[PATCH] MIPS: Fix PR target/98491 (ChangeLog)

[Xi Ruoyao]

On 2021-02-16 11:59 +0800, Xi Ruoyao wrote:
> On 2021-02-15 16:16 -0700, Jeff Law wrote:
> > 
> > 
> > On 2/12/21 7:17 AM, Xi Ruoyao wrote:
> > > On 2021-01-11 01:01 +0800, Xi Ruoyao wrote:
> > > > Hi Jeff and Jakub,
> > > > 
> > > > On 2021-01-04 14:19 -0700, Jeff Law wrote:
> > > > > On 1/4/21 2:00 PM, Jakub Jelinek wrote:
> > > > > > On Mon, Jan 04, 2021 at 01:51:59PM -0700, Jeff Law via Gcc-patches
> > > > > > wrote:
> > > > > > > > Sorry, I forgot to include the ChangeLog:
> > > > > > > > 
> > > > > > > >     gcc/ChangeLog:
> > > > > > > >     
> > > > > > > >     2020-12-31  Xi Ruoyao <xry111@mengyan1223.wang>
> > > > > > > >     
> > > > > > > >             PR target/98491
> > > > > > > >             * config/mips/mips.c (mips_symbol_insns): Do not use
> > > > > > > >               MSA_SUPPORTED_MODE_P if mode is MAX_MACHINE_MODE.
> > > > > > > So I absolutely agree the current code is wrong as it does an out
> > > > > > > of
> > > > > > > bounds array access.
> > > > > > > 
> > > > > > > 
> > > > > > > Would it be better to instead to change MSA_SUPPORTED_MODE_P to
> > > > > > > evaluate
> > > > > > > to zero if MODE is MAX_MACHINE_MODE?  That would protect all the
> > > > > > > uses
> > > > > > > of
> > > > > > > MSA_SUPPORTED_MODE_P.    Something like this perhaps?
> > > > > > But MAX_MACHINE_MODE is the one past last valid mode, I'm not aware
> > > > > > of
> > > > > > any target that would protect all macros that deal with modes that
> > > > > > way.
> > > > > > 
> > > > > > So, perhaps best would be stop using the MAX_MACHINE_MODE as magic
> > > > > > value
> > > > > > for that function and instead use say VOIDmode that shouldn't
> > > > > > normally
> > > > > > appear either?
> > > > > I think we have to allow VOIDmode because constants don't necessarily
> > > > > have modes.   And I certainly agree that using MAX_MACHINE_MODE like
> > > > > this is ugly and error prone (as we can see from the BZ).
> > > > > 
> > > > > I also couldn't convince myself that the code and comments were
> > > > > actually
> > > > > consistent, particularly for MSA targets which the comment claims can
> > > > > never handle constants for ld/st (and thus should be returning 0 for
> > > > > MAX_MACHINE_MODE).  Though maybe mips_symbol_insns_1 ultimately
> > > > > handles
> > > > > that correctly.
> > > > > 
> > > > > 
> > > > > > But I don't really see anything wrong on the mips_symbol_insns above
> > > > > > change either.
> > > > > Me neither.  I'm just questioning if bullet-proofing in the
> > > > > MSA_SUPPORTED_MODE_P would be a better option.  While I've worked in
> > > > > the
> > > > > MIPS port in the past, I don't really have any significannt experience
> > > > > with the MSA support.
> > > > I can't understand the comment either.  To me it looks like it's
> > > > possible to
> > > > remove this "if (MSA_SUPPORTED_P (mode)) return 0;"
> > > > 
> > > > CC Robert to get some help.
> > > Happy new lunar year folks.
> > > 
> > > I found a newer email address of Robert.  Hope it is still being used.
> > > 
> > > Could someone update MAINTAINERS file by the way?
> > If you have an updated email address, I can reach out to Robert and see
> > if he wants his entry updated or removed.
> 
>  His latest reply in gcc mail lists used Robert.Suchanek@mips.com.  But when I
> sent mail to it, the mail was just rejected with "access denied".  Google told
> me Office 365 mail service (used by mips.com) rejects mail to deleted accounts
> with "access denied". So I'm not sure if this email address is invalid again,
> or
> Office 365 just dislikes me...

Hi Jeff,

I think it's better to just fix the out-of-bound array access now by special
casing MAX_MACHINE_MODE, if we can't figure out if this entry should be removed.
Either in MSA_SUPPORTED_P or in mips_symbol_insns.

It's really "irrational" to leave such a obvious programming error in new GCC 11
release...  And I've built a Linux system (in Linux From Scratch way, X11 was
built and it runs correctly now) on the Loongson 3A4000 with patched GCC-10.2.0,
and "-O3 -mmsa" in CFLAGS for most packages so the change should be OK.
-- 
Xi Ruoyao <xry111@mengyan1223.wang>
School of Aerospace Science and Technology, Xidian University