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 | 12 +++-
tools/lib/bpf/libbpf.map | 3 +
tools/lib/bpf/linker.c | 143 ++++++++++++++++++++++++++++++++++++---
3 files changed, 145 insertions(+), 13 deletions(-)
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index b2ce3a72b11d..7a88830a3431 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -1784,21 +1784,29 @@ enum libbpf_tristate {
struct bpf_linker_opts {
/* size of this struct, for forward/backward compatibility */
size_t sz;
+ const char *filename;
};
-#define bpf_linker_opts__last_field sz
+#define bpf_linker_opts__last_field filename
struct bpf_linker_file_opts {
/* size of this struct, for forward/backward compatibility */
size_t sz;
+ const char *filename;
};
-#define bpf_linker_file_opts__last_field sz
+#define bpf_linker_file_opts__last_field filename
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, const char *name,
+ void *buf, int 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..23f2a30778f0 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -432,4 +432,7 @@ LIBBPF_1.5.0 {
} LIBBPF_1.4.0;
LIBBPF_1.6.0 {
+ 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 375896a94e6a..fd98469fa20d 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, ...) \
@@ -243,6 +250,54 @@ 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;
+}
+
+#define LINKER_MAX_FD_NAME_SIZE 24
+
+struct bpf_linker *bpf_linker__new_fd(int fd, struct bpf_linker_opts *opts)
+{
+ struct bpf_linker *linker;
+ const char *filename;
+ 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;
+
+ filename = OPTS_GET(opts, filename, NULL);
+ if (filename) {
+ linker->filename = strdup(filename);
+ } else {
+ linker->filename = malloc(LINKER_MAX_FD_NAME_SIZE);
+ if (!linker->filename)
+ return errno = ENOMEM, NULL;
+ snprintf(linker->filename, LINKER_MAX_FD_NAME_SIZE, "fd:%d", fd);
+ }
+
+ linker->fd = fd;
+ linker->fd_is_owned = false;
err = init_output_elf(linker);
if (err)
@@ -435,16 +490,15 @@ static int init_output_elf(struct bpf_linker *linker)
}
int bpf_linker__add_file(struct bpf_linker *linker, const char *filename,
- const struct bpf_linker_file_opts *opts)
+ const struct bpf_linker_file_opts *input_opts)
{
- struct src_obj obj = {};
- int err = 0, fd;
+ int fd, ret;
- if (!OPTS_VALID(opts, bpf_linker_file_opts))
- return libbpf_err(-EINVAL);
+ LIBBPF_OPTS(bpf_linker_file_opts, opts);
- if (!linker->elf)
- return libbpf_err(-EINVAL);
+ if (input_opts)
+ opts = *input_opts;
+ opts.filename = filename;
fd = open(filename, O_RDONLY | O_CLOEXEC);
if (fd < 0) {
@@ -452,6 +506,37 @@ int bpf_linker__add_file(struct bpf_linker *linker, const char *filename,
return -errno;
}
+ ret = bpf_linker__add_fd(linker, fd, &opts);
+
+ close(fd);
+
+ return ret;
+}
+
+int bpf_linker__add_fd(struct bpf_linker *linker, int fd,
+ const struct bpf_linker_file_opts *opts)
+{
+ struct src_obj obj = {};
+ const char *filename;
+ char name[LINKER_MAX_FD_NAME_SIZE];
+ int err = 0;
+
+ 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);
+
+ filename = OPTS_GET(opts, filename, NULL);
+ if (filename) {
+ obj.filename = filename;
+ } else {
+ snprintf(name, sizeof(name), "fd:%d", fd);
+ obj.filename = name;
+ }
obj.fd = fd;
err = err ?: linker_load_obj_file(linker, opts, &obj);
@@ -469,12 +554,47 @@ 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);
+ /* leave obj.fd for the caller to clean up if appropriate */
return libbpf_err(err);
}
+int bpf_linker__add_buf(struct bpf_linker *linker, const char *name,
+ void *buf, int buf_sz,
+ const struct bpf_linker_file_opts *input_opts)
+{
+ int fd, written, ret;
+
+ LIBBPF_OPTS(bpf_linker_file_opts, opts);
+
+ if (input_opts)
+ opts = *input_opts;
+ opts.filename = name;
+
+ fd = memfd_create(name, 0);
+ if (fd < 0) {
+ pr_warn("failed to create memfd '%s': %s\n", name, 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", name, errstr(errno));
+ return -errno;
+ }
+ written += ret;
+ }
+
+ ret = bpf_linker__add_fd(linker, fd, &opts);
+
+ if (fd >= 0)
+ close(fd);
+
+ return ret;
+}
+
static bool is_dwarf_sec_name(const char *name)
{
/* approximation, but the actual list is too long */
@@ -2691,9 +2811,10 @@ 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
