[PATCH v2 0/3] lib: Add software mul/div helpers and use them from nios2

[PATCH v2 0/3] lib: Add software mul/div helpers and use them from nios2

[Simon Schuster]

Recently, there have been linking failures on nios2 regarding libgcc
symbols that we reexport to modules (in particular __mulsi3 [0], and
__divsi3_table [1]).

In the resulting discussion, Arnd suggested [2] dropping the libgcc
dependency altogether, as -- while specific functions might be fine --
libgcc does not expect to run in a kernel-like freestanding environment.

To this end, Dinh Nguyen was kind enough to locate and extract
GPLv2-compliant versions of the software mul/div/mod functions required
by nios2 gcc and integrate them into the kernel. As Arnd also suggested
[3] that these might be helpful to other smaller architectures (such as
arc or openrisc), I've further extracted them to lib/ with corresponding
CONFIG_GENERIC_LIB_* options that allow selectively enabling and
exporting these as required.

The patch series compiles mostly^4 fine in a nios2 allyesconfig
without modpost errors; a quick boot test on a regular build also
completed successfully.

Best regards,
Simon

0: https://lore.kernel.org/lkml/20261019-nios2-mulsi3-v1-1-4fd75b1bacef@linutronix.de/
1: https://lore.kernel.org/lkml/20261026234452.1086974-1-sashal@kernel.org/
2: https://lore.kernel.org/lkml/686f4ca2-0fb6-4a73-9cdb-0edcccafdd62@app.fastmail.com/
3: https://lore.kernel.org/lkml/426c73b7-b4dc-4b68-9aa5-6145a13280bc@app.fastmail.com/
4: There seems to be an unrelated issue in linux-next regarding
   CONFIG_PNFS_BLOCK. Furthermore -Wno-attribute-alias
   -Wno-missing-prototypes -Wno-missing-declarations and
   -Wno-unused-function were required due to unrelated Werror-related
   compilation issues; but as this series concerns compiler intrinsics
   that are never explicitly referenced in code and it links fine this
   seems acceptable to me.

Signed-off-by: Simon Schuster <schuster.simon@siemens-energy.com>
---
Changes in v2:
- Reorganised to directly add to lib/* skipping arch/nios2/lib/math.c
- Dropped __gcc_bcmp as it is not actually needed
- Link to v1: https://lore.kernel.org/r/20261030-nios2-remove-usage-of-libgcc-v1-0-4e341c66082e@siemens-energy.com

---
Dinh Nguyen (2):
      lib: extract 32bit mul/div helpers from nios2 into GENERIC_LIB
      nios2: Drop usage of libgcc in favour of GENERIC_LIB_*

Simon Schuster (1):
      nios2: export __divsi3_table

 arch/nios2/Kconfig              | 10 +++++
 arch/nios2/Makefile             |  4 +-
 arch/nios2/kernel/nios2_ksyms.c | 22 ----------
 arch/nios2/lib/Makefile         |  1 +
 arch/nios2/lib/math.c           | 24 +++++++++++
 include/linux/libgcc.h          | 10 +++++
 lib/Kconfig                     | 15 +++++++
 lib/Makefile                    | 10 +++++
 lib/divmod.c                    | 94 +++++++++++++++++++++++++++++++++++++++++
 lib/mulsi3.c                    | 24 +++++++++++
 10 files changed, 189 insertions(+), 25 deletions(-)
---
base-commit: a39c950806213f6861d00f90729acaaa21f2d95a
change-id: 20261030-nios2-remove-usage-of-libgcc-63d9d0faad62

Best regards,
-- 
Simon Schuster <schuster.simon@siemens-energy.com>

[PATCH v2 1/3] lib: extract 32bit mul/div helpers from nios2 into GENERIC_LIB

[Simon Schuster]

From: Dinh Nguyen <dinguyen@kernel.org>

As suggested in 426c73b7-b4dc-4b68-9aa5-6145a13280bc@app.fastmail.com,
the software emulation of div/mul/mod on 32-bit platforms from nios2
might be of use to other smaller architectures as well when trying to
drop their libgcc dependency (e.g., arc, openrisc).
Therefore, extract and add them to lib/, guarded by respective
CONFIG_GENERIC_LIB_* options.

Symbols covered:
s32 __mulsi3(s32 a, s32 b);
s32 __divsi3(s32 a, s32 b);
s32 __udivsi3(s32 a, s32 b);
s32 __modsi3(s32 a, s32 b);
s32 __umodsi3(s32 a, s32 b);

Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>
Co-developed-by: Simon Schuster <schuster.simon@siemens-energy.com>
Signed-off-by: Simon Schuster <schuster.simon@siemens-energy.com>
---
 include/linux/libgcc.h | 10 ++++++
 lib/Kconfig            | 15 ++++++++
 lib/Makefile           | 10 ++++++
 lib/divmod.c           | 94 ++++++++++++++++++++++++++++++++++++++++++++++++++
 lib/mulsi3.c           | 24 +++++++++++++
 5 files changed, 153 insertions(+)

diff --git a/include/linux/libgcc.h b/include/linux/libgcc.h
index 0d68f9d6a6a7e..f5db35a9bc146 100644
--- a/include/linux/libgcc.h
+++ b/include/linux/libgcc.h
@@ -7,6 +7,7 @@
 #define __LIB_LIBGCC_H
 
 #include <asm/byteorder.h>
+#include <linux/types.h>
 
 typedef int word_type __attribute__ ((mode (__word__)));
 
@@ -34,6 +35,15 @@ long long notrace __lshrdi3(long long u, word_type b);
 long long notrace __muldi3(long long u, long long v);
 word_type notrace __ucmpdi2(unsigned long long a, unsigned long long b);
 
+/*
+ * Software 32-bit multiply for cores built without the hardware multiplier.
+ */
+s32 notrace __mulsi3(s32 a, s32 b);
+s32 notrace __divsi3(s32 a, s32 b);
+s32 notrace __udivsi3(s32 a, s32 b);
+s32 notrace __modsi3(s32 a, s32 b);
+s32 notrace __umodsi3(s32 a, s32 b);
+
 #ifdef CONFIG_HAVE_ARCH_LIBGCC_H
 #include <asm/libgcc.h>
 #endif
diff --git a/lib/Kconfig b/lib/Kconfig
index 1e42f5167c68b..16c2f2008b82c 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -611,6 +611,21 @@ config GENERIC_LIB_CMPDI2
 config GENERIC_LIB_UCMPDI2
 	bool
 
+config GENERIC_LIB_DIVSI3
+	bool
+
+config GENERIC_LIB_MODSI3
+	bool
+
+config GENERIC_LIB_UDIVSI3
+	bool
+
+config GENERIC_LIB_UMODSI3
+	bool
+
+config GENERIC_LIB_MULSI3
+	bool
+
 config GENERIC_LIB_DEVMEM_IS_ALLOWED
 	bool
 
diff --git a/lib/Makefile b/lib/Makefile
index a2afe954805cb..352a012baecba 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -337,6 +337,16 @@ obj-$(CONFIG_GENERIC_LIB_LSHRDI3) += lshrdi3.o
 obj-$(CONFIG_GENERIC_LIB_MULDI3) += muldi3.o
 obj-$(CONFIG_GENERIC_LIB_CMPDI2) += cmpdi2.o
 obj-$(CONFIG_GENERIC_LIB_UCMPDI2) += ucmpdi2.o
+obj-$(CONFIG_GENERIC_LIB_MULSI3) += mulsi3.o
+
+divmod-needed := $(or \
+	$(CONFIG_GENERIC_LIB_DIVSI3),\
+	$(CONFIG_GENERIC_LIB_MODSI3),\
+	$(CONFIG_GENERIC_LIB_UDIVSI3),\
+	$(CONFIG_GENERIC_LIB_UMODSI3))
+obj-$(divmod-needed) += divmod.o
+
+
 obj-$(CONFIG_OBJAGG) += objagg.o
 
 # pldmfw library
diff --git a/lib/divmod.c b/lib/divmod.c
new file mode 100644
index 0000000000000..cc1df6f9978ce
--- /dev/null
+++ b/lib/divmod.c
@@ -0,0 +1,94 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright Altera Corporation (C) 2026. All rights reserved.
+ */
+
+#include <linux/libgcc.h>
+#include <linux/export.h>
+#include <linux/types.h>
+
+static u32 udivmodsi4(u32 num, u32 den, int modwanted)
+{
+	u32 bit = 1;
+	u32 res = 0;
+
+	while (den < num && bit && !(den & (1U << 31))) {
+		den <<= 1;
+		bit <<= 1;
+	}
+
+	while (bit) {
+		if (num >= den) {
+			num -= den;
+			res |= bit;
+		}
+		bit >>= 1;
+		den >>= 1;
+	}
+
+	return modwanted ? num : res;
+}
+
+
+#ifdef CONFIG_GENERIC_LIB_DIVSI3
+s32 __divsi3(s32 a, s32 b)
+{
+	int neg = 0;
+	s32 res;
+
+	if (a < 0) {
+		a = -a;
+		neg = !neg;
+	}
+
+	if (b < 0) {
+		b = -b;
+		neg = !neg;
+	}
+
+	res = udivmodsi4(a, b, 0);
+	if (neg)
+		res = -res;
+
+	return res;
+}
+EXPORT_SYMBOL(__divsi3);
+#endif
+
+#ifdef CONFIG_GENERIC_LIB_MODSI3
+s32 __modsi3(s32 a, s32 b)
+{
+	int neg = 0;
+	s32 res;
+
+	if (a < 0) {
+		a = -a;
+		neg = 1;
+	}
+
+	if (b < 0)
+		b = -b;
+
+	res = udivmodsi4(a, b, 1);
+	if (neg)
+		res = -res;
+
+	return res;
+}
+EXPORT_SYMBOL(__modsi3);
+#endif
+
+#ifdef CONFIG_GENERIC_LIB_UDIVSI3
+s32 __udivsi3(s32 a, s32 b)
+{
+	return udivmodsi4(a, b, 0);
+}
+EXPORT_SYMBOL(__udivsi3);
+#endif
+
+#ifdef CONFIG_GENERIC_LIB_UMODSI3
+s32 __umodsi3(s32 a, s32 b)
+{
+	return udivmodsi4(a, b, 1);
+}
+EXPORT_SYMBOL(__umodsi3);
+#endif
diff --git a/lib/mulsi3.c b/lib/mulsi3.c
new file mode 100644
index 0000000000000..6596a6598de05
--- /dev/null
+++ b/lib/mulsi3.c
@@ -0,0 +1,24 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright Altera Corporation (C) 2026. All rights reserved.
+ */
+
+#include <linux/libgcc.h>
+#include <linux/export.h>
+#include <linux/types.h>
+
+s32 __mulsi3(s32 a, s32 b)
+{
+	s32 res = 0;
+	u32 cnt = a;
+
+	while (cnt) {
+		if (cnt & 1)
+			res += b;
+
+		b <<= 1;
+		cnt >>= 1;
+	}
+
+	return res;
+}
+EXPORT_SYMBOL(__mulsi3);

-- 
2.39.5

Re: [PATCH v2 1/3] lib: extract 32bit mul/div helpers from nios2 into GENERIC_LIB

[Vineet Gupta]

On 11/3/26 05:30, Simon Schuster wrote:
> From: Dinh Nguyen <dinguyen@kernel.org>
>
> As suggested in 426c73b7-b4dc-4b68-9aa5-6145a13280bc@app.fastmail.com,
> the software emulation of div/mul/mod on 32-bit platforms from nios2
> might be of use to other smaller architectures as well when trying to
> drop their libgcc dependency (e.g., arc, openrisc).
> Therefore, extract and add them to lib/, guarded by respective
> CONFIG_GENERIC_LIB_* options.
>
> Symbols covered:
> s32 __mulsi3(s32 a, s32 b);
> s32 __divsi3(s32 a, s32 b);
> s32 __udivsi3(s32 a, s32 b);
> s32 __modsi3(s32 a, s32 b);
> s32 __umodsi3(s32 a, s32 b);
>
> Suggested-by: Arnd Bergmann <arnd@arndb.de>
> Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>
> Co-developed-by: Simon Schuster <schuster.simon@siemens-energy.com>
> Signed-off-by: Simon Schuster <schuster.simon@siemens-energy.com>
> ---
>   include/linux/libgcc.h | 10 ++++++
>   lib/Kconfig            | 15 ++++++++
>   lib/Makefile           | 10 ++++++
>   lib/divmod.c           | 94 ++++++++++++++++++++++++++++++++++++++++++++++++++
>   lib/mulsi3.c           | 24 +++++++++++++
>   5 files changed, 153 insertions(+)
>
> diff --git a/include/linux/libgcc.h b/include/linux/libgcc.h
> index 0d68f9d6a6a7e..f5db35a9bc146 100644
> --- a/include/linux/libgcc.h
> +++ b/include/linux/libgcc.h
> @@ -7,6 +7,7 @@
>   #define __LIB_LIBGCC_H
>   
>   #include <asm/byteorder.h>
> +#include <linux/types.h>
>   
>   typedef int word_type __attribute__ ((mode (__word__)));
>   
> @@ -34,6 +35,15 @@ long long notrace __lshrdi3(long long u, word_type b);
>   long long notrace __muldi3(long long u, long long v);
>   word_type notrace __ucmpdi2(unsigned long long a, unsigned long long b);
>   
> +/*
> + * Software 32-bit multiply for cores built without the hardware multiplier.
> + */
> +s32 notrace __mulsi3(s32 a, s32 b);
> +s32 notrace __divsi3(s32 a, s32 b);
> +s32 notrace __udivsi3(s32 a, s32 b);
> +s32 notrace __modsi3(s32 a, s32 b);
> +s32 notrace __umodsi3(s32 a, s32 b);

Shouldn't the 'u' prefixed functions have unsigned int args, result.
It seems libgcc/?divmod.c doesn't but ARC does have nint_t for those 
which is unsigned.
Nios it seems was removed from gcc?

>   #ifdef CONFIG_HAVE_ARCH_LIBGCC_H
>   #include <asm/libgcc.h>
>   #endif
> diff --git a/lib/Kconfig b/lib/Kconfig
> index 1e42f5167c68b..16c2f2008b82c 100644
> --- a/lib/Kconfig
> +++ b/lib/Kconfig
> @@ -611,6 +611,21 @@ config GENERIC_LIB_CMPDI2
>   config GENERIC_LIB_UCMPDI2
>   	bool
>   
> +config GENERIC_LIB_DIVSI3
> +	bool
> +
> +config GENERIC_LIB_MODSI3
> +	bool
> +
> +config GENERIC_LIB_UDIVSI3
> +	bool
> +
> +config GENERIC_LIB_UMODSI3
> +	bool
> +
> +config GENERIC_LIB_MULSI3
> +	bool
> +
>   config GENERIC_LIB_DEVMEM_IS_ALLOWED
>   	bool
>   
> diff --git a/lib/Makefile b/lib/Makefile
> index a2afe954805cb..352a012baecba 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -337,6 +337,16 @@ obj-$(CONFIG_GENERIC_LIB_LSHRDI3) += lshrdi3.o
>   obj-$(CONFIG_GENERIC_LIB_MULDI3) += muldi3.o
>   obj-$(CONFIG_GENERIC_LIB_CMPDI2) += cmpdi2.o
>   obj-$(CONFIG_GENERIC_LIB_UCMPDI2) += ucmpdi2.o
> +obj-$(CONFIG_GENERIC_LIB_MULSI3) += mulsi3.o
> +
> +divmod-needed := $(or \
> +	$(CONFIG_GENERIC_LIB_DIVSI3),\
> +	$(CONFIG_GENERIC_LIB_MODSI3),\
> +	$(CONFIG_GENERIC_LIB_UDIVSI3),\
> +	$(CONFIG_GENERIC_LIB_UMODSI3))
> +obj-$(divmod-needed) += divmod.o
> +
> +
>   obj-$(CONFIG_OBJAGG) += objagg.o
>   
>   # pldmfw library
> diff --git a/lib/divmod.c b/lib/divmod.c
> new file mode 100644
> index 0000000000000..cc1df6f9978ce
> --- /dev/null
> +++ b/lib/divmod.c
> @@ -0,0 +1,94 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/* Copyright Altera Corporation (C) 2026. All rights reserved.
> + */
> +
> +#include <linux/libgcc.h>
> +#include <linux/export.h>
> +#include <linux/types.h>
> +
> +static u32 udivmodsi4(u32 num, u32 den, int modwanted)
> +{
> +	u32 bit = 1;
> +	u32 res = 0;
> +
> +	while (den < num && bit && !(den & (1U << 31))) {
> +		den <<= 1;
> +		bit <<= 1;
> +	}
> +
> +	while (bit) {
> +		if (num >= den) {
> +			num -= den;
> +			res |= bit;
> +		}
> +		bit >>= 1;
> +		den >>= 1;
> +	}
> +
> +	return modwanted ? num : res;
> +}
> +
> +
> +#ifdef CONFIG_GENERIC_LIB_DIVSI3
> +s32 __divsi3(s32 a, s32 b)
> +{
> +	int neg = 0;
> +	s32 res;
> +
> +	if (a < 0) {
> +		a = -a;
> +		neg = !neg;
> +	}
> +
> +	if (b < 0) {
> +		b = -b;
> +		neg = !neg;
> +	}
> +
> +	res = udivmodsi4(a, b, 0);
> +	if (neg)
> +		res = -res;
> +
> +	return res;
> +}
> +EXPORT_SYMBOL(__divsi3);
> +#endif
> +
> +#ifdef CONFIG_GENERIC_LIB_MODSI3
> +s32 __modsi3(s32 a, s32 b)
> +{
> +	int neg = 0;
> +	s32 res;
> +
> +	if (a < 0) {
> +		a = -a;
> +		neg = 1;
> +	}
> +
> +	if (b < 0)
> +		b = -b;
> +
> +	res = udivmodsi4(a, b, 1);
> +	if (neg)
> +		res = -res;
> +
> +	return res;
> +}
> +EXPORT_SYMBOL(__modsi3);
> +#endif
> +
> +#ifdef CONFIG_GENERIC_LIB_UDIVSI3
> +s32 __udivsi3(s32 a, s32 b)
> +{
> +	return udivmodsi4(a, b, 0);
> +}
> +EXPORT_SYMBOL(__udivsi3);
> +#endif
> +
> +#ifdef CONFIG_GENERIC_LIB_UMODSI3
> +s32 __umodsi3(s32 a, s32 b)
> +{
> +	return udivmodsi4(a, b, 1);
> +}
> +EXPORT_SYMBOL(__umodsi3);
> +#endif
> diff --git a/lib/mulsi3.c b/lib/mulsi3.c
> new file mode 100644
> index 0000000000000..6596a6598de05
> --- /dev/null
> +++ b/lib/mulsi3.c
> @@ -0,0 +1,24 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/* Copyright Altera Corporation (C) 2026. All rights reserved.
> + */
> +
> +#include <linux/libgcc.h>
> +#include <linux/export.h>
> +#include <linux/types.h>
> +
> +s32 __mulsi3(s32 a, s32 b)
> +{
> +	s32 res = 0;
> +	u32 cnt = a;
> +
> +	while (cnt) {
> +		if (cnt & 1)
> +			res += b;
> +
> +		b <<= 1;
> +		cnt >>= 1;
> +	}
> +
> +	return res;
> +}
> +EXPORT_SYMBOL(__mulsi3);
>

Re: [PATCH v2 1/3] lib: extract 32bit mul/div helpers from nios2 into GENERIC_LIB

[David Laight]

On Tue, 3 Nov 2026 20:23:23 -0800
Vineet Gupta <vgupta@kernel.org> wrote:

> Nios it seems was removed from gcc?

Yep, Intel deprecated it not long before demerging Altera.
Loosely on the basis that they have a RISCV soft cpu for the fpga.
gcc followed (even though the code to support it isn't that big
- I can probably find a copy, you can't download it any more),
as has busybox.

This annoyed the company I worked for (and probably a lot of telco).
RISCV isn't a replacement in any sense, it is missing a lot of
features (like custom instructions) and doesn't have the same level
of customisation.
I wouldn't run Linux on one (you might get 100MHz if you are lucky
and it is definitely in-order one instruction per clock), but it is
useful for 'control pane' logic that would be too complex and large
in straight VHDL/Verilog.
Typically only a few KB of code running in a tight loop.

I've a clean-room copy of the integer part of the cpu - written
in a few weeks (and I'm not really a hardware engineer).

David

Re: [PATCH v2 1/3] lib: extract 32bit mul/div helpers from nios2 into GENERIC_LIB

[Simon Schuster]

Hello Vineet,

On Tue, Nov 03, 2026 at 08:23:23PM -0800, Vineet Gupta wrote:
> > +/*
> > + * Software 32-bit multiply for cores built without the hardware multiplier.
> > + */
> > +s32 notrace __mulsi3(s32 a, s32 b);
> > +s32 notrace __divsi3(s32 a, s32 b);
> > +s32 notrace __udivsi3(s32 a, s32 b);
> > +s32 notrace __modsi3(s32 a, s32 b);
> > +s32 notrace __umodsi3(s32 a, s32 b);
> 
> Shouldn't the 'u' prefixed functions have unsigned int args, result.
> It seems libgcc/?divmod.c doesn't but ARC does have nint_t for those which
> is unsigned.
> Nios it seems was removed from gcc?

As David has correctly pointed out, nios2 was dropped from gcc with
release line 14.y being the last one to contain it.
So at least for nios2, it seems like it has always been the case that
__udivsi3/__umodsi3 were declared as taking and returning SItypes:

https://github.com/gcc-mirror/gcc/blob/releases/gcc-14/libgcc/config/nios2/lib2-divmod.c#L106

Given that both implementations continue to pass it through to a very
similarly looking udivmodsi4 as u32, I would assume that this has partly
relied on 'why should the compiler do any strange upcasts here, it will
just pass through the registers and be done with it and this is
implementation-defined-good-enough', so I would not mind rolling a v3
with u32s for __umodsi3 and __udivsi3. Are these the only two symbols
you are concerned about, and would these signatures work for you?

u32 notrace __udivsi3(u32 a, u32 b);
u32 notrace __umodsi3(u32 a, u32 b);

Best regards
Simon

Re: [PATCH v2 1/3] lib: extract 32bit mul/div helpers from nios2 into GENERIC_LIB

[Vineet Gupta]

On 11/6/26 05:07, Simon Schuster wrote:
> Hello Vineet,
>
> On Tue, Nov 03, 2026 at 08:23:23PM -0800, Vineet Gupta wrote:
>>> +/*
>>> + * Software 32-bit multiply for cores built without the hardware multiplier.
>>> + */
>>> +s32 notrace __mulsi3(s32 a, s32 b);
>>> +s32 notrace __divsi3(s32 a, s32 b);
>>> +s32 notrace __udivsi3(s32 a, s32 b);
>>> +s32 notrace __modsi3(s32 a, s32 b);
>>> +s32 notrace __umodsi3(s32 a, s32 b);
>> Shouldn't the 'u' prefixed functions have unsigned int args, result.
>> It seems libgcc/?divmod.c doesn't but ARC does have nint_t for those which
>> is unsigned.
>> Nios it seems was removed from gcc?
> As David has correctly pointed out, nios2 was dropped from gcc with
> release line 14.y being the last one to contain it.
> So at least for nios2, it seems like it has always been the case that
> __udivsi3/__umodsi3 were declared as taking and returning SItypes:
>
> https://github.com/gcc-mirror/gcc/blob/releases/gcc-14/libgcc/config/nios2/lib2-divmod.c#L106
>
> Given that both implementations continue to pass it through to a very
> similarly looking udivmodsi4 as u32, I would assume that this has partly
> relied on 'why should the compiler do any strange upcasts here, it will
> just pass through the registers and be done with it and this is
> implementation-defined-good-enough', so I would not mind rolling a v3
> with u32s for __umodsi3 and __udivsi3. Are these the only two symbols
> you are concerned about, and would these signatures work for you?
>
> u32 notrace __udivsi3(u32 a, u32 b);
> u32 notrace __umodsi3(u32 a, u32 b);

Yep that's what I had in my local version.

Thx,
-Vineet

[PATCH v2 2/3] nios2: export __divsi3_table

[Simon Schuster]

As noted in <20261026234452.1086974-1-sashal@kernel.org>, gcc can
occasionally emit references to __divsi3_table, so we need to include
that one in libgcc-less builds, as well.

The definition originates from gcc/config/nios2/lib2-divtable.c that
was distributed in source by Altera as part of the nios2eds in
gcc 3.4.1 (Altera Nios II 6.1 b197) under GPLv2 or later.

lib2-divtable.c does not carry an explicit copyright notice in the gcc
release, the associated nios2.h is: Copyright (C) 2005 Altera.

Nonetheless, the table can also be regenerated by the following snippet:

perl -e 'for my $row (0..15) {
  print join(", ", map { $_ == 0 ? 0 : "$row/$_" } 0..15), ",\n";
}'

Signed-off-by: Simon Schuster <schuster.simon@siemens-energy.com>
---
 arch/nios2/lib/Makefile |  1 +
 arch/nios2/lib/math.c   | 24 ++++++++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/arch/nios2/lib/Makefile b/arch/nios2/lib/Makefile
index 9d5bf1df520c1..86433dcaac7e5 100644
--- a/arch/nios2/lib/Makefile
+++ b/arch/nios2/lib/Makefile
@@ -7,3 +7,4 @@ lib-y += delay.o
 lib-y += memcpy.o
 lib-y += memmove.o
 lib-y += memset.o
+lib-y += math.o
diff --git a/arch/nios2/lib/math.c b/arch/nios2/lib/math.c
new file mode 100644
index 0000000000000..ae65cc11667fa
--- /dev/null
+++ b/arch/nios2/lib/math.c
@@ -0,0 +1,24 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <linux/export.h>
+#include <linux/types.h>
+
+u8 __divsi3_table[] = {
+0, 0/1, 0/2, 0/3, 0/4, 0/5, 0/6, 0/7, 0/8, 0/9, 0/10, 0/11, 0/12, 0/13, 0/14, 0/15,
+0, 1/1, 1/2, 1/3, 1/4, 1/5, 1/6, 1/7, 1/8, 1/9, 1/10, 1/11, 1/12, 1/13, 1/14, 1/15,
+0, 2/1, 2/2, 2/3, 2/4, 2/5, 2/6, 2/7, 2/8, 2/9, 2/10, 2/11, 2/12, 2/13, 2/14, 2/15,
+0, 3/1, 3/2, 3/3, 3/4, 3/5, 3/6, 3/7, 3/8, 3/9, 3/10, 3/11, 3/12, 3/13, 3/14, 3/15,
+0, 4/1, 4/2, 4/3, 4/4, 4/5, 4/6, 4/7, 4/8, 4/9, 4/10, 4/11, 4/12, 4/13, 4/14, 4/15,
+0, 5/1, 5/2, 5/3, 5/4, 5/5, 5/6, 5/7, 5/8, 5/9, 5/10, 5/11, 5/12, 5/13, 5/14, 5/15,
+0, 6/1, 6/2, 6/3, 6/4, 6/5, 6/6, 6/7, 6/8, 6/9, 6/10, 6/11, 6/12, 6/13, 6/14, 6/15,
+0, 7/1, 7/2, 7/3, 7/4, 7/5, 7/6, 7/7, 7/8, 7/9, 7/10, 7/11, 7/12, 7/13, 7/14, 7/15,
+0, 8/1, 8/2, 8/3, 8/4, 8/5, 8/6, 8/7, 8/8, 8/9, 8/10, 8/11, 8/12, 8/13, 8/14, 8/15,
+0, 9/1, 9/2, 9/3, 9/4, 9/5, 9/6, 9/7, 9/8, 9/9, 9/10, 9/11, 9/12, 9/13, 9/14, 9/15,
+0, 10/1, 10/2, 10/3, 10/4, 10/5, 10/6, 10/7, 10/8, 10/9, 10/10, 10/11, 10/12, 10/13, 10/14, 10/15,
+0, 11/1, 11/2, 11/3, 11/4, 11/5, 11/6, 11/7, 11/8, 11/9, 11/10, 11/11, 11/12, 11/13, 11/14, 11/15,
+0, 12/1, 12/2, 12/3, 12/4, 12/5, 12/6, 12/7, 12/8, 12/9, 12/10, 12/11, 12/12, 12/13, 12/14, 12/15,
+0, 13/1, 13/2, 13/3, 13/4, 13/5, 13/6, 13/7, 13/8, 13/9, 13/10, 13/11, 13/12, 13/13, 13/14, 13/15,
+0, 14/1, 14/2, 14/3, 14/4, 14/5, 14/6, 14/7, 14/8, 14/9, 14/10, 14/11, 14/12, 14/13, 14/14, 14/15,
+0, 15/1, 15/2, 15/3, 15/4, 15/5, 15/6, 15/7, 15/8, 15/9, 15/10, 15/11, 15/12, 15/13, 15/14, 15/15,
+};
+EXPORT_SYMBOL(__divsi3_table);

-- 
2.39.5

[PATCH v2 3/3] nios2: Drop usage of libgcc in favour of GENERIC_LIB_*

[Simon Schuster]

From: Dinh Nguyen <dinguyen@kernel.org>

Use the kernel's runtime support for lshrdi3, ashldi3, ashrdi3, muldi3,
and ucmpdi2, mulsi3, divsi3, udivsi3, modsi3, and umodsi3.

Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>
Co-developed-by: Simon Schuster <schuster.simon@siemens-energy.com>
Signed-off-by: Simon Schuster <schuster.simon@siemens-energy.com>
---
 arch/nios2/Kconfig              | 10 ++++++++++
 arch/nios2/Makefile             |  4 +---
 arch/nios2/kernel/nios2_ksyms.c | 22 ----------------------
 3 files changed, 11 insertions(+), 25 deletions(-)

diff --git a/arch/nios2/Kconfig b/arch/nios2/Kconfig
index 9c0e6eaeb005c..3082444b2b487 100644
--- a/arch/nios2/Kconfig
+++ b/arch/nios2/Kconfig
@@ -14,6 +14,16 @@ config NIOS2
 	select GENERIC_CPU_DEVICES
 	select GENERIC_IRQ_PROBE
 	select GENERIC_IRQ_SHOW
+	select GENERIC_LIB_LSHRDI3
+	select GENERIC_LIB_ASHLDI3
+	select GENERIC_LIB_ASHRDI3
+	select GENERIC_LIB_MULDI3
+	select GENERIC_LIB_UCMPDI2
+	select GENERIC_LIB_DIVSI3
+	select GENERIC_LIB_MODSI3
+	select GENERIC_LIB_UDIVSI3
+	select GENERIC_LIB_UMODSI3
+	select GENERIC_LIB_MULSI3
 	select HAVE_ARCH_TRACEHOOK
 	select HAVE_ARCH_KGDB
 	select HAVE_PAGE_SIZE_4KB
diff --git a/arch/nios2/Makefile b/arch/nios2/Makefile
index f1ff4ce0f1a2c..173588c31abf9 100644
--- a/arch/nios2/Makefile
+++ b/arch/nios2/Makefile
@@ -19,8 +19,6 @@ UTS_SYSNAME = Linux
 
 export MMU
 
-LIBGCC         := $(shell $(CC) $(KBUILD_CFLAGS) $(KCFLAGS) -print-libgcc-file-name)
-
 KBUILD_AFLAGS += -march=r$(CONFIG_NIOS2_ARCH_REVISION)
 
 KBUILD_CFLAGS += -pipe -D__linux__ -D__ELF__
@@ -37,7 +35,7 @@ KBUILD_CFLAGS += -DUTS_SYSNAME=\"$(UTS_SYSNAME)\"
 KBUILD_CFLAGS += -fno-builtin
 KBUILD_CFLAGS += -G 0
 
-libs-y		+= arch/nios2/lib/ $(LIBGCC)
+libs-y		+= arch/nios2/lib/
 
 INSTALL_PATH ?= /tftpboot
 nios2-boot := arch/$(ARCH)/boot
diff --git a/arch/nios2/kernel/nios2_ksyms.c b/arch/nios2/kernel/nios2_ksyms.c
index e8710a269b398..351664e236fac 100644
--- a/arch/nios2/kernel/nios2_ksyms.c
+++ b/arch/nios2/kernel/nios2_ksyms.c
@@ -21,25 +21,3 @@ EXPORT_SYMBOL(memmove);
 /* memory management */
 
 EXPORT_SYMBOL(flush_icache_range);
-
-/*
- * libgcc functions - functions that are used internally by the
- * compiler...  (prototypes are not correct though, but that
- * doesn't really matter since they're not versioned).
- */
-#define DECLARE_EXPORT(name)	extern void name(void); EXPORT_SYMBOL(name)
-
-DECLARE_EXPORT(__gcc_bcmp);
-DECLARE_EXPORT(__divsi3);
-DECLARE_EXPORT(__moddi3);
-DECLARE_EXPORT(__modsi3);
-DECLARE_EXPORT(__udivmoddi4);
-DECLARE_EXPORT(__udivsi3);
-DECLARE_EXPORT(__umoddi3);
-DECLARE_EXPORT(__umodsi3);
-DECLARE_EXPORT(__muldi3);
-DECLARE_EXPORT(__mulsi3);
-DECLARE_EXPORT(__ucmpdi2);
-DECLARE_EXPORT(__lshrdi3);
-DECLARE_EXPORT(__ashldi3);
-DECLARE_EXPORT(__ashrdi3);

-- 
2.39.5

Re: [PATCH v2 0/3] lib: Add software mul/div helpers and use them from nios2

[Arnd Bergmann]

On Tue, Nov 3, 2026, at 14:30, Simon Schuster wrote:
> Recently, there have been linking failures on nios2 regarding libgcc
> symbols that we reexport to modules (in particular __mulsi3 [0], and
> __divsi3_table [1]).
>
> In the resulting discussion, Arnd suggested [2] dropping the libgcc
> dependency altogether, as -- while specific functions might be fine --
> libgcc does not expect to run in a kernel-like freestanding environment.
>
> To this end, Dinh Nguyen was kind enough to locate and extract
> GPLv2-compliant versions of the software mul/div/mod functions required
> by nios2 gcc and integrate them into the kernel. As Arnd also suggested
> [3] that these might be helpful to other smaller architectures (such as
> arc or openrisc), I've further extracted them to lib/ with corresponding
> CONFIG_GENERIC_LIB_* options that allow selectively enabling and
> exporting these as required.
>

Looks good to me. I'll wait for Vineet to comment, as he wants to
use these on ARC as well, but plan to merge these in the asm-generic
tree for 7.5 then. I also tried the patch below on top of your
series to make openrisc build without libgcc, which worked.
I tried the same on parisc but failed because that one needs
several extra libgcc files.

I would have added the __divsi3_table symbol to lib/ as well for
consistency, but there is no difference in practice as other
architectures don't use this, so I don't mind.

> Furthermore -Wno-attribute-alias -Wno-missing-prototypes
> -Wno-missing-declarations and -Wno-unused-function were required due
> to unrelated Werror-related compilation issues, but as this series
> concerns compiler intrinsics that are never explicitly referenced
> in code and it links fine this  seems acceptable to me

It's certainly worth fixing these properly rather than turning them
off, but I agree that is clearly unrelated. For most of these it
should be sufficient to either mark functions as 'static' where
possible, or include the correct headers, and both of these are
generally good ideas anyway.

      Arnd

diff --git a/arch/openrisc/Kconfig b/arch/openrisc/Kconfig
index 6aaedc67a5e0..5be29befd86c 100644
--- a/arch/openrisc/Kconfig
+++ b/arch/openrisc/Kconfig
@@ -22,6 +22,16 @@ config OPENRISC
 	select GENERIC_IRQ_CHIP
 	select GENERIC_IRQ_PROBE
 	select GENERIC_IRQ_SHOW
+	select GENERIC_LIB_LSHRDI3
+	select GENERIC_LIB_ASHLDI3
+	select GENERIC_LIB_ASHRDI3
+	select GENERIC_LIB_MULDI3
+	select GENERIC_LIB_UCMPDI2
+	select GENERIC_LIB_DIVSI3
+	select GENERIC_LIB_MODSI3
+	select GENERIC_LIB_UDIVSI3
+	select GENERIC_LIB_UMODSI3
+	select GENERIC_LIB_MULSI3
 	select GENERIC_PCI_IOMAP
 	select GENERIC_IOREMAP
 	select GENERIC_CPU_DEVICES
diff --git a/arch/openrisc/Makefile b/arch/openrisc/Makefile
index 68249521db5a..38dc87bc6a3a 100644
--- a/arch/openrisc/Makefile
+++ b/arch/openrisc/Makefile
@@ -18,7 +18,6 @@
 KBUILD_DEFCONFIG := or1ksim_defconfig
 
 OBJCOPYFLAGS    := -O binary -R .note -R .comment -S
-LIBGCC 		:= $(shell $(CC) $(KBUILD_CFLAGS) -print-libgcc-file-name)
 
 KBUILD_CFLAGS	+= -pipe -ffixed-r10 -D__linux__
 KBUILD_CFLAGS	+= -msfimm -mshftimm
@@ -55,8 +54,6 @@ ifeq ($(CONFIG_OPENRISC_HAVE_INST_SEXT),y)
 	KBUILD_CFLAGS += $(call cc-option,-msext)
 endif
 
-libs-y		+= $(LIBGCC)
-
 PHONY += vmlinux.bin
 
 vmlinux.bin: vmlinux
diff --git a/arch/openrisc/kernel/or32_ksyms.c b/arch/openrisc/kernel/or32_ksyms.c
index 84a937a64e2a..7ae38030a9d4 100644
--- a/arch/openrisc/kernel/or32_ksyms.c
+++ b/arch/openrisc/kernel/or32_ksyms.c
@@ -27,19 +27,6 @@
 #include <asm/hardirq.h>
 #include <asm/delay.h>
 
-#define DECLARE_EXPORT(name) extern void name(void); EXPORT_SYMBOL(name)
-
-/* compiler generated symbols */
-DECLARE_EXPORT(__udivsi3);
-DECLARE_EXPORT(__divsi3);
-DECLARE_EXPORT(__umodsi3);
-DECLARE_EXPORT(__modsi3);
-DECLARE_EXPORT(__muldi3);
-DECLARE_EXPORT(__ashrdi3);
-DECLARE_EXPORT(__ashldi3);
-DECLARE_EXPORT(__lshrdi3);
-DECLARE_EXPORT(__ucmpdi2);
-
 EXPORT_SYMBOL(__copy_tofrom_user);
 EXPORT_SYMBOL(__clear_user);
 EXPORT_SYMBOL(memset);