Re: [PATCH] [gdbserver] Disable conditional breakpoints on no-hardware-single-step targets

[Pedro Alves <palves@redhat.com>]

On 05/11/2015 01:37 PM, Maciej W. Rozycki wrote:
> On Mon, 11 May 2015, Pedro Alves wrote:

>> I assume that mode switches on MIPS are similar to ARM, with special
>> branch instruction with mode encoded in in destination address?  If so,
>> starting from knowing the mode at PC, gdbserver should be able to
>> determine the mode of all the potential next instructions on its own.
> 
>  And that's where the issue is.  Assuming that you're in the standard ISA 
> mode, you can determine that the next instruction will switch the mode to 
> one of the compressed ISAs, either by checking the opcode (immediate jump, 
> JALX) or by reading the PC to be jumped to (register jumps, JALR and JR).  
> What you can't determine is which of the two compressed ISAs, either 
> MIPS16 or microMIPS one, the instruction will switch to.
> 
>  Given that the MIPS16 and the microMIPS mode cannot be implemented by a 
> processor both at a time you can will know which of the two is being used 
> once you have seen a breakpoint request for one of them.  However it may 
> be that none has been used so far and then you have no way to know, in the 
> current state of affairs.

That sounds solvable though: as that's a static property of the
target system/process, maybe gdbserver can fetch that info from elsewhere,
like somewhere under /proc, or from the auvx, or some bit set in the elf
binary (found at /proc/pid/exe).  Failing that, we can have gdb tell
gdbserver early with some new packet.

Thanks,
Pedro Alves