bpftool: Refactor disassembler for JIT-ed programs

Refactor disasm_print_insn() to extract the code specific to libbfd and
move it to dedicated functions. There is no functional change. This is
in preparation for supporting an alternative library for disassembling
the instructions.

Signed-off-by: Quentin Monnet <quentin@isovalent.com>
Tested-by: Niklas Söderlund <niklas.soderlund@corigine.com>
Acked-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20221025150329.97371-6-quentin@isovalent.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

src/jit_disasm.c

@@ -30,6 +30,14 @@
 #include "json_writer.h"
 #include "main.h"
 
+static int oper_count;
+
+typedef struct {
+	struct disassemble_info *info;
+	disassembler_ftype disassemble;
+	bfd *bfdf;
+} disasm_ctx_t;
+
 static int get_exec_path(char *tpath, size_t size)
 {
 	const char *path = "/proc/self/exe";
@@ -44,7 +52,6 @@ static int get_exec_path(char *tpath, size_t size)
 	return 0;
 }
 
-static int oper_count;
 static int printf_json(void *out, const char *fmt, va_list ap)
 {
 	char *s;
@@ -102,46 +109,44 @@ static int fprintf_json_styled(void *out,
 	return r;
 }
 
-int disasm_print_insn(unsigned char *image, ssize_t len, int opcodes,
-		      const char *arch, const char *disassembler_options,
-		      const struct btf *btf,
-		      const struct bpf_prog_linfo *prog_linfo,
-		      __u64 func_ksym, unsigned int func_idx,
-		      bool linum)
+static int init_context(disasm_ctx_t *ctx, const char *arch,
+			const char *disassembler_options,
+			unsigned char *image, ssize_t len)
 {
-	const struct bpf_line_info *linfo = NULL;
-	disassembler_ftype disassemble;
-	int count, i, pc = 0, err = -1;
-	struct disassemble_info info;
-	unsigned int nr_skip = 0;
+	struct disassemble_info *info;
 	char tpath[PATH_MAX];
 	bfd *bfdf;
 
-	if (!len)
-		return -1;
-
 	memset(tpath, 0, sizeof(tpath));
 	if (get_exec_path(tpath, sizeof(tpath))) {
 		p_err("failed to create disasembler (get_exec_path)");
 		return -1;
 	}
 
-	bfdf = bfd_openr(tpath, NULL);
-	if (!bfdf) {
+	ctx->bfdf = bfd_openr(tpath, NULL);
+	if (!ctx->bfdf) {
 		p_err("failed to create disassembler (bfd_openr)");
 		return -1;
 	}
-	if (!bfd_check_format(bfdf, bfd_object)) {
+	if (!bfd_check_format(ctx->bfdf, bfd_object)) {
 		p_err("failed to create disassembler (bfd_check_format)");
-		goto exit_close;
+		goto err_close;
 	}
+	bfdf = ctx->bfdf;
+
+	ctx->info = malloc(sizeof(struct disassemble_info));
+	if (!ctx->info) {
+		p_err("mem alloc failed");
+		goto err_close;
+	}
+	info = ctx->info;
 
 	if (json_output)
-		init_disassemble_info_compat(&info, stdout,
+		init_disassemble_info_compat(info, stdout,
 					     (fprintf_ftype) fprintf_json,
 					     fprintf_json_styled);
 	else
-		init_disassemble_info_compat(&info, stdout,
+		init_disassemble_info_compat(info, stdout,
 					     (fprintf_ftype) fprintf,
 					     fprintf_styled);
 
@@ -153,31 +158,76 @@ int disasm_print_insn(unsigned char *image, ssize_t len, int opcodes,
 			bfdf->arch_info = inf;
 		} else {
 			p_err("No libbfd support for %s", arch);
-			goto exit_close;
+			goto err_free;
 		}
 	}
 
-	info.arch = bfd_get_arch(bfdf);
-	info.mach = bfd_get_mach(bfdf);
+	info->arch = bfd_get_arch(bfdf);
+	info->mach = bfd_get_mach(bfdf);
 	if (disassembler_options)
-		info.disassembler_options = disassembler_options;
-	info.buffer = image;
-	info.buffer_length = len;
+		info->disassembler_options = disassembler_options;
+	info->buffer = image;
+	info->buffer_length = len;
 
-	disassemble_init_for_target(&info);
+	disassemble_init_for_target(info);
 
 #ifdef DISASM_FOUR_ARGS_SIGNATURE
-	disassemble = disassembler(info.arch,
-				   bfd_big_endian(bfdf),
-				   info.mach,
-				   bfdf);
+	ctx->disassemble = disassembler(info->arch,
+					bfd_big_endian(bfdf),
+					info->mach,
+					bfdf);
 #else
-	disassemble = disassembler(bfdf);
+	ctx->disassemble = disassembler(bfdf);
 #endif
-	if (!disassemble) {
+	if (!ctx->disassemble) {
 		p_err("failed to create disassembler");
-		goto exit_close;
+		goto err_free;
 	}
+	return 0;
+
+err_free:
+	free(info);
+err_close:
+	bfd_close(ctx->bfdf);
+	return -1;
+}
+
+static void destroy_context(disasm_ctx_t *ctx)
+{
+	free(ctx->info);
+	bfd_close(ctx->bfdf);
+}
+
+static int
+disassemble_insn(disasm_ctx_t *ctx, __maybe_unused unsigned char *image,
+		 __maybe_unused ssize_t len, int pc)
+{
+	return ctx->disassemble(pc, ctx->info);
+}
+
+int disasm_init(void)
+{
+	bfd_init();
+	return 0;
+}
+
+int disasm_print_insn(unsigned char *image, ssize_t len, int opcodes,
+		      const char *arch, const char *disassembler_options,
+		      const struct btf *btf,
+		      const struct bpf_prog_linfo *prog_linfo,
+		      __u64 func_ksym, unsigned int func_idx,
+		      bool linum)
+{
+	const struct bpf_line_info *linfo = NULL;
+	unsigned int nr_skip = 0;
+	int count, i, pc = 0;
+	disasm_ctx_t ctx;
+
+	if (!len)
+		return -1;
+
+	if (init_context(&ctx, arch, disassembler_options, image, len))
+		return -1;
 
 	if (json_output)
 		jsonw_start_array(json_wtr);
@@ -205,7 +255,8 @@ int disasm_print_insn(unsigned char *image, ssize_t len, int opcodes,
 			printf("%4x:\t", pc);
 		}
 
-		count = disassemble(pc, &info);
+		count = disassemble_insn(&ctx, image, len, pc);
+
 		if (json_output) {
 			/* Operand array, was started in fprintf_json. Before
 			 * that, make sure we have a _null_ value if no operand
@@ -241,15 +292,7 @@ int disasm_print_insn(unsigned char *image, ssize_t len, int opcodes,
 	if (json_output)
 		jsonw_end_array(json_wtr);
 
-	err = 0;
-
-exit_close:
-	bfd_close(bfdf);
-	return err;
-}
+	destroy_context(&ctx);
 
-int disasm_init(void)
-{
-	bfd_init();
 	return 0;
 }