perf annotate: Split out read_symbol()

The Capstone disassembler code has a useful code snippet to read the
bytes for a given code symbol into memory. Split it out into its own
function, so that the LLVM disassembler can use it in the next patch.
Signed-off-by: Steinar H. Gunderson <sesse@google.com>
Cc: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20240803152008.2818485-2-sesse@google.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/disasm.c

@@ -1372,6 +1372,53 @@ static int find_file_offset(u64 start, u64 len, u64 pgoff, void *arg)
 	return 0;
 }
 
+static u8 *
+read_symbol(const char *filename, struct map *map, struct symbol *sym,
+	    u64 *len, bool *is_64bit)
+{
+	struct dso *dso = map__dso(map);
+	struct nscookie nsc;
+	u64 start = map__rip_2objdump(map, sym->start);
+	u64 end = map__rip_2objdump(map, sym->end);
+	int fd, count;
+	u8 *buf = NULL;
+	struct find_file_offset_data data = {
+		.ip = start,
+	};
+
+	*is_64bit = false;
+
+	nsinfo__mountns_enter(dso__nsinfo(dso), &nsc);
+	fd = open(filename, O_RDONLY);
+	nsinfo__mountns_exit(&nsc);
+	if (fd < 0)
+		return NULL;
+
+	if (file__read_maps(fd, /*exe=*/true, find_file_offset, &data,
+			    is_64bit) == 0)
+		goto err;
+
+	*len = end - start;
+	buf = malloc(*len);
+	if (buf == NULL)
+		goto err;
+
+	count = pread(fd, buf, *len, data.offset);
+	close(fd);
+	fd = -1;
+
+	if ((u64)count != *len)
+		goto err;
+
+	return buf;
+
+err:
+	if (fd >= 0)
+		close(fd);
+	free(buf);
+	return NULL;
+}
+
 static void print_capstone_detail(cs_insn *insn, char *buf, size_t len,
 				  struct annotate_args *args, u64 addr)
 {
@@ -1572,19 +1619,13 @@ static int symbol__disassemble_capstone(char *filename, struct symbol *sym,
 {
 	struct annotation *notes = symbol__annotation(sym);
 	struct map *map = args->ms.map;
-	struct dso *dso = map__dso(map);
-	struct nscookie nsc;
 	u64 start = map__rip_2objdump(map, sym->start);
-	u64 end = map__rip_2objdump(map, sym->end);
-	u64 len = end - start;
+	u64 len;
 	u64 offset;
-	int i, fd, count;
+	int i, count;
 	bool is_64bit = false;
 	bool needs_cs_close = false;
 	u8 *buf = NULL;
-	struct find_file_offset_data data = {
-		.ip = start,
-	};
 	csh handle;
 	cs_insn *insn;
 	char disasm_buf[512];
@@ -1593,31 +1634,9 @@ static int symbol__disassemble_capstone(char *filename, struct symbol *sym,
 	if (args->options->objdump_path)
 		return -1;
 
-	nsinfo__mountns_enter(dso__nsinfo(dso), &nsc);
-	fd = open(filename, O_RDONLY);
-	nsinfo__mountns_exit(&nsc);
-	if (fd < 0)
-		return -1;
-
-	if (file__read_maps(fd, /*exe=*/true, find_file_offset, &data,
-			    &is_64bit) == 0)
-		goto err;
-
-	if (open_capstone_handle(args, is_64bit, &handle) < 0)
-		goto err;
-
-	needs_cs_close = true;
-
-	buf = malloc(len);
+	buf = read_symbol(filename, map, sym, &len, &is_64bit);
 	if (buf == NULL)
-		goto err;
-
-	count = pread(fd, buf, len, data.offset);
-	close(fd);
-	fd = -1;
-
-	if ((u64)count != len)
-		goto err;
+		return -1;
 
 	/* add the function address and name */
 	scnprintf(disasm_buf, sizeof(disasm_buf), "%#"PRIx64" <%s>:",
@@ -1635,6 +1654,11 @@ static int symbol__disassemble_capstone(char *filename, struct symbol *sym,
 
 	annotation_line__add(&dl->al, &notes->src->source);
 
+	if (open_capstone_handle(args, is_64bit, &handle) < 0)
+		goto err;
+
+	needs_cs_close = true;
+
 	count = cs_disasm(handle, buf, len, start, len, &insn);
 	for (i = 0, offset = 0; i < count; i++) {
 		int printed;
@@ -1679,8 +1703,6 @@ static int symbol__disassemble_capstone(char *filename, struct symbol *sym,
 	return count < 0 ? count : 0;
 
 err:
-	if (fd >= 0)
-		close(fd);
 	if (needs_cs_close) {
 		struct disasm_line *tmp;