<div dir="ltr">On Thu, Jan 4, 2018 at 9:14 AM, John Reagan via llvm-dev <span dir="ltr"><<a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a>></span> wrote:<br><div class="gmail_extra"><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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<p><font face="Courier New, Courier, monospace">We use .note
descriptors with ELF on OpenVMS. We have self-describing
entries with tags and lengths. The compiler encodes stuff for
the linker such as compiler version, compilation date-time,
module name, final severity of the compilation, etc. The
linker itself then adds/modifies the .note entries to insert
linker version, link date/time, etc. We also use .notes to
record floating point settings used on the compilation (ie,
VAX float vs IEEE float with denorms vs IEEE float without
denorms, etc.) We currently don't have options that impact
the linker's behavior but that is reasonable.</font></p></div></div></blockquote><div>The note that I am describing would be part of the LLVM namespace. It would be named ".note.linker-options". These notes should *not* be preserved across the actual link. The notes that you are describing sound very much like the ones in the ARM ELF specification (although they call them attributes).<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div text="#000000" bgcolor="#FFFFFF"><div class="m_-7138785077021501552moz-text-html" lang="x-unicode">
<p><font face="Courier New, Courier, monospace">I would like to
see something with tags so that our linker can identify .notes
that it cares about vs .notes that it should ignore.<br></font></p></div></div></blockquote><div>Since they are in the vendor namespace, you should already be able to determine that. You are using a different vendor namespace, and the two would not collide and you would be able to easily identify the notes that you can ignore. Unless your frontend emits the metadata, no such note would even be created in the first place.</div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div text="#000000" bgcolor="#FFFFFF"><div class="m_-7138785077021501552moz-text-html" lang="x-unicode"><p><font face="Courier New, Courier, monospace">
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<p><font face="Courier New, Courier, monospace">For our x86 work,
we're starting to generate them at the MC boundary so they
show up both in the ELF and in an .s file.</font></p></div></div></blockquote><div>Yes, this is the same as what happens here. </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div text="#000000" bgcolor="#FFFFFF"><div class="m_-7138785077021501552moz-text-html" lang="x-unicode">
<p><font face="Courier New, Courier, monospace">What we plan to do
is to generate module metadata which would then get turned
into MC calls.<br>
</font></p>
<p><font face="Courier New, Courier, monospace">Here's what we
generate on OpenVMS Itanium (we don't do .s files there)</font></p>
<p><font face="Courier New, Courier, monospace">Analyze Object
File 4-JAN-2018
11:44:44.78 <wbr> <wbr>
Page 1<br>
WORK20:[JREAGAN]HW.OBJ;73<br>
ANALYZ I01-55<br>
<br>
This is an OpenVMS IA64 (Elf format) object file<br>
<br>
Module Identification Information, in note section 2.<br>
<br>
Module name: <wbr> "HW"<br>
Module version: <wbr> "V1.0"<br>
Creation date/time: <wbr> " 9-JUN-2017
10:30"<br>
Language name: <wbr> "VSI C
V7.4-001"<br>
<br>
Elf Header Information, at file address 0.<br>
<br>
Class: <wbr> ELF-64<br>
Data: <wbr> Little-endian
byte order<br>
Elf Header Version: <wbr> 1.<br>
OS ABI: <wbr> OpenVMS<br>
OS ABI Version: <wbr> 2.<br>
Type: <wbr> Object<br>
Machine Architecture: <wbr> IA_64<br>
Elf File Version: <wbr> 1.<br>
VMS Completion Code: SUCCESS<br>
</font></p>
<p><font face="Courier New, Courier, monospace">...</font></p>
<p><font face="Courier New, Courier, monospace">SECTION DATA 2.
(0002) SHDR$K_SHT_NOTE 00000000000000A8
(168.) bytes<br>
".note"<br>
FileAddr Offset in Section 2. (0002)<br>
-------- ---------------------------<br>
000000C0 00000000 Note Entry 0.<br>
000000C0 00000000 Note Name Size:
0000000000000008 8. <wbr>
nhdr$q_nh_namesz<br>
000000C8 00000008 Note Descriptor size:
000000000000002A 42. <wbr>
nhdr$q_nh_descsz<br>
000000D0 00000010 Note Type:
0000000000000001 1. NT_VMS_MHD
nhdr$q_nh_type<br>
000000D8 00000018 Note Name: "IPF/VMS"<br>
000000E0 00000020 Descriptor:<br>
000000E0 00000020 Creation Date/Time: " 9-JUN-2017
10:30"<br>
000000F1 00000031 Last Patch Date/Time: " 9-JUN-2017
10:30"<br>
00000102 00000042 Module Name: "HW"<br>
00000105 00000045 Module Version: "V1.0"<br>
<br>
00000110 00000050 Note Entry 1.<br>
00000110 00000050 Note Name Size:
0000000000000008 8. <wbr>
nhdr$q_nh_namesz<br>
00000118 00000058 Note Descriptor size:
000000000000000F 15. <wbr>
nhdr$q_nh_descsz<br>
00000120 00000060 Note Type:
0000000000000002 2. NT_VMS_LNM
nhdr$q_nh_type<br>
00000128 00000068 Note Name: "IPF/VMS"<br>
00000130 00000070 Descriptor:<br>
00000130 00000070 Language Name: "VSI C
V7.4-001"<br>
<br>
00000140 00000080 Note Entry 2.<br>
00000140 00000080 Note Name Size:
0000000000000008 8. <wbr>
nhdr$q_nh_namesz<br>
00000148 00000088 Note Descriptor size:
0000000000000008 8. <wbr>
nhdr$q_nh_descsz<br>
00000150 00000090 Note Type:
0000000000000006 6. NT_VMS_FPMODE
nhdr$q_nh_type<br>
00000158 00000098 Note Name: "IPF/VMS"<br>
00000160 000000A0 Descriptor:<br>
00000160 000000A0 Floating-Point Mode:
0000000009800000 IEEE DENORM_RESULTS<br>
</font></p>
<p><font face="Courier New, Courier, monospace">On OpenVMS x86,
here's what we have in our .s files at the moment (subject to
change)</font></p>
<p><font face="Courier New, Courier, monospace">
.section .note,"",@note<br>
.quad 8<br>
.quad 44<br>
.quad 1<br>
.ascii "IPF/VMS"<br>
.byte 0<br>
.ascii " 4-JAN-2018 11:49"<br>
.ascii " 4-JAN-2018 11:49"<br>
.ascii ".MAIN."<br>
.byte 0<br>
.ascii "V1"<br>
.byte 0<br>
.align 8<br>
.quad 8<br>
.quad 14<br>
.quad 2<br>
.ascii "IPF/VMS"<br>
.byte 0<br>
.ascii "XMAC X6.0-004"<br>
.byte 0<br>
.align 8<br>
</font><br>
</p>
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<br></blockquote></div><br><br clear="all"><div><br></div>-- <br><div class="gmail_signature" data-smartmail="gmail_signature">Saleem Abdulrasool<br>compnerd (at) compnerd (dot) org</div>
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