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Re: [PATCH 3/4] Enable tracing of pseudo-registers on ARM
- From: Pedro Alves <palves at redhat dot com>
- To: Yao Qi <qiyaoltc at gmail dot com>, Marcin KoÅcielnicki <koriakin at 0x04 dot net>
- Cc: Antoine Tremblay <antoine dot tremblay at ericsson dot com>, gdb-patches at sourceware dot org, Gary Benson <gbenson at redhat dot com>
- Date: Mon, 15 Feb 2016 10:57:52 +0000
- Subject: Re: [PATCH 3/4] Enable tracing of pseudo-registers on ARM
- Authentication-results: sourceware.org; auth=none
- References: <1452188697-23870-1-git-send-email-antoine dot tremblay at ericsson dot com> <1452188697-23870-4-git-send-email-antoine dot tremblay at ericsson dot com> <86egcineq0 dot fsf at gmail dot com> <56BE002F dot 7050305 at 0x04 dot net> <86egcee0a6 dot fsf at gmail dot com>
On 02/15/2016 10:27 AM, Yao Qi wrote:
> Marcin KoÅcielnicki <koriakin@0x04.net> writes:
>
>>
>> Matter of fact, our support for >64-bit quantities in tracepoints is
>> very poor at the moment - they can only be collected wholesale when
>> they're single registers or contig memory areas. Use in expressions
>> is out (if you happen to have something interesting in low 32 bits of
>> a vector reg, sorry). Likewise, stiching them together with
>> DW_op_piece (or whatever that was called) also fails (see
>> https://sourceware.org/bugzilla/show_bug.cgi?id=17015). We could
>> definitely use some improvement there...
>
> Yeah, agreed.
>
I think the that ultimate long term solution would pass actual DWARF
expressions to the target side as collect actions. AX predates DWARF; probably
if we were starting now we'd base it on DWARF. Then for the most part,
we'd stop getting into trouble with mapping DWARF constructs to AX.
I imagine we'd reuse gdb/dwarf2expr.c somehow, similarly to get-next-pcs,
and that we'd maybe lower/rewrite some of the the DWARF before passing
it to the target, to e.g., maybe avoid relying on debug info types or
the frame/unwind machinery.
+Gary, since given Infinity is based on DWARF expressions, it may
be Gary's already looked at factoring out gdb/dwarf2expr.c.
Not a trivial project though...
Thanks,
Pedro Alves