From: "H.J. Lu" <hjl.tools@gmail.com>
To: Jan Beulich <jbeulich@suse.com>
Cc: Binutils <binutils@sourceware.org>
Subject: Re: [PATCH] i386: Allow GOT32 relocations against ABS symbols
Date: Tue, 8 Feb 2022 05:20:35 -0800 [thread overview]
Message-ID: <CAMe9rOr=7FOB4MAZC3AzPwqKjRmg2d550pAhFyd4iLirNT09fw@mail.gmail.com> (raw)
In-Reply-To: <272c580b-7428-3cc6-9a21-e9aa802eeb90@suse.com>
On Tue, Feb 8, 2022 at 5:11 AM Jan Beulich <jbeulich@suse.com> wrote:
>
> On 08.02.2022 14:02, H.J. Lu wrote:
> > On Tue, Feb 8, 2022 at 12:37 AM Jan Beulich <jbeulich@suse.com> wrote:
> >>
> >> On 08.02.2022 01:03, H.J. Lu via Binutils wrote:
> >>> GOT32 relocations are allowed since absolute value + addend is stored in
> >>> the GOT slot.
> >>
> >> Before permitting this and with you specifically mentioning addends
> >> here, I think it needs to be clarified what ...
> >>
> >>> --- /dev/null
> >>> +++ b/ld/testsuite/ld-i386/pr28870.s
> >>> @@ -0,0 +1,6 @@
> >>> + .text
> >>> + .globl _start
> >>> +_start:
> >>> + addl foo@GOT(%ebx), %eax
> >>> + cmpl $0, foo@GOT(%ebx)
> >>> +foo = 2
> >>
> >> ... missing (here) variants thereof actually mean (and whether the use
> >> of addends actually works as intended):
> >>
> >> mov $v@got+3, %eax # bogus, meaningless operand
> >> mov $(v+3)@got, %eax # wrong (gets treated same as above)
> >>
> >> Comments are my own, preliminary judgement.
> >
> > GOT relocations should only be used as @got or @got(%reg).
> > Other variants are undefined.
>
> Which raises two questions:
>
> 1) Why did you say "absolute value + addend is stored in the GOT slot" in
> the description? Where would an addend come from if it can't be specified
> in the assembly source?
addend came from GOTPCREL relocation. There is no addend for
GOT32.
> 2) Why isn't the assembler at least warning about such undefined uses?
A warning is useful.
--
H.J.
prev parent reply other threads:[~2022-02-08 13:21 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-08 0:03 H.J. Lu
2022-02-08 8:37 ` Jan Beulich
2022-02-08 13:02 ` H.J. Lu
2022-02-08 13:10 ` Jan Beulich
2022-02-08 13:20 ` H.J. Lu [this message]
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