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Message-Id: <20260105071231.2501-1-kiraskyler@163.com>
Date: Mon, 5 Jan 2026 15:12:31 +0800
From: WanLi Niu <kiraskyler@....com>
To: Quentin Monnet <qmo@...nel.org>
Cc: Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>,
Martin KaFai Lau <martin.lau@...ux.dev>,
Eduard Zingerman <eddyz87@...il.com>,
Song Liu <song@...nel.org>,
Yonghong Song <yonghong.song@...ux.dev>,
John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...nel.org>,
Stanislav Fomichev <sdf@...ichev.me>,
Hao Luo <haoluo@...gle.com>,
Jiri Olsa <jolsa@...nel.org>,
WanLi Niu <kiraskyler@....com>,
Menglong Dong <menglong8.dong@...il.com>,
bpf@...r.kernel.org,
linux-kernel@...r.kernel.org,
WanLi Niu <niuwl1@...natelecom.cn>,
Menglong Dong <dongml2@...natelecom.cn>
Subject: [PATCH v4 bpf-next] bpftool: Make skeleton C++ compatible with explicit casts
From: WanLi Niu <niuwl1@...natelecom.cn>
Fix C++ compilation errors in generated skeleton by adding explicit
pointer casts and using integer subtraction for offset calculation.
Use struct outer::inner syntax under __cplusplus to access nested skeleton map
structs, ensuring C++ compilation compatibility while preserving C support
error: invalid conversion from 'void*' to '<obj_name>*' [-fpermissive]
| skel = skel_alloc(sizeof(*skel));
| ~~~~~~~~~~^~~~~~~~~~~~~~~
| |
| void*
error: arithmetic on pointers to void
| skel->ctx.sz = (void *)&skel->links - (void *)skel;
| ~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~
error: assigning to 'struct <obj_name>__<ident> *' from incompatible type 'void *'
| skel-><ident> = skel_prep_map_data((void *)data, 4096,
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| sizeof(data) - 1);
| ~~~~~~~~~~~~~~~~~
error: assigning to 'struct <obj_name>__<ident> *' from incompatible type 'void *'
| skel-><ident> = skel_finalize_map_data(&skel->maps.<ident>.initial_value,
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| 4096, PROT_READ | PROT_WRITE, skel->maps.<ident>.map_fd);
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Minimum reproducer:
$ cat test.bpf.c
int val; // placed in .bss section
#include "vmlinux.h"
#include <bpf/bpf_helpers.h>
SEC("raw_tracepoint/sched_wakeup_new") int handle(void *ctx) { return 0; }
$ cat test.cpp
#include <cerrno>
extern "C" {
#include "test.bpf.skel.h"
}
$ bpftool btf dump file /sys/kernel/btf/vmlinux format c > vmlinux.h
$ clang -g -O2 -target bpf -c test.bpf.c -o test.bpf.o
$ bpftool gen skeleton test.bpf.o -L > test.bpf.skel.h
$ g++ -c test.cpp -I.
Signed-off-by: WanLi Niu <niuwl1@...natelecom.cn>
Co-developed-by: Menglong Dong <dongml2@...natelecom.cn>
Signed-off-by: Menglong Dong <dongml2@...natelecom.cn>
---
changelog:
v4:
- Add a minimum reproducer to demonstrate the issue, as suggested by Yonghong Song
v3: https://lore.kernel.org/all/20260104021402.2968-1-kiraskyler@163.com/
- Fix two additional <obj_name>__<ident> type mismatches as suggested by Yonghong Song
v2: https://lore.kernel.org/all/20251231102929.3843-1-kiraskyler@163.com/
- Use generic (struct %1$s *) instead of project-specific (struct trace_bpf *)
v1: https://lore.kernel.org/all/20251231092541.3352-1-kiraskyler@163.com/
---
tools/bpf/bpftool/gen.c | 16 ++++++++++++----
1 file changed, 12 insertions(+), 4 deletions(-)
diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
index 993c7d9484a4..010861b7d0ea 100644
--- a/tools/bpf/bpftool/gen.c
+++ b/tools/bpf/bpftool/gen.c
@@ -731,10 +731,10 @@ static int gen_trace(struct bpf_object *obj, const char *obj_name, const char *h
{ \n\
struct %1$s *skel; \n\
\n\
- skel = skel_alloc(sizeof(*skel)); \n\
+ skel = (struct %1$s *)skel_alloc(sizeof(*skel)); \n\
if (!skel) \n\
goto cleanup; \n\
- skel->ctx.sz = (void *)&skel->links - (void *)skel; \n\
+ skel->ctx.sz = (__u64)&skel->links - (__u64)skel; \n\
",
obj_name, opts.data_sz);
bpf_object__for_each_map(map, obj) {
@@ -755,13 +755,17 @@ static int gen_trace(struct bpf_object *obj, const char *obj_name, const char *h
\n\
\"; \n\
\n\
+ #ifdef __cplusplus \n\
+ skel->%1$s = (struct %3$s::%3$s__%1$s *)skel_prep_map_data((void *)data, %2$zd,\n\
+ #else \n\
skel->%1$s = skel_prep_map_data((void *)data, %2$zd,\n\
+ #endif \n\
sizeof(data) - 1);\n\
if (!skel->%1$s) \n\
goto cleanup; \n\
skel->maps.%1$s.initial_value = (__u64) (long) skel->%1$s;\n\
} \n\
- ", ident, bpf_map_mmap_sz(map));
+ ", ident, bpf_map_mmap_sz(map), obj_name);
}
codegen("\
\n\
@@ -857,12 +861,16 @@ static int gen_trace(struct bpf_object *obj, const char *obj_name, const char *h
codegen("\
\n\
+ #ifdef __cplusplus \n\
+ skel->%1$s = (struct %4$s::%4$s__%1$s *)skel_finalize_map_data(&skel->maps.%1$s.initial_value,\n\
+ #else \n\
skel->%1$s = skel_finalize_map_data(&skel->maps.%1$s.initial_value, \n\
+ #endif \n\
%2$zd, %3$s, skel->maps.%1$s.map_fd);\n\
if (!skel->%1$s) \n\
return -ENOMEM; \n\
",
- ident, bpf_map_mmap_sz(map), mmap_flags);
+ ident, bpf_map_mmap_sz(map), mmap_flags, obj_name);
}
codegen("\
\n\
--
2.39.1
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