linux-kernel - Re: [PATCH] kgdbts: unify/generalize gdb breakpoint adjustment

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Date:	Thu, 4 Jun 2009 21:50:49 -0400
From:	Mike Frysinger <vapier.adi@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	jason.wessel@...driver.com, kgdb-bugreport@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kgdbts: unify/generalize gdb breakpoint adjustment

On Thu, Jun 4, 2009 at 21:04, Andrew Morton wrote:
> On Thu, 4 Jun 2009 20:55:40 -0400 Mike Frysinger wrote:
>> On Thu, Jun 4, 2009 at 20:50, Andrew Morton wrote:
>> > On Tue, __2 Jun 2009 03:17:30 -0400 Mike Frysinger wrote:
>> >> + __ __ instruction_pointer(&kgdbts_regs) += offset;
>> >
>> > instruction_pointer() cannot be used as an lvalue, thankfully.
>> >
>> > x86_64:
>> >
>> > drivers/misc/kgdbts.c: In function 'check_and_rewind_pc':
>> > drivers/misc/kgdbts.c:306: error: invalid lvalue in assignment
>>
>> should be easy to fix:
>> --- a/arch/x86/include/asm/ptrace.h
>> +++ b/arch/x86/include/asm/ptrace.h
>> @@ -236,10 +236,7 @@
>>  #endif
>>  }
>>
>> -static inline unsigned long instruction_pointer(struct pt_regs *regs)
>> -{
>> -   return regs->ip;
>> -}
>> +#define instruction_pointer(regs) ((regs)->ip)
>>
>>  static inline unsigned long frame_pointer(struct pt_regs *regs)
>>  {
>
> argh, that's soooooo tasteless.  Look, this:
>
>        instruction_pointer(&kgdbts_regs) += offset;
>
> is just daft.  It's not C!

it is C.  taste is one thing, but valid C is still valid C.

> It makes no sense to define something which
> looks like a function and to then assign values to it.  It means that
> instruction_pointer() _must_ be implemented as a macro, violating basic
> concepts of encapsualtion/layering/hiding/etc.
>
> Doing
>
> void instruction_pointer_set(struct pt_regs *regs, some_suitable_type val);
>
> will save many vomit bags.

and force everyone to implement the same copy & paste set of get/set
modifiers ?  x86 is the only one where instruction_pointer() isnt a
define.
-mike
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