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From:   David Laight <David.Laight@ACULAB.COM>
To:     'Mark Rutland' <mark.rutland@arm.com>,
        "linux-arm-kernel@lists.infradead.org" 
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Subject: RE: [PATCH 0/8] arm64/ftrace: Add support for
 DYNAMIC_FTRACE_WITH_CALL_OPS
Thread-Topic: [PATCH 0/8] arm64/ftrace: Add support for
 DYNAMIC_FTRACE_WITH_CALL_OPS
Thread-Index: AQHZJDKgXMrizOIIlkyvOnatOuVuDa6XWT2g
Date:   Tue, 10 Jan 2023 08:55:58 +0000
Message-ID: <34e0144b19e149d99719a5ffc834f228@AcuMS.aculab.com>
References: <20230109135828.879136-1-mark.rutland@arm.com>
In-Reply-To: <20230109135828.879136-1-mark.rutland@arm.com>
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From: Mark Rutland
> Sent: 09 January 2023 13:58
> 
> This series adds a new DYNAMIC_FTRACE_WITH_CALL_OPS mechanism, and
> enables support for this on arm64. This significantly reduces the
> overhead of tracing when a callsite/tracee has a single associated
> tracer, avoids a number of issues that make it undesireably and
> infeasible to use dynamically-allocated trampolines (e.g. branch range
> limitations), and makes it possible to implement support for
> DYNAMIC_FTRACE_WITH_DIRECT_CALLS in future.
> 
> The main idea is to give each ftrace callsite an associated pointer to
> an ftrace_ops. The architecture's ftrace_caller trampoline can recover
> the ops pointer and invoke ops->func from this without needing to use
> ftrace_ops_list_func, which has to iterate through all registered ops.
> 
> To do this, we use -fpatchable-function-entry=M,N, there N NOPs are
> placed before the function entry point...

Doesn't this bump the minimum gcc version up to something like 9.0 ?

How does it interact with the 'CFI stuff' that also uses the same area?

	David

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