tcc -run: support custom stdin with -rstdin FILE

When tcc -run is used with input file from stdin, then run_main's
stdin (which is tcc's stdin) is already EOF after we've read it.
If the program operates exclusively on stdin, then it cannot be used.

This commit adds an option -rstdin FILE which sets run_main's stdin.

Can also be used in such case to set run_main's stdin to the tty,
using -rstdin /dev/tty (posix) or -rstdin con (windows).

Author: avih

libtcc.c

@@ -1547,6 +1547,7 @@ enum {
     TCC_OPTION_rdynamic,
     TCC_OPTION_pthread,
     TCC_OPTION_run,
+    TCC_OPTION_rstdin,
     TCC_OPTION_w,
     TCC_OPTION_E,
     TCC_OPTION_M,
@@ -1637,6 +1638,7 @@ static const TCCOption tcc_options[] = {
     { "o", TCC_OPTION_o, TCC_OPTION_HAS_ARG },
     { "pthread", TCC_OPTION_pthread, 0},
     { "run", TCC_OPTION_run, TCC_OPTION_HAS_ARG | TCC_OPTION_NOSEP },
+    { "rstdin", TCC_OPTION_rstdin, TCC_OPTION_HAS_ARG },
     { "rdynamic", TCC_OPTION_rdynamic, 0 },
     { "r", TCC_OPTION_r, 0 },
     { "Wl,", TCC_OPTION_Wl, TCC_OPTION_HAS_ARG | TCC_OPTION_NOSEP },
@@ -2041,6 +2043,12 @@ PUB_FUNC int tcc_parse_args(TCCState *s, int *pargc, char ***pargv)
             goto set_output_type;
 #else
             return tcc_error_noabort("-run is not available in a cross compiler");
+#endif
+#ifdef TCC_IS_NATIVE
+        case TCC_OPTION_rstdin:
+            /* custom stdin for run_main */
+            s->run_stdin = optarg;
+            break;
 #endif
         case TCC_OPTION_v:
             do ++s->verbose; while (*optarg++ == 'v');

tcc.c

@@ -35,7 +35,7 @@ static const char help[] =
     "General options:\n"
     "  -c           compile only - generate an object file\n"
     "  -o outfile   set output filename\n"
-    "  -run         run compiled source\n"
+    "  -run         run compiled source [with custom stdin: -rstdin FILE]\n"
     "  -fflag       set or reset (with 'no-' prefix) 'flag' (see tcc -hh)\n"
     "  -Wwarning    set or reset (with 'no-' prefix) 'warning' (see tcc -hh)\n"
     "  -w           disable all warnings\n"

tcc.h

@@ -976,6 +976,7 @@ struct TCCState {
     const char *run_main; /* entry for tcc_run() */
     void *run_ptr; /* runtime_memory */
     unsigned run_size; /* size of runtime_memory  */
+    const char *run_stdin; /* custom stdin file for run_main */
 #ifdef _WIN64
     void *run_function_table; /* unwind data */
 #endif

tccrun.c

@@ -233,6 +233,17 @@ LIBTCCAPI int tcc_run(TCCState *s1, int argc, char **argv)
     prog_main = (void*)get_sym_addr(s1, s1->run_main, 1, 1);
     if ((addr_t)-1 == (addr_t)prog_main)
         return -1;
+
+    /* custom stdin for run_main, mainly if stdin is/was an input file.
+     * fileno(stdin) should remain 0, as posix mandates to use the smallest
+     * free fd, which is 0 after the initial fclose in freopen. windows too.
+     * to set stdin to the tty, use /dev/tty (posix) or con (windows).
+     */
+    if (s1->run_stdin && !freopen(s1->run_stdin, "r", stdin)) {
+        tcc_error_noabort("failed to reopen stdin from '%s'", s1->run_stdin);
+        return -1;
+    }
+
     errno = 0; /* clean errno value */
     fflush(stdout);
     fflush(stderr);