Re: [Qemu-devel] [PATCH] target-arm: Fix and improve AA32 singlestep translation completion code

[Sergey Fedorov <serge.fdrv@gmail.com>]

On 26.11.2015 15:33, Peter Maydell wrote:
> On 25 November 2015 at 18:02, Sergey Fedorov <serge.fdrv@gmail.com> wrote:
>> The AArch32 translation completion code for singlestep enabled/active
>> case was a way more confusing and too repetitive then it needs to be.
>> Probably that was the cause for a bug to be introduced into it at some
>> point. The bug was that SWI/HVC/SMC exception would be generated in
>> condition-failed instruction code path whereas it shouldn't.
> So I did some testing, and I think this is a bug that's not actually
> really visible to Linux guests. For both QEMU's gdbstub and for gdb
> running within a system emulation, gdb for 32-bit ARM will prefer to
> do singlestep via setting breakpoints rather than trying to use the
> gdbstub's singlestep command. So while we should definitely fix it
> (and the code cleanup is nice) I think we don't need to do this for 2.5,
> and I'm going to put this on my review-for-2.6 list. Do you agree?

Sure, that's okay. I just wanted to finish this before I move on to
something else.

BTW, I used the following quick-and-dirty Perl script to do testing (it
was helpful to detect some bugs in my first attempts):

#!/usr/bin/perl

use strict;
use warnings;

use IO::Socket::INET;

our $addr = 'localhost:1234';

sub recv_pack {
    my $sock = shift;
    my $c = $sock->getc() || die();
    if ($c eq '+') {
        return $c;
    }
    if ($c eq '-') {
        die;
    }
    if ($c eq '$') {
        my $packet = $c;
        while (($c = $sock->getc()) ne '#') {
            defined($c) || die();
            $packet .= $c;
        }
        $sock->getc();
        $sock->getc();
        $sock->print('+') || die();
        return $packet;
    }
    return "";
}

sub wait_ack {
    my $sock = shift;
    my $pack = recv_pack($sock);
    while ($pack ne "+") {
        $pack = recv_pack($sock);
    }
}

sub send_pack {
    my $sock = shift;
    my $packet = shift;
    my $sum = unpack("%8C*", $packet);
    $packet = '$' . $packet . '#' . sprintf("%hhx", $sum);
    $sock->print($packet) || die();
    wait_ack($sock);
}

our $sock = IO::Socket::INET->new($addr) || die();

our $quit = 0;

$SIG{INT} = sub { $quit = 1; };

my $nr_packets = 0;

while (!$quit) {
    send_pack($sock, 's');
    recv_pack($sock);
    printf("\r%d packets sent", ++$nr_packets);
    STDOUT->flush();
}

print("\n");

send_pack($sock, 'c');

Best regards,
Sergey