Hello,
When trying to build the current Linux master with a gcc 7.x toolchain
for mips64r6-n32, I'm getting the following build failure:
crypto/scompress.o: In function `.L31':
scompress.c:(.text+0x2a0): undefined reference to `__multi3'
drivers/base/component.o: In function `.L97':
component.c:(.text+0x4a4): undefined reference to `__multi3'
drivers/base/component.o: In function `component_master_add_with_match':
component.c:(.text+0x8c4): undefined reference to `__multi3'
net/core/ethtool.o: In function `ethtool_set_per_queue_coalesce':
ethtool.c:(.text+0x1ab0): undefined reference to `__multi3'
Makefile:1000: recipe for target 'vmlinux' failed
make[2]: *** [vmlinux] Error 1
Taking the example from net/core/ethtool.o, objdump says:
1aac: 00408025 move s0,v0
1ab0: e8000000 balc 1ab4 <ethtool_set_per_queue_coalesce+0x7c>
1ab4: 14600000 bnez v1,1ab8 <ethtool_set_per_queue_coalesce+0x80>
And readelf tells us:
Relocation section '.rela.text' at offset 0xaa00 contains 1189 entries:
Offset Info Type Sym. Value Sym. Name + Addend
[...]
000000001ab0 023a0000003d R_MIPS_PC26_S2 0000000000000000 __multi3 - 4
Type2: R_MIPS_NONE
Type3: R_MIPS_NONE
[...]
Symbol table '.symtab' contains 586 entries:
[...]
570: 0000000000000000 0 OBJECT GLOBAL DEFAULT UND __multi3
__multi3() is normally provided by libgcc, but of course the kernel
doesn't link with libgcc.
The bug can be reproduced by building with the toolchain available at
http://toolchains.free-electrons.com/downloads/2017.08-rc1-fix-binutils/toolchains/mips64r6el-n32/tarballs/mips64r6el-n32--glibc--bleeding-edge-2017.05-1453-ga703fdd-1.tar.bz2
and building with the attached kernel configuration file.
It is not clear to me if this is a kernel issue (lack of __multi3 in
arch/mips/lib/), or a gcc bug in that it shouldn't emit a call to this
function.
FWIW, sparc64 had a similar issue, and they added __multi3 in their
libgcc replacement, see commit
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/arch/sparc/lib?id=1b4af13ff2cc6897557bb0b8d9e2fad4fa4d67aa.
Best regards,
Thomas Petazzoni
--
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
Attachment:
defconfig
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