tcc: Draft suppoprt for -MD/-MF options

In build systems, this is used to automatically collect target
dependencies, e.g.

    ---- 8< (hello.c) ----
    #include "hello.h"
    #include <stdio.h>

    int main()
    {
        printf("Hello World!\n");
        return 0;
    }

$ tcc -MD -c hello.c    # -> hello.o, hello.d
$ cat hello.d
hello.o : \
        hello.c \
        hello.h \
        /usr/include/stdio.h \
        /usr/include/features.h \
        /usr/include/bits/predefs.h \
        /usr/include/sys/cdefs.h \
        /usr/include/bits/wordsize.h \
        /usr/include/gnu/stubs.h \
        /usr/include/bits/wordsize.h \
        /usr/include/gnu/stubs-32.h \
        /home/kirr/local/tcc/lib/tcc/include/stddef.h \
        /usr/include/bits/types.h \
        /usr/include/bits/wordsize.h \
        /usr/include/bits/typesizes.h \
        /usr/include/libio.h \
        /usr/include/_G_config.h \
        /usr/include/wchar.h \
        /home/kirr/local/tcc/lib/tcc/include/stdarg.h \
        /usr/include/bits/stdio_lim.h \
        /usr/include/bits/sys_errlist.h \

NOTE: gcc supports -MD only for .c -> .o, but in tcc, we generate
dependencies for whatever action is being taken. E.g. for .c -> exe, the
result will be:

$ tcc -MD -o hello hello.c  # -> hello, hello.d
hello: \
        /usr/lib/crt1.o \
        /usr/lib/crti.o \
        hello.c \
        hello.h \
        /usr/include/stdio.h \
        /usr/include/features.h \
        /usr/include/bits/predefs.h \
        /usr/include/sys/cdefs.h \
        /usr/include/bits/wordsize.h \
        /usr/include/gnu/stubs.h \
        /usr/include/bits/wordsize.h \
        /usr/include/gnu/stubs-32.h \
        /home/kirr/local/tcc/lib/tcc/include/stddef.h \
        /usr/include/bits/types.h \
        /usr/include/bits/wordsize.h \
        /usr/include/bits/typesizes.h \
        /usr/include/libio.h \
        /usr/include/_G_config.h \
        /usr/include/wchar.h \
        /home/kirr/local/tcc/lib/tcc/include/stdarg.h \
        /usr/include/bits/stdio_lim.h \
        /usr/include/bits/sys_errlist.h \
        /usr/lib/libc.so \
        /lib/libc.so.6 \
        /usr/lib/ld-linux.so.2 \
        /lib/ld-linux.so.2 \
        /usr/lib/libc_nonshared.a \
        /lib/libc.so.6 \
        /usr/lib/libc_nonshared.a \
        /home/kirr/local/tcc/lib/tcc/libtcc1.a \
        /usr/lib/crtn.o \

So tcc dependency generator is a bit more clever than one used in gcc :)

Also, I've updated TODO and Changelog (in not-yet-released section).

v2:

(Taking inputs from grischka and me myself)

- put code to generate deps file into a function.
- used tcc_fileextension() instead of open-coding
- generate deps only when compilation/preprocessing was successful

v3:

- use pstrcpy instead of snprintf(buf, sizeof(buf), "%s", ...)

tcc.c

@@ -32,6 +32,8 @@ static int output_type;
 static int reloc_output;
 static const char *outfile;
 static int do_bench = 0;
+static int gen_deps;
+static const char *deps_outfile;
 
 #define TCC_OPTION_HAS_ARG 0x0001
 #define TCC_OPTION_NOSEP   0x0002 /* cannot have space before option and arg */
@@ -74,6 +76,9 @@ static void help(void)
 #ifdef CONFIG_TCC_BACKTRACE
            "  -bt N       show N callers in stack traces\n"
 #endif
+           "Misc options:\n"
+           "  -MD         generate target dependencies for make\n"
+           "  -MF depfile put generated dependencies here\n"
            );
 }
 
@@ -115,6 +120,8 @@ enum {
     TCC_OPTION_w,
     TCC_OPTION_pipe,
     TCC_OPTION_E,
+    TCC_OPTION_MD,
+    TCC_OPTION_MF,
     TCC_OPTION_x,
 };
 
@@ -154,6 +161,8 @@ static const TCCOption tcc_options[] = {
     { "w", TCC_OPTION_w, 0 },
     { "pipe", TCC_OPTION_pipe, 0},
     { "E", TCC_OPTION_E, 0},
+    { "MD", TCC_OPTION_MD, 0},
+    { "MF", TCC_OPTION_MF, TCC_OPTION_HAS_ARG },
     { "x", TCC_OPTION_x, TCC_OPTION_HAS_ARG },
     { NULL },
 };
@@ -374,6 +383,12 @@ static int parse_args(TCCState *s, int argc, char **argv)
             case TCC_OPTION_E:
                 output_type = TCC_OUTPUT_PREPROCESS;
                 break;
+            case TCC_OPTION_MD:
+                gen_deps = 1;
+                break;
+            case TCC_OPTION_MF:
+                deps_outfile = optarg;
+                break;
             case TCC_OPTION_x:
                 break;
             default:
@@ -479,14 +494,20 @@ int main(int argc, char **argv)
         if (do_bench)
             tcc_print_stats(s, getclock_us() - start_time);
 
-        if (s->output_type == TCC_OUTPUT_PREPROCESS) {
-            if (outfile)
-                fclose(s->outfile);
-        } else if (s->output_type == TCC_OUTPUT_MEMORY)
+        if (s->output_type == TCC_OUTPUT_MEMORY)
             ret = tcc_run(s, argc - optind, argv + optind);
         else {
-            ret = tcc_output_file(s, outfile ? outfile : tcc_default_target(s));
-            ret = ret ? 1 : 0;
+            if (s->output_type == TCC_OUTPUT_PREPROCESS) {
+                if (outfile)
+                    fclose(s->outfile);
+            } else {
+                ret = tcc_output_file(s, outfile ? outfile : tcc_default_target(s));
+                ret = ret ? 1 : 0;
+            }
+
+            /* dump collected dependencies */
+            if (gen_deps && !ret)
+                tcc_gen_makedeps(s, outfile, deps_outfile);
         }
     }