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

On Fri, Oct 9, 2020 at 4:38 PM Steven Rostedt [off-list ref] wrote:

On Fri, 9 Oct 2020 14:05:48 -0700
Sami Tolvanen [off-list ref] wrote:

quoted

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