diff mbox series

[bpf-next] libbpf: Extend linker API to support in-memory ELF files

Message ID 20241120170206.2592931-1-ajor@meta.com (mailing list archive)
State New
Delegated to: BPF
Headers show
Series [bpf-next] libbpf: Extend linker API to support in-memory ELF files | expand

Checks

Context Check Description
netdev/series_format success Single patches do not need cover letters
netdev/tree_selection success Clearly marked for bpf-next
netdev/ynl success Generated files up to date; no warnings/errors; no diff in generated;
netdev/fixes_present success Fixes tag not required for -next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 3 this patch: 3
netdev/build_tools fail Errors and warnings before: 2 (+0) this patch: 22 (+0)
netdev/cc_maintainers warning 11 maintainers not CCed: kpsingh@kernel.org jolsa@kernel.org eddyz87@gmail.com ast@kernel.org song@kernel.org haoluo@google.com john.fastabend@gmail.com daniel@iogearbox.net yonghong.song@linux.dev martin.lau@linux.dev sdf@fomichev.me
netdev/build_clang success Errors and warnings before: 3 this patch: 3
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 3 this patch: 3
netdev/checkpatch warning WARNING: line length of 81 exceeds 80 columns WARNING: line length of 82 exceeds 80 columns WARNING: line length of 83 exceeds 80 columns WARNING: line length of 84 exceeds 80 columns WARNING: line length of 90 exceeds 80 columns
netdev/build_clang_rust success No Rust files in patch. Skipping build
netdev/kdoc success Errors and warnings before: 264 this patch: 264
netdev/source_inline success Was 0 now: 0
bpf/vmtest-bpf-next-VM_Test-0 success Logs for Lint
bpf/vmtest-bpf-next-VM_Test-1 success Logs for ShellCheck
bpf/vmtest-bpf-next-VM_Test-2 success Logs for Unittests
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bpf/vmtest-bpf-next-PR fail PR summary
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Commit Message

Alastair Robertson Nov. 20, 2024, 5:02 p.m. UTC 
The new_fd, add_fd and finalize_fd functions correspond to the original
new, add_file and finalize 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   |   9 ++
 tools/lib/bpf/libbpf.map |   4 +
 tools/lib/bpf/linker.c   | 229 +++++++++++++++++++++++++++++----------
 3 files changed, 185 insertions(+), 57 deletions(-)
diff mbox series

Patch

diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index b2ce3a72b11d..aae8f954c4fc 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -1796,10 +1796,19 @@  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(const char *name, 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,
+				  const char *name, int fd,
+				  const struct bpf_linker_file_opts *opts);
+LIBBPF_API int bpf_linker__add_buf(struct bpf_linker *linker, const char *name,
+				   void *buffer, int buffer_sz,
+				   const struct bpf_linker_file_opts *opts);
 LIBBPF_API int bpf_linker__finalize(struct bpf_linker *linker);
+LIBBPF_API int bpf_linker__finalize_fd(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..e767f34c1d08 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 {
+		bpf_linker__new_fd;
+		bpf_linker__add_fd;
+		bpf_linker__add_buf;
+		bpf_linker__finalize_fd;
 } LIBBPF_1.5.0;
diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c
index cf71d149fe26..6571ed8b858f 100644
--- a/tools/lib/bpf/linker.c
+++ b/tools/lib/bpf/linker.c
@@ -4,6 +4,8 @@ 
  *
  * Copyright (c) 2021 Facebook
  */
+#define _GNU_SOURCE
+
 #include <stdbool.h>
 #include <stddef.h>
 #include <stdio.h>
@@ -16,6 +18,7 @@ 
 #include <elf.h>
 #include <libelf.h>
 #include <fcntl.h>
+#include <sys/mman.h>
 #include "libbpf.h"
 #include "btf.h"
 #include "libbpf_internal.h"
@@ -157,9 +160,9 @@  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,
+static int linker_load_obj_file(struct bpf_linker *linker,
 				const struct bpf_linker_file_opts *opts,
 				struct src_obj *obj);
 static int linker_sanity_check_elf(struct src_obj *obj);
@@ -233,9 +236,56 @@  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)
+		return errno = ENOMEM, NULL;
+
+	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);
+	if (err)
+		goto err_out;
+
+	return linker;
+
+err_out:
+	bpf_linker__free(linker);
+	return errno = -err, NULL;
+}
+
+struct bpf_linker *bpf_linker__new_fd(const char *name, int fd,
+				      struct bpf_linker_opts *opts)
+{
+	struct bpf_linker *linker;
+	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;
+
+	linker->filename = strdup(name);
+	if (!linker->filename)
+		return errno = ENOMEM, NULL;
+
+	linker->fd = fd;
 
-	err = init_output_elf(linker, filename);
+	err = init_output_elf(linker);
 	if (err)
 		goto err_out;
 
@@ -294,23 +344,12 @@  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");
@@ -436,10 +475,9 @@  static int init_output_elf(struct bpf_linker *linker, const char *file)
 	return 0;
 }
 
-int bpf_linker__add_file(struct bpf_linker *linker, const char *filename,
-			 const struct bpf_linker_file_opts *opts)
+static int linker_add_common(struct bpf_linker *linker, struct src_obj *obj,
+			     const struct bpf_linker_file_opts *opts)
 {
-	struct src_obj obj = {};
 	int err = 0;
 
 	if (!OPTS_VALID(opts, bpf_linker_file_opts))
@@ -448,25 +486,91 @@  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);
-	err = err ?: linker_append_sec_data(linker, &obj);
-	err = err ?: linker_append_elf_syms(linker, &obj);
-	err = err ?: linker_append_elf_relos(linker, &obj);
-	err = err ?: linker_append_btf(linker, &obj);
-	err = err ?: linker_append_btf_ext(linker, &obj);
+	err = err ?: linker_load_obj_file(linker, opts, 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);
+	err = err ?: linker_append_btf(linker, obj);
+	err = err ?: linker_append_btf_ext(linker, obj);
 
 	/* free up src_obj resources */
-	free(obj.btf_type_map);
-	btf__free(obj.btf);
-	btf_ext__free(obj.btf_ext);
-	free(obj.secs);
-	free(obj.sym_map);
-	if (obj.elf)
-		elf_end(obj.elf);
+	free(obj->btf_type_map);
+	btf__free(obj->btf);
+	btf_ext__free(obj->btf_ext);
+	free(obj->secs);
+	free(obj->sym_map);
+	if (obj->elf)
+		elf_end(obj->elf);
+	/* leave obj->fd for the caller to clean up if appropriate */
+
+	return libbpf_err(err);
+}
+
+int bpf_linker__add_file(struct bpf_linker *linker, const char *filename,
+			 const struct bpf_linker_file_opts *opts)
+{
+	struct src_obj obj = {};
+	int ret;
+
+	obj.filename = filename;
+	obj.fd = open(filename, O_RDONLY | O_CLOEXEC);
+	if (obj.fd < 0) {
+		pr_warn("failed to open file '%s': %s\n", filename, errstr(errno));
+		return -errno;
+	}
+
+	ret = linker_add_common(linker, &obj, opts);
+
 	if (obj.fd >= 0)
 		close(obj.fd);
 
-	return libbpf_err(err);
+	return ret;
+}
+
+int bpf_linker__add_fd(struct bpf_linker *linker, const char *name, int fd,
+		       const struct bpf_linker_file_opts *opts)
+{
+	struct src_obj obj = {};
+
+	if (fd < 0)
+		return libbpf_err(-EINVAL);
+
+	obj.filename = name;
+	obj.fd = fd;
+
+	return linker_add_common(linker, &obj, opts);
+}
+
+int bpf_linker__add_buf(struct bpf_linker *linker, const char *name,
+			void *buffer, int buffer_sz,
+			const struct bpf_linker_file_opts *opts)
+{
+	struct src_obj obj = {};
+	int written, ret;
+
+	obj.filename = name;
+	obj.fd = memfd_create(name, 0);
+	if (obj.fd < 0) {
+		pr_warn("failed to create memfd '%s': %s\n", name, errstr(errno));
+		return -errno;
+	}
+
+	written = 0;
+	while (written < buffer_sz) {
+		ret = write(obj.fd, buffer, buffer_sz);
+		if (ret < 0) {
+			pr_warn("failed to write '%s': %s\n", name, errstr(errno));
+			return -errno;
+		}
+		written += ret;
+	}
+
+	ret = linker_add_common(linker, &obj, opts);
+
+	if (obj.fd >= 0)
+		close(obj.fd);
+
+	return ret;
 }
 
 static bool is_dwarf_sec_name(const char *name)
@@ -534,7 +638,7 @@  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,
+static int linker_load_obj_file(struct bpf_linker *linker,
 				const struct bpf_linker_file_opts *opts,
 				struct src_obj *obj)
 {
@@ -554,20 +658,12 @@  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) {
 		err = -errno;
-		pr_warn_elf("failed to parse ELF file '%s'", filename);
+		pr_warn_elf("failed to parse ELF file '%s'", obj->filename);
 		return err;
 	}
 
@@ -575,7 +671,7 @@  static int linker_load_obj_file(struct bpf_linker *linker, const char *filename,
 	ehdr = elf64_getehdr(obj->elf);
 	if (!ehdr) {
 		err = -errno;
-		pr_warn_elf("failed to get ELF header for %s", filename);
+		pr_warn_elf("failed to get ELF header for %s", obj->filename);
 		return err;
 	}
 
@@ -583,7 +679,7 @@  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) {
@@ -593,7 +689,7 @@  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;
 	}
 
@@ -601,13 +697,13 @@  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)) {
 		err = -errno;
-		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 err;
 	}
 
@@ -620,7 +716,7 @@  static int linker_load_obj_file(struct bpf_linker *linker, const char *filename,
 		if (!shdr) {
 			err = -errno;
 			pr_warn_elf("failed to get section #%zu header for %s",
-				    sec_idx, filename);
+				    sec_idx, obj->filename);
 			return err;
 		}
 
@@ -628,7 +724,7 @@  static int linker_load_obj_file(struct bpf_linker *linker, const char *filename,
 		if (!sec_name) {
 			err = -errno;
 			pr_warn_elf("failed to get section #%zu name for %s",
-				    sec_idx, filename);
+				    sec_idx, obj->filename);
 			return err;
 		}
 
@@ -636,7 +732,7 @@  static int linker_load_obj_file(struct bpf_linker *linker, const char *filename,
 		if (!data) {
 			err = -errno;
 			pr_warn_elf("failed to get section #%zu (%s) data from %s",
-				    sec_idx, sec_name, filename);
+				    sec_idx, sec_name, obj->filename);
 			return err;
 		}
 
@@ -672,7 +768,7 @@  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;
@@ -683,7 +779,7 @@  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;
@@ -700,7 +796,7 @@  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;
 		}
@@ -2634,7 +2730,7 @@  static int linker_append_btf_ext(struct bpf_linker *linker, struct src_obj *obj)
 	return 0;
 }
 
-int bpf_linker__finalize(struct bpf_linker *linker)
+int linker_finalize_common(struct bpf_linker *linker)
 {
 	struct dst_sec *sec;
 	size_t strs_sz;
@@ -2693,9 +2789,28 @@  int bpf_linker__finalize(struct bpf_linker *linker)
 	}
 
 	elf_end(linker->elf);
+	linker->elf = NULL;
+
+	/* leave linker->fd for the caller to close if appropriate */
+
+	return 0;
+}
+
+int bpf_linker__finalize(struct bpf_linker *linker)
+{
+	linker_finalize_common(linker);
+
 	close(linker->fd);
+	linker->fd = -1;
 
-	linker->elf = NULL;
+	return 0;
+}
+
+int bpf_linker__finalize_fd(struct bpf_linker *linker)
+{
+	linker_finalize_common(linker);
+
+	/* linker->fd was opened by the caller, so do not close it here */
 	linker->fd = -1;
 
 	return 0;