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Re: GDB Remote debug: Why several "$Z0,address,length" msg when only set one breakpoint?


On 08/26/2014 03:57 AM, Peng Fan wrote:
Hi,

Currently, I am hacking uboot arm kgdb and adding breakpoint support.

The steps is as following:
(gdb) b do_bootz
Breakpoint 1, do_bootz (cmdtp=0x8784ca14 <_u_boot_list_2_cmd_2_bootz>, flag=0, argc=1, argv=0xbf552a20) at common/cmd_bootm.c:1928
(gdb) c
Continuing.
Sending packet: $m87809580,4#7a...Ack
Packet received: f0452de9
Sending packet: $m87809580,4#7a...Ack
Packet received: f0452de9
Sending packet: $Z0,87809584,4#c7...Ack
Packet received: OK
Sending packet: $Hc0#db...Ack
Packet received:
Sending packet: $c#63...Ack
Packet received: T050f:84958087;0d:a41355bf;
Sending packet: $z0,87809584,4#e7...Ack
Packet received: OK
Sending packet: $qTStatus#49...Ack
Packet received:
Sending packet: $Z0,87800000,4#ad...Ack
Packet received: OK
Sending packet: $Z0,87809580,4#c3...Ack
Packet received: OK
Sending packet: $Hc0#db...Ack
Packet received:
Sending packet: $c#63...Ack

Actually the breakpoint is at 0x87809580, but why first set breakpoint at 0x87809584 then remove it then set breakpoint at 0x87809580?

Also the first time set a breakpoint then continue.
(gdb) c
Continuing.
Sending packet: $qTStatus#49...Ack
Packet received:
Sending packet: $Z0,87800000,4#ad...Ack
Packet received: OK
Packet Z0 (software-breakpoint) is supported
Sending packet: $Z0,87809580,4#c3...Ack
Packet received: OK
Sending packet: $vCont?#49...Ack
Packet received:
Packet vCont (verbose-resume) is NOT supported
Sending packet: $Hc0#db...Ack
Packet received:
Sending packet: $c#63...Ack

why two Z0 here? I only set break at 0x87809580, but gdb send a break set at 0x87800000 which is the beginning of the elf entry.

Thanks.
Peng.



ARM does not have hardware single-stepping support, so GDB needs to simulate it with continue requests and breakpoints.

Regarding additional breakpoints, GDB has its own internal breakpoints, so your session may not be restricted to the breakpoints you created.

On third reason, depending on the mode, GDB inserts and removes breakpoints with every program stop.


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