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Re: [RFC PATCH glibc 1/4] glibc: Perform rseq(2) registration at C startup and thread creation (v6)
- From: Mathieu Desnoyers <mathieu dot desnoyers at efficios dot com>
- To: Joseph Myers <joseph at codesourcery dot com>
- Cc: carlos <carlos at redhat dot com>, Florian Weimer <fweimer at redhat dot com>, Szabolcs Nagy <szabolcs dot nagy at arm dot com>, libc-alpha <libc-alpha at sourceware dot org>, Thomas Gleixner <tglx at linutronix dot de>, Ben Maurer <bmaurer at fb dot com>, Peter Zijlstra <peterz at infradead dot org>, "Paul E. McKenney" <paulmck at linux dot vnet dot ibm dot com>, Boqun Feng <boqun dot feng at gmail dot com>, Will Deacon <will dot deacon at arm dot com>, Dave Watson <davejwatson at fb dot com>, Paul Turner <pjt at google dot com>, Rich Felker <dalias at libc dot org>, linux-kernel <linux-kernel at vger dot kernel dot org>, linux-api <linux-api at vger dot kernel dot org>
- Date: Thu, 31 Jan 2019 11:37:08 -0500 (EST)
- Subject: Re: [RFC PATCH glibc 1/4] glibc: Perform rseq(2) registration at C startup and thread creation (v6)
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----- On Jan 30, 2019, at 4:10 PM, Joseph Myers joseph@codesourcery.com wrote:
> On Wed, 30 Jan 2019, Mathieu Desnoyers wrote:
>
>> #if defined (__NR_rseq) && !defined (RSEQ_SIG)
>> # error "UAPI headers support rseq system call, but glibc does not define
>> RSEQ_SIG."
>> #endif
>>
>> Would that take care of your concerns ?
>
> That would of course need appropriate conditionals based on the most
> recent kernel version for which a given glibc version has been updated, so
> that using new kernel headers with an existing glibc release does not make
> the build fail (cf. the test of syscall-names.list).
The test I hint at above would not be for the glibc build per se. It would
be for a check that glibc implements support for all the system calls
available in the kernel headers (if such a test target currently exists).
> And being able to
> write such a test only solves one half of the problem - it needs to be
> easy to determine what value to put in that header in glibc for an
> architecture that's newly gained support in the kernel, *without* needing
> any architecture expertise.
I'm afraid this requirement is incompatible with the nature of the RSEQ
signature. This signature may be required to be a specific trap instruction
by the architecture, so deciding on its value without architecture expertise
is not possible.
Thanks,
Mathieu
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com