[PATCH 1/2] RISC-V: implement private GCC library

[Heinrich Schuchardt]

On 12/2/25 04:57, Yao Zi wrote:
> On Mon, Dec 01, 2025 at 06:49:03PM +0100, Heinrich Schuchardt wrote:
>> The following functions are provided:
>>
>> Count leading zero bits
>>
>> * int __clzsi2 (unsigned int a)
>> * int __clzdi2 (unsigned long a)
>> * int __clzti2 (unsigned long long a)
>>
>> Count trailing zero bits
>>
>> * int __ctzsi2 (unsigned int a)
>> * int __ctzdi2 (unsigned long a)
>> * int __ctzti2 (unsigned long long a)
>>
>> Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>
>> ---
> 
> I noted there's another series with the same subject[1] sent almost at
> the same time, and I couldn't tell the difference at the first glance.
> Is this an incident?

Thank you for reviewing.

That was my mistake. I have set the first mail series [1] to superseded 
in Patchwork.

> 
>>   arch/Kconfig            |   1 +
>>   arch/riscv/lib/Makefile |   2 +
>>   arch/riscv/lib/clz.c    | 105 ++++++++++++++++++++++++++++++++++++++++
>>   arch/riscv/lib/ctz.c    |  95 ++++++++++++++++++++++++++++++++++++
>>   lib/Kconfig             |   2 +-
>>   5 files changed, 204 insertions(+), 1 deletion(-)
>>   create mode 100644 arch/riscv/lib/clz.c
>>   create mode 100644 arch/riscv/lib/ctz.c
>>
>> diff --git a/arch/Kconfig b/arch/Kconfig
>> index 3133f892f94..4af0da2485f 100644
>> --- a/arch/Kconfig
>> +++ b/arch/Kconfig
>> @@ -159,6 +159,7 @@ config PPC
>>   config RISCV
>>   	bool "RISC-V architecture"
>>   	select CREATE_ARCH_SYMLINK
>> +	select HAVE_PRIVATE_LIBGCC if 64BIT
> 
> Are 32-bit platforms excluded for lacking of enough library functions?
> Should we exclude !RISCV_ISA_F || !RISCV_ISA_D platforms as well? Though
> there's no in-tree 64-bit port without F/D extension.

As I am not aware of any RVA23 distro for 32bit RISC-V, I see no current 
need.

32-bit support will require additionally implementing __ashldi3, 
__lshldi3, __udivdi3.

If you want to implement these extra functions, you cannot trust the 
documentation. The functions don't take the arguments described in 
https://gcc.gnu.org/onlinedocs/gccint/Integer-library-routines.html. E.g 
__ashldi3 expects a 64 bit value passed in registers a0 (low bits), a1 
(high bits) while the shift is passed in a2. 32-bit __udivdi3 expects 
two 64-bit values.

See 
https://github.com/gcc-mirror/gcc/blob/addda4a7e8593c37c90eb4c1d7edda29fa4bde31/libgcc/libgcc2.c#L412

libgcc is published under GPL-3 and therefore we cannot simply copy that 
code into our GPL-2 project.

Best regards

Heinrich

> 
>>   	select HAVE_SETJMP
>>   	select HAVE_INITJMP
>>   	select SUPPORT_ACPI
> 
> Regards,
> Yao Zi
> 
> [1]: https://lore.kernel.org/u-boot/20251201174705.652626-1-zfsdt@canonical.com/