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SubjectRe: 2.5.4 Compile Error
Robert Love wrote:
> On Mon, 2002-02-11 at 01:02, John Weber wrote:
>
>
>>The function thread_saved_pc() is a mystery to me. It is declared with
>>a return type of unsigned long, and yet return this:
>>
>>((unsigned long *)tsk->thread->esp)[3]
>>
>>This is confusing to me in many ways:
>>- the "thread" member of task struct is not a pointer
>>- esp is of type unsigned long, so I don't understand the cast, and
>>I certainly don't understand the [3] here.
>>
>>Can anyone explain this code to me?
>>
>
> The problem is an interdependency between processor.h and sched.h.
>
> The old code was the same, except it did
>
> t->esp
>
> where t was a thread_struct, instead of what we do now
>
> t->thread->esp
>
> where t is a task_struct. And thus whereby before we passed
>
> p->thread
>

I understand all this, but thread is not a pointer.
So shouldn't it be t->thread.esp ?

> as the argument, now you pass just `p'. I.e., its the same net-affect.
> The error is because the function needs access to both task_struct (in
> sched.h) and thread_struct (in processor.h) but the two are interrelated
> so we can't include them in each other.

Hmm... OK.

> The contents of esp is a memory address, so typecasting it to (unsigned
> long *) is OK.
>
> As for the [3], p[3] is the same as
> *(p+3)
> ie,
> *(p+sizeof(p))
> so that is legal.

*(p + (3*sizeof(p))) ?

I understand the syntax, but I don't understand why one would want to
return the address of something 3 longs away. What is this function
supposed to be doing?



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