From: "H.J. Lu" <hjl.tools@gmail.com>
To: Fangrui Song <i@maskray.me>
Cc: Alan Modra <amodra@gmail.com>, bd1976 llvm <bd1976llvm@gmail.com>,
Binutils <binutils@sourceware.org>
Subject: Re: Empty section flags
Date: Sat, 4 Apr 2020 07:17:56 -0700 [thread overview]
Message-ID: <CAMe9rOr8eWyyCHWof=UuB_fQQOV8oyWkt_qgA=x6Go_J391baQ@mail.gmail.com> (raw)
In-Reply-To: <BY5PR07MB7316A97E0E9709AD37A71E36CBE40@BY5PR07MB7316.namprd07.prod.outlook.com>
On Tue, Mar 3, 2020 at 1:20 PM Fangrui Song <i@maskray.me> wrote:
>
> On Sun, Feb 9, 2020 at 9:21 PM Alan Modra <amodra@gmail.com> wrote:
> >
> > On Thu, Feb 06, 2020 at 05:25:33PM +0000, bd1976 llvm wrote:
> > > Hi Alan, thanks for the input here. I wonder if it wouldn't be more
> > > consistent to error in all cases - even in the case of different group
> > > signatures. The only exception would need to be for the special section
> > > names (.text, .debug_str, etc...) that the assembler has special knowledge
> > > of (as you explained).
> >
> > Yes, let's see how that goes.
> > https://sourceware.org/ml/binutils/2020-02/msg00129.html
> >
> > > I wonder why creating multiple sections with the
> > > same name for section directives with different group signatures was
> > > implemented - why not just require the use of a distinct section name for
> > > these?
> >
> > I think plain ".text" for a group's text section is fine. Distict
> > names would just be yet another thing to track for a group.
> >
> > > Or, now that GNU has the ",unique,N" assembly extension (
> > > https://sourceware.org/ml/binutils/2020-02/msg00028.html) that could be
> > > used if the section name is fixed - it would then be explicit in the source
> > > code that another section with the same name will be created.
> >
> > Perhaps, but we aren't designing a new toolchain. Backwards
> > compatibility can't be discarded without compelling reasons.
> >
> > --
> > Alan Modra
> > Australia Development Lab, IBM
>
> For empty flags, should there be an error as well?
>
> .section .foo,"ax",@progbits; .byte 1
> .section .foo,"",@progbits; .byte 2 # no diagnostic
> .section .foo,"a",@progbits; .byte 3 # Error: changed section
> attributes for .foo
>
> Context: https://github.com/ClangBuiltLinux/linux/issues/913
>
> I lean toward an error for consistency, and I will try making the LLVM
> MC side rule stick.
[hjl@gnu-cfl-2 tmp]$ cat x.s
.section .foo,"",@progbits; .byte 2
[hjl@gnu-cfl-2 tmp]$ gcc -c x.s
[hjl@gnu-cfl-2 tmp]$ readelf -SW x.o | grep foo
[ 4] .foo PROGBITS 0000000000000000 000040
000001 00 0 0 1
[hjl@gnu-cfl-2 tmp]$
Unless it is disallowed by gABI/psABI, assembler should allow it.
Sometimes, I found a need to create odd object files, like zero-sized
relocation section, for linker test. Assembler should have more
flexibilities within gABI/psABI.
--
H.J.
next prev parent reply other threads:[~2020-04-04 14:18 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-06 7:38 .section directives with the same name but different fields Fangrui Song
2020-02-06 8:33 ` Alan Modra
2020-02-06 9:19 ` Fangrui Song
2020-02-06 14:09 ` Alan Modra
2020-02-06 17:25 ` bd1976 llvm
2020-02-10 5:21 ` Alan Modra
2020-03-03 21:20 ` Empty section flags Fangrui Song
2020-04-04 14:17 ` H.J. Lu [this message]
2020-04-04 16:38 ` Fangrui Song
2020-04-04 16:45 ` H.J. Lu
2020-04-13 21:32 ` Fangrui Song
[not found] ` <CAN30aBGpQecmszv-JsZwVTNrOTW0dGt4zUjas7Cx6b-B3XwjgQ@mail.gmail.com>
2020-04-04 0:43 ` Fangrui Song
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='CAMe9rOr8eWyyCHWof=UuB_fQQOV8oyWkt_qgA=x6Go_J391baQ@mail.gmail.com' \
--to=hjl.tools@gmail.com \
--cc=amodra@gmail.com \
--cc=bd1976llvm@gmail.com \
--cc=binutils@sourceware.org \
--cc=i@maskray.me \
/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 read-only IMAP folder(s) and NNTP newsgroup(s).