Minor fixes to 2001/anonymous/README.md

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Cody Boone Ferguson committed 2023-05-25 11:14:38 -07:00
1 parent cf44ff9c91
commit e268529397
1 file changed
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@@ -19,21 +19,21 @@ make
supplementary program and the program itself (both of which segfaulted and once
that was fixed only the binary was modified; it was not run but according to the
author's remarks it should be executed). He managed to do this with linux
but it will not work with macOS (see [bugs.md](/bugs.md) for why this is); this
is not a bug but a feature inherent in what it does.
but it will not work with macOS (see [bugs.md](/bugs.md) for why this is); _this
is not a bug, it's a feature_ inherent in what it does!
Although it took a fair bit of debugging it turns out all that had to change
was:
The following had to be done in order to get this to work:
- `#include <sys/mman.h>` for `mmap()` and `munmap()`.
- have `main()` call another function which is no longer a recursive function;
this prevented `main()` from entering an infinite recursive loop.
Without either of these it would crash and prevent modification of the 32-bit
[ELF](https://en.wikipedia.org/wiki/Executable_and_Linkable_Format) (not elf :-)
) binary. But again see [bugs.md](/bugs.md) here. The following change was also
made to be more portable, in case the constants `PROT_READ` and/or `PROT_WRITE`
are not standardised:
[ELF](https://en.wikipedia.org/wiki/Executable_and_Linkable_Format) (not elf :-) )
binary. But again see [bugs.md](/bugs.md) here.
The following change was also made to be more portable, in case the constants
`PROT_READ` and/or `PROT_WRITE` are not standardised:
Change `3` in the call to `mmap()` to be `PROT_READ|PROT_WRITE`: just in case
`PROT_READ|PROT_WRITE` does not equal 3 (though it seems to be equal in both
@@ -42,12 +42,13 @@ macOS and linux).
There was one other thing that had to be done though. Since the program used to
recursively call (infinite recursion, seemingly) `main()` and since that cannot
be done what had to be done instead is after the new function (`pain()` since it
was a pain to fix :-) ) returns to first call `munmap()` and `close()` (else
one would get text file busy error) and then the program can call `execv()` again like the
function `pain()` (was in `main()`) did but with a slight change. See commit
`2159caec4677e0f25ad704a74e04c8196fd6c343` for details. Notice that
the location of the calls to `munmap()` and `close()` followed by `execv()` do
matter!
was a pain to fix :-) ) returns to first call `munmap()` and `close()` (else one
would get text file busy error) and then the program can call `execv()` again
like the function `pain()` (was in `main()`) did but with a slight change. See
commit `2159caec4677e0f25ad704a74e04c8196fd6c343` for more details.
Notice that the location of the calls to `munmap()` and `close()` followed by
`execv()` _does matter_!
NOTE: there might be educational value to see the progress of this fix; if you
wish to see, try: