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Date:   Tue, 7 Apr 2020 20:25:19 +0800
From:   Jiaxun Yang <jiaxun.yang@flygoat.com>
To:     "Xu, Yanfei" <yanfei.xu@windriver.com>
Cc:     Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: BUG: mips: errors when compiling kernel with a large initramfs
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On Tue, 7 Apr 2020 17:58:23 +0800
"Xu, Yanfei" <yanfei.xu@windriver.com> wrote:

> Hi,
>=20
>=20
> It fails to compile mips kernel with large initramfs (at link time).
>=20
> kernel version: 5.6.0
>=20
>=20
> Steps to reproduce:
>=20
> 1. git clone mainline kernel
>=20
> 2. set ARCH=3Dmips and CROSS_COMPILE=3Dmips-linux-gnu-
>=20
> 3. make defconfig
>=20
> 4.enable initramfs support and set the path about initramfs source
> file
>=20
> 5.make -j24
>=20
> [KEY] when your initramfs files is too large, and cause=20
> usr/initramfs_data.cpio.gz
>=20
> compiled is larger than 225M, you will get the following error. BTW,
> x86 doesn't
>=20
> have this issue that I have tested.
>=20
> ------------------------------error=20
> messages-----------------------------------------
>=20
>  =C2=A0 CHK=C2=A0=C2=A0=C2=A0=C2=A0 include/generated/compile.h
>  =C2=A0 LD=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 vmlinux.o
>  =C2=A0 MODPOST vmlinux.o
>  =C2=A0 MODINFO modules.builtin.modinfo
>  =C2=A0 GEN=C2=A0=C2=A0=C2=A0=C2=A0 modules.builtin
>  =C2=A0 LD=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 .tmp_vmlinux.kallsyms1
> kernel/configs.o: In function `ikconfig_cleanup':
> /home/wrsadmin/work/linux/kernel/linux-master/kernel/configs.c:72:(.exit.=
text+0x8):=20
> relocation truncated to fit: R_MIPS_26 against `remove_proc_entry'
> fs/binfmt_script.o: In function `exit_script_binfmt':
> /home/wrsadmin/work/linux/kernel/linux-master/fs/binfmt_script.c:165:(.ex=
it.text+0x4):=20
> relocation truncated to fit: R_MIPS_26 against `unregister_binfmt'
> fs/binfmt_elf.o: In function `exit_elf_binfmt':
> /home/wrsadmin/work/linux/kernel/linux-master/fs/binfmt_elf.c:2393:(.exit=
.text+0x4):=20
> relocation truncated to fit: R_MIPS_26 against `unregister_binfmt'
> fs/mbcache.o: In function `mbcache_exit':
> /home/wrsadmin/work/linux/kernel/linux-master/fs/mbcache.c:429:(.exit.tex=
t+0x4):=20
> relocation truncated to fit: R_MIPS_26 against `kmem_cache_destroy'
> fs/nfs_common/grace.o: In function `exit_grace':
> /home/wrsadmin/work/linux/kernel/linux-master/fs/nfs_common/grace.c:133:(=
.exit.text+0x4):=20
> relocation truncated to fit: R_MIPS_26 against
> `unregister_pernet_subsys' fs/ext4/super.o: In function
> `ext4_destroy_lazyinit_thread':
> /home/wrsadmin/work/linux/kernel/linux-master/fs/ext4/super.c:3456:(.exit=
.text+0x24):
> relocation truncated to fit: R_MIPS_26 against `kthread_stop'
> fs/ext4/super.o: In function `unregister_as_ext2':
> /home/wrsadmin/work/linux/kernel/linux-master/fs/ext4/super.c:6126:(.exit=
.text+0x30):
> relocation truncated to fit: R_MIPS_26 against
> `unregister_filesystem' fs/ext4/super.o: In function
> `unregister_as_ext3':
> /home/wrsadmin/work/linux/kernel/linux-master/fs/ext4/super.c:6155:(.exit=
.text+0x3c):
> relocation truncated to fit: R_MIPS_26 against
> `unregister_filesystem' fs/ext4/super.o: In function `ext4_exit_fs':
> /home/wrsadmin/work/linux/kernel/linux-master/fs/ext4/super.c:6261:(.exit=
.text+0x48):
> relocation truncated to fit: R_MIPS_26 against
> `unregister_filesystem' fs/ext4/super.o: In function
> `destroy_inodecache':
> /home/wrsadmin/work/linux/kernel/linux-master/fs/ext4/super.c:1218:(.exit=
.text+0x50):
> relocation truncated to fit: R_MIPS_26 against `rcu_barrier'
> /home/wrsadmin/work/linux/kernel/linux-master/fs/ext4/super.c:1219:(.exit=
.text+0x5c):
> additional relocation overflows omitted from the output
> Makefile:1086: recipe for target 'vmlinux' failed make[1]: ***
> [vmlinux] Error 1 Makefile:1058: recipe for target
> 'autoksyms_recursive' failed make: *** [autoksyms_recursive] Error 2
>=20
>=20
> Any comment will be appreciated.

Actually I think that won't work even if you managed to workaround
reloc issue.

MIPS have limited LOW MEM range accessible via KSEG0 (512M, but can be
less if your system place some MMIO register in that range). Kernel
image will be placed here together with built-in initramfs, and a
lot of memory like Page Table can only be allocated from here.

Such a huge initrd will occupy the whole LOW MEM range leaving no space
for others.

It seems like your system is 32bit, we have no solution for that
hardware limitaion. For 64bit system you may try to move your kernel
into XKPHYS instead of KSEG0.

Thanks

--
Jiaxun Yang

>=20
> Thanks,
>=20
> Yanfei
>=20