libbpf: add support for bpf_call

- recognize relocation emitted by llvm
- since all regular function will be kept in .text section and llvm
  takes care of pc-relative offsets in bpf_call instruction
  simply copy all of .text to relevant program section while adjusting
  bpf_call instructions in program section to point to newly copied
  body of instructions from .text
- do so for all programs in the elf file
- set all programs types to the one passed to bpf_prog_load()

Note for elf files with multiple programs that use different
functions in .text section we need to do 'linker' style logic.
This work is still TBD

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

2 files changed, 128 insertions, 44 deletions

diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
index 6534889e2b2f..9f44c196931e 100644
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h
@@ -40,7 +40,7 @@ int bpf_create_map_in_map(enum bpf_map_type map_type, const char *name,
                           __u32 map_flags);
 
 /* Recommend log buffer size */
-#define BPF_LOG_BUF_SIZE 65536
+#define BPF_LOG_BUF_SIZE (256 * 1024)
 int bpf_load_program_name(enum bpf_prog_type type, const char *name,
                           const struct bpf_insn *insns,
                           size_t insns_cnt, const char *license,
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 65d0d0aff4fa..5b83875b3594 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -174,12 +174,19 @@ struct bpf_program {
         char *name;
         char *section_name;
         struct bpf_insn *insns;
-        size_t insns_cnt;
+        size_t insns_cnt, main_prog_cnt;
         enum bpf_prog_type type;
 
-        struct {
+        struct reloc_desc {
+                enum {
+                        RELO_LD64,
+                        RELO_CALL,
+                } type;
                 int insn_idx;
-                int map_idx;
+                union {
+                        int map_idx;
+                        int text_off;
+                };
         } *reloc_desc;
         int nr_reloc;
 
@@ -234,6 +241,7 @@ struct bpf_object {
                 } *reloc;
                 int nr_reloc;
                 int maps_shndx;
+                int text_shndx;
         } efile;
         /*
          * All loaded bpf_object is linked in a list, which is
@@ -375,9 +383,13 @@ bpf_object__init_prog_names(struct bpf_object *obj)
         size_t pi, si;
 
         for (pi = 0; pi < obj->nr_programs; pi++) {
-                char *name = NULL;
+                const char *name = NULL;
 
                 prog = &obj->programs[pi];
+                if (prog->idx == obj->efile.text_shndx) {
+                        name = ".text";
+                        goto skip_search;
+                }
 
                 for (si = 0; si < symbols->d_size / sizeof(GElf_Sym) && !name;
                      si++) {
@@ -405,7 +417,7 @@ bpf_object__init_prog_names(struct bpf_object *obj)
                                    prog->section_name);
                         return -EINVAL;
                 }
-
+skip_search:
                 prog->name = strdup(name);
                 if (!prog->name) {
                         pr_warning("failed to allocate memory for prog sym %s\n",
@@ -795,6 +807,8 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
                 } else if ((sh.sh_type == SHT_PROGBITS) &&
                            (sh.sh_flags & SHF_EXECINSTR) &&
                            (data->d_size > 0)) {
+                        if (strcmp(name, ".text") == 0)
+                                obj->efile.text_shndx = idx;
                         err = bpf_object__add_program(obj, data->d_buf,
                                                       data->d_size, name, idx);
                         if (err) {
@@ -856,11 +870,14 @@ bpf_object__find_prog_by_idx(struct bpf_object *obj, int idx)
 }
 
 static int
-bpf_program__collect_reloc(struct bpf_program *prog,
-                           size_t nr_maps, GElf_Shdr *shdr,
-                           Elf_Data *data, Elf_Data *symbols,
-                           int maps_shndx, struct bpf_map *maps)
+bpf_program__collect_reloc(struct bpf_program *prog, GElf_Shdr *shdr,
+                           Elf_Data *data, struct bpf_object *obj)
 {
+        Elf_Data *symbols = obj->efile.symbols;
+        int text_shndx = obj->efile.text_shndx;
+        int maps_shndx = obj->efile.maps_shndx;
+        struct bpf_map *maps = obj->maps;
+        size_t nr_maps = obj->nr_maps;
         int i, nrels;
 
         pr_debug("collecting relocating info for: '%s'\n",
@@ -893,8 +910,10 @@ bpf_program__collect_reloc(struct bpf_program *prog,
                                    GELF_R_SYM(rel.r_info));
                         return -LIBBPF_ERRNO__FORMAT;
                 }
+                pr_debug("relo for %ld value %ld name %d\n",
+                         rel.r_info >> 32, sym.st_value, sym.st_name);
 
-                if (sym.st_shndx != maps_shndx) {
+                if (sym.st_shndx != maps_shndx && sym.st_shndx != text_shndx) {
                         pr_warning("Program '%s' contains non-map related relo data pointing to section %u\n",
                                    prog->section_name, sym.st_shndx);
                         return -LIBBPF_ERRNO__RELOC;
@@ -903,6 +922,17 @@ bpf_program__collect_reloc(struct bpf_program *prog,
                 insn_idx = rel.r_offset / sizeof(struct bpf_insn);
                 pr_debug("relocation: insn_idx=%u\n", insn_idx);
 
+                if (insns[insn_idx].code == (BPF_JMP | BPF_CALL)) {
+                        if (insns[insn_idx].src_reg != BPF_PSEUDO_CALL) {
+                                pr_warning("incorrect bpf_call opcode\n");
+                                return -LIBBPF_ERRNO__RELOC;
+                        }
+                        prog->reloc_desc[i].type = RELO_CALL;
+                        prog->reloc_desc[i].insn_idx = insn_idx;
+                        prog->reloc_desc[i].text_off = sym.st_value;
+                        continue;
+                }
+
                 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);
@@ -924,6 +954,7 @@ bpf_program__collect_reloc(struct bpf_program *prog,
                         return -LIBBPF_ERRNO__RELOC;
                 }
 
+                prog->reloc_desc[i].type = RELO_LD64;
                 prog->reloc_desc[i].insn_idx = insn_idx;
                 prog->reloc_desc[i].map_idx = map_idx;
         }
@@ -963,27 +994,76 @@ bpf_object__create_maps(struct bpf_object *obj)
 }
 
 static int
+bpf_program__reloc_text(struct bpf_program *prog, struct bpf_object *obj,
+                        struct reloc_desc *relo)
+{
+        struct bpf_insn *insn, *new_insn;
+        struct bpf_program *text;
+        size_t new_cnt;
+
+        if (relo->type != RELO_CALL)
+                return -LIBBPF_ERRNO__RELOC;
+
+        if (prog->idx == obj->efile.text_shndx) {
+                pr_warning("relo in .text insn %d into off %d\n",
+                           relo->insn_idx, relo->text_off);
+                return -LIBBPF_ERRNO__RELOC;
+        }
+
+        if (prog->main_prog_cnt == 0) {
+                text = bpf_object__find_prog_by_idx(obj, obj->efile.text_shndx);
+                if (!text) {
+                        pr_warning("no .text section found yet relo into text exist\n");
+                        return -LIBBPF_ERRNO__RELOC;
+                }
+                new_cnt = prog->insns_cnt + text->insns_cnt;
+                new_insn = realloc(prog->insns, new_cnt * sizeof(*insn));
+                if (!new_insn) {
+                        pr_warning("oom in prog realloc\n");
+                        return -ENOMEM;
+                }
+                memcpy(new_insn + prog->insns_cnt, text->insns,
+                       text->insns_cnt * sizeof(*insn));
+                prog->insns = new_insn;
+                prog->main_prog_cnt = prog->insns_cnt;
+                prog->insns_cnt = new_cnt;
+        }
+        insn = &prog->insns[relo->insn_idx];
+        insn->imm += prog->main_prog_cnt - relo->insn_idx;
+        pr_debug("added %zd insn from %s to prog %s\n",
+                 text->insns_cnt, text->section_name, prog->section_name);
+        return 0;
+}
+
+static int
 bpf_program__relocate(struct bpf_program *prog, struct bpf_object *obj)
 {
-        int i;
+        int i, err;
 
         if (!prog || !prog->reloc_desc)
                 return 0;
 
         for (i = 0; i < prog->nr_reloc; i++) {
-                int insn_idx, map_idx;
-                struct bpf_insn *insns = prog->insns;
+                if (prog->reloc_desc[i].type == RELO_LD64) {
+                        struct bpf_insn *insns = prog->insns;
+                        int insn_idx, map_idx;
 
-                insn_idx = prog->reloc_desc[i].insn_idx;
-                map_idx = prog->reloc_desc[i].map_idx;
+                        insn_idx = prog->reloc_desc[i].insn_idx;
+                        map_idx = prog->reloc_desc[i].map_idx;
 
-                if (insn_idx >= (int)prog->insns_cnt) {
-                        pr_warning("relocation out of range: '%s'\n",
-                                   prog->section_name);
-                        return -LIBBPF_ERRNO__RELOC;
+                        if (insn_idx >= (int)prog->insns_cnt) {
+                                pr_warning("relocation out of range: '%s'\n",
+                                           prog->section_name);
+                                return -LIBBPF_ERRNO__RELOC;
+                        }
+                        insns[insn_idx].src_reg = BPF_PSEUDO_MAP_FD;
+                        insns[insn_idx].imm = obj->maps[map_idx].fd;
+                } else {
+                        err = bpf_program__reloc_text(prog, obj,
+                                                      &prog->reloc_desc[i]);
+                        if (err)
+                                return err;
                 }
-                insns[insn_idx].src_reg = BPF_PSEUDO_MAP_FD;
-                insns[insn_idx].imm = obj->maps[map_idx].fd;
         }
 
         zfree(&prog->reloc_desc);
@@ -1026,7 +1106,6 @@ static int bpf_object__collect_reloc(struct bpf_object *obj)
                 Elf_Data *data = obj->efile.reloc[i].data;
                 int idx = shdr->sh_info;
                 struct bpf_program *prog;
-                size_t nr_maps = obj->nr_maps;
 
                 if (shdr->sh_type != SHT_REL) {
                         pr_warning("internal error at %d\n", __LINE__);
@@ -1040,11 +1119,9 @@ static int bpf_object__collect_reloc(struct bpf_object *obj)
                         return -LIBBPF_ERRNO__RELOC;
                 }
 
-                err = bpf_program__collect_reloc(prog, nr_maps,
+                err = bpf_program__collect_reloc(prog,
                                                  shdr, data,
-                                                 obj->efile.symbols,
-                                                 obj->efile.maps_shndx,
-                                                 obj->maps);
+                                                 obj);
                 if (err)
                         return err;
         }
@@ -1197,6 +1274,8 @@ bpf_object__load_progs(struct bpf_object *obj)
         int err;
 
         for (i = 0; i < obj->nr_programs; i++) {
+                if (obj->programs[i].idx == obj->efile.text_shndx)
+                        continue;
                 err = bpf_program__load(&obj->programs[i],
                                         obj->license,
                                         obj->kern_version);
@@ -1859,7 +1938,7 @@ long libbpf_get_error(const void *ptr)
 int bpf_prog_load(const char *file, enum bpf_prog_type type,
                   struct bpf_object **pobj, int *prog_fd)
 {
-        struct bpf_program *prog;
+        struct bpf_program *prog, *first_prog = NULL;
         struct bpf_object *obj;
         int err;
 
@@ -1867,25 +1946,30 @@ int bpf_prog_load(const char *file, enum bpf_prog_type type,
         if (IS_ERR(obj))
                 return -ENOENT;
 
-        prog = bpf_program__next(NULL, obj);
-        if (!prog) {
-                bpf_object__close(obj);
-                return -ENOENT;
-        }
-
-        /*
-         * If type is not specified, try to guess it based on
-         * section name.
-         */
-        if (type == BPF_PROG_TYPE_UNSPEC) {
-                type = bpf_program__guess_type(prog);
+        bpf_object__for_each_program(prog, obj) {
+                /*
+                 * If type is not specified, try to guess it based on
+                 * section name.
+                 */
                 if (type == BPF_PROG_TYPE_UNSPEC) {
-                        bpf_object__close(obj);
-                        return -EINVAL;
+                        type = bpf_program__guess_type(prog);
+                        if (type == BPF_PROG_TYPE_UNSPEC) {
+                                bpf_object__close(obj);
+                                return -EINVAL;
+                        }
                 }
+
+                bpf_program__set_type(prog, type);
+                if (prog->idx != obj->efile.text_shndx && !first_prog)
+                        first_prog = prog;
+        }
+
+        if (!first_prog) {
+                pr_warning("object file doesn't contain bpf program\n");
+                bpf_object__close(obj);
+                return -ENOENT;
         }
 
-        bpf_program__set_type(prog, type);
         err = bpf_object__load(obj);
         if (err) {
                 bpf_object__close(obj);
@@ -1893,6 +1977,6 @@ int bpf_prog_load(const char *file, enum bpf_prog_type type,
         }
 
         *pobj = obj;
-        *prog_fd = bpf_program__fd(prog);
+        *prog_fd = bpf_program__fd(first_prog);
         return 0;
 }