #define bpf__strerror_head(err, buf, size) \
> char sbuf[STRERR_BUFSIZE], *emsg;\
> if (!size)\
> return 0;\
> if (err < 0)\
> err = -err;\
> - emsg = strerror_r(err, sbuf, sizeof(sbuf));\
> + bpf_loader_strerror(err, sbuf, sizeof(sbuf));\
> + emsg = sbuf;\
> switch (err) {\
> default:\
> scnprintf(buf, size, "%s", emsg);\
> @@ -345,8 +366,9 @@ int bpf__strerror_load(struct bpf_object *obj __maybe_unused,
> int err, char *buf, size_t size)
> {
> bpf__strerror_head(err, buf, size);
> - bpf__strerror_entry(EINVAL, "%s: Are you root and runing a CONFIG_BPF_SYSCALL kernel?",
> - emsg)
> + bpf__strerror_entry(LIBBPF_ERRNO__ELOAD,
> + "%s: Validate your program and check 'license'/'version' sections in your object",
> + emsg);
> bpf__strerror_end(buf, size);
> return 0;
> }
> diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
> index bee6058..c75b25d 100644
> --- a/tools/perf/util/parse-events.c
> +++ b/tools/perf/util/parse-events.c
> @@ -632,11 +632,11 @@ int parse_events_load_bpf(struct parse_events_evlist *data,
> struct bpf_object *obj;
>
> obj = bpf__prepare_load(bpf_file_name, source);
> - if (IS_ERR(obj) || !obj) {
> + if (IS_ERR(obj)) {
> char errbuf[BUFSIZ];
> int err;
>
> - err = obj ? PTR_ERR(obj) : -EINVAL;
> + err = PTR_ERR(obj);
>
> if (err == -ENOTSUP)
> snprintf(errbuf, sizeof(errbuf),
> --
> 1.8.3.4
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