perf annotate: Use libsubcmd's run-command.h to fork objdump

Reduce duplicated logic by using the subcmd library. Ensure when errors
occur they are reported to the caller. Before this patch, if no lines
are read the error status is 0.
Signed-off-by: NIan Rogers <irogers@google.com>
Tested-by: NArnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jin Yao <yao.jin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Song Liu <songliubraving@fb.com>
Cc: Stephane Eranian <eranian@google.com>
Cc: clang-built-linux@googlegroups.com
Link: http://lore.kernel.org/lkml/20191010183649.23768-3-irogers@google.com
Link: http://lore.kernel.org/lkml/20191015003418.62563-1-irogers@google.com
[ merged follow up fix for NULL termination as in the 2nd link above ]
Signed-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/annotate.c

@@ -43,6 +43,7 @@
 #include <linux/string.h>
 #include <bpf/libbpf.h>
 #include <subcmd/parse-options.h>
+#include <subcmd/run-command.h>
 
 /* FIXME: For the HE_COLORSET */
 #include "ui/browser.h"
@@ -1864,12 +1865,19 @@ static int symbol__disassemble(struct symbol *sym, struct annotate_args *args)
 	struct kcore_extract kce;
 	bool delete_extract = false;
 	bool decomp = false;
-	int stdout_fd[2];
 	int lineno = 0;
 	int nline;
-	pid_t pid;
 	char *line;
 	size_t line_len;
+	const char *objdump_argv[] = {
+		"/bin/sh",
+		"-c",
+		NULL, /* Will be the objdump command to run. */
+		"--",
+		NULL, /* Will be the symfs path. */
+		NULL,
+	};
+	struct child_process objdump_process;
 	int err = dso__disassemble_filename(dso, symfs_filename, sizeof(symfs_filename));
 
 	if (err)
@@ -1899,7 +1907,7 @@ static int symbol__disassemble(struct symbol *sym, struct annotate_args *args)
 
 		if (dso__decompress_kmodule_path(dso, symfs_filename,
 						 tmp, sizeof(tmp)) < 0)
-			goto out;
+			return -1;
 
 		decomp = true;
 		strcpy(symfs_filename, tmp);
@@ -1924,38 +1932,28 @@ static int symbol__disassemble(struct symbol *sym, struct annotate_args *args)
 
 	pr_debug("Executing: %s\n", command);
 
-	err = -1;
-	if (pipe(stdout_fd) < 0) {
-		pr_err("Failure creating the pipe to run %s\n", command);
-		goto out_free_command;
-	}
-
-	pid = fork();
-	if (pid < 0) {
-		pr_err("Failure forking to run %s\n", command);
-		goto out_close_stdout;
-	}
+	objdump_argv[2] = command;
+	objdump_argv[4] = symfs_filename;
 
-	if (pid == 0) {
-		close(stdout_fd[0]);
-		dup2(stdout_fd[1], 1);
-		close(stdout_fd[1]);
-		execl("/bin/sh", "sh", "-c", command, "--", symfs_filename,
-		      NULL);
-		perror(command);
-		exit(-1);
+	/* Create a pipe to read from for stdout */
+	memset(&objdump_process, 0, sizeof(objdump_process));
+	objdump_process.argv = objdump_argv;
+	objdump_process.out = -1;
+	if (start_command(&objdump_process)) {
+		pr_err("Failure starting to run %s\n", command);
+		err = -1;
+		goto out_free_command;
 	}
 
-	close(stdout_fd[1]);
-
-	file = fdopen(stdout_fd[0], "r");
+	file = fdopen(objdump_process.out, "r");
 	if (!file) {
 		pr_err("Failure creating FILE stream for %s\n", command);
 		/*
 		 * If we were using debug info should retry with
 		 * original binary.
 		 */
-		goto out_free_command;
+		err = -1;
+		goto out_close_stdout;
 	}
 
 	/* Storage for getline. */
@@ -1979,8 +1977,14 @@ static int symbol__disassemble(struct symbol *sym, struct annotate_args *args)
 	}
 	free(line);
 
-	if (nline == 0)
+	err = finish_command(&objdump_process);
+	if (err)
+		pr_err("Error running %s\n", command);
+
+	if (nline == 0) {
+		err = -1;
 		pr_err("No output from %s\n", command);
+	}
 
 	/*
 	 * kallsyms does not have symbol sizes so there may a nop at the end.
@@ -1990,23 +1994,21 @@ static int symbol__disassemble(struct symbol *sym, struct annotate_args *args)
 		delete_last_nop(sym);
 
 	fclose(file);
-	err = 0;
+
+out_close_stdout:
+	close(objdump_process.out);
+
 out_free_command:
 	free(command);
-out_remove_tmp:
-	close(stdout_fd[0]);
 
+out_remove_tmp:
 	if (decomp)
 		unlink(symfs_filename);
 
 	if (delete_extract)
 		kcore_extract__delete(&kce);
-out:
-	return err;
 
-out_close_stdout:
-	close(stdout_fd[1]);
-	goto out_free_command;
+	return err;
 }
 
 static void calc_percent(struct sym_hist *sym_hist,