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Citando Pedro Alves <palves@redhat.com>:
Hi JoÃo, On 10/28/2014 04:01 PM, joaoandreferro@sapo.pt wrote:Hello all, I've been using GDB (in fact, conjuged with KGDB) lately to do some kernel debugging. I've been testing some GDB commands, and a doubt arised while using the "set" command, trying to change the value of some registers. I've been able to successfully change the value of all the registers provided by the "info registers" command (i. e., in my case $eax, $ecx, $edx, $ebx, $esp, $ebp, $esi, $edi, $eip, $eflags, $cs, $ss, $ds, $es, $fs and $gs) *except* for $esp, $ss, $fs and $gs. Why is it so? I've been making these tests after hitting a hardware breakpoint, then I set the values with e. g. "set $es = 0xf1c2007c", and verifiy the assignemt with "info reg $es". As I've pointed out, it works with the majority of the registers, except for that four (in this particular case, the first command doesn't output any error, but the second command shows me that the registers remain with the initial value). By the way, I've started GDB with the -write option (checked it inside GDb with the "show write" command). My GDB version is 7.2. If someone knows something about this situation and can share it with me, it would be great.I'd guess that it's kgdb itself that is blocking those writes. Try "set debug remote 1" before the "set $foo = " command. Thanks, Pedro Alves
Hello Pedro,Thanks for your answer. I turned "set debug remote 1" on again, and strangely, the output tells me that "set-register" is not supported, but only when I'm able to change the register value (see the output below). First, I've tried with a register which I can successfully change the value, and then with another one where I wasn't able to do it in the past. Do you know why this behaviour occurs? Meanwhile, I'll ask the same in the KGDB mailing list. Like I've mentioned, output below:
(gdb) info reg $es es 0x7b 123 (gdb) set $es = 0x7c Sending packet: $Pd=7c000000#ab...Ack Packet received: Packet P (set-register) is NOT supportedSending packet: $G14000000ccb59cc00000000067000000089fcbf10c9fcbf1ac309dc00000000079154ac09600000060000000680000007b009dc07c000000ffff0000ffff0000#61...Ack
Packet received: OK Sending packet: $g#67...AckPacket received: 14000000ccb59cc00000000067000000089fcbf10c9fcbf1ac309dc00000000079154ac09600000060000000680000007b009dc07c000000ffff0000ffff0000
(gdb) info reg $es es 0x7c 124 (gdb) info reg $ss ss 0x68 104 (gdb) set $ss = 0x69Sending packet: $G14000000ccb59cc00000000067000000089fcbf10c9fcbf1ac309dc00000000079154ac09600000060000000690000007b009dc07c000000ffff0000ffff0000#62...Ack
Packet received: OK Sending packet: $g#67...AckPacket received: 14000000ccb59cc00000000067000000089fcbf10c9fcbf1ac309dc00000000079154ac09600000060000000680000007b009dc07c000000ffff0000ffff0000
(gdb) info reg $ss ss 0x68 104 Best regards, JoÃo
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