Reduce stack usage by ~0.5k

main() uses ~0.5k of stack for local variables and such. When we enter
main tracing loop, most of these variables are no longer used.
But they still take up stack for the entire life of strace.
We can avoid this wastage if we move init code into a separate function.
(Need to be careful and not allow automatic inlining).

* strace.c (init): New function. Most of pre-existing code of
main is now living here.
(main): Call init() to do initialization.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

diff --git a/strace.c b/strace.c
index 6196e67e02949830728f25072d9b8764d0883aac..a17adb394f5da887cfd2e1f24e47277118ab0135 100644 (file)
--- a/strace.c
+++ b/strace.c
@@ -1128,8 +1128,7 @@ test_ptrace_seize(void)
 #  define test_ptrace_seize() ((void)0)
 # endif
 
-/* Noinline: don't want main to have struct utsname permanently on stack */
-static void __attribute__ ((noinline))
+static void
 get_os_release(void)
 {
        struct utsname u;
@@ -1140,8 +1139,16 @@ get_os_release(void)
                die_out_of_memory();
 }
 
-int
-main(int argc, char *argv[])
+/*
+ * Initialization part of main() was eating much stack (~0.5k),
+ * which was unused after init.
+ * We can reuse it if we move init code into a separate function.
+ *
+ * Don't want main() to inline us and defeat the reason
+ * we have a separate function.
+ */
+static void __attribute__ ((noinline))
+init(int argc, char *argv[])
 {
        struct tcb *tcp;
        int c;
@@ -1426,26 +1433,6 @@ main(int argc, char *argv[])
         * -p PID1,PID2: yes (there are already more than one pid)
         */
        print_pid_pfx = (outfname && followfork < 2 && (followfork == 1 || nprocs > 1));
-
-       if (trace() < 0)
-               exit(1);
-
-       cleanup();
-       fflush(NULL);
-       if (exit_code > 0xff) {
-               /* Avoid potential core file clobbering.  */
-               struct rlimit rlim = {0, 0};
-               setrlimit(RLIMIT_CORE, &rlim);
-
-               /* Child was killed by a signal, mimic that.  */
-               exit_code &= 0xff;
-               signal(exit_code, SIG_DFL);
-               raise(exit_code);
-               /* Paranoia - what if this signal is not fatal?
-                  Exit with 128 + signo then.  */
-               exit_code += 128;
-       }
-       exit(exit_code);
 }
 
 static void
@@ -2132,3 +2119,31 @@ trace(void)
        }
        return 0;
 }
+
+int
+main(int argc, char *argv[])
+{
+       init(argc, argv);
+
+       /* Run main tracing loop */
+       if (trace() < 0)
+               return 1;
+
+       cleanup();
+       fflush(NULL);
+       if (exit_code > 0xff) {
+               /* Avoid potential core file clobbering.  */
+               struct rlimit rlim = {0, 0};
+               setrlimit(RLIMIT_CORE, &rlim);
+
+               /* Child was killed by a signal, mimic that.  */
+               exit_code &= 0xff;
+               signal(exit_code, SIG_DFL);
+               raise(exit_code);
+               /* Paranoia - what if this signal is not fatal?
+                  Exit with 128 + signo then.  */
+               exit_code += 128;
+       }
+
+       return exit_code;
+}