Given that vmlinux.h is not compatible with headers like stdint.h, NULL poses
an annoying problem: it is defined as #define, so is not captured in BTF, so
is not emitted into vmlinux.h. This leads to users either sticking to explicit
0, or defining their own NULL (as progs/skb_pkt_end.c does).
It's pretty trivial for bpftool to generate NULL definition, though, so let's
just do that. This might cause compilation warning for existing BPF
applications:
progs/skb_pkt_end.c:7:9: warning: 'NULL' macro redefined [-Wmacro-redefined]
progs/skb_pkt_end.c:7:9: error: 'NULL' macro redefined
[-Werror,-Wmacro-redefined]
#define NULL 0
^
/tmp/linux/tools/testing/selftests/bpf/tools/include/vmlinux.h:4:9: note:
previous definition is here
#define NULL ((void *)0)
^
It is trivial to fix, though, so long-term benefits outweight temporary
inconveniences.
Signed-off-by: Andrii Nakryiko <[email protected]>
---
tools/bpf/bpftool/btf.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
index 62953bbf68b4..ff6a76632873 100644
--- a/tools/bpf/bpftool/btf.c
+++ b/tools/bpf/bpftool/btf.c
@@ -405,6 +405,8 @@ static int dump_btf_c(const struct btf *btf,
printf("#ifndef __VMLINUX_H__\n");
printf("#define __VMLINUX_H__\n");
printf("\n");
+ printf("#define NULL ((void *)0)\n");
+ printf("\n");
printf("#ifndef BPF_NO_PRESERVE_ACCESS_INDEX\n");
printf("#pragma clang attribute push
(__attribute__((preserve_access_index)), apply_to = record)\n");
printf("#endif\n\n");
--
2.30.2
