[Nix-dev] Inspecting getenv(3) calls

[Ludovic Courtès]

/* Display looked up environment variables.

   Compile as shown at the bottom of this file.

   Run with:

     $ LD_PRELOAD=./getenv.so some-program

   Written by Ludovic Court?s <ludo at gnu.org>.  Hereby placed under the
   LGPLv3+.
 */

#include <stdio.h>
#include <gnu/lib-names.h>
#include <dlfcn.h>

static void *glibc;
static char * (*glibc_getenv) (const char *);

static void load_glibc (void) __attribute__ ((__constructor__));

static void
load_glibc (void)
{
  glibc = dlopen (LIBC_SO, RTLD_LAZY);
  glibc_getenv = dlsym (glibc, "getenv");
}

char *
getenv (const char *name)
{
  char *result;

  result = glibc_getenv (name);

  printf ("getenv (\"%s\") = %s%s%s\n", name,
	  result ? "\"" : "",
	  result ? result : "NULL",
	  result ? "\"" : "");

  return result;
}

/*
   Local Variables:
   compile-command: "gcc -Wall -shared -fPIC -o getenv.so getenv.c"
   End:
 */
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