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bpftool: Support merging multiple module BTFs in btf dump

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Add support for specifying multiple file sources in 'bpftool btf dump'
to generate a single C header containing types from vmlinux plus
multiple kernel modules:

  bpftool btf dump file /sys/kernel/btf/mod1 file /sys/kernel/btf/mod2 format c

This is useful for BPF programs that need to access types defined in
kernel modules. Previously this required a separate bpftool invocation
for each module, producing separate headers that could not be combined
due to overlapping vmlinux type definitions.

The implementation collects all file paths, then for the multi-file
case creates an empty split BTF on the vmlinux base and iteratively
merges each module's types into it via btf__add_btf(). The single-file
code path is preserved exactly to avoid any regression risk.

Auto-detection of vmlinux as the base BTF from sysfs paths works as
before. If vmlinux itself appears in the file list it is skipped with
a warning since its types are already provided by the base.

Assisted-by: Claude:claude-opus-4-6

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Link: https://lore.kernel.org/bpf/b19c2760ffe48cec546dd3810d237f8cad20d606.1772657690.git.josef@toxicpanda.com
This commit is contained in:
Josef Bacik
2026-03-04 15:56:51 -05:00
committed by Andrii Nakryiko
parent be872ccf37
commit d8d5c01511
3 changed files with 121 additions and 17 deletions
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11
tools/bpf/bpftool/Documentation/bpftool-btf.rst
View File

@@ -27,7 +27,7 @@ BTF COMMANDS
| **bpftool** **btf dump** *BTF_SRC* [**format** *FORMAT*] [**root_id** *ROOT_ID*]
| **bpftool** **btf help**
|
| *BTF_SRC* := { **id** *BTF_ID* | **prog** *PROG* | **map** *MAP* [{**key** | **value** | **kv** | **all**}] | **file** *FILE* }
| *BTF_SRC* := { **id** *BTF_ID* | **prog** *PROG* | **map** *MAP* [{**key** | **value** | **kv** | **all**}] | **file** *FILE* [**file** *FILE*]... }
| *FORMAT* := { **raw** | **c** [**unsorted**] }
| *MAP* := { **id** *MAP_ID* | **pinned** *FILE* }
| *PROG* := { **id** *PROG_ID* | **pinned** *FILE* | **tag** *PROG_TAG* | **name** *PROG_NAME* }
@@ -58,9 +58,12 @@ bpftool btf dump *BTF_SRC* [format *FORMAT*] [root_id *ROOT_ID*]
When **prog** is provided, it's expected that program has associated BTF
object with BTF types.
When specifying *FILE*, an ELF file is expected, containing .BTF section
with well-defined BTF binary format data, typically produced by clang or
pahole.
When specifying *FILE*, an ELF file or a raw BTF file (e.g. from
``/sys/kernel/btf/``) is expected. Multiple **file** arguments may be
given to merge BTF from several kernel modules into a single output.
When sysfs paths are used, vmlinux BTF is loaded automatically as the
base; if vmlinux itself appears in the file list it is skipped.
A base BTF can also be specified explicitly with **-B**.
**format** option can be used to override default (raw) output format. Raw
(**raw**) or C-syntax (**c**) output formats are supported. With C-style

6
tools/bpf/bpftool/bash-completion/bpftool
View File

@@ -961,10 +961,14 @@ _bpftool()
*)
# emit extra options
case ${words[3]} in
id|file)
id)
COMPREPLY=( $( compgen -W "root_id" -- "$cur" ) )
_bpftool_once_attr 'format'
;;
file)
COMPREPLY=( $( compgen -W "root_id file" -- "$cur" ) )
_bpftool_once_attr 'format'
;;
map|prog)
if [[ ${words[3]} == "map" ]] && [[ $cword == 6 ]]; then
COMPREPLY+=( $( compgen -W "key value kv all" -- "$cur" ) )

121
tools/bpf/bpftool/btf.c
View File

@@ -28,6 +28,7 @@
#define FASTCALL_DECL_TAG "bpf_fastcall"
#define MAX_ROOT_IDS 16
#define MAX_BTF_FILES 64
static const char * const btf_kind_str[NR_BTF_KINDS] = {
[BTF_KIND_UNKN] = "UNKNOWN",
@@ -878,6 +879,45 @@ static bool btf_is_kernel_module(__u32 btf_id)
return btf_info.kernel_btf && strncmp(btf_name, "vmlinux", sizeof(btf_name)) != 0;
}
static struct btf *merge_btf_files(const char **files, int nr_files,
struct btf *vmlinux_base)
{
struct btf *combined, *mod;
int ret;
combined = btf__new_empty_split(vmlinux_base);
if (!combined) {
p_err("failed to create combined BTF: %s", strerror(errno));
return NULL;
}
for (int j = 0; j < nr_files; j++) {
mod = btf__parse_split(files[j], vmlinux_base);
if (!mod) {
p_err("failed to load BTF from %s: %s", files[j], strerror(errno));
btf__free(combined);
return NULL;
}
ret = btf__add_btf(combined, mod);
btf__free(mod);
if (ret < 0) {
p_err("failed to merge BTF from %s: %s", files[j], strerror(-ret));
btf__free(combined);
return NULL;
}
}
ret = btf__dedup(combined, NULL);
if (ret) {
p_err("failed to dedup combined BTF: %s", strerror(-ret));
btf__free(combined);
return NULL;
}
return combined;
}
static int do_dump(int argc, char **argv)
{
bool dump_c = false, sort_dump_c = true;
@@ -958,20 +998,76 @@ static int do_dump(int argc, char **argv)
NEXT_ARG();
} else if (is_prefix(src, "file")) {
const char sysfs_prefix[] = "/sys/kernel/btf/";
struct btf *vmlinux_base = base_btf;
const char *files[MAX_BTF_FILES];
int nr_files = 0;
if (!base_btf &&
strncmp(*argv, sysfs_prefix, sizeof(sysfs_prefix) - 1) == 0 &&
strcmp(*argv, sysfs_vmlinux) != 0)
base = get_vmlinux_btf_from_sysfs();
btf = btf__parse_split(*argv, base ?: base_btf);
if (!btf) {
err = -errno;
p_err("failed to load BTF from %s: %s",
*argv, strerror(errno));
goto done;
/* First grab our argument, filtering out the sysfs_vmlinux. */
if (strcmp(*argv, sysfs_vmlinux) != 0) {
files[nr_files++] = *argv;
} else {
p_info("skipping %s (will be loaded as base)", *argv);
}
NEXT_ARG();
while (argc && is_prefix(*argv, "file")) {
NEXT_ARG();
if (!REQ_ARGS(1)) {
err = -EINVAL;
goto done;
}
/* Filter out any sysfs vmlinux entries. */
if (strcmp(*argv, sysfs_vmlinux) == 0) {
p_info("skipping %s (will be loaded as base)", *argv);
NEXT_ARG();
continue;
}
if (nr_files >= MAX_BTF_FILES) {
p_err("too many BTF files (max %d)", MAX_BTF_FILES);
err = -E2BIG;
goto done;
}
files[nr_files++] = *argv;
NEXT_ARG();
}
/* Auto-detect vmlinux base if any file is from sysfs */
if (!vmlinux_base) {
for (int j = 0; j < nr_files; j++) {
if (strncmp(files[j], sysfs_prefix, sizeof(sysfs_prefix) - 1) == 0) {
base = get_vmlinux_btf_from_sysfs();
vmlinux_base = base;
break;
}
}
}
/* All files were the sysfs_vmlinux, handle it like we used to */
if (nr_files == 0) {
nr_files = 1;
files[0] = sysfs_vmlinux;
}
if (nr_files == 1) {
btf = btf__parse_split(files[0], base ?: base_btf);
if (!btf) {
err = -errno;
p_err("failed to load BTF from %s: %s", files[0], strerror(errno));
goto done;
}
} else {
if (!vmlinux_base) {
p_err("base BTF is required when merging multiple BTF files; use -B/--base-btf or use sysfs paths");
err = -EINVAL;
goto done;
}
btf = merge_btf_files(files, nr_files, vmlinux_base);
if (!btf) {
err = -errno;
goto done;
}
}
} else {
err = -1;
p_err("unrecognized BTF source specifier: '%s'", src);
@@ -1445,7 +1541,8 @@ static int do_help(int argc, char **argv)
" %1$s %2$s dump BTF_SRC [format FORMAT] [root_id ROOT_ID]\n"
" %1$s %2$s help\n"
"\n"
" BTF_SRC := { id BTF_ID | prog PROG | map MAP [{key | value | kv | all}] | file FILE }\n"
" BTF_SRC := { id BTF_ID | prog PROG | map MAP [{key | value | kv | all}] |\n"
" file FILE [file FILE]... }\n"
" FORMAT := { raw | c [unsorted] }\n"
" " HELP_SPEC_MAP "\n"
" " HELP_SPEC_PROGRAM "\n"