libtool-compatibility cmd.exe wrapper

cmd.c

// libtool-compatibility cmd.exe wrapper
// Converts libtool's Cygwin-style "cmd //c ..." to "cmd /c ..."
//   $ cc -nostartfiles -o cmd.exe cmd.c
// This is free and unencumbered software released into the public domain.

#define MAX_PATH 260
#define COUNTOF(a) (int)(sizeof(a) / sizeof(0[a]))
#define FATAL "cmd.exe (fake): CreateProcessW() failed\n"
#define CMDEXE "\\cmd.exe"

typedef unsigned short char16_t;

typedef struct {
  int cb;
  void *a, *b, *c;
  int d, e, f, g, h, i, j, k;
  short l, m;
  void *n, *o, *p, *q;
} StartupInfo;

typedef struct {
    void *process;
    void *thread;
    int pid;
    int tid;
} ProcessInformation;

int CreateProcessW(
    void *, void *, void *, void *, int, int, void *, void *, void *, void *
) __attribute((dllimport,stdcall));
char16_t *GetCommandLineW(void)
    __attribute((dllimport,stdcall));
int GetExitCodeProcess(void *, int *)
    __attribute((dllimport,stdcall));
void *GetStdHandle(int)
    __attribute((dllimport,stdcall));
int GetSystemDirectoryW(void *, int)
    __attribute((dllimport,stdcall));
int WaitForSingleObject(void *, int)
    __attribute((dllimport,stdcall));
int WriteFile(void *, void *, int, int *, void *)
    __attribute((dllimport,stdcall));

// Find the end of argv[0].
static char16_t *findargs(char16_t *s)
{
    if (s[0] == '"') {
        for (s++;; s++) {  // quoted argv[0]
            switch (*s) {
            case   0: return s;
            case '"': return s + 1;
            }
        }
    } else {
        for (;; s++) {  // unquoted argv[0]
            switch (*s) {
            case    0:
            case '\t':
            case  ' ': return s;
            }
        }
    }
}

static int space(char16_t c)
{
    return c==' ' || c=='\t';
}

static char16_t *skipspace(char16_t *s)
{
    for (;space(*s); s++) {}
    return s;
}

static int targetmatch(char16_t *s)
{
    return s[0]=='/' && s[1]=='/' && s[2]=='c' && (!s[3] || space(s[3]));
}

#if __i386
__attribute((force_align_arg_pointer))
#endif
__attribute((externally_visible))
int mainCRTStartup(void)
{
    // Locate the real cmd.exe
    char16_t cmdexe[MAX_PATH+COUNTOF(CMDEXE)];
    int len = GetSystemDirectoryW(cmdexe, MAX_PATH);
    for (int i = 0; i < COUNTOF(CMDEXE); i++) {
        cmdexe[len++] = CMDEXE[i];
    }

    // Chop argv[0] so that it's a harmless empty string, then stomp the
    // first '/' in "//c" into a space if present.
    char16_t *cmdline = findargs(GetCommandLineW());
    char16_t *argv1 = skipspace(cmdline);
    if (targetmatch(argv1)) {
        *argv1 = ' ';
    }

    StartupInfo si = {0};
    si.cb = sizeof(si);
    ProcessInformation pi;
    if (!CreateProcessW(cmdexe, cmdline, 0, 0, 1, 0, 0, 0, &si, &pi)) {
        int dummy;
        WriteFile(GetStdHandle(-12), FATAL, COUNTOF(FATAL)-1, &dummy, 0);
        return -1;
    }

    int ret;
    WaitForSingleObject(pi.process, -1);
    GetExitCodeProcess(pi.process, &ret);
    return ret;
}