RE: [MUSL] microMIPS32R2 O32 port

[Jaydeep Patil <Jaydeep.Patil@imgtec.com>]

Hi Rich,

Could you please find some time to review this?

Thanks,
Jaydeep

>-----Original Message-----
>From: Jaydeep Patil [mailto:Jaydeep.Patil@imgtec.com]
>Sent: 11 May 2017 AM 08:56
>To: musl@lists.openwall.com; Rich Felker
>Cc: Szabolcs Nagy; Andre McCurdy
>Subject: RE: [musl] [MUSL] microMIPS32R2 O32 port
>
>Hi Rich,
>
>Could you please find some time to review
>https://github.com/JaydeepIMG/musl-1/tree/micromips32r2_v3 branch?
>
>Thanks,
>Jaydeep
>
>>-----Original Message-----
>>From: Jaydeep Patil [mailto:Jaydeep.Patil@imgtec.com]
>>Sent: 26 April 2017 PM 12:44
>>To: Rich Felker
>>Cc: Szabolcs Nagy; musl@lists.openwall.com; Andre McCurdy
>>Subject: RE: [musl] [MUSL] microMIPS32R2 O32 port
>>
>>>-----Original Message-----
>>>From: Rich Felker [mailto:dalias@aerifal.cx] On Behalf Of Rich Felker
>>>Sent: 25 April 2017 PM 10:23
>>>To: Jaydeep Patil
>>>Cc: Szabolcs Nagy; musl@lists.openwall.com; Andre McCurdy
>>>Subject: Re: [musl] [MUSL] microMIPS32R2 O32 port
>>>
>>>On Tue, Apr 25, 2017 at 04:45:29AM +0000, Jaydeep Patil wrote:
>>>> > But syscall_cp.s needs some care because saved instruction pointer
>>>> >values are compared against these labels. In micromips mode, do the
>>>> >labels evaluate with the +1 low bit offset?
>>>>
>>>> Yes, in microMIPS mode, ISA bit (0th bit) is set for labels. However
>>>> I don't see any issue with following comparison
>>>>
>>>> pc >= (uintptr_t)__cp_begin && pc < (uintptr_t)__cp_end
>>>>
>>>> The ISA bit will be set even for PC in the saved context.
>>>
>>>Agreed, I think it should work as expected.
>>>
>>>> >> >> diff --git a/src/thread/mips/syscall_cp.s
>>>> >> >> b/src/thread/mips/syscall_cp.s index d284626..9c5f55e 100644
>>>> >> >> --- a/src/thread/mips/syscall_cp.s
>>>> >> >> +++ b/src/thread/mips/syscall_cp.s
>>>> >> >> @@ -1,5 +1,5 @@
>>>> >> >>  .set    noreorder
>>>> >> >> -
>>>> >> >> +.set    nomicromips
>>>> >> >>  .global __cp_begin
>>>> >> >>  .hidden __cp_begin
>>>> >> >>  .type   __cp_begin,@function
>>>> >> >
>>>> >> >I'm also unclear on the motivation of this one. Before (v1) you
>>>> >> >had a lot of changes to replace .s files with something
>>>> >> >micromips-compatible (removing branch delay slots); now (v2)
>>>> >> >those changes are not included. So are .s files even being built
>>>> >> >as micromips at all? If not, why is the above needed? If so, how
>>>> >> >do the files
>>>> >with delay slots work?
>>>> >>
>>>> >> Branch delay slots are removed (called as compact instructions)
>>>> >> in the newer MIPS/microMIPS cores (in development).
>>>> >> The MIPS/microMIPS R2-R6 still support instructions with delay slot.
>>>> >> Assembler takes care of converting a BRANCH + NOP to its
>>>> >> appropriate compact instruction (BEQ + NOP to BEQC).
>>>> >> With the v1 branch I was trying to create generic hand-written
>>>> >> assembly which can be used for newer cores with the compact
>>>> >> instructions.
>>>> >> However I realized that it would appropriate to create a new arch
>>>> >> instead of creating generic assembly.
>>>> >> Thus in v2 branch I modified only those functions which would
>>>> >> create issues when compiled with interlinking on.
>>>> >
>>>> >Based on the discussions so far, I don't think pure-micromips
>>>> >qualifies as a new arch. If it would be possible to take a program
>>>> >compiled as micromips- only, and run it with the libc.so/ldso built
>>>> >for plain mips on a machine that supports both forms of code, then
>>>> >it's not a separate arch, and as I understand it this should be possible.
>>>>
>>>> Yes, in the context of miroMIPSR2-R5, we don't need to create a new
>arch.
>>>>
>>>> >Rich
>>>>
>>>> I will create v3 if you are OK with this approach.
>>>
>>>OK. Can you factor it as one patch that's the minimal needed to make
>>>the .c files (including ones that include the crt_arch.h/reloc.h asm
>>>code) build correctly in micromips mode, which should be quick to
>>>review/accept, and a second (if you want to do this phase now; if not
>>>you can leave it til later) that makes the .s files micromips-compatible?
>>
>>Please refer to https://github.com/JaydeepIMG/musl-
>>1/tree/micromips32r2_v3 for changes (also attached as a patch).
>>I will push a separate patch to make .s file microMIPS-only compatible.
>>
>>>Rich
>>
>>Thanks,
>>Jaydeep