[PATCH v2] RISC-V: Make R_RISCV_SUB6 conforms to riscv ABI standard

[Xiao Zeng]

On Wed, Nov 23, 2022 at 12:00:00 AM  Nelson Chu <nelson@rivosinc.com> wrote:
>
>Thanks for fixing this.  We also need to add the out-of-range check
>for R_RISCV_SUB6 in the riscv_elf_add_sub_reloc, and the overflow
>checks for all ADD/SUB/SET relocations, but since they can be added in
>the later patches, so I committed this one after passing the
>riscv-gnu-toolchain regressions. 

OK. In the next patch, I will solve this problem.

>
>Thanks
>Nelson
>
>On Mon, Nov 21, 2022 at 8:02 PM <zengxiao@eswincomputing.com> wrote:
>>
>> From: Xiao Zeng <zengxiao@eswincomputing.com>
>>
>> The R_RISCV_SUB6 only the lower 6 bits of the code are valid, which
>> can be found in 8.5. Relocations of:
>> https://github.com/riscv-non-isa/riscv-elf-psabi-doc/releases/download/v1.0-rc4/riscv-abi.pdf
>>
>> bfd/ChangeLog:
>>
>>         * elfnn-riscv.c (riscv_elf_relocate_section): Take the R_RISCV_SUB6
>>         lower 6 bits as the significant bit.
>>         * elfxx-riscv.c (riscv_elf_add_sub_reloc): Likewise.
>> ---
>>  bfd/elfnn-riscv.c | 4 ++++
>>  bfd/elfxx-riscv.c | 4 ++++
>>  2 files changed, 8 insertions(+)
>>
>> diff --git a/bfd/elfnn-riscv.c b/bfd/elfnn-riscv.c
>> index 0570a971b5a..a02aa64786e 100644
>> --- a/bfd/elfnn-riscv.c
>> +++ b/bfd/elfnn-riscv.c
>> @@ -2427,6 +2427,10 @@ riscv_elf_relocate_section (bfd *output_bfd,
>>           break;
>>
>>         case R_RISCV_SUB6:
>> +         relocation = (old_value & ~howto->dst_mask)
>> +                      | (((old_value & howto->dst_mask) - relocation)
>> +                         & howto->dst_mask);
>> +         break;
>
>The old_value needs to be defined, but it's easy enough to add, so I fixed it. 

Thanks Nelson

>
>>         case R_RISCV_SUB8:
>>         case R_RISCV_SUB16:
>>         case R_RISCV_SUB32:
>> diff --git a/bfd/elfxx-riscv.c b/bfd/elfxx-riscv.c
>> index afbde56b9e5..2db24acf7a5 100644
>> --- a/bfd/elfxx-riscv.c
>> +++ b/bfd/elfxx-riscv.c
>> @@ -994,6 +994,10 @@ riscv_elf_add_sub_reloc (bfd *abfd,
>>        relocation = old_value + relocation;
>>        break;
>>      case R_RISCV_SUB6:
>> +      relocation = (old_value & ~howto->dst_mask)
>> +                   | (((old_value & howto->dst_mask) - relocation)
>> +                     & howto->dst_mask);
>> +      break;
>>      case R_RISCV_SUB8:
>>      case R_RISCV_SUB16:
>>      case R_RISCV_SUB32:
>> --
>> 2.34.1
>> 

Thanks
Xiao