LD_PRELOAD termite to support filesystem:https:// style URL patterns

termite-preload.c

// Add support for filesystem+https:// style URL
// url_regex.hh   scheme:// -> (scheme:)+//
// gcc preload.c -ldl -fPIC -shared -o preload.so
// LD_PRELOAD=./preload.so /usr/bin/termite

#ifndef _GNU_SOURCE
# define _GNU_SOURCE 1
#endif
#include <assert.h>
#include <dlfcn.h>
#include <stdio.h>
#include <string.h>
#include <sys/mman.h>

/*
http://permalink.gmane.org/gmane.comp.lib.glibc.alpha/61520

- Library initializers and finalizers (Run in dep order)
- Library constructors and destructors (Run in dep order)
- Prioritized constructors and destructors (Run in dep order, and # order)
- LD_PRELOAD initializer run last before the application is initialized.
- Non-zero initialized data from .data in the ELF image.

.init / .init_array sections in LD_PRELOAD shared objects are called after DT_NEEDED shared objects, thus we need to preload a function called by .init/.init_array sections in libvte.so

https://developer.gnome.org/gio/stable/GResource.html#g-static-resource-get-resource
*/
void g_static_resource_init(void* static_resource)
{
  static long initialized = 0;
  if (! initialized) {
    initialized = 1;

    size_t size = 0x200000;
    mprotect((void*)0x400000, size, PROT_READ | PROT_WRITE | PROT_EXEC);

    // scheme://  ->  (scheme:)+//   i.e. append a '+'
    const char orig[] = "(?:[[:alpha:]][+-.[:alnum:]]*:)";
    char *p = (char*)memmem((char*)0x400000, size, orig, strlen(orig));
    assert(p);
    p += strlen(orig);
    char *q = strchr(p, '\0');
    assert(q[1] == '\0');
    for (; p < q; q--)
      *q = q[-1];
    *p = '+';

    mprotect((void*)0x400000, size, PROT_READ | PROT_EXEC);
  }

  void (*real)(void*) = (void(*)(void*))dlsym(RTLD_NEXT, __func__);
  real(static_resource);
}