[llvm-dev] Linker Option support for ELF

[John Reagan via llvm-dev]

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.

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.

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.

What we plan to do is to generate module metadata which would then get 
turned into MC calls.

Here's what we generate on OpenVMS Itanium (we don't do .s files there)

Analyze Object File                           4-JAN-2018 11:44:44.78 Page 1
WORK20:[JREAGAN]HW.OBJ;73
ANALYZ I01-55

This is an OpenVMS IA64 (Elf format) object file

Module Identification Information, in note section 2.

     Module name:                                "HW"
     Module version:                             "V1.0"
     Creation date/time:                         " 9-JUN-2017 10:30"
     Language name:                              "VSI C V7.4-001"

Elf Header Information, at file address 0.

     Class:                                      ELF-64
     Data:                                       Little-endian byte order
     Elf Header Version:                         1.
     OS ABI:                                     OpenVMS
     OS ABI Version:                             2.
     Type:                                       Object
     Machine Architecture:                       IA_64
     Elf File Version:                           1.
     VMS Completion Code:                        SUCCESS

...

SECTION DATA 2. (0002)                       SHDR$K_SHT_NOTE 
00000000000000A8 (168.) bytes
".note"
FileAddr Offset in Section 2. (0002)
-------- ---------------------------
000000C0 00000000  Note Entry 0.
000000C0 00000000    Note Name Size: 0000000000000008       8. 
nhdr$q_nh_namesz
000000C8 00000008    Note Descriptor size: 000000000000002A      42. 
nhdr$q_nh_descsz
000000D0 00000010    Note Type: 0000000000000001       1. NT_VMS_MHD 
nhdr$q_nh_type
000000D8 00000018    Note Name:                  "IPF/VMS"
000000E0 00000020    Descriptor:
000000E0 00000020      Creation Date/Time:       " 9-JUN-2017 10:30"
000000F1 00000031      Last Patch Date/Time:     " 9-JUN-2017 10:30"
00000102 00000042      Module Name:              "HW"
00000105 00000045      Module Version:           "V1.0"

00000110 00000050  Note Entry 1.
00000110 00000050    Note Name Size: 0000000000000008       8. 
nhdr$q_nh_namesz
00000118 00000058    Note Descriptor size: 000000000000000F      15. 
nhdr$q_nh_descsz
00000120 00000060    Note Type: 0000000000000002       2. NT_VMS_LNM 
nhdr$q_nh_type
00000128 00000068    Note Name:                  "IPF/VMS"
00000130 00000070    Descriptor:
00000130 00000070      Language Name:            "VSI C V7.4-001"

00000140 00000080  Note Entry 2.
00000140 00000080    Note Name Size: 0000000000000008       8. 
nhdr$q_nh_namesz
00000148 00000088    Note Descriptor size: 0000000000000008       8. 
nhdr$q_nh_descsz
00000150 00000090    Note Type: 0000000000000006       6. NT_VMS_FPMODE 
nhdr$q_nh_type
00000158 00000098    Note Name:                  "IPF/VMS"
00000160 000000A0    Descriptor:
00000160 000000A0      Floating-Point Mode: 0000000009800000          
IEEE DENORM_RESULTS

On OpenVMS x86, here's what we have in our .s files at the moment 
(subject to change)

.section        .note,"", at note
         .quad   8
         .quad   44
         .quad   1
         .ascii  "IPF/VMS"
         .byte   0
         .ascii  " 4-JAN-2018 11:49"
         .ascii  " 4-JAN-2018 11:49"
         .ascii  ".MAIN."
         .byte   0
         .ascii  "V1"
         .byte   0
         .align  8
         .quad   8
         .quad   14
         .quad   2
         .ascii  "IPF/VMS"
         .byte   0
         .ascii  "XMAC X6.0-004"
         .byte   0
         .align  8

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20180104/b70f3b26/attachment.html>