* [PATCH bpf-next v3 1/2] libbpf: Pull file-opening logic up to top-level functions
2024-12-11 16:40 [PATCH bpf-next v3 0/2] libbpf: Extend linker API to support in-memory ELF files Alastair Robertson
@ 2024-12-11 16:40 ` Alastair Robertson
2024-12-12 23:29 ` Andrii Nakryiko
2024-12-11 16:40 ` [PATCH bpf-next v3 2/2] libbpf: Extend linker API to support in-memory ELF files Alastair Robertson
2024-12-12 23:30 ` [PATCH bpf-next v3 0/2] " patchwork-bot+netdevbpf
2 siblings, 1 reply; 6+ messages in thread
From: Alastair Robertson @ 2024-12-11 16:40 UTC (permalink / raw)
To: bpf, andrii; +Cc: Alastair Robertson
Move the filename arguments and file-descriptor handling from
init_output_elf() and linker_load_obj_file() and instead handle them
at the top-level in bpf_linker__new() and bpf_linker__add_file().
This will allow the inner functions to be shared with a new,
non-filename-based, API in the next commit.
Signed-off-by: Alastair Robertson <ajor@meta.com>
---
tools/lib/bpf/linker.c | 83 +++++++++++++++++++++---------------------
1 file changed, 41 insertions(+), 42 deletions(-)
diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c
index e56ba6e67451..eb2ac7afce01 100644
--- a/tools/lib/bpf/linker.c
+++ b/tools/lib/bpf/linker.c
@@ -157,10 +157,9 @@ struct bpf_linker {
#define pr_warn_elf(fmt, ...) \
libbpf_print(LIBBPF_WARN, "libbpf: " fmt ": %s\n", ##__VA_ARGS__, elf_errmsg(-1))
-static int init_output_elf(struct bpf_linker *linker, const char *file);
+static int init_output_elf(struct bpf_linker *linker);
-static int linker_load_obj_file(struct bpf_linker *linker, const char *filename,
- const struct bpf_linker_file_opts *opts,
+static int linker_load_obj_file(struct bpf_linker *linker,
struct src_obj *obj);
static int linker_sanity_check_elf(struct src_obj *obj);
static int linker_sanity_check_elf_symtab(struct src_obj *obj, struct src_sec *sec);
@@ -233,9 +232,20 @@ struct bpf_linker *bpf_linker__new(const char *filename, struct bpf_linker_opts
if (!linker)
return errno = ENOMEM, NULL;
- linker->fd = -1;
+ linker->filename = strdup(filename);
+ if (!linker->filename) {
+ err = -ENOMEM;
+ goto err_out;
+ }
+
+ linker->fd = open(filename, O_WRONLY | O_CREAT | O_TRUNC | O_CLOEXEC, 0644);
+ if (linker->fd < 0) {
+ err = -errno;
+ pr_warn("failed to create '%s': %d\n", filename, err);
+ goto err_out;
+ }
- err = init_output_elf(linker, filename);
+ err = init_output_elf(linker);
if (err)
goto err_out;
@@ -294,23 +304,12 @@ static Elf64_Sym *add_new_sym(struct bpf_linker *linker, size_t *sym_idx)
return sym;
}
-static int init_output_elf(struct bpf_linker *linker, const char *file)
+static int init_output_elf(struct bpf_linker *linker)
{
int err, str_off;
Elf64_Sym *init_sym;
struct dst_sec *sec;
- linker->filename = strdup(file);
- if (!linker->filename)
- return -ENOMEM;
-
- linker->fd = open(file, O_WRONLY | O_CREAT | O_TRUNC | O_CLOEXEC, 0644);
- if (linker->fd < 0) {
- err = -errno;
- pr_warn("failed to create '%s': %s\n", file, errstr(err));
- return err;
- }
-
linker->elf = elf_begin(linker->fd, ELF_C_WRITE, NULL);
if (!linker->elf) {
pr_warn_elf("failed to create ELF object");
@@ -440,7 +439,7 @@ int bpf_linker__add_file(struct bpf_linker *linker, const char *filename,
const struct bpf_linker_file_opts *opts)
{
struct src_obj obj = {};
- int err = 0;
+ int err = 0, fd;
if (!OPTS_VALID(opts, bpf_linker_file_opts))
return libbpf_err(-EINVAL);
@@ -448,7 +447,16 @@ int bpf_linker__add_file(struct bpf_linker *linker, const char *filename,
if (!linker->elf)
return libbpf_err(-EINVAL);
- err = err ?: linker_load_obj_file(linker, filename, opts, &obj);
+ fd = open(filename, O_RDONLY | O_CLOEXEC);
+ if (fd < 0) {
+ pr_warn("failed to open file '%s': %s\n", filename, errstr(errno));
+ return -errno;
+ }
+
+ obj.filename = filename;
+ obj.fd = fd;
+
+ err = err ?: linker_load_obj_file(linker, &obj);
err = err ?: linker_append_sec_data(linker, &obj);
err = err ?: linker_append_elf_syms(linker, &obj);
err = err ?: linker_append_elf_relos(linker, &obj);
@@ -534,8 +542,7 @@ static struct src_sec *add_src_sec(struct src_obj *obj, const char *sec_name)
return sec;
}
-static int linker_load_obj_file(struct bpf_linker *linker, const char *filename,
- const struct bpf_linker_file_opts *opts,
+static int linker_load_obj_file(struct bpf_linker *linker,
struct src_obj *obj)
{
int err = 0;
@@ -554,26 +561,18 @@ static int linker_load_obj_file(struct bpf_linker *linker, const char *filename,
#error "Unknown __BYTE_ORDER__"
#endif
- pr_debug("linker: adding object file '%s'...\n", filename);
-
- obj->filename = filename;
+ pr_debug("linker: adding object file '%s'...\n", obj->filename);
- obj->fd = open(filename, O_RDONLY | O_CLOEXEC);
- if (obj->fd < 0) {
- err = -errno;
- pr_warn("failed to open file '%s': %s\n", filename, errstr(err));
- return err;
- }
obj->elf = elf_begin(obj->fd, ELF_C_READ_MMAP, NULL);
if (!obj->elf) {
- pr_warn_elf("failed to parse ELF file '%s'", filename);
+ pr_warn_elf("failed to parse ELF file '%s'", obj->filename);
return -EINVAL;
}
/* Sanity check ELF file high-level properties */
ehdr = elf64_getehdr(obj->elf);
if (!ehdr) {
- pr_warn_elf("failed to get ELF header for %s", filename);
+ pr_warn_elf("failed to get ELF header for %s", obj->filename);
return -EINVAL;
}
@@ -581,7 +580,7 @@ static int linker_load_obj_file(struct bpf_linker *linker, const char *filename,
obj_byteorder = ehdr->e_ident[EI_DATA];
if (obj_byteorder != ELFDATA2LSB && obj_byteorder != ELFDATA2MSB) {
err = -EOPNOTSUPP;
- pr_warn("unknown byte order of ELF file %s\n", filename);
+ pr_warn("unknown byte order of ELF file %s\n", obj->filename);
return err;
}
if (link_byteorder == ELFDATANONE) {
@@ -591,7 +590,7 @@ static int linker_load_obj_file(struct bpf_linker *linker, const char *filename,
obj_byteorder == ELFDATA2MSB ? "big" : "little");
} else if (link_byteorder != obj_byteorder) {
err = -EOPNOTSUPP;
- pr_warn("byte order mismatch with ELF file %s\n", filename);
+ pr_warn("byte order mismatch with ELF file %s\n", obj->filename);
return err;
}
@@ -599,12 +598,12 @@ static int linker_load_obj_file(struct bpf_linker *linker, const char *filename,
|| ehdr->e_machine != EM_BPF
|| ehdr->e_ident[EI_CLASS] != ELFCLASS64) {
err = -EOPNOTSUPP;
- pr_warn_elf("unsupported kind of ELF file %s", filename);
+ pr_warn_elf("unsupported kind of ELF file %s", obj->filename);
return err;
}
if (elf_getshdrstrndx(obj->elf, &obj->shstrs_sec_idx)) {
- pr_warn_elf("failed to get SHSTRTAB section index for %s", filename);
+ pr_warn_elf("failed to get SHSTRTAB section index for %s", obj->filename);
return -EINVAL;
}
@@ -616,21 +615,21 @@ static int linker_load_obj_file(struct bpf_linker *linker, const char *filename,
shdr = elf64_getshdr(scn);
if (!shdr) {
pr_warn_elf("failed to get section #%zu header for %s",
- sec_idx, filename);
+ sec_idx, obj->filename);
return -EINVAL;
}
sec_name = elf_strptr(obj->elf, obj->shstrs_sec_idx, shdr->sh_name);
if (!sec_name) {
pr_warn_elf("failed to get section #%zu name for %s",
- sec_idx, filename);
+ sec_idx, obj->filename);
return -EINVAL;
}
data = elf_getdata(scn, 0);
if (!data) {
pr_warn_elf("failed to get section #%zu (%s) data from %s",
- sec_idx, sec_name, filename);
+ sec_idx, sec_name, obj->filename);
return -EINVAL;
}
@@ -666,7 +665,7 @@ static int linker_load_obj_file(struct bpf_linker *linker, const char *filename,
err = libbpf_get_error(obj->btf);
if (err) {
pr_warn("failed to parse .BTF from %s: %s\n",
- filename, errstr(err));
+ obj->filename, errstr(err));
return err;
}
sec->skipped = true;
@@ -677,7 +676,7 @@ static int linker_load_obj_file(struct bpf_linker *linker, const char *filename,
err = libbpf_get_error(obj->btf_ext);
if (err) {
pr_warn("failed to parse .BTF.ext from '%s': %s\n",
- filename, errstr(err));
+ obj->filename, errstr(err));
return err;
}
sec->skipped = true;
@@ -694,7 +693,7 @@ static int linker_load_obj_file(struct bpf_linker *linker, const char *filename,
break;
default:
pr_warn("unrecognized section #%zu (%s) in %s\n",
- sec_idx, sec_name, filename);
+ sec_idx, sec_name, obj->filename);
err = -EINVAL;
return err;
}
--
2.43.5
^ permalink raw reply related [flat|nested] 6+ messages in thread* [PATCH bpf-next v3 2/2] libbpf: Extend linker API to support in-memory ELF files
2024-12-11 16:40 [PATCH bpf-next v3 0/2] libbpf: Extend linker API to support in-memory ELF files Alastair Robertson
2024-12-11 16:40 ` [PATCH bpf-next v3 1/2] libbpf: Pull file-opening logic up to top-level functions Alastair Robertson
@ 2024-12-11 16:40 ` Alastair Robertson
2024-12-12 23:29 ` Andrii Nakryiko
2024-12-12 23:30 ` [PATCH bpf-next v3 0/2] " patchwork-bot+netdevbpf
2 siblings, 1 reply; 6+ messages in thread
From: Alastair Robertson @ 2024-12-11 16:40 UTC (permalink / raw)
To: bpf, andrii; +Cc: Alastair Robertson
The new_fd and add_fd functions correspond to the original new and
add_file functions, but accept an FD instead of a file name. This
gives API consumers the option of using anonymous files/memfds to
avoid writing ELFs to disk.
This new API will be useful for performing linking as part of
bpftrace's JIT compilation.
The add_buf function is a convenience wrapper that does the work of
creating a memfd for the caller.
Signed-off-by: Alastair Robertson <ajor@meta.com>
---
tools/lib/bpf/libbpf.h | 5 ++
tools/lib/bpf/libbpf.map | 4 +
tools/lib/bpf/linker.c | 163 ++++++++++++++++++++++++++++++++++-----
3 files changed, 152 insertions(+), 20 deletions(-)
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index b2ce3a72b11d..d45807103565 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -1796,9 +1796,14 @@ struct bpf_linker_file_opts {
struct bpf_linker;
LIBBPF_API struct bpf_linker *bpf_linker__new(const char *filename, struct bpf_linker_opts *opts);
+LIBBPF_API struct bpf_linker *bpf_linker__new_fd(int fd, struct bpf_linker_opts *opts);
LIBBPF_API int bpf_linker__add_file(struct bpf_linker *linker,
const char *filename,
const struct bpf_linker_file_opts *opts);
+LIBBPF_API int bpf_linker__add_fd(struct bpf_linker *linker, int fd,
+ const struct bpf_linker_file_opts *opts);
+LIBBPF_API int bpf_linker__add_buf(struct bpf_linker *linker, void *buf, size_t buf_sz,
+ const struct bpf_linker_file_opts *opts);
LIBBPF_API int bpf_linker__finalize(struct bpf_linker *linker);
LIBBPF_API void bpf_linker__free(struct bpf_linker *linker);
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 54b6f312cfa8..a8b2936a1646 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -432,4 +432,8 @@ LIBBPF_1.5.0 {
} LIBBPF_1.4.0;
LIBBPF_1.6.0 {
+ global:
+ bpf_linker__add_buf;
+ bpf_linker__add_fd;
+ bpf_linker__new_fd;
} LIBBPF_1.5.0;
diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c
index eb2ac7afce01..6b3b86d98f6c 100644
--- a/tools/lib/bpf/linker.c
+++ b/tools/lib/bpf/linker.c
@@ -4,6 +4,10 @@
*
* Copyright (c) 2021 Facebook
*/
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE
+#endif
+
#include <stdbool.h>
#include <stddef.h>
#include <stdio.h>
@@ -16,6 +20,7 @@
#include <elf.h>
#include <libelf.h>
#include <fcntl.h>
+#include <sys/mman.h>
#include "libbpf.h"
#include "btf.h"
#include "libbpf_internal.h"
@@ -152,6 +157,8 @@ struct bpf_linker {
/* global (including extern) ELF symbols */
int glob_sym_cnt;
struct glob_sym *glob_syms;
+
+ bool fd_is_owned;
};
#define pr_warn_elf(fmt, ...) \
@@ -159,6 +166,9 @@ struct bpf_linker {
static int init_output_elf(struct bpf_linker *linker);
+static int bpf_linker_add_file(struct bpf_linker *linker, int fd,
+ const char *filename);
+
static int linker_load_obj_file(struct bpf_linker *linker,
struct src_obj *obj);
static int linker_sanity_check_elf(struct src_obj *obj);
@@ -190,7 +200,7 @@ void bpf_linker__free(struct bpf_linker *linker)
if (linker->elf)
elf_end(linker->elf);
- if (linker->fd >= 0)
+ if (linker->fd >= 0 && linker->fd_is_owned)
close(linker->fd);
strset__free(linker->strtab_strs);
@@ -244,6 +254,49 @@ struct bpf_linker *bpf_linker__new(const char *filename, struct bpf_linker_opts
pr_warn("failed to create '%s': %d\n", filename, err);
goto err_out;
}
+ linker->fd_is_owned = true;
+
+ err = init_output_elf(linker);
+ if (err)
+ goto err_out;
+
+ return linker;
+
+err_out:
+ bpf_linker__free(linker);
+ return errno = -err, NULL;
+}
+
+struct bpf_linker *bpf_linker__new_fd(int fd, struct bpf_linker_opts *opts)
+{
+ struct bpf_linker *linker;
+ char filename[32];
+ int err;
+
+ if (fd < 0)
+ return errno = EINVAL, NULL;
+
+ if (!OPTS_VALID(opts, bpf_linker_opts))
+ return errno = EINVAL, NULL;
+
+ if (elf_version(EV_CURRENT) == EV_NONE) {
+ pr_warn_elf("libelf initialization failed");
+ return errno = EINVAL, NULL;
+ }
+
+ linker = calloc(1, sizeof(*linker));
+ if (!linker)
+ return errno = ENOMEM, NULL;
+
+ snprintf(filename, sizeof(filename), "fd:%d", fd);
+ linker->filename = strdup(filename);
+ if (!linker->filename) {
+ err = -ENOMEM;
+ goto err_out;
+ }
+
+ linker->fd = fd;
+ linker->fd_is_owned = false;
err = init_output_elf(linker);
if (err)
@@ -435,23 +488,11 @@ static int init_output_elf(struct bpf_linker *linker)
return 0;
}
-int bpf_linker__add_file(struct bpf_linker *linker, const char *filename,
- const struct bpf_linker_file_opts *opts)
+static int bpf_linker_add_file(struct bpf_linker *linker, int fd,
+ const char *filename)
{
struct src_obj obj = {};
- int err = 0, fd;
-
- if (!OPTS_VALID(opts, bpf_linker_file_opts))
- return libbpf_err(-EINVAL);
-
- if (!linker->elf)
- return libbpf_err(-EINVAL);
-
- fd = open(filename, O_RDONLY | O_CLOEXEC);
- if (fd < 0) {
- pr_warn("failed to open file '%s': %s\n", filename, errstr(errno));
- return -errno;
- }
+ int err = 0;
obj.filename = filename;
obj.fd = fd;
@@ -471,12 +512,93 @@ int bpf_linker__add_file(struct bpf_linker *linker, const char *filename,
free(obj.sym_map);
if (obj.elf)
elf_end(obj.elf);
- if (obj.fd >= 0)
- close(obj.fd);
return libbpf_err(err);
}
+int bpf_linker__add_file(struct bpf_linker *linker, const char *filename,
+ const struct bpf_linker_file_opts *opts)
+{
+ int fd, ret;
+
+ if (!OPTS_VALID(opts, bpf_linker_file_opts))
+ return libbpf_err(-EINVAL);
+
+ if (!linker->elf)
+ return libbpf_err(-EINVAL);
+
+ fd = open(filename, O_RDONLY | O_CLOEXEC);
+ if (fd < 0) {
+ pr_warn("failed to open file '%s': %s\n", filename, errstr(errno));
+ return -errno;
+ }
+
+ ret = bpf_linker_add_file(linker, fd, filename);
+
+ close(fd);
+
+ return ret;
+}
+
+int bpf_linker__add_fd(struct bpf_linker *linker, int fd,
+ const struct bpf_linker_file_opts *opts)
+{
+ char filename[32];
+ int ret;
+
+ if (!OPTS_VALID(opts, bpf_linker_file_opts))
+ return libbpf_err(-EINVAL);
+
+ if (!linker->elf)
+ return libbpf_err(-EINVAL);
+
+ if (fd < 0)
+ return libbpf_err(-EINVAL);
+
+ snprintf(filename, sizeof(filename), "fd:%d", fd);
+
+ ret = bpf_linker_add_file(linker, fd, filename);
+
+ return ret;
+}
+
+int bpf_linker__add_buf(struct bpf_linker *linker, void *buf, size_t buf_sz,
+ const struct bpf_linker_file_opts *opts)
+{
+ char filename[32];
+ int fd, written, ret;
+
+ if (!OPTS_VALID(opts, bpf_linker_file_opts))
+ return libbpf_err(-EINVAL);
+
+ if (!linker->elf)
+ return libbpf_err(-EINVAL);
+
+ snprintf(filename, sizeof(filename), "mem:%p+%zu", buf, buf_sz);
+
+ fd = memfd_create(filename, 0);
+ if (fd < 0) {
+ pr_warn("failed to create memfd '%s': %s\n", filename, errstr(errno));
+ return -errno;
+ }
+
+ written = 0;
+ while (written < buf_sz) {
+ ret = write(fd, buf, buf_sz);
+ if (ret < 0) {
+ pr_warn("failed to write '%s': %s\n", filename, errstr(errno));
+ return -errno;
+ }
+ written += ret;
+ }
+
+ ret = bpf_linker_add_file(linker, fd, filename);
+
+ close(fd);
+
+ return ret;
+}
+
static bool is_dwarf_sec_name(const char *name)
{
/* approximation, but the actual list is too long */
@@ -2686,9 +2808,10 @@ int bpf_linker__finalize(struct bpf_linker *linker)
}
elf_end(linker->elf);
- close(linker->fd);
-
linker->elf = NULL;
+
+ if (linker->fd_is_owned)
+ close(linker->fd);
linker->fd = -1;
return 0;
--
2.43.5
^ permalink raw reply related [flat|nested] 6+ messages in thread