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@xxxxxxxx>
---
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
