GDB breakpoint implementation for multithreaded programms

GDB breakpoint implementation for multithreaded programms

[Sofia]

I'm writing my GDB stub and trying to set breakpoints on different threads. 
When I don't ask GDB about the number of threads, It works fine as a single-
threaded application and breakpoints are set correctly. But when I enter - 
'info threads', something strange happens.

Firstly, GDB reads the contents of all threads' registers(it's OK). Then I 
enter 'continue' and see that breakpoints are not set at all threads my 
program has. I don't understand why, but the packet Z0(breakpoint packet) is 
only sent to inactive thread. The documentation says that if the thread id is 
not specified, breakpoints will be set at all threads. What's wrong with this 
or where can I read about such GDB behavior?

Re: GDB breakpoint implementation for multithreaded programms

[Luis Machado]

On 05/10/2014 06:56 PM, Sofia wrote:
> I'm writing my GDB stub and trying to set breakpoints on different threads.
> When I don't ask GDB about the number of threads, It works fine as a single-
> threaded application and breakpoints are set correctly. But when I enter -
> 'info threads', something strange happens.
>
> Firstly, GDB reads the contents of all threads' registers(it's OK). Then I
> enter 'continue' and see that breakpoints are not set at all threads my
> program has. I don't understand why, but the packet Z0(breakpoint packet) is
> only sent to inactive thread. The documentation says that if the thread id is
> not specified, breakpoints will be set at all threads. What's wrong with this
> or where can I read about such GDB behavior?
>
>
>

Is this a software breakpoint (Z0/z0) or a hardware breakpoint we are 
talking about?

A software breakpoint should be valid for all threads if the threads are 
executing a shared piece of code. If these breakpoints are not 
triggering, we may have a bug somewhere.

For hardware breakpoints, the target code (in this case, the remote 
stub) is responsible for replicating the hardware breakpoint settings 
(register contents) to all threads upon their creation.

What version of GDB are you using?