bpftool: Use syscall/loader program in "prog load" and "gen skeleton" command.

Add -L flag to bpftool to use libbpf gen_trace facility and syscall/loader program
for skeleton generation and program loading.

"bpftool gen skeleton -L" command will generate a "light skeleton" or "loader skeleton"
that is similar to existing skeleton, but has one major difference:
$ bpftool gen skeleton lsm.o > lsm.skel.h
$ bpftool gen skeleton -L lsm.o > lsm.lskel.h
$ diff lsm.skel.h lsm.lskel.h
@@ -5,34 +4,34 @@
 #define __LSM_SKEL_H__

 #include <stdlib.h>
-#include <bpf/libbpf.h>
+#include <bpf/bpf.h>

The light skeleton does not use majority of libbpf infrastructure.
It doesn't need libelf. It doesn't parse .o file.
It only needs few sys_bpf wrappers. All of them are in bpf/bpf.h file.
In future libbpf/bpf.c can be inlined into bpf.h, so not even libbpf.a would be
needed to work with light skeleton.

"bpftool prog load -L file.o" command is introduced for debugging of syscall/loader
program generation. Just like the same command without -L it will try to load
the programs from file.o into the kernel. It won't even try to pin them.

"bpftool prog load -L -d file.o" command will provide additional debug messages
on how syscall/loader program was generated.
Also the execution of syscall/loader program will use bpf_trace_printk() for
each step of loading BTF, creating maps, and loading programs.
The user can do "cat /.../trace_pipe" for further debug.

An example of fexit_sleep.lskel.h generated from progs/fexit_sleep.c:
struct fexit_sleep {
	struct bpf_loader_ctx ctx;
	struct {
		struct bpf_map_desc bss;
	} maps;
	struct {
		struct bpf_prog_desc nanosleep_fentry;
		struct bpf_prog_desc nanosleep_fexit;
	} progs;
	struct {
		int nanosleep_fentry_fd;
		int nanosleep_fexit_fd;
	} links;
	struct fexit_sleep__bss {
		int pid;
		int fentry_cnt;
		int fexit_cnt;
	} *bss;
};

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210514003623.28033-18-alexei.starovoitov@gmail.com

tools/bpf/bpftool/Makefile

@@ -136,7 +136,7 @@ endif
 
 BPFTOOL_BOOTSTRAP := $(BOOTSTRAP_OUTPUT)bpftool
 
-BOOTSTRAP_OBJS = $(addprefix $(BOOTSTRAP_OUTPUT),main.o common.o json_writer.o gen.o btf.o)
+BOOTSTRAP_OBJS = $(addprefix $(BOOTSTRAP_OUTPUT),main.o common.o json_writer.o gen.o btf.o xlated_dumper.o btf_dumper.o) $(OUTPUT)disasm.o
 OBJS = $(patsubst %.c,$(OUTPUT)%.o,$(SRCS)) $(OUTPUT)disasm.o
 
 VMLINUX_BTF_PATHS ?= $(if $(O),$(O)/vmlinux)				\

tools/bpf/bpftool/gen.c

@@ -18,6 +18,7 @@
 #include <sys/stat.h>
 #include <sys/mman.h>
 #include <bpf/btf.h>
+#include <bpf/bpf_gen_internal.h>
 
 #include "json_writer.h"
 #include "main.h"
@@ -274,6 +275,327 @@ static void codegen(const char *template, ...)
 	free(s);
 }
 
+static void print_hex(const char *data, int data_sz)
+{
+	int i, len;
+
+	for (i = 0, len = 0; i < data_sz; i++) {
+		int w = data[i] ? 4 : 2;
+
+		len += w;
+		if (len > 78) {
+			printf("\\\n");
+			len = w;
+		}
+		if (!data[i])
+			printf("\\0");
+		else
+			printf("\\x%02x", (unsigned char)data[i]);
+	}
+}
+
+static size_t bpf_map_mmap_sz(const struct bpf_map *map)
+{
+	long page_sz = sysconf(_SC_PAGE_SIZE);
+	size_t map_sz;
+
+	map_sz = (size_t)roundup(bpf_map__value_size(map), 8) * bpf_map__max_entries(map);
+	map_sz = roundup(map_sz, page_sz);
+	return map_sz;
+}
+
+static void codegen_attach_detach(struct bpf_object *obj, const char *obj_name)
+{
+	struct bpf_program *prog;
+
+	bpf_object__for_each_program(prog, obj) {
+		const char *tp_name;
+
+		codegen("\
+			\n\
+			\n\
+			static inline int					    \n\
+			%1$s__%2$s__attach(struct %1$s *skel)			    \n\
+			{							    \n\
+				int prog_fd = skel->progs.%2$s.prog_fd;		    \n\
+			", obj_name, bpf_program__name(prog));
+
+		switch (bpf_program__get_type(prog)) {
+		case BPF_PROG_TYPE_RAW_TRACEPOINT:
+			tp_name = strchr(bpf_program__section_name(prog), '/') + 1;
+			printf("\tint fd = bpf_raw_tracepoint_open(\"%s\", prog_fd);\n", tp_name);
+			break;
+		case BPF_PROG_TYPE_TRACING:
+			printf("\tint fd = bpf_raw_tracepoint_open(NULL, prog_fd);\n");
+			break;
+		default:
+			printf("\tint fd = ((void)prog_fd, 0); /* auto-attach not supported */\n");
+			break;
+		}
+		codegen("\
+			\n\
+										    \n\
+				if (fd > 0)					    \n\
+					skel->links.%1$s_fd = fd;		    \n\
+				return fd;					    \n\
+			}							    \n\
+			", bpf_program__name(prog));
+	}
+
+	codegen("\
+		\n\
+									    \n\
+		static inline int					    \n\
+		%1$s__attach(struct %1$s *skel)				    \n\
+		{							    \n\
+			int ret = 0;					    \n\
+									    \n\
+		", obj_name);
+
+	bpf_object__for_each_program(prog, obj) {
+		codegen("\
+			\n\
+				ret = ret < 0 ? ret : %1$s__%2$s__attach(skel);   \n\
+			", obj_name, bpf_program__name(prog));
+	}
+
+	codegen("\
+		\n\
+			return ret < 0 ? ret : 0;			    \n\
+		}							    \n\
+									    \n\
+		static inline void					    \n\
+		%1$s__detach(struct %1$s *skel)				    \n\
+		{							    \n\
+		", obj_name);
+
+	bpf_object__for_each_program(prog, obj) {
+		codegen("\
+			\n\
+				skel_closenz(skel->links.%1$s_fd);	    \n\
+			", bpf_program__name(prog));
+	}
+
+	codegen("\
+		\n\
+		}							    \n\
+		");
+}
+
+static void codegen_destroy(struct bpf_object *obj, const char *obj_name)
+{
+	struct bpf_program *prog;
+	struct bpf_map *map;
+
+	codegen("\
+		\n\
+		static void						    \n\
+		%1$s__destroy(struct %1$s *skel)			    \n\
+		{							    \n\
+			if (!skel)					    \n\
+				return;					    \n\
+			%1$s__detach(skel);				    \n\
+		",
+		obj_name);
+
+	bpf_object__for_each_program(prog, obj) {
+		codegen("\
+			\n\
+				skel_closenz(skel->progs.%1$s.prog_fd);	    \n\
+			", bpf_program__name(prog));
+	}
+
+	bpf_object__for_each_map(map, obj) {
+		const char * ident;
+
+		ident = get_map_ident(map);
+		if (!ident)
+			continue;
+		if (bpf_map__is_internal(map) &&
+		    (bpf_map__def(map)->map_flags & BPF_F_MMAPABLE))
+			printf("\tmunmap(skel->%1$s, %2$zd);\n",
+			       ident, bpf_map_mmap_sz(map));
+		codegen("\
+			\n\
+				skel_closenz(skel->maps.%1$s.map_fd);	    \n\
+			", ident);
+	}
+	codegen("\
+		\n\
+			free(skel);					    \n\
+		}							    \n\
+		",
+		obj_name);
+}
+
+static int gen_trace(struct bpf_object *obj, const char *obj_name, const char *header_guard)
+{
+	struct bpf_object_load_attr load_attr = {};
+	DECLARE_LIBBPF_OPTS(gen_loader_opts, opts);
+	struct bpf_map *map;
+	int err = 0;
+
+	err = bpf_object__gen_loader(obj, &opts);
+	if (err)
+		return err;
+
+	load_attr.obj = obj;
+	if (verifier_logs)
+		/* log_level1 + log_level2 + stats, but not stable UAPI */
+		load_attr.log_level = 1 + 2 + 4;
+
+	err = bpf_object__load_xattr(&load_attr);
+	if (err) {
+		p_err("failed to load object file");
+		goto out;
+	}
+	/* If there was no error during load then gen_loader_opts
+	 * are populated with the loader program.
+	 */
+
+	/* finish generating 'struct skel' */
+	codegen("\
+		\n\
+		};							    \n\
+		", obj_name);
+
+
+	codegen_attach_detach(obj, obj_name);
+
+	codegen_destroy(obj, obj_name);
+
+	codegen("\
+		\n\
+		static inline struct %1$s *				    \n\
+		%1$s__open(void)					    \n\
+		{							    \n\
+			struct %1$s *skel;				    \n\
+									    \n\
+			skel = calloc(sizeof(*skel), 1);		    \n\
+			if (!skel)					    \n\
+				goto cleanup;				    \n\
+			skel->ctx.sz = (void *)&skel->links - (void *)skel; \n\
+		",
+		obj_name, opts.data_sz);
+	bpf_object__for_each_map(map, obj) {
+		const char *ident;
+		const void *mmap_data = NULL;
+		size_t mmap_size = 0;
+
+		ident = get_map_ident(map);
+		if (!ident)
+			continue;
+
+		if (!bpf_map__is_internal(map) ||
+		    !(bpf_map__def(map)->map_flags & BPF_F_MMAPABLE))
+			continue;
+
+		codegen("\
+			\n\
+				skel->%1$s =					 \n\
+					mmap(NULL, %2$zd, PROT_READ | PROT_WRITE,\n\
+					     MAP_SHARED | MAP_ANONYMOUS, -1, 0); \n\
+				if (skel->%1$s == (void *) -1)			 \n\
+					goto cleanup;				 \n\
+				memcpy(skel->%1$s, (void *)\"\\			 \n\
+			", ident, bpf_map_mmap_sz(map));
+		mmap_data = bpf_map__initial_value(map, &mmap_size);
+		print_hex(mmap_data, mmap_size);
+		printf("\", %2$zd);\n"
+		       "\tskel->maps.%1$s.initial_value = (__u64)(long)skel->%1$s;\n",
+		       ident, mmap_size);
+	}
+	codegen("\
+		\n\
+			return skel;					    \n\
+		cleanup:						    \n\
+			%1$s__destroy(skel);				    \n\
+			return NULL;					    \n\
+		}							    \n\
+									    \n\
+		static inline int					    \n\
+		%1$s__load(struct %1$s *skel)				    \n\
+		{							    \n\
+			struct bpf_load_and_run_opts opts = {};		    \n\
+			int err;					    \n\
+									    \n\
+			opts.ctx = (struct bpf_loader_ctx *)skel;	    \n\
+			opts.data_sz = %2$d;				    \n\
+			opts.data = (void *)\"\\			    \n\
+		",
+		obj_name, opts.data_sz);
+	print_hex(opts.data, opts.data_sz);
+	codegen("\
+		\n\
+		\";							    \n\
+		");
+
+	codegen("\
+		\n\
+			opts.insns_sz = %d;				    \n\
+			opts.insns = (void *)\"\\			    \n\
+		",
+		opts.insns_sz);
+	print_hex(opts.insns, opts.insns_sz);
+	codegen("\
+		\n\
+		\";							    \n\
+			err = bpf_load_and_run(&opts);			    \n\
+			if (err < 0)					    \n\
+				return err;				    \n\
+		", obj_name);
+	bpf_object__for_each_map(map, obj) {
+		const char *ident, *mmap_flags;
+
+		ident = get_map_ident(map);
+		if (!ident)
+			continue;
+
+		if (!bpf_map__is_internal(map) ||
+		    !(bpf_map__def(map)->map_flags & BPF_F_MMAPABLE))
+			continue;
+		if (bpf_map__def(map)->map_flags & BPF_F_RDONLY_PROG)
+			mmap_flags = "PROT_READ";
+		else
+			mmap_flags = "PROT_READ | PROT_WRITE";
+
+		printf("\tskel->%1$s =\n"
+		       "\t\tmmap(skel->%1$s, %2$zd, %3$s, MAP_SHARED | MAP_FIXED,\n"
+		       "\t\t\tskel->maps.%1$s.map_fd, 0);\n",
+		       ident, bpf_map_mmap_sz(map), mmap_flags);
+	}
+	codegen("\
+		\n\
+			return 0;					    \n\
+		}							    \n\
+									    \n\
+		static inline struct %1$s *				    \n\
+		%1$s__open_and_load(void)				    \n\
+		{							    \n\
+			struct %1$s *skel;				    \n\
+									    \n\
+			skel = %1$s__open();				    \n\
+			if (!skel)					    \n\
+				return NULL;				    \n\
+			if (%1$s__load(skel)) {				    \n\
+				%1$s__destroy(skel);			    \n\
+				return NULL;				    \n\
+			}						    \n\
+			return skel;					    \n\
+		}							    \n\
+		", obj_name);
+
+	codegen("\
+		\n\
+									    \n\
+		#endif /* %s */						    \n\
+		",
+		header_guard);
+	err = 0;
+out:
+	return err;
+}
+
 static int do_skeleton(int argc, char **argv)
 {
 	char header_guard[MAX_OBJ_NAME_LEN + sizeof("__SKEL_H__")];
@@ -283,7 +605,7 @@ static int do_skeleton(int argc, char **argv)
 	struct bpf_object *obj = NULL;
 	const char *file, *ident;
 	struct bpf_program *prog;
-	int fd, len, err = -1;
+	int fd, err = -1;
 	struct bpf_map *map;
 	struct btf *btf;
 	struct stat st;
@@ -365,7 +687,25 @@ static int do_skeleton(int argc, char **argv)
 	}
 
 	get_header_guard(header_guard, obj_name);
-	codegen("\
+	if (use_loader) {
+		codegen("\
+		\n\
+		/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */   \n\
+		/* THIS FILE IS AUTOGENERATED! */			    \n\
+		#ifndef %2$s						    \n\
+		#define %2$s						    \n\
+									    \n\
+		#include <stdlib.h>					    \n\
+		#include <bpf/bpf.h>					    \n\
+		#include <bpf/skel_internal.h>				    \n\
+									    \n\
+		struct %1$s {						    \n\
+			struct bpf_loader_ctx ctx;			    \n\
+		",
+		obj_name, header_guard
+		);
+	} else {
+		codegen("\
 		\n\
 		/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */   \n\
 									    \n\
@@ -381,7 +721,8 @@ static int do_skeleton(int argc, char **argv)
 			struct bpf_object *obj;				    \n\
 		",
 		obj_name, header_guard
-	);
+		);
+	}
 
 	if (map_cnt) {
 		printf("\tstruct {\n");
@@ -389,7 +730,10 @@ static int do_skeleton(int argc, char **argv)
 			ident = get_map_ident(map);
 			if (!ident)
 				continue;
-			printf("\t\tstruct bpf_map *%s;\n", ident);
+			if (use_loader)
+				printf("\t\tstruct bpf_map_desc %s;\n", ident);
+			else
+				printf("\t\tstruct bpf_map *%s;\n", ident);
 		}
 		printf("\t} maps;\n");
 	}
@@ -397,14 +741,22 @@ static int do_skeleton(int argc, char **argv)
 	if (prog_cnt) {
 		printf("\tstruct {\n");
 		bpf_object__for_each_program(prog, obj) {
-			printf("\t\tstruct bpf_program *%s;\n",
-			       bpf_program__name(prog));
+			if (use_loader)
+				printf("\t\tstruct bpf_prog_desc %s;\n",
+				       bpf_program__name(prog));
+			else
+				printf("\t\tstruct bpf_program *%s;\n",
+				       bpf_program__name(prog));
 		}
 		printf("\t} progs;\n");
 		printf("\tstruct {\n");
 		bpf_object__for_each_program(prog, obj) {
-			printf("\t\tstruct bpf_link *%s;\n",
-			       bpf_program__name(prog));
+			if (use_loader)
+				printf("\t\tint %s_fd;\n",
+				       bpf_program__name(prog));
+			else
+				printf("\t\tstruct bpf_link *%s;\n",
+				       bpf_program__name(prog));
 		}
 		printf("\t} links;\n");
 	}
@@ -415,6 +767,10 @@ static int do_skeleton(int argc, char **argv)
 		if (err)
 			goto out;
 	}
+	if (use_loader) {
+		err = gen_trace(obj, obj_name, header_guard);
+		goto out;
+	}
 
 	codegen("\
 		\n\
@@ -584,19 +940,7 @@ static int do_skeleton(int argc, char **argv)
 		file_sz);
 
 	/* embed contents of BPF object file */
-	for (i = 0, len = 0; i < file_sz; i++) {
-		int w = obj_data[i] ? 4 : 2;
-
-		len += w;
-		if (len > 78) {
-			printf("\\\n");
-			len = w;
-		}
-		if (!obj_data[i])
-			printf("\\0");
-		else
-			printf("\\x%02x", (unsigned char)obj_data[i]);
-	}
+	print_hex(obj_data, file_sz);
 
 	codegen("\
 		\n\

tools/bpf/bpftool/main.c

@@ -29,6 +29,7 @@ bool show_pinned;
 bool block_mount;
 bool verifier_logs;
 bool relaxed_maps;
+bool use_loader;
 struct btf *base_btf;
 struct pinned_obj_table prog_table;
 struct pinned_obj_table map_table;
@@ -392,6 +393,7 @@ int main(int argc, char **argv)
 		{ "mapcompat",	no_argument,	NULL,	'm' },
 		{ "nomount",	no_argument,	NULL,	'n' },
 		{ "debug",	no_argument,	NULL,	'd' },
+		{ "use-loader",	no_argument,	NULL,	'L' },
 		{ "base-btf",	required_argument, NULL, 'B' },
 		{ 0 }
 	};
@@ -409,7 +411,7 @@ int main(int argc, char **argv)
 	hash_init(link_table.table);
 
 	opterr = 0;
-	while ((opt = getopt_long(argc, argv, "VhpjfmndB:",
+	while ((opt = getopt_long(argc, argv, "VhpjfLmndB:",
 				  options, NULL)) >= 0) {
 		switch (opt) {
 		case 'V':
@@ -452,6 +454,9 @@ int main(int argc, char **argv)
 				return -1;
 			}
 			break;
+		case 'L':
+			use_loader = true;
+			break;
 		default:
 			p_err("unrecognized option '%s'", argv[optind - 1]);
 			if (json_output)

tools/bpf/bpftool/main.h

@@ -90,6 +90,7 @@ extern bool show_pids;
 extern bool block_mount;
 extern bool verifier_logs;
 extern bool relaxed_maps;
+extern bool use_loader;
 extern struct btf *base_btf;
 extern struct pinned_obj_table prog_table;
 extern struct pinned_obj_table map_table;

tools/bpf/bpftool/prog.c

@@ -16,6 +16,7 @@
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <sys/syscall.h>
+#include <dirent.h>
 
 #include <linux/err.h>
 #include <linux/perf_event.h>
@@ -24,6 +25,8 @@
 #include <bpf/bpf.h>
 #include <bpf/btf.h>
 #include <bpf/libbpf.h>
+#include <bpf/bpf_gen_internal.h>
+#include <bpf/skel_internal.h>
 
 #include "cfg.h"
 #include "main.h"
@@ -1499,7 +1502,7 @@ static int load_with_options(int argc, char **argv, bool first_prog_only)
 	set_max_rlimit();
 
 	obj = bpf_object__open_file(file, &open_opts);
-	if (IS_ERR_OR_NULL(obj)) {
+	if (libbpf_get_error(obj)) {
 		p_err("failed to open object file");
 		goto err_free_reuse_maps;
 	}
@@ -1645,8 +1648,110 @@ err_free_reuse_maps:
 	return -1;
 }
 
+static int count_open_fds(void)
+{
+	DIR *dp = opendir("/proc/self/fd");
+	struct dirent *de;
+	int cnt = -3;
+
+	if (!dp)
+		return -1;
+
+	while ((de = readdir(dp)))
+		cnt++;
+
+	closedir(dp);
+	return cnt;
+}
+
+static int try_loader(struct gen_loader_opts *gen)
+{
+	struct bpf_load_and_run_opts opts = {};
+	struct bpf_loader_ctx *ctx;
+	int ctx_sz = sizeof(*ctx) + 64 * max(sizeof(struct bpf_map_desc),
+					     sizeof(struct bpf_prog_desc));
+	int log_buf_sz = (1u << 24) - 1;
+	int err, fds_before, fd_delta;
+	char *log_buf;
+
+	ctx = alloca(ctx_sz);
+	memset(ctx, 0, ctx_sz);
+	ctx->sz = ctx_sz;
+	ctx->log_level = 1;
+	ctx->log_size = log_buf_sz;
+	log_buf = malloc(log_buf_sz);
+	if (!log_buf)
+		return -ENOMEM;
+	ctx->log_buf = (long) log_buf;
+	opts.ctx = ctx;
+	opts.data = gen->data;
+	opts.data_sz = gen->data_sz;
+	opts.insns = gen->insns;
+	opts.insns_sz = gen->insns_sz;
+	fds_before = count_open_fds();
+	err = bpf_load_and_run(&opts);
+	fd_delta = count_open_fds() - fds_before;
+	if (err < 0) {
+		fprintf(stderr, "err %d\n%s\n%s", err, opts.errstr, log_buf);
+		if (fd_delta)
+			fprintf(stderr, "loader prog leaked %d FDs\n",
+				fd_delta);
+	}
+	free(log_buf);
+	return err;
+}
+
+static int do_loader(int argc, char **argv)
+{
+	DECLARE_LIBBPF_OPTS(bpf_object_open_opts, open_opts);
+	DECLARE_LIBBPF_OPTS(gen_loader_opts, gen);
+	struct bpf_object_load_attr load_attr = {};
+	struct bpf_object *obj;
+	const char *file;
+	int err = 0;
+
+	if (!REQ_ARGS(1))
+		return -1;
+	file = GET_ARG();
+
+	obj = bpf_object__open_file(file, &open_opts);
+	if (libbpf_get_error(obj)) {
+		p_err("failed to open object file");
+		goto err_close_obj;
+	}
+
+	err = bpf_object__gen_loader(obj, &gen);
+	if (err)
+		goto err_close_obj;
+
+	load_attr.obj = obj;
+	if (verifier_logs)
+		/* log_level1 + log_level2 + stats, but not stable UAPI */
+		load_attr.log_level = 1 + 2 + 4;
+
+	err = bpf_object__load_xattr(&load_attr);
+	if (err) {
+		p_err("failed to load object file");
+		goto err_close_obj;
+	}
+
+	if (verifier_logs) {
+		struct dump_data dd = {};
+
+		kernel_syms_load(&dd);
+		dump_xlated_plain(&dd, (void *)gen.insns, gen.insns_sz, false, false);
+		kernel_syms_destroy(&dd);
+	}
+	err = try_loader(&gen);
+err_close_obj:
+	bpf_object__close(obj);
+	return err;
+}
+
 static int do_load(int argc, char **argv)
 {
+	if (use_loader)
+		return do_loader(argc, argv);
 	return load_with_options(argc, argv, true);
 }
 

tools/bpf/bpftool/xlated_dumper.c

@@ -196,6 +196,9 @@ static const char *print_imm(void *private_data,
 	else if (insn->src_reg == BPF_PSEUDO_MAP_VALUE)
 		snprintf(dd->scratch_buff, sizeof(dd->scratch_buff),
 			 "map[id:%u][0]+%u", insn->imm, (insn + 1)->imm);
+	else if (insn->src_reg == BPF_PSEUDO_MAP_IDX_VALUE)
+		snprintf(dd->scratch_buff, sizeof(dd->scratch_buff),
+			 "map[idx:%u]+%u", insn->imm, (insn + 1)->imm);
 	else if (insn->src_reg == BPF_PSEUDO_FUNC)
 		snprintf(dd->scratch_buff, sizeof(dd->scratch_buff),
 			 "subprog[%+d]", insn->imm);