Messages in this thread | | | Subject | Re: [PATCH v2 2/4] MIPS: microMIPS: Fix the judgment of mm_jr16_op and mm_jalr_op | From | Jinyang He <> | Date | Mon, 8 Feb 2021 09:13:13 +0800 |
| |
On 02/08/2021 05:31 AM, Maciej W. Rozycki wrote:
> On Thu, 21 Jan 2021, Jinyang He wrote: > >> mm16_r5_format.rt is 5 bits, so directly judge the value if equal or not. >> mm_jalr_op requires 7th to 16th bits. These 10 which bits generated by > The minor opcode extension field is comprised of bits 15:6, not 16:7 as > your description suggests. Please be accurate with statements. > >> shifting u_format.uimmediate by 6 may be affected by sign extension. > Why? The `uimmediate' bit-field member is unsigned for a reason. No > sign-extension is made on unsigned data with the right-shift operation. > >> Thus, take out the 10 bits for comparison. >> >> Without this patch, errors may occur, such as these bits are all ones. > How did you come to this conclusion? > >> diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c >> index d737234..74d7fd8 100644 >> --- a/arch/mips/kernel/process.c >> +++ b/arch/mips/kernel/process.c >> @@ -292,8 +292,8 @@ static inline int is_jump_ins(union mips_instruction *ip) >> * microMIPS is kind of more fun... >> */ >> if (mm_insn_16bit(ip->word >> 16)) { >> - if ((ip->mm16_r5_format.opcode == mm_pool16c_op && >> - (ip->mm16_r5_format.rt & mm_jr16_op) == mm_jr16_op)) >> + if (ip->mm16_r5_format.opcode == mm_pool16c_op && >> + ip->mm16_r5_format.rt == mm_jr16_op) >> return 1; >> return 0; >> } > Code style changes should be submitted on their own as separate patches. > >> @@ -305,7 +305,7 @@ static inline int is_jump_ins(union mips_instruction *ip) >> if (ip->r_format.opcode != mm_pool32a_op || >> ip->r_format.func != mm_pool32axf_op) >> return 0; >> - return ((ip->u_format.uimmediate >> 6) & mm_jalr_op) == mm_jalr_op; >> + return ((ip->u_format.uimmediate >> 6) & GENMASK(9, 0)) == mm_jalr_op; > You've now excluded JALR.HB, JALRS, and JALRS.HB instructions. The mask > was there for a reason. If you can't be bothered to verify microMIPS > changes say with QEMU, then at the very least please check documentation. > The intent of this code is clear and these instructions are even spelled > out explicitly in the comment at the top. It's my fault. :-(
How amazing the opcode design is!
Thanks, Jinyang
> Thomas, please revert this change as I can see you've already taken it. > It's plain wrong. > > Maciej
| |