Re: [Qemu-devel] [PATCH v4 00/20] instrument: Add basic event instrumentation

[Lluís Vilanova]

Emilio G Cota writes:

> On Thu, Sep 07, 2017 at 12:58:05 +0200, Markus Armbruster wrote:
>> Lluís Vilanova <address@hidden> writes:
>> 
>> > This series adds an API to add instrumentation events.
>> >
>> > It also provides additional APIs for:
>> > * Controlling tracing events
>> > * Peek/poke guest memory
>> >
>> > There's still missing APIs for (can be added in later series?):
>> > * Provide something like tracing's per-vCPU trace states (i.e., so that 
>> > each
>> >   vCPU can have different instrumentation code). It's still not clear to 
>> > me if
>> >   we should extend the per-vCPU bitmap with instrumentation events, or 
>> > otherwise
>> >   somehow reuse the bits in tracing events (since they're currently 
>> > limited).
>> > * Peek/poke guest registers
>> >
>> > The instrumentation code is dynamically loaded as a library into QEMU 
>> > either
>> > when it starts or later using its remote control interfaces.
>> >
>> > Signed-off-by: Lluís Vilanova <address@hidden>
>> 
>> Taking a step back.
>> 
>> This looks like a way to dynamically load arbitrary code.  What
>> interfaces can this code use?  Your cover letter should answer this.
>> 
>> As long as the answer is "everything the dynamic linker is willing to
>> resolve", this series heading nowhere.  We can talk about an interface
>> for plugins, but "anything goes" is not on the menu.

> A simple solution to this is to only export the API symbols by passing
> --dynamic-file to the linker -- see patch 2 of the following series for an
> example (ELF-only, although I'm pretty sure this can be achieved on Windows
> as well):
>   https://lists.gnu.org/archive/html/qemu-devel/2017-09/msg01446.html

Sorry, I adapted the instr series in a rush and missed your series. I'm now
preparing a new version that fixes this without the flags you mention (missed to
add a line in this series).


Thanks,
  Lluis