Re: [PATCH bpf-next] riscv, bpf: Fix RV32 broken build, and silence RV64 warning

[Daniel Borkmann <daniel@xxxxxxxxxxxxx>]

On 11/3/21 12:54 PM, Björn Töpel wrote:
> Commit 252c765bd764 ("riscv, bpf: Add BPF exception tables") only
> addressed RV64, and broke the RV32 build [1]. Fix by gating the exception
> tables code with CONFIG_ARCH_RV64I.
>
> Further, silence a "-Wmissing-prototypes" warning [2] in the RV64 BPF
> JIT.
>
> [1] https://lore.kernel.org/llvm/202111020610.9oy9Rr0G-lkp@xxxxxxxxx/
> [2] https://lore.kernel.org/llvm/202110290334.2zdMyRq4-lkp@xxxxxxxxx/
>
> Fixes: 252c765bd764 ("riscv, bpf: Add BPF exception tables")
> Signed-off-by: Björn Töpel <bjorn@xxxxxxxxxx>
> ---
> Tong/Daniel: The RV32 build has been broken since Thursday. I'll try
> to fast-track a bit, and commit a quick-fix for it. Hope that's OK
> with you, Tong!
>
> I've verified the build on my machine using riscv32 GCC 9.3.0 and
> riscv64 GCC 11.2.0.

Thanks for the fix Bjorn!

> arch/riscv/mm/extable.c         | 4 ++--
>   arch/riscv/net/bpf_jit_comp64.c | 2 ++
>   2 files changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/mm/extable.c b/arch/riscv/mm/extable.c
> index 18bf338303b6..ddb7d3b99e89 100644
> --- a/arch/riscv/mm/extable.c
> +++ b/arch/riscv/mm/extable.c
> @@ -11,7 +11,7 @@
>   #include <linux/module.h>
>   #include <linux/uaccess.h>
>   
> -#ifdef CONFIG_BPF_JIT
> +#if defined(CONFIG_BPF_JIT) && defined(CONFIG_ARCH_RV64I)
>   int rv_bpf_fixup_exception(const struct exception_table_entry *ex, struct pt_regs *regs);
>   #endif
>   
> @@ -23,7 +23,7 @@ int fixup_exception(struct pt_regs *regs)
>   	if (!fixup)
>   		return 0;
>   
> -#ifdef CONFIG_BPF_JIT
> +#if defined(CONFIG_BPF_JIT) && defined(CONFIG_ARCH_RV64I)
>   	if (regs->epc >= BPF_JIT_REGION_START && regs->epc < BPF_JIT_REGION_END)
>   		return rv_bpf_fixup_exception(fixup, regs);
>   #endif
> diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
> index 2ca345c7b0bf..f2a779c7e225 100644
> --- a/arch/riscv/net/bpf_jit_comp64.c
> +++ b/arch/riscv/net/bpf_jit_comp64.c
> @@ -459,6 +459,8 @@ static int emit_call(bool fixed, u64 addr, struct rv_jit_context *ctx)
>   #define BPF_FIXUP_OFFSET_MASK   GENMASK(26, 0)
>   #define BPF_FIXUP_REG_MASK      GENMASK(31, 27)
>   
> +int rv_bpf_fixup_exception(const struct exception_table_entry *ex,
> +				struct pt_regs *regs);

I'm okay to take this as a quick fix, but if its not too much hassle, could we add a
arch/riscv/include/asm/extable.h in similar fashion like arm64 or x86 where we move
the ex_handler_bpf() signature there, did you have a chance to check?

>   int rv_bpf_fixup_exception(const struct exception_table_entry *ex,
>   				struct pt_regs *regs)
>   {
>
> base-commit: cc0356d6a02e064387c16a83cb96fe43ef33181e

Thanks,
Daniel