From: "Jan Beulich" <JBeulich@suse.com>
To: Daniel Kiper <daniel.kiper@oracle.com>
Cc: Juergen Gross <JGross@suse.com>,
stefano.stabellini@eu.citrix.com, andrew.cooper3@citrix.com,
cardoe@cardoe.com, pgnet.dev@gmail.com, ning.sun@intel.com,
david.vrabel@citrix.com, xen-devel@lists.xenproject.org,
qiaowei.ren@intel.com, richard.l.maliszewski@intel.com,
gang.wei@intel.com, fu.wei@linaro.org
Subject: Re: [PATCH v3 07/16] x86/boot: create *.lnk files with linker script
Date: Fri, 17 Jun 2016 04:04:20 -0600 [thread overview]
Message-ID: <5763E74402000078000F60E5@prv-mh.provo.novell.com> (raw)
In-Reply-To: <20160617090639.GM5490@olila.local.net-space.pl>
>>> On 17.06.16 at 11:06, <daniel.kiper@oracle.com> wrote:
> On Tue, May 24, 2016 at 06:52:39AM -0600, Jan Beulich wrote:
>> >>> On 24.05.16 at 14:28, <daniel.kiper@oracle.com> wrote:
>> > On Tue, May 24, 2016 at 03:05:06AM -0600, Jan Beulich wrote:
>> >> >>> On 15.04.16 at 14:33, <daniel.kiper@oracle.com> wrote:
>> >> > + /DISCARD/ : {
>> >> > + /*
>> >> > + * .got.plt section is used only by dynamic linker
>> >> > + * and our output is not supposed to be loaded by
>> >> > + * dynamic linker. Additionally, it just contains
>> >> > + * .PLT0 which is referenced from nowhere. So, we
>> >> > + * can safely drop .got.plt here.
>> >> > + *
>> >> > + * Ha! This should be really discarded here. However,
>> >> > + * .got.plt section contains _GLOBAL_OFFSET_TABLE_
>> >> > + * symbol too and it is used as a reference for relative
>> >> > + * addressing (and only for that thing). Hence, ld
>> >> > + * complains if we remove that section because it
>> >> > + * cannot find _GLOBAL_OFFSET_TABLE_. So, drop .got.plt
>> >> > + * section during conversion to plain binary format.
>> >> > + * Please check build32.mk for more details.
>> >> > + */
>> >> > + /* *(.got.plt) */
>> >> > + }
>> >>
>> >> I'm afraid this needs more investigation: Afaik there should be no
>> >
>> > I am not sure what else we should look for.
>>
>> The reason why such an empty .got.plt gets created in the first place.
>> If e.g. that turns out to be a bug in (some versions of) binutils, then
>> that bug should be named here as the reason.
>
> If PIC/PIE code is build then .got.plt exists in executable even if it
> is not linked with dynamic libraries.
Well - then just don't force -fPIC or -fPIE for the compilation of this
code?
>> >> reason for the linker to create an otherwise empty .got.plt in the
>> >
>> > As I wrote above. It contains _GLOBAL_OFFSET_TABLE_ which is used
>> > as a reference for relative addressing.
>>
>> But we don't use any such, so without being needed I don't think
>> the symbol needs to be created.
>
> R_386_GOTPC and R_386_GOTOFF relocations use address of
> _GLOBAL_OFFSET_TABLE_
> as a reference. So, it is needed during linking phase. However, later it is
> not needed. Hence, .got.plt with _GLOBAL_OFFSET_TABLE_ and .PLT0 can safely
> be dropped.
These two relocation types should not appear for non-PIC/PIE code.
Jan
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next prev parent reply other threads:[~2016-06-17 10:04 UTC|newest]
Thread overview: 94+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-15 12:33 [PATCH v3 00/16] x86: multiboot2 protocol support Daniel Kiper
2016-04-15 12:33 ` [PATCH v3 01/16] x86/boot: do not create unwind tables Daniel Kiper
2016-04-15 15:45 ` Andrew Cooper
2016-04-15 12:33 ` [PATCH v3 02/16] x86: zero BSS using stosl instead of stosb Daniel Kiper
2016-04-15 13:57 ` Konrad Rzeszutek Wilk
2016-04-15 15:48 ` Andrew Cooper
2016-04-15 12:33 ` [PATCH v3 03/16] x86/boot: call reloc() using cdecl calling convention Daniel Kiper
2016-04-15 15:56 ` Andrew Cooper
2016-06-17 8:41 ` Daniel Kiper
2016-06-17 9:30 ` Jan Beulich
2016-05-24 8:42 ` Jan Beulich
2016-04-15 12:33 ` [PATCH v3 04/16] x86/boot/reloc: create generic alloc and copy functions Daniel Kiper
2016-04-15 12:33 ` [PATCH v3 05/16] x86/boot: use %ecx instead of %eax Daniel Kiper
2016-04-15 12:33 ` [PATCH v3 06/16] x86/boot/reloc: Rename some variables and rearrange code a bit Daniel Kiper
2016-04-15 12:33 ` [PATCH v3 07/16] x86/boot: create *.lnk files with linker script Daniel Kiper
2016-04-15 14:04 ` Konrad Rzeszutek Wilk
2016-05-24 9:05 ` Jan Beulich
2016-05-24 12:28 ` Daniel Kiper
2016-05-24 12:52 ` Jan Beulich
2016-06-17 9:06 ` Daniel Kiper
2016-06-17 10:04 ` Jan Beulich [this message]
2016-06-17 10:34 ` Daniel Kiper
2016-04-15 12:33 ` [PATCH v3 08/16] x86: add multiboot2 protocol support Daniel Kiper
2016-05-24 15:46 ` Jan Beulich
2016-05-25 16:34 ` Daniel Kiper
2016-05-26 10:28 ` Andrew Cooper
2016-05-27 8:08 ` Jan Beulich
2016-05-27 8:13 ` Andrew Cooper
2016-05-27 8:24 ` Jan Beulich
2016-05-27 8:11 ` Jan Beulich
2016-04-15 12:33 ` [PATCH v3 09/16] efi: explicitly define efi struct in xen/arch/x86/efi/stub.c Daniel Kiper
2016-05-25 7:03 ` Jan Beulich
2016-05-25 16:45 ` Daniel Kiper
2016-05-27 8:16 ` Jan Beulich
2016-06-01 15:07 ` Daniel Kiper
2016-07-05 18:33 ` Daniel Kiper
2016-07-06 6:55 ` Jan Beulich
2016-07-06 10:27 ` Daniel Kiper
2016-07-06 12:00 ` Jan Beulich
2016-07-06 12:55 ` Daniel Kiper
2016-04-15 12:33 ` [PATCH v3 10/16] efi: create efi_enabled() Daniel Kiper
2016-05-25 7:20 ` Jan Beulich
2016-05-25 17:15 ` Daniel Kiper
2016-05-26 10:31 ` Andrew Cooper
2016-05-27 8:22 ` Jan Beulich
2016-06-01 15:23 ` Daniel Kiper
2016-06-01 15:41 ` Jan Beulich
2016-06-01 19:28 ` Daniel Kiper
2016-06-02 8:06 ` Jan Beulich
2016-04-15 12:33 ` [PATCH v3 11/16] efi: build xen.gz with EFI code Daniel Kiper
2016-05-25 7:53 ` Jan Beulich
2016-05-25 19:07 ` Daniel Kiper
2016-05-27 8:31 ` Jan Beulich
2016-06-01 15:48 ` Daniel Kiper
2016-06-01 15:58 ` Jan Beulich
2016-06-01 19:39 ` Daniel Kiper
2016-04-15 12:33 ` [PATCH v3 12/16 - RFC] x86/efi: create new early memory allocator Daniel Kiper
2016-05-25 8:39 ` Jan Beulich
2016-05-25 19:48 ` Daniel Kiper
2016-05-27 8:37 ` Jan Beulich
2016-06-01 15:58 ` Daniel Kiper
2016-06-01 16:02 ` Jan Beulich
2016-06-01 19:53 ` Daniel Kiper
2016-06-02 8:11 ` Jan Beulich
2016-06-02 10:43 ` Daniel Kiper
2016-06-02 11:10 ` Jan Beulich
2016-06-01 16:01 ` Daniel Kiper
2016-07-05 18:26 ` Daniel Kiper
2016-07-06 7:22 ` Jan Beulich
2016-07-06 11:15 ` Daniel Kiper
2016-04-15 12:33 ` [PATCH v3 13/16 - RFC] x86: add multiboot2 protocol support for EFI platforms Daniel Kiper
2016-05-25 9:32 ` Jan Beulich
2016-05-25 10:29 ` Jan Beulich
2016-05-25 21:02 ` Daniel Kiper
2016-05-27 9:02 ` Jan Beulich
2016-06-01 19:03 ` Daniel Kiper
2016-06-02 8:34 ` Jan Beulich
2016-06-02 16:12 ` Daniel Kiper
2016-06-03 9:26 ` Jan Beulich
2016-06-03 17:06 ` Konrad Rzeszutek Wilk
2016-04-15 12:33 ` [PATCH v3 14/16] x86/boot: implement early command line parser in C Daniel Kiper
2016-05-25 10:33 ` Jan Beulich
2016-05-25 21:36 ` Daniel Kiper
2016-05-27 9:33 ` Jan Beulich
2016-06-02 8:15 ` Daniel Kiper
2016-06-02 8:39 ` Jan Beulich
2016-04-15 12:33 ` [PATCH v3 15/16 - RFC] x86: make Xen early boot code relocatable Daniel Kiper
2016-05-25 10:48 ` Jan Beulich
2016-04-15 12:33 ` [PATCH v3 16/16] x86: add multiboot2 protocol support for relocatable images Daniel Kiper
2016-05-25 11:03 ` Jan Beulich
2016-06-01 13:35 ` Daniel Kiper
2016-06-01 14:44 ` Jan Beulich
2016-06-01 19:16 ` Daniel Kiper
2016-06-02 8:41 ` Jan Beulich
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