Re: [Crash-utility] [PATCH v2] crash: dis: introduce count in reverse and forward mode
On Fri 2019-06-21 11:45 -0400, Dave Anderson wrote:
----- Original Message -----
> Changes since v1:
>
> - Update 'dis' help page
> - Resolve patch fuzz
>
>
> The purpose of this patch is to add support for a count value in reverse
> or forward mode, during disassembly:
>
> 'dis [-r|-f] [symbol|address] [count]'
>
> For example:
>
> crash> dis -f list_del+0x16 4
> 0xffffffff812b3346 <list_del+22>: jne 0xffffffff812b3381
<list_del+81>
> 0xffffffff812b3348 <list_del+24>: mov (%rbx),%rax
> 0xffffffff812b334b <list_del+27>: mov 0x8(%rax),%r8
> 0xffffffff812b334f <list_del+31>: cmp %r8,%rbx
>
> crash> dis -r list_del+0x16 4
> 0xffffffff812b333c <list_del+12>: mov 0x8(%rdi),%rax
> 0xffffffff812b3340 <list_del+16>: mov (%rax),%r8
> 0xffffffff812b3343 <list_del+19>: cmp %r8,%rdi
> 0xffffffff812b3346 <list_del+22>: jne 0xffffffff812b3381
<list_del+81>
[ ... ]
Hi Dave,
To be honest, it's not clear how that can be addressed, because
any patches
to printcmd.c must be applicable to the non-ppc64le and the ppc64le versions
of the file.
Unfortunately, I believe this is the underlying issue.
I did not compile test under ppc64le.
So let's take a step back, and consider the risk/reward of this
quite intrusive
patchset to such a crucial gdb file.
In my opinion and if I understand correctly, the original GDB commit
bb556f1facb ("Add negative repeat count to 'x' command") is rather
self-contained and should not cause an issue. I was particularly careful in
this regard. Moving forward, I could strip out all but absolutely necessary
changes from the original GDB commit, to support this feature.
First, "dis -f <address> <count>" is pretty
much meaningless. In order
to accomplish that, just don't use the "-f" argument!
I agree - this is superficial; count in forward mode was added since
reverse mode also accepts a count.
Secondly, for "dis -r <address> count", you could
simply run "dis -r <address> | tail -4".
For that matter, is it really all that onerous to see the fully disassembled function
up to the target address?
Personally, I would prefer to avoid using an external command in this
particular case. Especially since the GDB command examine supports a
positive or negative (i.e. in GDB release 7.12 and above) count.
And again, even if you wanted to support it, it also seems like it
could be accomplished
within the cmd_dis() function, given that the full output is pre-gathered into a tmpfile
prior to being displayed.
We can indeed but it would be easier to utilise GDB for this as explained above.
If you don't mind another iteration, I'll attempt to address the above
build issues. Please let me know your thoughts.
Kind regards,
--
Aaron Tomlin