* Re: ptrace on i386
@ 2001-12-01 10:46 Manfred Spraul
0 siblings, 0 replies; 3+ messages in thread
From: Manfred Spraul @ 2001-12-01 10:46 UTC (permalink / raw)
To: Frank Cornelis; +Cc: linux-kernel
>
> In linux/arch/i386/kernel/ptrace.c next code is being used in the xxxreg
> functions:
> if (regno > GS*4)
> regno -= 2*4;
> Why this discontinuity?
Backward compatibility. The syscall entry point changed between 2.0 and 2.2, but
that change must remain invisible to user space apps. the "-= 2*4" converts old offsets
to new offsets (or the other way around)
--
Manfred
^ permalink raw reply [flat|nested] 3+ messages in thread* ptrace on i386
@ 2001-12-01 10:17 Frank Cornelis
2001-12-01 13:56 ` Brian Gerst
0 siblings, 1 reply; 3+ messages in thread
From: Frank Cornelis @ 2001-12-01 10:17 UTC (permalink / raw)
To: linux-kernel; +Cc: Frank.Cornelis
Hi,
In linux/arch/i386/kernel/ptrace.c next code is being used in the xxxreg
functions:
if (regno > GS*4)
regno -= 2*4;
Why this discontinuity? It doesn't prevent ORIG_EAX and EIP from being
written and makes the defines CS, EIF, ... from linux/include/asm/ptrace.h
useless. BTW: regno should really call reg_offset since it's no register
number but an offset.
Please CC me,
Frank.
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: ptrace on i386
2001-12-01 10:17 Frank Cornelis
@ 2001-12-01 13:56 ` Brian Gerst
0 siblings, 0 replies; 3+ messages in thread
From: Brian Gerst @ 2001-12-01 13:56 UTC (permalink / raw)
To: Frank Cornelis; +Cc: linux-kernel
Frank Cornelis wrote:
>
> Hi,
>
> In linux/arch/i386/kernel/ptrace.c next code is being used in the xxxreg
> functions:
> if (regno > GS*4)
> regno -= 2*4;
> Why this discontinuity? It doesn't prevent ORIG_EAX and EIP from being
> written and makes the defines CS, EIF, ... from linux/include/asm/ptrace.h
> useless. BTW: regno should really call reg_offset since it's no register
> number but an offset.
It's because the %fs and %gs segment registers are not saved on the
stack upon kernel entry anymore. Thus, the following values have to be
shifted by 2 positions to maintain compatability with the ptrace
register structure.
--
Brian Gerst
^ permalink raw reply [flat|nested] 3+ messages in thread
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2001-12-01 10:46 ptrace on i386 Manfred Spraul
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2001-12-01 10:17 Frank Cornelis
2001-12-01 13:56 ` Brian Gerst
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