If the -R <base_btf> option is used, we can display BTF
that has been generated with base reference BTF in its
reconciled form. For example if we build a module with
base reference BTF:
BTF_BASE_REF=1 make -C. M=path/2/module
...we can display its content relative to that base
reference BTF via
bpftool btf dump file path/2/module
Alternatively, we can display content reconciled with
(a possibly changed) base BTF via
bpftool btf dump -R vmlinux path/2/module
The latter mirrors how the kernel will handle such split
BTF; it reconciles its representation with the running
kernel, and if successful, renumbers BTF ids to reference
the current vmlinux BTF.
Signed-off-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
---
tools/bpf/bpftool/Documentation/bpftool-btf.rst | 17 +++++++++++++++++
tools/bpf/bpftool/btf.c | 14 ++++++++++++--
tools/bpf/bpftool/main.c | 14 +++++++++++++-
tools/bpf/bpftool/main.h | 2 ++
4 files changed, 44 insertions(+), 3 deletions(-)
diff --git a/tools/bpf/bpftool/Documentation/bpftool-btf.rst b/tools/bpf/bpftool/Documentation/bpftool-btf.rst
index 342716f74ec4..97b6426367e6 100644
--- a/tools/bpf/bpftool/Documentation/bpftool-btf.rst
+++ b/tools/bpf/bpftool/Documentation/bpftool-btf.rst
@@ -90,6 +90,23 @@ OPTIONS
to autodetect the path for the base object, and passing
this option is optional. When the main BTF object is passed
through other handles, this option becomes necessary.
+ -R, --reconcile-base-btf *FILE*
+ When split BTF is generated with base reference BTF,
+ the latter is stored in a .BTF.base_ref section and allows
+ us to later reconcile split BTF and a potentially-changed
+ base BTF by noting that type ids in the split BTF that
+ refer to base BTF refer to specific integers, structs etc.
+ By passing base BTF via the -R option, we can carry out
+ that reconciliation operation between split/base reference
+ BTF and base BTF. If successful, the split BTF will then
+ refer to the base BTF types from *reconcile-base-btf*.
+
+ If this argument is not used, split BTF is shown relative
+ to .BTF.base_ref data as a base; however in this mode
+ it is not possible to generate "C" output, since the
+ information retained in .BTF.base_ref is just enough to
+ clarify what a type id refers to, but does not contain
+ full type details for all types.
EXAMPLES
========
diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
index f1e0ea06f05f..355b56eff9f2 100644
--- a/tools/bpf/bpftool/btf.c
+++ b/tools/bpf/bpftool/btf.c
@@ -644,8 +644,17 @@ static int do_dump(int argc, char **argv)
base_btf = btf__parse_opts(*argv, &optp);
if (base_btf)
btf = btf__parse_split(*argv, base_btf);
- if (btf)
+ if (btf && reconcile_base_btf) {
+ err = btf__reconcile(btf, reconcile_base_btf);
+ if (err) {
+ p_err("coud not reconcile BTF from '%s' with base BTF '%s': %s\n",
+ *argv, reconcile_base_btf_path,
+ strerror(-err));
+ goto done;
+ }
+ } else {
c_compat = false;
+ }
}
if (!btf) {
err = -errno;
@@ -1088,7 +1097,8 @@ static int do_help(int argc, char **argv)
" " HELP_SPEC_MAP "\n"
" " HELP_SPEC_PROGRAM "\n"
" " HELP_SPEC_OPTIONS " |\n"
- " {-B|--base-btf} }\n"
+ " {-B|--base-btf}\n"
+ " {-R|--reconcile-base-btf}}\n"
"",
bin_name, "btf");
diff --git a/tools/bpf/bpftool/main.c b/tools/bpf/bpftool/main.c
index 08d0ac543c67..33ac0ca77162 100644
--- a/tools/bpf/bpftool/main.c
+++ b/tools/bpf/bpftool/main.c
@@ -32,6 +32,8 @@ bool verifier_logs;
bool relaxed_maps;
bool use_loader;
struct btf *base_btf;
+struct btf *reconcile_base_btf;
+const char *reconcile_base_btf_path;
struct hashmap *refs_table;
static void __noreturn clean_and_exit(int i)
@@ -448,6 +450,7 @@ int main(int argc, char **argv)
{ "debug", no_argument, NULL, 'd' },
{ "use-loader", no_argument, NULL, 'L' },
{ "base-btf", required_argument, NULL, 'B' },
+ { "reconcile-base-btf", required_argument, NULL, 'R' },
{ 0 }
};
bool version_requested = false;
@@ -473,7 +476,7 @@ int main(int argc, char **argv)
bin_name = "bpftool";
opterr = 0;
- while ((opt = getopt_long(argc, argv, "VhpjfLmndB:l",
+ while ((opt = getopt_long(argc, argv, "VhpjfLmndB:lR:",
options, NULL)) >= 0) {
switch (opt) {
case 'V':
@@ -516,6 +519,15 @@ int main(int argc, char **argv)
return -1;
}
break;
+ case 'R':
+ reconcile_base_btf_path = optarg;
+ reconcile_base_btf = btf__parse(optarg, NULL);
+ if (!reconcile_base_btf) {
+ p_err("failed to parse base BTF for reconciliation at '%s': %d\n",
+ optarg, -errno);
+ return -1;
+ }
+ break;
case 'L':
use_loader = true;
break;
diff --git a/tools/bpf/bpftool/main.h b/tools/bpf/bpftool/main.h
index b8bb08d10dec..c84bfc1d9135 100644
--- a/tools/bpf/bpftool/main.h
+++ b/tools/bpf/bpftool/main.h
@@ -83,6 +83,8 @@ extern bool verifier_logs;
extern bool relaxed_maps;
extern bool use_loader;
extern struct btf *base_btf;
+extern struct btf *reconcile_base_btf;
+extern const char *reconcile_base_btf_path;
extern struct hashmap *refs_table;
void __printf(1, 2) p_err(const char *fmt, ...);
--
2.39.3
