Subject: Re: [PATCH bpf-next] bpftool: fix bpftool build by switching to bpf_object__open_file()

From: Stanislav Fomichev <[email-masked]>
Date: Mon, 7 Oct 2019 14:46:50 -0700

On 10/07, Andrii Nakryiko wrote:
> As part of libbpf in 5e61f2707029 ("libbpf: stop enforcing kern_version,
> populate it for users") non-LIBBPF_API __bpf_object__open_xattr() API
> was removed from libbpf.h header. This broke bpftool, which relied on
> that function. This patch fixes the build by switching to newly added
> bpf_object__open_file() which provides the same capabilities, but is
> official and future-proof API.
> 
> Fixes: 5e61f2707029 ("libbpf: stop enforcing kern_version, populate it for users")
> Reported-by: Stanislav Fomichev <[email-masked]>
> Signed-off-by: Andrii Nakryiko <[email-masked]>
> ---
>  tools/bpf/bpftool/main.c |  4 ++--
>  tools/bpf/bpftool/main.h |  2 +-
>  tools/bpf/bpftool/prog.c | 22 ++++++++++++----------
>  3 files changed, 15 insertions(+), 13 deletions(-)
> 
> diff --git a/tools/bpf/bpftool/main.c b/tools/bpf/bpftool/main.c
> index 93d008687020..4764581ff9ea 100644
> --- a/tools/bpf/bpftool/main.c
> +++ b/tools/bpf/bpftool/main.c
> @@ -27,7 +27,7 @@ bool json_output;
>  bool show_pinned;
>  bool block_mount;
>  bool verifier_logs;
> -int bpf_flags;
> +bool relaxed_maps;
>  struct pinned_obj_table prog_table;
>  struct pinned_obj_table map_table;
>  
> @@ -396,7 +396,7 @@ int main(int argc, char **argv)
>  			show_pinned = true;
>  			break;
>  		case 'm':
> -			bpf_flags = MAPS_RELAX_COMPAT;
> +			relaxed_maps = true;
>  			break;
>  		case 'n':
>  			block_mount = true;
> diff --git a/tools/bpf/bpftool/main.h b/tools/bpf/bpftool/main.h
> index af9ad56c303a..2899095f8254 100644
> --- a/tools/bpf/bpftool/main.h
> +++ b/tools/bpf/bpftool/main.h
> @@ -94,7 +94,7 @@ extern bool json_output;
>  extern bool show_pinned;
>  extern bool block_mount;
>  extern bool verifier_logs;
> -extern int bpf_flags;
> +extern bool relaxed_maps;
>  extern struct pinned_obj_table prog_table;
>  extern struct pinned_obj_table map_table;
>  
> diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c
> index 43fdbbfe41bb..8191cd595963 100644
> --- a/tools/bpf/bpftool/prog.c
> +++ b/tools/bpf/bpftool/prog.c
> @@ -1092,9 +1092,7 @@ static int do_run(int argc, char **argv)
>  static int load_with_options(int argc, char **argv, bool first_prog_only)
>  {
>  	struct bpf_object_load_attr load_attr = { 0 };
> -	struct bpf_object_open_attr open_attr = {
> -		.prog_type = BPF_PROG_TYPE_UNSPEC,
> -	};
> +	enum bpf_prog_type prog_type = BPF_PROG_TYPE_UNSPEC;
>  	enum bpf_attach_type expected_attach_type;
>  	struct map_replace *map_replace = NULL;
>  	struct bpf_program *prog = NULL, *pos;
> @@ -1105,11 +1103,16 @@ static int load_with_options(int argc, char **argv, bool first_prog_only)
>  	const char *pinfile;
>  	unsigned int i, j;
>  	__u32 ifindex = 0;
> +	const char *file;
>  	int idx, err;
>  
> +	LIBBPF_OPTS(bpf_object_open_opts, open_opts,
> +		.relaxed_maps = relaxed_maps,
> +	);
> +
>  	if (!REQ_ARGS(2))
>  		return -1;
> -	open_attr.file = GET_ARG();
> +	file = GET_ARG();
>  	pinfile = GET_ARG();
>  
>  	while (argc) {
> @@ -1118,7 +1121,7 @@ static int load_with_options(int argc, char **argv, bool first_prog_only)
>  
>  			NEXT_ARG();
>  
> -			if (open_attr.prog_type != BPF_PROG_TYPE_UNSPEC) {
> +			if (prog_type != BPF_PROG_TYPE_UNSPEC) {
>  				p_err("program type already specified");
>  				goto err_free_reuse_maps;
>  			}
> @@ -1135,8 +1138,7 @@ static int load_with_options(int argc, char **argv, bool first_prog_only)
>  			strcat(type, *argv);
>  			strcat(type, "/");
>  
> -			err = libbpf_prog_type_by_name(type,
> -						       &open_attr.prog_type,
> +			err = libbpf_prog_type_by_name(type, &prog_type,
>  						       &expected_attach_type);
>  			free(type);
>  			if (err < 0)
> @@ -1224,16 +1226,16 @@ static int load_with_options(int argc, char **argv, bool first_prog_only)
>  
>  	set_max_rlimit();
>  
> -	obj = __bpf_object__open_xattr(&open_attr, bpf_flags);
> +	obj = bpf_object__open_file(file, &open_opts);
>  	if (IS_ERR_OR_NULL(obj)) {
>  		p_err("failed to open object file");
>  		goto err_free_reuse_maps;
>  	}
>  
>  	bpf_object__for_each_program(pos, obj) {
> -		enum bpf_prog_type prog_type = open_attr.prog_type;
> +		enum bpf_prog_type prog_type = prog_type;
Are you sure it works that way?

$ cat tmp.c
#include <stdio.h>

int main()
{
	int x = 1;
	printf("outer x=%d\n", x);

	{
		int x = x;
		printf("inner x=%d\n", x);
	}

	return 0;
}

$ gcc tmp.c && ./a.out
outer x=1
inner x=0

Other than that:
Reviewed-by: Stanislav Fomichev <[email-masked]>

>  
> -		if (open_attr.prog_type == BPF_PROG_TYPE_UNSPEC) {
> +		if (prog_type == BPF_PROG_TYPE_UNSPEC) {
>  			const char *sec_name = bpf_program__title(pos, false);
>  
>  			err = libbpf_prog_type_by_name(sec_name, &prog_type,
> -- 
> 2.17.1
>