66 lines
1.9 KiB
C
66 lines
1.9 KiB
C
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/* 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 can be used to illustrates how the kernel sets up the
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* startup routine. Call with "-e" to specify any of the functions as the
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* entry point instead of 'main'; compare otool(1)/objdump(1) output and
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* exit codes.
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*
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* To display the entry point of the program:
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* NetBSD:
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* - readelf -h a.out | grep ntry
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* - objdump -d a.out
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*
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* Mac OS X:
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* - otool -l a.out | grep ntry # decimal address
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* - otool -v -t a.out # hex address
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <unistd.h>
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int
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bar(void) {
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printf("bar rules!\n");
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exit(EXIT_FAILURE);
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/* Unlike foo(), this will not cause a segfault, since we are not
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* returning; we explicitly call exit(3). */
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}
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int
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foo(void) {
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printf("Foo for the win!\n");
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return EXIT_FAILURE;
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/* Note: this will cause a segfault on NetBSD, because this function
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* returns, but there is nothing to return to: the routines set up
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* by the kernel remain set up for 'main', we just told the linker
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* to jump into 'foo' at program start. Compare objdump(1)
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* output.
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* Note: on OS X, we do not segfault! */
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}
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int
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main(int argc, char **argv) {
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(void)argc;
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(void)argv;
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printf("main is at 0x%lX\n", (unsigned long)&main);
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/* Note that we do explicitly _not_ return an error here, nor call
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* any of the exit(3) functions. Your compiler may warn you
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* about this. We're also not casting the return value of printf(3)
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* to void. Inspect the return value. */
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}
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