[llvm-dev] xray && shared library support

[David Blaikie via llvm-dev]

Last I was aware xray's basically unmaintained - so probably the "current
status" is whatever's checked in and not much more than that.

On Thu, Jul 1, 2021 at 11:48 AM Billie Alsup (balsup) via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> I've come across an email thread from 2018 regarding xray support for
> shared libraries.  Is there a current status on this effort?
>
> If this is not in active development, has there been any analysis on the
> effort required to add such support?
>
>
>
> I have experimented with clang-12 and see that shared library functions
> are still not patched automatically via patch_premain.
>
> I have not yet looked at any APIs that might allow me to pass in a
> shared-library-specific table of addresses to patch.
>
> Similarly, it is unclear how function ids should be adjusted (if
> necessary) to be globally unique across shared objects.
>
> I'm not even sure what kind of APIs would be needed.
>
> Should patch/unpatch be global in nature, or should we be able to target a
> specific shared library (or set of shared libraries)?
>
> I do see an API to patch/unpatch an individual function, but it is unclear
> if that would actually work against a function in a shared library due to
> the single XrayInstrMap involved.
>
> Should APIs take such a map as a parameter?  Should a new dynamic
> XrayInstrMap be computed with all preloaded shared libraries?
>
> How should dlopen'd libraries be handled?
>
> I also note that even with -fxray-instrument, the shared library does not
> automatically get the xray support functions from compiler-rt.
>
> That has implications for dlopen'd libraries without an xray-enabled
> primary elf object.
>
> For example, trying to get statistics from an xray-instrumented shared
> library loaded from python.
>
>
>
> I'm guessing this is just the tip of the iceberg, and am hoping there is
> already a design, or perhaps some discussion about the issues involved with
> supporting shared libraries.
>
> Ideally, someone would come back and say it is already being worked, and
> will be available in release X !
>
>
>
> Where might I find information related to this topic?
>
> https://llvm.org/docs/XRay.html mentions a number of ongoing efforts for
> expanding the toolset, but doesn't link to them.
>
> https://llvm.org/docs/XRayExample.html has some Next Steps, but doesn't
> mention shared libraries.
>
> Is there another wiki that goes into more detail?
>
>
>
>
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