linux-kernel - Re: [PATCH] tracing/syscalls: ignore numbers outside NR

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Message-ID: <20141030113523.GQ27405@n2100.arm.linux.org.uk>
Date:	Thu, 30 Oct 2014 11:35:23 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Rabin Vincent <rabin@....in>,
	linux-arm-kernel@...ts.infradead.org,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tracing/syscalls: ignore numbers outside NR_syscalls'
 range

On Thu, Oct 30, 2014 at 07:30:28AM -0400, Steven Rostedt wrote:
> On Thu, 30 Oct 2014 11:14:41 +0000
> Russell King - ARM Linux <linux@....linux.org.uk> wrote:
> 
> 
> > We have always had syscall number range of 0x900000 or so.  The tracing
> > design does not expect that.  Therefore, the tracing design did not take
> > account of ARM when it was created.  Therefore, it's up to the tracing
> > people to decide how to properly fit their ill-designed subsystem into
> > one of the popular and well-established kernel architectures - or at
> > least suggest a way to work around this issue.
> > 
> 
> 
> Fine, lets define a MAX_SYSCALL_NR that is by default NR_syscalls, but
> an architecture can override it.
> 
> In trace_syscalls.c, where the checks are done, have this:
> 
> #ifndef MAX_SYSCALL_NR
> # define MAX_SYSCALL_NR NR_syscalls
> #endif
> 
> change all the checks to test against MAX_SYSCALL_NR instead of
> NR_syscalls.
> 
> Then in arch/arm/include/asm/syscall.h have:
> 
> #define MAX_SYSCALL_NR 0xa00000
> 
> or whatever would be the highest syscall number for ARM.

Or do we just ignore the high "special" ARM syscalls and treat them (from
the tracing point of view) as non-syscalls, avoiding the allocation of
something around 1.2MB for the syscall bitmap.  I really don't know, I
don't use any of this tracing stuff, so it isn't something I care about.

Maybe those who do use the facility should have an input here?

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