Date: Thu, 4 Jun 2020 15:52:51 -0400 From: Rich Felker <dalias@...c.org> To: erny hombre <hombre67@....at> Cc: musl@...ts.openwall.com Subject: Re: Data abort in __set_thread_area On Thu, Jun 04, 2020 at 09:36:37PM +0200, erny hombre wrote: > 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 ? You need to either provide compatible kuser_helper functions mapped at 0xffff0000, or ensure HWCAP_TLS is set in the aux vector's AT_HWCAP to indicate that the hardware thread pointer and atomics are available on the particular cpu model. Alternatively you can just ensure you build targeting armv7-a (to make this the toolchain default configure it --with-arch=armv7-a) so that this all gets hard-coded at compile time and there is no runtime selection of atomics/tls access method. Rich
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