Re: [PATCH v8 00/16] Add support for Clang LTO

Arnd Bergmann
2020-12-08T13:55:53Z

On Tue, Dec 8, 2020 at 1:15 PM Arnd Bergmann <arnd@kernel.org> wrote:
> On Tue, Dec 1, 2020 at 10:37 PM 'Sami Tolvanen' via Clang Built Linux <clang-built-linux@googlegroups.com> wrote:
>
> - many builds complain about thousands of duplicate symbols in the kernel, e.g.
> ld.lld: error: duplicate symbol: qrtr_endpoint_post
> >>> defined in net/qrtr/qrtr.lto.o
> >>> defined in net/qrtr/qrtr.o
> ld.lld: error: duplicate symbol: init_module
> >>> defined in crypto/842.lto.o
> >>> defined in crypto/842.o
> ld.lld: error: duplicate symbol: init_module
> >>> defined in net/netfilter/nfnetlink_log.lto.o
> >>> defined in net/netfilter/nfnetlink_log.o
> ld.lld: error: duplicate symbol: vli_from_be64
> >>> defined in crypto/ecc.lto.o
> >>> defined in crypto/ecc.o
> ld.lld: error: duplicate symbol: __mod_of__plldig_clk_id_device_table
> >>> defined in drivers/clk/clk-plldig.lto.o
> >>> defined in drivers/clk/clk-plldig.o

A small update here: I see this behavior with every single module
build, including 'tinyconfig' with one module enabled, and 'defconfig'.

I tuned the randconfig setting using KCONFIG_PROBABILITY=2:2:1
now, which only enables a few symbols. With this I see faster build
times (obvioulsy), aroudn 30 seconds per kernel, and all small builds
with CONFIG_MODULES disabled so far succeed.
It appears that the problems I saw originally only happen for larger
configurations, or possibly a combination of Kconfig options that don't
happen that often on randconfig builds with low
KCONFIG_PROBABILITY.

Arnd