Re: [PATCH bpf-next] riscv, bpf: fix some compiler error

[tongtiangen <tongtiangen@huawei.com>]

On 2021/11/2 23:45, Björn Töpel wrote:
> On Tue, 2 Nov 2021 at 15:40, Tong Tiangen <tongtiangen@huawei.com> wrote:
>>
>> This patch fix two compile errors:
>> 1. when CONFIG_BPF_JIT and CONFIG_ARCH_32I is open, There is the following
>> compiler error:
>>   error: undefined symbol: rv_bpf_fixup_exception
>>
>
> Good catch for the RV32!
>
>> 2. when CONFIG_BPF_JIT and CONFIG_ARCH_64I is open, There is the following
>> compiler error (W=1):
>>   error: no previous prototype for 'rv_bpf_fixup_exception'
>>
>> In this patch, asm/extable.h is introduced,  the rv_bpf_fixup_exception
>> function declaration is added to this file. in addition, the definition of
>> exception_table_entry is moved from asm-generic/extable.h to this file.
>>
>
> This is way too complicated. More below.
>
>> Fixes: 252c765bd764 ("riscv, bpf: Add BPF exception tables")
>> Signed-off-by: Tong Tiangen <tongtiangen@huawei.com>
>> ---
>>  arch/riscv/include/asm/Kbuild    |  1 -
>>  arch/riscv/include/asm/extable.h | 49 ++++++++++++++++++++++++++++++++
>>  arch/riscv/include/asm/uaccess.h | 13 ---------
>>  arch/riscv/mm/extable.c          |  8 +-----
>>  4 files changed, 50 insertions(+), 21 deletions(-)
>>  create mode 100644 arch/riscv/include/asm/extable.h
>>
>> diff --git a/arch/riscv/include/asm/Kbuild b/arch/riscv/include/asm/Kbuild
>> index 445ccc97305a..57b86fd9916c 100644
>> --- a/arch/riscv/include/asm/Kbuild
>> +++ b/arch/riscv/include/asm/Kbuild
>> @@ -1,6 +1,5 @@
>>  # SPDX-License-Identifier: GPL-2.0
>>  generic-y += early_ioremap.h
>> -generic-y += extable.h
>>  generic-y += flat.h
>>  generic-y += kvm_para.h
>>  generic-y += user.h
>> diff --git a/arch/riscv/include/asm/extable.h b/arch/riscv/include/asm/extable.h
>> new file mode 100644
>> index 000000000000..aa0332b053fb
>> --- /dev/null
>> +++ b/arch/riscv/include/asm/extable.h
>> @@ -0,0 +1,49 @@
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +#ifndef __ASM_EXTABLE_H
>> +#define __ASM_EXTABLE_H
>> +
>> +/*
>> + * The exception table consists of pairs of addresses: the first is the
>> + * address of an instruction that is allowed to fault, and the second is
>> + * the address at which the program should continue.  No registers are
>> + * modified, so it is entirely up to the continuation code to figure out
>> + * what to do.
>> + *
>> + * All the routines below use bits of fixup code that are out of line
>> + * with the main instruction path.  This means when everything is well,
>> + * we don't even have to jump over them.  Further, they do not intrude
>> + * on our cache or tlb entries.
>> + */
>> +struct exception_table_entry {
>> +       unsigned long insn, fixup;
>> +};
>> +
>> +struct pt_regs;
>> +int fixup_exception(struct pt_regs *regs);
>> +
>> +#if defined(CONFIG_MMU)
>> +static inline bool rv_in_bpf_jit(struct pt_regs *regs)
>> +{
>> +       if (!IS_ENABLED(CONFIG_BPF_JIT) || !IS_ENABLED(CONFIG_64BIT))
>> +               return false;
>> +
>> +       return regs->epc >= BPF_JIT_REGION_START && regs->epc < BPF_JIT_REGION_END;
>> +}
>> +#else
>> +static inline bool rv_in_bpf_jit(struct pt_regs *regs)
>> +{
>> +       return false;
>> +}
>> +#endif
>> +
>> +#if defined(CONFIG_BPF_JIT) && defined(CONFIG_64BIT)
>> +int rv_bpf_fixup_exception(const struct exception_table_entry *ex, struct pt_regs *regs);
>> +#else
>> +static inline int rv_bpf_fixup_exception(const struct exception_table_entry *ex,
>> +                                        struct pt_regs *regs)
>> +{
>> +       return 0;
>> +}
>> +#endif
>> +
>> +#endif
>> diff --git a/arch/riscv/include/asm/uaccess.h b/arch/riscv/include/asm/uaccess.h
>> index f314ff44c48d..96ea91dc0e9c 100644
>> --- a/arch/riscv/include/asm/uaccess.h
>> +++ b/arch/riscv/include/asm/uaccess.h
>> @@ -56,19 +56,6 @@ static inline int __access_ok(unsigned long addr, unsigned long size)
>>         return size <= TASK_SIZE && addr <= TASK_SIZE - size;
>>  }
>>
>> -/*
>> - * The exception table consists of pairs of addresses: the first is the
>> - * address of an instruction that is allowed to fault, and the second is
>> - * the address at which the program should continue.  No registers are
>> - * modified, so it is entirely up to the continuation code to figure out
>> - * what to do.
>> - *
>> - * All the routines below use bits of fixup code that are out of line
>> - * with the main instruction path.  This means when everything is well,
>> - * we don't even have to jump over them.  Further, they do not intrude
>> - * on our cache or tlb entries.
>> - */
>> -
>>  #define __LSW  0
>>  #define __MSW  1
>>
>> diff --git a/arch/riscv/mm/extable.c b/arch/riscv/mm/extable.c
>> index 18bf338303b6..264f465db5bb 100644
>> --- a/arch/riscv/mm/extable.c
>> +++ b/arch/riscv/mm/extable.c
>> @@ -11,10 +11,6 @@
>>  #include <linux/module.h>
>>  #include <linux/uaccess.h>
>>
>> -#ifdef CONFIG_BPF_JIT
>> -int rv_bpf_fixup_exception(const struct exception_table_entry *ex, struct pt_regs *regs);
>> -#endif
>> -
>>  int fixup_exception(struct pt_regs *regs)
>>  {
>>         const struct exception_table_entry *fixup;
>> @@ -23,10 +19,8 @@ int fixup_exception(struct pt_regs *regs)
>>         if (!fixup)
>>                 return 0;
>>
>> -#ifdef CONFIG_BPF_JIT
>> -       if (regs->epc >= BPF_JIT_REGION_START && regs->epc < BPF_JIT_REGION_END)
>> +       if (rv_in_bpf_jit(regs))
>>                 return rv_bpf_fixup_exception(fixup, regs);
>> -#endif
>>
>
> The only changes that are needed are:
> 1. Simply gate with CONFIG_BPF_JIT && CONFIG_ARCH_RV64I, instead of of
> CONFIG_BPF_JIT
>
> 2. Forward declaration of the rv_bpf_fixup_exception() in bpf_jit_comp64.c.
>
Hi Björn:
 From the perspective of development, introduce asm/extable.h is also prepare for the
subsequent modification of exception_table_entry, such as:
   1. https://lkml.org/lkml/2021/10/20/591
   2. https://lore.kernel.org/linux-arm-kernel/20211019160219.5202-11-mark.rutland@arm.com/

Therefore, the prototype declarations and definitions related to kernel config are placed in head file,
which can avoid compiler error and simplify the rendering of functions.

Thanks.
Tong.

>
> Björn
> .
>