linux-kernel - Re: [PATCH 2/5] ptrace: implement PTRACE

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Message-Id: <201106180959.38847.vda.linux@googlemail.com>
Date:	Sat, 18 Jun 2011 09:59:38 +0200
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	oleg@...hat.com, jan.kratochvil@...hat.com,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, indan@....nu, bdonlan@...il.com,
	pedro@...esourcery.com
Subject: Re: [PATCH 2/5] ptrace: implement PTRACE_SEIZE

On Saturday 18 June 2011 09:55, Denys Vlasenko wrote:
> On Tuesday 14 June 2011 11:20, Tejun Heo wrote:
>    #define PTRACE_EVENT_FORK    1
>    #define PTRACE_EVENT_VFORK   2
>    #define PTRACE_EVENT_CLONE   3
> >  #define PTRACE_EVENT_EXEC	4
> >  #define PTRACE_EVENT_VFORK_DONE	5
> >  #define PTRACE_EVENT_EXIT	6
> > +#define PTRACE_EVENT_STOP	7
> 
> Er... these constants were corresponding exactly to
> bit positions in ptrace options which enable them:
> 
> #define PTRACE_O_TRACESYSGOOD   0x00000001
> #define PTRACE_O_TRACEFORK      0x00000002
> #define PTRACE_O_TRACEVFORK     0x00000004
> #define PTRACE_O_TRACECLONE     0x00000008
> #define PTRACE_O_TRACEEXEC      0x00000010
> #define PTRACE_O_TRACEVFORKDONE 0x00000020
> #define PTRACE_O_TRACEEXIT      0x00000040
> 
> For example, PTRACE_O_TRACEEXEC is 4th bit, PTRACE_EVENT_EXEC is 4.
> 
> If we'd define PTRACE_EVENT_STOP as 7, any future added
> PTRACE_O_foo bit with value 0x00000080 will be unable
> to follow this convention.
> 
> I propose to define PTRACE_EVENT_STOP as 64 instead, leaving 64 low
> PTRACE_EVENT_foo constants for possible future PTRACE_O_foo bits.
> 
> [32 should be enough too, but I feel paranoid today :)]

...unless we plan to introduce PTRACE_O_TRACESTOP (with value 0x00000080)
which enables PTRACE_INTERRUPT and stop notifications independently
of PTRACE_SEIZE. Which would be very useful for e.g. strace.

Then, PTRACE_EVENT_STOP indeed should be 7.

-- 
vda

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