Re: [RFC 1/3] [gdb] Call gdbarch_get_syscall_number less often

[John Baldwin <jhb@FreeBSD.org>]

On 11/21/23 1:19 PM, Simon Marchi wrote:
> On 11/21/23 13:03, John Baldwin wrote:
>> I think you can use linux_nat_target::set_syscall_catchpoint to do the
>> invalidation.  From my reading it is called each time a syscall catchpoint
>> is added or removed, and needed is set to false if there are no more
>> catchpoints (so syscall catches are disabled).   I think that means
>> you could do something like:
>>
>> linux_nat_target::set_syscall_catchpoint ()
>> {
>>    if (!needed)
>>      iterate_over_lwps (ptid_t (pid), [] (struct lwp_info *lp)
>>                         {
>>                           lp->syscall_number = -1;
>>                         });
>> }
> 
> What about this corner case of a corner case:
> 
>   1. you have a syscall catchpoint, you hit it (the syscall entry)
>   2. you delete the syscall catchpoint
>   3. you create a syscall catchpoint again
>   4. you continue, expecting to hit the syscall exit
> 
> Will step 2 cause set_syscall_catchpoint to be called, and will we
> therefore lose the information that would have been useful at step 4?

Yes, but I think the generation counter idea is subject to the same issue
unless in both cases you actually defer the geneation bump (or clearing
syscall_number to -1) until you resume the lwp.  For that approach
perhaps you could reset syscall_number to -1 in linux_resume_one_lwp_throw
if catch_syscalls_enabled is zero?

-- 
John Baldwin