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From: olcott <polcott333@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: Memory protection between compilation units?
Date: Sat, 21 Jun 2025 15:49:10 -0500
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On 6/11/2025 8:32 AM, Mateusz Viste wrote:
> This might not be a strictly C question, but it definitely concerns all
> C programmers.
> 
> Earlier today, I fixed an out-of-bounds write bug. An obvious issue:
> 
>    static int *socks[0xffff];
> 
>    void update_my_socks(int *sock, int val) {
>      socks[val & 0xffff] = sock;
>    }
> 
> While the presented issue is common knowledge for anyone familiar with
> C, *locating* the bug was challenging. The program did not crash at the
> moment of the out-of-bounds write but much later - somewhere entirely
> different, in a different object file that maintained a static pointer
> for tracking a position in a linked list. To my surprise, the pointer
> was randomly reset to NULL about once a week, causing a segfault.
> Tracing this back to an unrelated out-of-bounds write elsewhere in the
> code was tedious, to say the least.
> 
> This raises a question: how can such corruptions be detected sooner?
> Protected mode prevents interference between programs but doesn’t
> safeguard a program from corrupting itself. Is there a way to enforce
> memory protection between module files of the same program? After all,
> static objects shouldn't be accessible outside their compilation unit.
> 
> How would you approach this?
> 
> Mateusz
> 

https://en.cppreference.com/w/c/types/integer.html
One way to fix the problem in the above specific
case is to define: void update_my_socks(int *sock, uint16_t val)


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Copyright 2025 Olcott "Talent hits a target no one else can hit; Genius
hits a target no one else can see." Arthur Schopenhauer