musl - Data abort in __set_thread

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Message-ID: <trinity-7c4ee463-1932-4f52-ae7a-73091ec42133-1591299397810@3c-app-gmx-bap65>
Date: Thu, 4 Jun 2020 21:36:37 +0200
From: erny hombre <hombre67@....at>
To: musl@...ts.openwall.com
Subject: Data abort in __set_thread_area

Hello,

I am writing an operating system for an ARM processor (Cortex-A9). For the user programs I want to use musl libc. I have built a toolchain with musl-cross-make (musl 1.2.0). I can link a user program with libc.a. After loading the program, I call _start. Then I run into a data abort in function __set_thread_area (/musl-1.2.0/src/env/__libc_start_main.c) at this statement:
int ver = *(int *)0xffff0ffc;
The data abort is reasonable, because no memory is mapped at this virtual address. I don't know what's the purpose of this code. Can anybody explain me what this function does and which environment is needed to make it work ?

Thanks,
Erwin

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