[PATCH v2 bpf-next] bpftool: Make skeleton C++ compatible with explicit casts

[WanLi Niu]

From: WanLi Niu <niuwl1@xxxxxxxxxxxxxxx>

Fix C++ compilation errors in generated skeleton by adding explicit
pointer casts and using integer subtraction for offset calculation.

error: invalid conversion from 'void*' to 'trace_bpf*' [-fpermissive]
      |         skel = skel_alloc(sizeof(*skel));
      |                ~~~~~~~~~~^~~~~~~~~~~~~~~
      |                          |
      |                          void*

error: invalid use of 'void'
      |         skel->ctx.sz = (void *)&skel->links - (void *)skel;

Signed-off-by: WanLi Niu <niuwl1@xxxxxxxxxxxxxxx>
Co-developed-by: Menglong Dong <dongml2@xxxxxxxxxxxxxxx>
Signed-off-by: Menglong Dong <dongml2@xxxxxxxxxxxxxxx>
---
 tools/bpf/bpftool/gen.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
index 993c7d9484a4..71446a776130 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) {
-- 
2.39.1