linux-kernel - Failing randconfig builds with CONFIG_TRIM_UNUSED

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Date:	Thu, 28 Apr 2016 14:41:10 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Nicolas Pitre <nicolas.pitre@...aro.org>
Cc:	linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org
Subject: Failing randconfig builds with CONFIG_TRIM_UNUSED_KSYMS

Hi Nico,

My randconfig build testing has encountered a couple of additional
failures with CONFIG_TRIM_UNUSED_KSYMS=y, both rather rare at
happening once in a few thousand randconfig builds. I have attached
two .config files that presumably refer to different problems I
see on linux-next:

0x1A1E54C2_defconfig fails every time with
ERROR: "__aeabi_idivmod" [lib/cordic.ko] undefined!

Apparently, this is because lib/cordic.ko is the only module using
this symbol (some built-in code uses it) here.

0xEA8A78CD_defconfig is stranger, as it only sometime breaks when I build
in a newly created object directory or after "make clean", but
not if I retry the build:

$ rm -rf build/0xEA8A78CD
$ mkdir build/0xEA8A78CD
$ make O=build/0xEA8A78CD 0xEA8A78CD_defconfig
$ make O=build/0xEA8A78CD -skj12
ERROR: "memory_cgrp_subsys_enabled_key" [fs/ncpfs/ncpfs.ko] undefined!
$ make O=build/0xEA8A78CD -skj12
$ # SUCCESS
$ rm -rf build/0xEA8A78CD_defconfig/fs/ncpfs/  build/0xEA8A78CD_defconfig/include/generated/autoksyms.h build/0xEA8A78CD_defconfig/kernel/cgroup.o
$ make O=build/0xEA8A78CD -skj12
ERROR: "memory_cgrp_subsys_enabled_key" [fs/ncpfs/ncpfs.ko] undefined!

Here, the memory_cgrp_subsys_enabled_key variable gets created
and exported from kernel/cgroup.c in the SUBSYS macro, and gets used
through multiple inline functions through
ncp_file_mmap_fault() -> mem_cgroup_count_vm_event() -> mem_cgroup_disabled()

	Arnd
View attachment "0x1A1E54C2_defconfig" of type "text/plain" (29839 bytes)

View attachment "0xEA8A78CD_defconfig" of type "text/plain" (89883 bytes)