musl - magic constants in some startup code

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Date: Fri, 31 Oct 2014 09:31:37 -0400
From: Richard Gorton <rcgorton@...nitive-electronics.com>
To: musl@...ts.openwall.com
Subject: magic constants in some startup code

We're using musl for our processor architecture; as part of doing the bring-up work, I need to fully understand process launching and thread creation.

As I'm reading through the source code, I see (more than one) 'magic' constants that I do not fully understand (musl 1.1.5), and would like to know 'how and why':

src/env/__init_tls.c:
	static long long builtin_tls[(sizeof(struct pthread) + 64)/sizeof(long long)];

I'm guessing that 64 is an arbitrary 'small' default amount of TLS?  Or is this to hold another specific bit of data?

----

src/env/__stack_chk_fail.c
	else __stack_chk_guard = (uintptr_t)&__stack_chk_guard * 1103515245;

the number equates to 0x41c64e6d.
Called from __init_libc as:
	 __init_ssp((void *)aux[AT_RANDOM]); 
The kernel is putting a random number into aux[AT_RANDOM] at process initialization.
Why not just put a predictable arbitrary number into __stack_chk_guard?

Regards,
	Richard
	rcgorton@...-e.com

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