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Re: How are watchpoints handled? (remote serial)

From: Juha Aaltonen <turbopultti at gmail dot com>
To: gdb-mailing list <gdb at sourceware dot org>
Date: Wed, 11 Nov 2015 01:39:53 +0200
Subject: Re: How are watchpoints handled? (remote serial)
Authentication-results: sourceware.org; auth=none
References: <CAHR0xd6NgsRELcdpbmVjGGQusv756kWMwj5G+NpWE_oN1ErBHA at mail dot gmail dot com> <CAHR0xd6ewc1mQPa=si85=acf3Miuw5Yg6H3tPgKRXNb=1xSZDQ at mail dot gmail dot com>

With single-step the same thing - installs both watchpoint and breakpoint.

w \x00]0x00008180 in __delay_169 () at ../blinky.c:211
211                g_testloc = 1;
(gdb) stepi
Sending packet:
$m81b0,4#c8...[\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][
r +]Ack
[$][0][0][0][0][0][0][0][0][#][8][0]Packet received: 00000000
[
w \x00]Sending packet:
$Z2,81b0,4#13...[\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][
r +]Ack
[$][O][K][#][9][a]Packet received: OK
[
w \x00]Sending packet: $p19#da...[\x00][\x00][\x00][\x00][\x00][\x00][\x00][
r +]Ack
[$][9][7][0][1][0][0][6][0][#][9][7]Packet received: 97010060
[
w \x00]Sending packet:
$m8180,4#9e...[\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][
r +]Ack
[$][0][0][3][0][8][7][e][5][#][c][c]Packet received: 003087e5
[
w \x00]Sending packet:
$m8180,4#9e...[\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][
r +]Ack
[$][0][0][3][0][8][7][e][5][#][c][c]Packet received: 003087e5
[
w \x00]Sending packet:
$Z0,8184,4#eb...[\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][
r +]Ack
[$][O][K][#][9][a]Packet received: OK
[
w \x00]Sending packet: $c#63...[\x00][\x00][\x00][\x00][\x00][
r +]Ack
[$][T][0][5][#][b][9]Packet received: T05
[
w \x00]Sending packet: $g#67...[\x00][\x00][\x00][\x00][\x00][
r +]Ack
[$][8][8][1][3][0][0][0][0][2][c][0][1][0][0][0][0][8][8][1][3][0][0][0][0][0][1][0][0][0][0][0][0][0][a][0][0][0][0][0][0][0][3][0][0][0][0][0][0][e][8][0][3][0][0][0][0][b][0][8][1][0][0][0][0][2][c][0][a][0][2][1][f][2][3][0][0][0][0][0][0][2][8][0][a][0][2][1][f][2][4][0][a][0][2][1][f][3][3][0][c][0][1][1][f][a][0][9][7][0][0][0][0][8][0][8][1][0][0][0][0][8][0][8][1][0][0][0][0][0][9][0][0][0][0][9][0][0][9][0][0][0][0][9][0][0][9][0][0][0][0][9][0][0][9][0][0][0][0][9][0][0][9][0][0][0][0][9][0][0][9][0][0][0][0][9][0][0][9][0][0][0][0][9][0][0][9][0][0][0][0][9][0][0][9][0][0][0][0][9][0][9][7][0][1][0][0][6][0][#][2][3]Packet
received: 881300002c01000088130000010000000a00000003000000e8030000b08100002c0a021f23000000280a021f240a021f330c011fa0970000808100008081000009000090090000900900009009000090090000900900009009000090090000900900009097010060
[
w \x00]Sending packet:
$m8180,4#9e...[\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][
r +]Ack
[$][0][0][3][0][8][7][e][5][#][c][c]Packet received: 003087e5

... (lots of memory reads) ...

[
w \x00]Sending packet:
$m8180,4#9e...[\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][
r +]Ack
[$][0][0][3][0][8][7][e][5][#][c][c]Packet received: 003087e5
[
w \x00]Sending packet:
$z0,8184,4#0b...[\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][
r +]Ack
[$][O][K][#][9][a]Packet received: OK
[
w \x00]Sending packet:
$z2,81b0,4#33...[\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][
r +]Ack
[$][O][K][#][9][a]Packet received: OK
[
w \x00]0x00008180    211                g_testloc = 1;
(gdb)



The g_testloc never gets set to 1.

On Wed, Nov 11, 2015 at 1:26 AM, Juha Aaltonen <turbopultti@gmail.com> wrote:
> Maybe that's a bug in gdb-multiarch 7.7.1?
> Remote-debugging an ARM (watch g_testloc):
>
> (This is as it should be.)
> gdbarch_dump: have_nonsteppable_watchpoint = 1
>
>
> w \x00]0x00008180 in __delay_169 () at ../blinky.c:211
> 211                g_testloc = 1;
> (gdb) cont
> Continuing.
> Sending packet:
> $m81b0,4#c8...[\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][
> r +]Ack
> [$][0][0][0][0][0][0][0][0][#][8][0]Packet received: 00000000
> [
> w \x00]Sending packet:
> $Z2,81b0,4#13...[\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][
> r +]Ack
> [$][O][K][#][9][a]Packet received: OK
> [
> w \x00]Sending packet: $c#63...[\x00][\x00][\x00][\x00][\x00][
> r +]Ack
> [$][T][0][5][#][b][9]Packet received: T05
> [
> w \x00]Sending packet: $g#67...[\x00][\x00][\x00][\x00][\x00][
> r +]Ack
> [$][8][8][1][3][0][0][0][0][2][c][0][1][0][0][0][0][8][8][1][3][0][0][0][0][0][1][0][0][0][0][0][0][0][a][0][0][0][0][0][0][0][3][0][0][0][0][0][0][e][8][0][3][0][0][0][0][b][0][8][1][0][0][0][0][2][c][0][a][0][2][1][f][2][3][0][0][0][0][0][0][2][8][0][a][0][2][1][f][2][4][0][a][0][2][1][f][4][3][0][c][0][1][1][f][a][0][9][7][0][0][0][0][8][0][8][1][0][0][0][0][8][0][8][1][0][0][0][0][0][9][0][0][0][0][9][0][0][9][0][0][0][0][9][0][0][9][0][0][0][0][9][0][0][9][0][0][0][0][9][0][0][9][0][0][0][0][9][0][0][9][0][0][0][0][9][0][0][9][0][0][0][0][9][0][0][9][0][0][0][0][9][0][0][9][0][0][0][0][9][0][9][7][0][1][0][0][6][0][#][2][4]Packet
> received: 881300002c01000088130000010000000a00000003000000e8030000b08100002c0a021f23000000280a021f240a021f430c011fa0970000808100008081000009000090090000900900009009000090090000900900009009000090090000900900009097010060
> [
> w \x00]Sending packet:
> $m8180,4#9e...[\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][
> r +]Ack
> [$][0][0][3][0][8][7][e][5][#][c][c]Packet received: 003087e5
> [
> ... (lots of memory reads) ...
> [
> w \x00]Sending packet:
> $m8180,4#9e...[\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][
> r +]Ack
> [$][0][0][3][0][8][7][e][5][#][c][c]Packet received: 003087e5
> [
> w \x00]
> Program received signal SIGTRAP, Trace/breakpoint trap.
> Sending packet:
> $z2,81b0,4#33...[\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][\x00][
> r +]Ack
> [$][O][K][#][9][a]Packet received: OK
> [
> w \x00]0x00008180 in __delay_169 () at ../blinky.c:211
> 211                g_testloc = 1;
> (gdb)
>
>
> No stepping over watchpoint.
>
>
> On Tue, Nov 10, 2015 at 12:57 AM, Juha Aaltonen <turbopultti@gmail.com> wrote:
>> How should the watchpoints be handled by remote stub/server?
>> It seems that when 'cont'-command is given, gdb re-installs watchpoint
>> and sends 'c'-packet.
>>
>> If the return address is the trap address, the watchpoint trigs again,
>> but if the address is advanced,
>> the access is not done at all, because the watchpoint makes exception
>> before the access is made.

References:
- How are watchpoints handled? (remote serial)
  - From: Juha Aaltonen
- Re: How are watchpoints handled? (remote serial)
  - From: Juha Aaltonen

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