Re: Evolution

From: Herbert Kleebauer (klee_at_unibwm.de)
Date: 11/20/03 

Date: Thu, 20 Nov 2003 11:15:04 +0100

Randall Hyde wrote:

Many words, opinions but no facts (reminds me on Beth), so
nothing to answer. Just two remarks:

> Also, a construct like "**p=++i;" often gets
> replaced by something else when the programmer sees the number of
> instructions this code explodes into.

Using a 15 year old DOS C compiler (Turbo C 2.01)
without any optimization I get for "main(){**p=++i;}"

_main proc near
        inc word ptr DGROUP:_i
        mov ax,word ptr DGROUP:_i
        mov bx,word ptr DGROUP:_p
        mov bx,word ptr [bx]
        mov word ptr [bx],ax
@1:
        ret
_main endp

What's wrong with this code?

> > (it is great if you can
> > use hardware breakpoints by using the processor debug registers
> > in your debugger).
>
> ????
> Hardware breakpoints are available in debuggers under Windows

Then please tell me how (without modifying the task switch
routine in Windows or running the debugger with CPL=0).

>From MSDN:

Since the four debug registers are global to the system, they
should typically only be touched by a kernel mode debugger. See
Knowledge Base Article Q137199, " PRB: Debuggers Cannot
Use Debug Register Breakpoints" for more information.

See also the following MSDN Library CD article: Q105275,
"Using the 'BR' Command in WDEB386.EXE".

Relevant Pages

  • Re: GetThreadContext and debug register problem
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  • Re: Why do Intels processors provide four debug registers rather than only one?
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    (microsoft.public.development.device.drivers)
  • Re: Evolution
    ... > Hardware breakpoints are available in debuggers under Windows ... I said "use hardware breakpoints in your debugger" and not "use ... can use hardware breakpoints (I can use the debug registers only ...
    (alt.lang.asm)