[PATCH bpf-next] riscv, bpf: Fix missing sign-ext for signed 1-byte and 2-byte kfunc args

[PATCH bpf-next] riscv, bpf: Fix missing sign-ext for signed 1-byte and 2-byte kfunc args

[Pu Lehui]

From: Pu Lehui <pulehui@huawei.com>

On RV64, the ABI requires sign-extension for signed 1-byte and 2-byte
kfunc args. However, the RV64 JIT currently does not perform
sign-extension for such kfunc args.

Before commit 7ce090afbf72 ("bpf: Infer zext_dst based on static
register liveness analysis"), state pruning could potentially omit
zero-extension of 32-bit subregisters, which inadvertently masked the
above issue by making the args appear as if they had been properly
sign-extended. After that commit, the problem is exposed, causing the
kfunc_call/kfunc_call_test4 selftest to fail.

Fix this by extending the existing sign-extension logic to handle signed
1-byte and 2-byte kfunc args as well.

Fixes: 443574b03387 ("riscv, bpf: Fix kfunc parameters incompatibility between bpf and riscv abi")
Signed-off-by: Pu Lehui <pulehui@huawei.com>
---
 arch/riscv/net/bpf_jit_comp64.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
index 2504df1fa111..74efe4b138d2 100644
--- a/arch/riscv/net/bpf_jit_comp64.c
+++ b/arch/riscv/net/bpf_jit_comp64.c
@@ -1823,9 +1823,10 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
 
 			for (idx = 0; idx < fm->nr_args; idx++) {
 				u8 reg = bpf_to_rv_reg(BPF_REG_1 + idx, ctx);
+				bool sign = fm->arg_flags[idx] & BTF_FMODEL_SIGNED_ARG;
 
-				if (fm->arg_size[idx] == sizeof(int))
-					emit_sextw(reg, reg, ctx);
+				if (sign_extend(reg, reg, fm->arg_size[idx], sign, ctx))
+					return -EINVAL;
 			}
 		}
 
-- 
2.34.1

Re: [PATCH bpf-next] riscv, bpf: Fix missing sign-ext for signed 1-byte and 2-byte kfunc args

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] The patch introduces a call to a `sign_extend()` function that is undeclared and undefined, resulting in a compilation failure.
--

--- Patch [1]: [PATCH bpf-next] riscv, bpf: Fix missing sign-ext for signed 1-byte and 2-byte kfunc args ---
commit 47567ad8c96e02d677f1ae5123565efa9cf1b55f
Author: Pu Lehui <pulehui@huawei.com>

riscv, bpf: Fix missing sign-ext for signed 1-byte and 2-byte kfunc args

This commit updates the RISC-V BPF JIT to sign-extend 1-byte and 2-byte
kfunc arguments as required by the RV64 ABI. This addresses an issue exposed
by recent state pruning liveness analysis changes.

> diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
> index 10e01ff06312d..0c6de02eb33a8 100644
> --- a/arch/riscv/net/bpf_jit_comp64.c
> +++ b/arch/riscv/net/bpf_jit_comp64.c
> @@ -1784,9 +1784,10 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
>  
>  			for (idx = 0; idx < fm->nr_args; idx++) {
>  				u8 reg = bpf_to_rv_reg(BPF_REG_1 + idx, ctx);
> +				bool sign = fm->arg_flags[idx] & BTF_FMODEL_SIGNED_ARG;
>  
> -				if (fm->arg_size[idx] == sizeof(int))
> -					emit_sextw(reg, reg, ctx);
> +				if (sign_extend(reg, reg, fm->arg_size[idx], sign, ctx))
> +					return -EINVAL;

[Severity: Low]
Is sign_extend() declared in this context?

It appears this function might be missing from this file or requires an
unapplied prerequisite patch. Looking through the source, there doesn't
appear to be a sign_extend() function defined in the RISC-V BPF JIT code
that matches this 5-argument signature. Will this cause a build failure due
to an undeclared function?

>  			}
>  		}
>

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260814064726.3607615-1-pulehui@huaweicloud.com?part=1

Re: [PATCH bpf-next] riscv, bpf: Fix missing sign-ext for signed 1-byte and 2-byte kfunc args

[Pu Lehui]

On 2026/8/14 14:57, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [Low] The patch introduces a call to a `sign_extend()` function that is undeclared and undefined, resulting in a compilation failure.
> --
> 
> --- Patch [1]: [PATCH bpf-next] riscv, bpf: Fix missing sign-ext for signed 1-byte and 2-byte kfunc args ---
> commit 47567ad8c96e02d677f1ae5123565efa9cf1b55f
> Author: Pu Lehui <pulehui@huawei.com>
> 
> riscv, bpf: Fix missing sign-ext for signed 1-byte and 2-byte kfunc args
> 
> This commit updates the RISC-V BPF JIT to sign-extend 1-byte and 2-byte
> kfunc arguments as required by the RV64 ABI. This addresses an issue exposed
> by recent state pruning liveness analysis changes.
> 
>> diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
>> index 10e01ff06312d..0c6de02eb33a8 100644
>> --- a/arch/riscv/net/bpf_jit_comp64.c
>> +++ b/arch/riscv/net/bpf_jit_comp64.c
>> @@ -1784,9 +1784,10 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
>>   
>>   			for (idx = 0; idx < fm->nr_args; idx++) {
>>   				u8 reg = bpf_to_rv_reg(BPF_REG_1 + idx, ctx);
>> +				bool sign = fm->arg_flags[idx] & BTF_FMODEL_SIGNED_ARG;
>>   
>> -				if (fm->arg_size[idx] == sizeof(int))
>> -					emit_sextw(reg, reg, ctx);
>> +				if (sign_extend(reg, reg, fm->arg_size[idx], sign, ctx))
>> +					return -EINVAL;
> 
> [Severity: Low]
> Is sign_extend() declared in this context?

No, sign_extend() has been add by commit fd2e08128944a("riscv, bpf: Sign 
extend struct ops return values properly"), and there is no building 
failure.

> 
> It appears this function might be missing from this file or requires an
> unapplied prerequisite patch. Looking through the source, there doesn't
> appear to be a sign_extend() function defined in the RISC-V BPF JIT code
> that matches this 5-argument signature. Will this cause a build failure due
> to an undeclared function?
> 
>>   			}
>>   		}
>>
> 

Re: [PATCH bpf-next] riscv, bpf: Fix missing sign-ext for signed 1-byte and 2-byte kfunc args

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Daniel Borkmann <daniel@iogearbox.net>:

On Fri, 14 Aug 2026 06:47:26 +0000 you wrote:
> From: Pu Lehui <pulehui@huawei.com>
> 
> On RV64, the ABI requires sign-extension for signed 1-byte and 2-byte
> kfunc args. However, the RV64 JIT currently does not perform
> sign-extension for such kfunc args.
> 
> Before commit 7ce090afbf72 ("bpf: Infer zext_dst based on static
> register liveness analysis"), state pruning could potentially omit
> zero-extension of 32-bit subregisters, which inadvertently masked the
> above issue by making the args appear as if they had been properly
> sign-extended. After that commit, the problem is exposed, causing the
> kfunc_call/kfunc_call_test4 selftest to fail.
> 
> [...]

Here is the summary with links:
  - [bpf-next] riscv, bpf: Fix missing sign-ext for signed 1-byte and 2-byte kfunc args
    https://git.kernel.org/bpf/bpf-next/c/f2aaa6215910

You are awesome, thank you!
-- 
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