From: "H.J. Lu" <hjl.tools@gmail.com>
To: Jan Beulich <jbeulich@suse.com>
Cc: Binutils <binutils@sourceware.org>
Subject: Re: [PATCH] elf/x86-64: Subtract __ImageBase for R_AMD64_IMAGEBASE
Date: Tue, 23 Feb 2021 06:47:49 -0800 [thread overview]
Message-ID: <CAMe9rOoaAYdS6d-aT_a-4muNq7n3pOsmMgv54Yv9gmae9K4m1Q@mail.gmail.com> (raw)
In-Reply-To: <7e855896-7a78-2b57-2b98-b5ced44915b1@suse.com>
On Tue, Feb 23, 2021 at 6:10 AM Jan Beulich <jbeulich@suse.com> wrote:
>
> On 23.02.2021 14:31, H.J. Lu wrote:
> > On Tue, Feb 23, 2021 at 5:15 AM Jan Beulich <jbeulich@suse.com> wrote:
> >>
> >> On 23.02.2021 13:15, H.J. Lu via Binutils wrote:
> >>> When linking PE/x86-64 inputs to generate ELF executable, we need to
> >>> subtract __ImageBase, aka __executable_start, for R_AMD64_IMAGEBASE
> >>> relocation.
> >>
> >> Do you really mean PE/x86-64, not the respective COFF objects? In the
> >
> > What is the difference? How should I call object files generated by
> > Microsoft Visual Studio?
>
> The call them COFF themselves, I believe.
I have an impression that Windows relocations are different from regular
COFF relocations. coff-x86_64.c has COFF_WITH_PE in many places.
My patch is only for Windows/PE:
&& strcmp (abfd->xvec->name, "pe-x86-64") == 0
> >> description this may not matter much, but since there's at least one
> >> code comment also saying so, which may confuse readers, I'd like to
> >> understand this.
> >>
> >> Also, in how far is this x86-64-specific?
> >
> > I don't know.
> >
> >>> --- a/ld/testsuite/ld-x86-64/pe-x86-64-1.od
> >>> +++ b/ld/testsuite/ld-x86-64/pe-x86-64-1.od
> >>> @@ -2,6 +2,7 @@
> >>> .*: +file format .*
> >>>
> >>> SYMBOL TABLE:
> >>> +0+400000 g .text\$mn 0000000000000000 __executable_start
> >>> 0+401000 g .text\$mn 0000000000000000 getaddr1
> >>> 0+401020 g .text\$mn 0000000000000000 begin
> >>> 0+403014 g .bss 0000000000000000 __bss_start
> >>
> >> I don't think this artifical symbol should appear in the symbol
> >
> > This symbol is generated by linker. It should be harmless.
>
> According to my experience, stray symbols can be confusing or worse.
__executable_start is well defined by linker.
> >> table. I also wonder what the consequences are if a set of linked
> >> object files specifies a symbol of this name.
> >
> > __executable_start is generated by linker. If __ImageBase is
> > defined to another value, that value will be used as image base.
>
> So if I have an object defining __executable_start, which of the
> two will relocations be resolved against?
>
Your __executable_start will be used.
--
H.J.
next prev parent reply other threads:[~2021-02-23 14:48 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-23 12:15 H.J. Lu
2021-02-23 13:15 ` Jan Beulich
2021-02-23 13:31 ` H.J. Lu
2021-02-23 14:10 ` Jan Beulich
2021-02-23 14:47 ` H.J. Lu [this message]
2021-02-23 15:02 ` Jan Beulich
2021-02-23 15:07 ` H.J. Lu
2021-02-23 15:11 ` Jan Beulich
2021-02-23 17:50 ` [PATCH v2] " H.J. Lu
2021-02-25 2:09 ` Alan Modra
2021-02-28 2:38 ` [PATCH v3] " H.J. Lu
2021-03-01 12:19 ` Alan Modra
2021-03-01 13:44 ` H.J. Lu
2021-03-04 13:14 ` Alan Modra
2021-03-04 13:54 ` [PATCH v4] " H.J. Lu
2021-03-05 5:17 ` Alan Modra
2021-03-05 5:29 ` H.J. Lu
2021-03-05 13:57 ` Alan Modra
2021-03-05 18:26 ` [PATCH v5] " H.J. Lu
2021-03-06 0:11 ` Alan Modra
2021-03-06 1:00 ` [PATCH v6] " H.J. Lu
2021-03-07 4:16 ` Alan Modra
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