From: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
To: "Maciej W. Rozycki" <macro@orcam.me.uk>
Cc: Jinyang He <hejinyang@loongson.cn>,
Jiaxun Yang <jiaxun.yang@flygoat.com>,
linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org,
Paul Burton <paulburton@kernel.org>,
Jun-Ru Chang <jrjang@realtek.com>
Subject: Re: [PATCH v2 2/4] MIPS: microMIPS: Fix the judgment of mm_jr16_op and mm_jalr_op
Date: Tue, 9 Feb 2021 17:14:20 +0100 [thread overview]
Message-ID: <20210209161420.GA15428@alpha.franken.de> (raw)
In-Reply-To: <alpine.DEB.2.21.2102072200300.35623@angie.orcam.me.uk>
On Sun, Feb 07, 2021 at 10:31:38PM +0100, 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.
>
> Thomas, please revert this change as I can see you've already taken it.
> It's plain wrong.
It's now reverted in mips-next.
Thomas.
--
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea. [ RFC1925, 2.3 ]
next prev parent reply other threads:[~2021-02-09 16:16 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-21 5:31 [PATCH v2 0/4] MIPS: process: Some fixes and improvements about get_frame_info() Jinyang He
2021-01-21 5:31 ` [PATCH v2 1/4] MIPS: process: Remove unnecessary headers inclusion Jinyang He
2021-01-21 9:28 ` Huacai Chen
2021-01-21 5:31 ` [PATCH v2 2/4] MIPS: microMIPS: Fix the judgment of mm_jr16_op and mm_jalr_op Jinyang He
2021-02-07 21:31 ` Maciej W. Rozycki
2021-02-08 1:13 ` Jinyang He
2021-02-09 16:14 ` Thomas Bogendoerfer [this message]
2021-01-21 5:31 ` [PATCH v2 3/4] MIPS: Fix get_frame_info() handing of function size Jinyang He
2021-01-21 5:31 ` [PATCH v2 4/4] MIPS: Add is_jr_ra_ins() to end the loop early Jinyang He
2021-01-25 11:24 ` [PATCH v2 0/4] MIPS: process: Some fixes and improvements about get_frame_info() Thomas Bogendoerfer
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20210209161420.GA15428@alpha.franken.de \
--to=tsbogend@alpha.franken.de \
--cc=hejinyang@loongson.cn \
--cc=jiaxun.yang@flygoat.com \
--cc=jrjang@realtek.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mips@vger.kernel.org \
--cc=macro@orcam.me.uk \
--cc=paulburton@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).