[PATCH v5 00/29] Add support for Clang LTO

[Sami Tolvanen]

On Fri, Oct 9, 2020 at 4:38 PM Steven Rostedt <rostedt at goodmis.org> wrote:
>
> On Fri, 9 Oct 2020 14:05:48 -0700
> Sami Tolvanen <samitolvanen at google.com> wrote:
>
> > Ah yes, X86_DECODER_SELFTEST seems to be broken in tip/master. If you
> > prefer, I have these patches on top of mainline here:
> >
> >   https://github.com/samitolvanen/linux/tree/clang-lto
> >
> > Testing your config with LTO on this tree, it does build and boot for
> > me, although I saw a couple of new objtool warnings, and with LLVM=1,
> > one warning from llvm-objdump.
>
> Thanks, I disabled X86_DECODER_SELFTEST and it now builds.
>
> I forced the objdump mcount logic with the below patch, which produces:
>
> CONFIG_FTRACE_MCOUNT_RECORD=y
> CONFIG_FTRACE_MCOUNT_USE_OBJTOOL=y
>
> But I don't see the __mcount_loc sections being created.
>
> I applied patches 1 - 6.

Patch 6 is missing the part where we actually pass --mcount to
objtool, it's in patch 11 ("kbuild: lto: postpone objtool"). I'll fix
this in v6. In the meanwhile, please apply patches 1-11 to test the
objtool change. Do you have any thoughts about the approach otherwise?

Sami