Re: [PATCH] nios2: ksyms: Declare __mulsi3 export

* Re: [PATCH] nios2: ksyms: Declare __mulsi3 export
       [not found] <20261019-nios2-mulsi3-v1-1-4fd75b1bacef@linutronix.de>
@ 2026-10-19 11:16 ` Arnd Bergmann
  2026-10-19 14:34   ` Dinh Nguyen
  0 siblings, 1 reply; 3+ messages in thread
From: Arnd Bergmann @ 2026-10-19 11:16 UTC (permalink / raw)
  To: Thomas Weißschuh, Dinh Nguyen,
	schuster.simon@siemens-energy.com, Ley Foon Tan
  Cc: linux-kernel, kernel test robot, linux-snps-arc, linux-parisc,
	linux-openrisc@vger.kernel.org

On Mon, Oct 19, 2026, at 11:49, Thomas Weißschuh wrote:
> GCC may emit libcalls to __mulsi3(). As modpost is not aware that this
> function is provided through the linked in libgcc, it fails:
>
> ERROR: modpost: kernel/locking/test-ww_mutex.ko: symbol '__mulsi3' undefined!
> ERROR: modpost: kernel/time/test_udelay.ko: symbol '__mulsi3' undefined!
> ERROR: modpost: kernel/resource_kunit.ko: symbol '__mulsi3' undefined!
> ERROR: modpost: fs/fuse/virtiofs.ko: symbol '__mulsi3' undefined!
> etc.
>
> Make sure modpost can see the symbol from libgcc.
>
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: 
> https://lore.kernel.org/oe-kbuild-all/202610171933.J4bFOfL8-lkp@intel.com/
> Fixes: 2fc8483fdcde ("nios2: Build infrastructure")
> Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>

Acked-by: Arnd Bergmann <arnd@arndb.de>

The patch looks correct to me, but it would also be nice to not use
libgcc at all. What I see is that only arc, nios2, openrisc and
parisc still link against the toolchain-provided libgcc, everything
else uses the kernel's own runtime.

It's probably not even that hard to do right, here is what I found
is imported from libgcc.

* Generic library helper exists, can be enabled through Kconfig:

=== __lshrdi3 ===
arch/arc/kernel/arcksyms.c
arch/nios2/kernel/nios2_ksyms.c
arch/openrisc/kernel/or32_ksyms.c
arch/parisc/kernel/parisc_ksyms.c
-> lib/lshrdi3.c
=== __ashldi3 ===
arch/arc/kernel/arcksyms.c
arch/nios2/kernel/nios2_ksyms.c
arch/openrisc/kernel/or32_ksyms.c
arch/parisc/kernel/parisc_ksyms.c
-> lib/ashldi3.c
=== __ashrdi3 ===
arch/arc/kernel/arcksyms.c
arch/nios2/kernel/nios2_ksyms.c
arch/openrisc/kernel/or32_ksyms.c
arch/parisc/kernel/parisc_ksyms.c
-> lib/ashrdi3.c
=== __cmpdi2 ===
arch/arc/kernel/arcksyms.c
-> lib/cmpdi2.c
=== __muldi3 ===
arch/arc/kernel/arcksyms.c
arch/nios2/kernel/nios2_ksyms.c
arch/openrisc/kernel/or32_ksyms.c
arch/parisc/kernel/parisc_ksyms.c
-> lib/muldi3.c
=== __ucmpdi2 ===
arch/arc/kernel/arcksyms.c
arch/nios2/kernel/nios2_ksyms.c
arch/openrisc/kernel/or32_ksyms.c
arch/parisc/kernel/parisc_ksyms.c
-> lib/ucmpdi2.c

* 64-bit division probably should not be provided on arc or
  nios2 (and sparc32, which has a private copy).
  parisc64 should get these from libgcc/libgcc2.c.

=== __divdi3 ===
arch/parisc/kernel/parisc_ksyms.c
=== __udivmoddi4 ===
arch/nios2/kernel/nios2_ksyms.c
=== __udivdi3 ===
arch/arc/kernel/arcksyms.c
arch/parisc/kernel/parisc_ksyms.c
=== __umoddi3 ===
arch/nios2/kernel/nios2_ksyms.c
arch/parisc/kernel/parisc_ksyms.c
=== __moddi3 ===
arch/nios2/kernel/nios2_ksyms.c
arch/parisc/kernel/parisc_ksyms.c

* floating-point math should not be provided by kernel:

=== __divdf3 ===
arch/arc/kernel/arcksyms.c
=== __divsf3 ===
arch/arc/kernel/arcksyms.c
=== __fixunsdfsi ===
arch/arc/kernel/arcksyms.c
=== __floatunsidf ===
arch/arc/kernel/arcksyms.c
=== __floatunsisf ===
arch/arc/kernel/arcksyms.c
=== __muldf3 ===
arch/arc/kernel/arcksyms.c

* no generic implementation in kernel, need to copy from
  libgcc/lib1funcs.S code:

=== __divsi3 ===
arch/arc/kernel/arcksyms.c
arch/nios2/kernel/nios2_ksyms.c
arch/openrisc/kernel/or32_ksyms.c
-> arch/arm/lib/lib1funcs.S
   arch/m68k/lib/divsi3.S
   arch/microblaze/lib/divsi3.S
   arch/xtensa/lib/divsi3.S
=== __modsi3 ===
arch/arc/kernel/arcksyms.c
arch/nios2/kernel/nios2_ksyms.c
arch/openrisc/kernel/or32_ksyms.c
-> arch/m68k/lib/modsi3.S
   arch/microblaze/lib/modsi3.S
   arch/xtensa/lib/modsi3.S
=== __udivsi3 ===
arch/arc/kernel/arcksyms.c
arch/nios2/kernel/nios2_ksyms.c
arch/openrisc/kernel/or32_ksyms.c
-> arch/arm/lib/lib1funcs.S
   arch/m68k/lib/udivsi3.S
   arch/microblaze/lib/udivsi3.S
   arch/sh/lib/udivsi3.S
   arch/xtensa/lib/udivsi3.S
=== __umodsi3 ===
arch/arc/kernel/arcksyms.c
arch/nios2/kernel/nios2_ksyms.c
arch/openrisc/kernel/or32_ksyms.c
-> arch/arm/lib/lib1funcs.S
   arch/m68k/lib/umodsi3.S
   arch/microblaze/lib/umodsi3.S
   arch/xtensa/lib/umodsi3.S

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