87 lines
2.1 KiB
C
87 lines
2.1 KiB
C
/* This file is part of the sample code and exercises
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* used by the class "Advanced Programming in the UNIX
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* Environment" taught by Jan Schaumann
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* <jschauma@netmeister.org> at Stevens Institute of
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* Technology.
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*
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* This file is in the public domain.
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*
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* You don't have to, but if you feel like
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* acknowledging where you got this code, you may
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* reference me by name, email address, or point
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* people to the course website:
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* https://stevens.netmeister.org/631/
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*/
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/* This program allows us to visualize the layout of a
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* process in memory, printing the addresses of
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* various parts of the program, including components
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* in the text, data, and bss segments as well as on
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* the heap and the stack.
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*
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* This program can also illustrate a stack overflow
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* if compiled with '-DSTACKOVERFLOW'.
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*/
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#include <err.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <unistd.h>
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extern char **environ;
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int
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arraySize(char **a) {
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int n = 0;
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char **tmp = a;
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while (*tmp++) {
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n++;
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}
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return n;
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}
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void
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printArray(char **a, char *name) {
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int n = arraySize(a);
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(void)printf("0x%12lX %-7s[%d]\n", (unsigned long)&a[n], name, n);
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(void)printf("0x%12lX %-7s[%d] (0x%12lX '%s')\n", (unsigned long)&a[n-1], name, n-1, (unsigned long)a[n-1], a[n-1]);
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(void)printf("0x%12lX %-7s[0] (0x%12lX '%s')\n", (unsigned long)&a[0], name, (unsigned long)a[0], a[0]);
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(void)printf("\n");
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}
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int
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main(int argc, char **argv, char **envp) {
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(void)argc;
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(void)argv;
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(void)printf("At program start:\n");
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printArray(envp, "envp");
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printArray(environ, "environ");
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if (setenv("FOO", "a longer value", 1) < 0) {
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err(EXIT_FAILURE, "unable to setenv(3)");
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/* NOTREACHED */
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}
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printf("After setenv(3):\n");
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printArray(envp, "envp");
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printArray(environ, "environ");
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if (putenv("BAR=another variable") < 0) {
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err(EXIT_FAILURE, "unable to putenv(3)");
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/* NOTREACHED */
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}
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printf("After putenv(3):\n");
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printArray(envp, "envp");
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printArray(environ, "environ");
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if (unsetenv("FOO") < 0) {
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err(EXIT_FAILURE, "unable to unsetenv(3)");
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/* NOTREACHED */
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}
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printf("After unsetenv(3):\n");
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printArray(envp, "envp");
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printArray(environ, "environ");
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return EXIT_SUCCESS;
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}
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