Re: Fedora 33 System-Wide Change proposal: CompilerPolicy Change

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Hi,

On Fri, 2020-06-05 at 09:25 -0600, Jeff Law wrote:
> The LTO bytecode streams do not survive past any given package build.  ie, they
> are used within the build, then discarded.  They're not supposed to show up in
> any installed libraries.
> 
> Thus the fact that the two compilers use totally different LTO representations
> (and always will) is a non-issue here.

One issue I am concerned about here is debuginfo quality. GCC produced
pretty bad debuginfo with LTO in older versions. The EarlyDebug work
did make it usable. And we needed some work on the DARF consumers to
correctly process GCC 10 LTO produced DWARF (I actually have two small
patches for elfutils pending so it correctly parses the cross CU-
references GCC 10 LTO now produces).

I don't know if anybody did any analysis on llvm LTO produced
debuginfo. In the past it was observed that llvm doesn't do VTA (Var
Tracking Assignments) that is default in GCC. And VTA is really
important for debugging and performance/tracing tools like systemtap.
So even without LTO I am concerned about the observability of llvm
generated binaries.

Cheers,

Mark
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