skeetocrt example CRT

README.md

Example CRT

Grab a copy of w64devkit. Then in this repository:

$ make

Then add it to your $PATH. Then (anywhere) you can build the example:

$ skeeto-cc -o example.exe example.c
$ ./example world
Hello, world

To build the example program using this mini CRT which only has printf, fputc, and fflush.

crt0.c

#include <stdio.h>

typedef typeof(sizeof(0))   size_t;
typedef typeof(L'.')        wchar_t;

enum {
    CP_UTF8 = 65001,
};

#define W32(r) __declspec(dllimport) r __stdcall
W32(wchar_t **) CommandLineToArgvW(wchar_t *, int *);
W32(wchar_t *)  GetCommandLineW();
W32(void *)     GetProcessHeap();
W32(void *)     HeapAlloc(void *, int, size_t);
W32(int)        WideCharToMultiByte(int,int,wchar_t*,int,char*,int,void*,void*);

int main(int argc, char **argv);

void __main() {}

int __stdcall mainCRTStartup()
{
    wchar_t  *cmd   = GetCommandLineW();
    int       argc  = 0;
    wchar_t **wargv = CommandLineToArgvW(cmd, &argc);
    void     *heap  = GetProcessHeap();
    int       size  = sizeof(char*)*(argc + 1);
    char     **argv = HeapAlloc(heap, 0, size);
    for (int i = 0; i < argc; i++) {
        int len = WideCharToMultiByte(CP_UTF8, 0, wargv[i], -1, 0, 0, 0, 0);
        argv[i] = HeapAlloc(heap, 0, len);
        WideCharToMultiByte(CP_UTF8, 0, wargv[i], -1, argv[i], len, 0, 0);
    }
    argv[argc] = 0;

    int r = main(argc, argv);
    fflush(stdout);
    fflush(stderr);
    return r;
}

example.c

// $ skeeto-cc -o example.exe example.c
#include <stdio.h>

int main(int argc, char **argv)
{
    printf("Hello, %s\n", argv[argc-1]);
}

Makefile

ALL = skeetocrt.dll skeetocrt.dll.a crt0.o

all: $(ALL)

skeetocrt.dll skeetocrt.dll.a: skeetocrt.c stdio.h
	cc -shared -g3 -fno-builtin -nostartfiles --entry=0 \
	    -Wl,--out-implib=skeetocrt.dll.a -o skeetocrt.dll skeetocrt.c

crt0.o: crt0.c stdio.h
	cc -c -g3 -fno-builtin -nostdlib -nostdinc -isystem . -o crt0.o crt0.c 

clean:
	rm -f $(ALL)

skeeto-cc.sh

#!/bin/sh
SYSROOT=$(cd -- $(dirname -- $0) && pwd)
exec cc -nostdlib -nostdinc -isystem "$SYSROOT" -L"$SYSROOT" "$@" \
    "$SYSROOT"/crt0.o -lskeetocrt -lkernel32 -lshell32

skeetocrt.c

#include <limits.h>

#define W32(r) __declspec(dllimport) r __stdcall
W32(void *) GetStdHandle(int);
W32(int)    WriteFile(void *, void *, int, int *, void *);

typedef struct __FILE {
    int   fd;
    int   len;
    char *buf;
    char  mem[1<<12];
} FILE;

FILE *__getstd(int fd)
{
    static FILE std[3] = {
        {.fd=0, .buf=std[0].mem},
        {.fd=1, .buf=std[1].mem},
        {.fd=2, .buf=std[2].mem},
    };
    return fd>=0 && fd<=2 ? std+fd : 0;
}

int fflush(FILE *f)
{
    if (f->len) {
        void *h = GetStdHandle(-10u - f->fd);
        int r = -!WriteFile(h, f->buf, f->len, &(int){0}, 0);
        f->len = 0;
        return r;
    }
    return 0;
}

int fputc(int c, FILE *f)
{
    if (f->len == (int)sizeof(f->buf)) {
        if (fflush(f)) {
            return -1;
        }
    }
    f->buf[f->len++] = c;
    return 0;
}

int printf(char const *fmt, ...)
{
    __builtin_va_list ap;
    __builtin_va_start(ap, fmt);

    FILE *f   = __getstd(1);
    int   len = 0;
    for (;;) {
        switch (*fmt) {
        case 0:
            __builtin_va_end(ap);
            return len;
        case '%':
            fmt++;
            switch (*fmt) {
            case 0: return -1;
            case '%':
                    if (len==INT_MAX || fputc(*fmt++, f)) {
                        return -1;
                    }
                    len++;
                    break;
            case 's':
                    fmt++;
                    char *s = __builtin_va_arg(ap, char *);
                    for (; *s; s++) {
                        if (len==INT_MAX || fputc(*s, f)) {
                            return -1;
                        }
                        len++;
                    }
            }
            break;
        default:
            if (len==INT_MAX || fputc(*fmt++, f)) {
                return -1;
            }
            len++;
        }
    }
}

stdio.h

#pragma once

#define stdout (__getstd(1))
#define stderr (__getstd(2))

typedef struct __FILE FILE;
FILE *__getstd(int fd);
int printf(char const *, ...);
int fflush(FILE *);
int fputc(int , FILE *);