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Re: [RFC PATCH 08/10] arm64/sve: ptrace: Wire up vector length control and reporting
- From: Pedro Alves <palves at redhat dot com>
- To: Yao Qi <qiyaoltc at gmail dot com>, Dave Martin <Dave dot Martin at arm dot com>
- Cc: linux-arch at vger dot kernel dot org, Florian Weimer <fweimer at redhat dot com>, libc-alpha at sourceware dot org, Ard Biesheuvel <ard dot biesheuvel at linaro dot org>, Marc Zyngier <Marc dot Zyngier at arm dot com>, gdb at sourceware dot org, Joseph Myers <joseph at codesourcery dot com>, Szabolcs Nagy <szabolcs dot nagy at arm dot com>, linux-arm-kernel at lists dot infradead dot org, Alan Hayward <alan dot hayward at arm dot com>, Torvald Riegel <triegel at redhat dot com>, Christoffer Dall <christoffer dot dall at linaro dot org>
- Date: Mon, 16 Jan 2017 15:47:55 +0000
- Subject: Re: [RFC PATCH 08/10] arm64/sve: ptrace: Wire up vector length control and reporting
- Authentication-results: sourceware.org; auth=none
- References: <1484220369-23970-1-git-send-email-Dave.Martin@arm.com> <1484220369-23970-9-git-send-email-Dave.Martin@arm.com> <20170116122038.GG28060@E107787-LIN> <20170116133231.GO3699@e103592.cambridge.arm.com> <20170116151156.GI28060@E107787-LIN>
On 01/16/2017 03:11 PM, Yao Qi wrote:
>
>> >
>> > gdb must already re-detect the vector length on stop, since the target
>> > could have called the prctl() in the meantime.
> Yes, gdb assumes the vector length may be changed, so it re-detects on
> every stop, but I don't see the need for gdb to change the vector length.
>
Do we need to consider inferior function calls here?
Say the program is stopped in code that assumes "vector length N", and
the user does "print some_function_that_assumes_some_other_vector_length ()".
Is that a use case we need to cover?
If so, to make it work correctly, the debugger needs to be able to change the
vector length to the length assumed by that called function, and then
restore it back after the call completes (or is aborted).
I have no idea whether the debugger will be able to figure
out a function's assumed vector length from debug info or some such.
Thanks,
Pedro Alves