linux-kernel - Re: rseq/arm32: choosing rseq code signature

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Message-ID: <87pnpsd91x.fsf@oldenburg2.str.redhat.com>
Date:   Thu, 11 Apr 2019 14:24:10 +0200
From:   Florian Weimer <fweimer@...hat.com>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     Will Deacon <will.deacon@....com>,
        libc-alpha <libc-alpha@...rceware.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Carlos O'Donell <carlos@...hat.com>
Subject: Re: rseq/arm32: choosing rseq code signature

* Mathieu Desnoyers:

> /*
>  * TODO: document trap instruction objdump output on each sub-architecture
>  * instruction sets, as well as instruction set extensions.
>  */
> #define RSEQ_SIG 0x########

Will RSEQ_SIG actually be needed at run time outside the rseq
implementation library (whether it's glibc or something else)?

Actually rseq users will emit the signature directly into the text
section, right?  They never have to load it into a register, I assume.

My concern is that on some architectures, the very act of referencing
RSEQ_SIG will put it into the text section, as a non-instruction, which
is not what we want.

Thanks,
Florian