started implementing go64 [closes #12]

It can load elf files directly.

include/go64.h

@@ -0,0 +1,7 @@
+#ifndef GO64_H
+#define GO64_H
+
+void pltcall32(__dpmi_regs *regs, __dpmi_paddr addr);
+int elfexec(const char *path, int argc, char **argv);
+
+#endif

src/libc/compat/go64/elfexec.c

@@ -0,0 +1,103 @@
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <assert.h>
+#include <errno.h>
+#include <sys/segments.h>
+#include <io.h>
+#include <dpmi.h>
+#include <crt0.h>
+#include <go64.h>
+
+#ifndef PAGE_SIZE
+#define PAGE_SIZE 4096
+#endif
+#define _PAGE_MASK	(~(PAGE_SIZE-1))
+/* to align the pointer to the (next) page boundary */
+#define PAGE_ALIGN(addr)	(((addr)+PAGE_SIZE-1)&_PAGE_MASK)
+
+// https://github.com/vonj/snippets.org/blob/master/strrpbrk.c
+static char *strrpbrk(const char *szString, const char *szChars)
+{
+      const char  *p;
+      char        *p0, *p1;
+
+      for (p = szChars, p0 = p1 = NULL; p && *p; ++p)
+      {
+            p1 = strrchr(szString, *p);
+            if (p1 && p1 > p0)
+                  p0 = p1;
+      }
+      return p0;
+}
+
+int elfexec(const char *path, int argc, char **argv)
+{
+    int err, fd, len, errn;
+    const char *p;
+    unsigned fname;
+    __dpmi_paddr api;
+    __dpmi_shminfo shmi;
+    __dpmi_meminfo dm;
+    __dpmi_regs regs;
+    int en_dis = !(_crt0_startup_flags & _CRT0_FLAG_NEARPTR);
+
+    err = __dpmi_get_vendor_specific_api_entry_point("DJ64", &api);
+    if (err) {
+        fprintf(stderr, "DJ64 support missing\n");
+        return -1;
+    }
+    memset(&regs, 0, sizeof(regs));
+    regs.d.ebx = 3;  // get version
+    pltcall32(&regs, api);
+    if (regs.d.eax < 2) {
+        fprintf(stderr, "unsupported DJ64 version %i\n", regs.d.eax);
+        return -1;
+    }
+    fd = open(path, O_RDONLY | O_BINARY);
+    if (fd == -1) {
+        fprintf(stderr, "failed to open %s: %s\n", path, strerror(errno));
+        return -1;
+    }
+    len = filelength(fd);
+    p = strrpbrk(path, "/\\");
+    if (!p)
+        p = path;
+    fname = malloc32(strlen(p) + 1);
+    strcpy(DATA_PTR(fname), p);
+    shmi.size_requested = len;
+    shmi.name_offset = fname;
+    shmi.name_selector = _my_ds();
+    err = __dpmi_allocate_shared_memory(&shmi);
+    assert(!err);
+    free32(fname);
+    if (en_dis)
+        __djgpp_nearptr_enable();
+    err = read(fd, djaddr2ptr(shmi.address), len);
+    errn = errno;
+    if (en_dis)
+        __djgpp_nearptr_disable();
+    close(fd);
+    if (err == -1) {
+        fprintf(stderr, "error reading %s: %s\n", path, strerror(errn));
+        return -1;
+    }
+    if (err != len) {
+        fprintf(stderr, "read returned %i, need %i\n", err, len);
+        return -1;
+    }
+    dm.handle = shmi.handle;
+    dm.address = shmi.address;
+    dm.size = shmi.size;
+    err = __dpmi_free_physical_address_mapping(&dm);
+    assert(!err);
+    memset(&regs, 0, sizeof(regs));
+    regs.d.ebx = 2;  // exec
+    regs.x.di = shmi.handle & 0xffff;
+    regs.x.si = shmi.handle >> 16;
+    pltcall32(&regs, api);
+    __dpmi_free_shared_memory(shmi.handle);
+    return regs.d.eax;
+}

src/libc/compat/go64/makefile

@@ -0,0 +1,7 @@
+# Copyright (C) 1995 DJ Delorie, see COPYING.DJ for details
+TOP=../..
+
+AS_SRC += pltcall32.S
+SRC += elfexec.c
+
+include $(TOP)/../makefile.inc

src/libc/compat/go64/pltcall32.S

@@ -0,0 +1,20 @@
+#include <libc/asmdefs.h>
+
+	FUNC(_pltcall32)
+	ENTER
+	pushal
+	movl ARG1, %ebx
+.irpc i,76543210
+	pushl \i*4(%ebx)
+.endr
+	movl %ebp, 8(%esp)  // keep ebp untouched
+	popal
+	movl __plt_handle, %eax
+	lcalll *ARG2
+	pushal
+	movl ARG1, %ebx
+.irpc i,01234567
+	popl \i*4(%ebx)
+.endr
+	popal
+	LEAVE