[Qemu-devel] Question about do_interrupt (target-i386/op_helper.c)

[Qemu-devel] Question about do_interrupt (target-i386/op_helper.c)

[陳韋任]

Hi all,

  I am looking at do_interrupt (target-i386/op_helper.c) and find something
strange. Code sinpt below,

void do_interrupt(CPUState *env1)
{
    CPUState *saved_env;

    saved_env = env;
    env = env1;

    ...
}

In i386-linux-user, cpu_exec (cpu-exec.c) calls do_interrupt like this,

  do_interrupt(env);

My questions are: 1) It seems to me the parameter of do_interrupt (envl) should
be the same as env inside do_interrupt (which comes from dyngen-exec.h's #define).
Why we need to assign envl to env here? Is it redundant, or I miss something? 2)
In target-i386/op_helper.c, some functions use the global env, while others use
function parameter env. Is it necessary? Or we can unify how they use env?

  Thanks.

Regards,
chenwj

-- 
Wei-Ren Chen (陳韋任)
Computer Systems Lab, Institute of Information Science,
Academia Sinica, Taiwan (R.O.C.)
Tel:886-2-2788-3799 #1667
Homepage: http://people.cs.nctu.edu.tw/~chenwj

Re: [Qemu-devel] Question about do_interrupt (target-i386/op_helper.c)

[Peter Maydell]

On 19 January 2012 08:24, 陳韋任 <chenwj@iis.sinica.edu.tw> wrote:
> My questions are: 1) It seems to me the parameter of do_interrupt (envl) should
> be the same as env inside do_interrupt (which comes from dyngen-exec.h's #define).

In cpu_exec() env is a local variable. In do_interrupt() it is the global
variable (held in a specific register via "asm(AREG0)"). The two aren't
necessarily the same value, hence the fiddling about.

> In target-i386/op_helper.c, some functions use the global env, while others use
> function parameter env. Is it necessary? Or we can unify how they use env?

There have been some recent patch series attempting to reduce the use of
global env, but it's not a trivial changeover.

-- PMM

Re: [Qemu-devel] Question about do_interrupt (target-i386/op_helper.c)

[陳韋任]

> In cpu_exec() env is a local variable. In do_interrupt() it is the global
> variable (held in a specific register via "asm(AREG0)"). The two aren't
> necessarily the same value, hence the fiddling about.

  Do you mean we sync env with envl at this point?

Regards,
chenwj

-- 
Wei-Ren Chen (陳韋任)
Computer Systems Lab, Institute of Information Science,
Academia Sinica, Taiwan (R.O.C.)
Tel:886-2-2788-3799 #1667
Homepage: http://people.cs.nctu.edu.tw/~chenwj