13 ms·

A few folks have asked me the generic ABI status (unmaintained?) and the availability of an up-to-date specification (no). I compiled “History” and “Evolution o

A few folks have asked me the generic ABI status (unmaintained?) and the availability of an up-to-date specification (no). I compiled “History” and “Evolution of the generic ABI” in the blog post. I have two specific questions: - Key features (symbol visibility, section groups, SHF_MERGE, etc) were all available as of April 2001. Where can we find the discussion mailing lists? Are they still available? - How does the ABI end up being “All rights reserved” by SCO? Tool Interface Standard (TIS) Portable Formats Specification, version 1.2 effectively put the specification in the public domain.

Joker_vD 2y ago
> How does the ABI end up being “All rights reserved” by SCO? Text of the spec is copyrighted by the SCO, they did not put it in public domain. That's what "All rights reserved" was intended to mean even though this phrase has not been meaning anything since 2000.
- LegionMammal978 2y ago
  Yeah, it's not like they could copyright the ELF format anyway, only that particular description, or any particular implementation they had. Pretty much everyone seems to agree that file formats themselves aren't copyrightable expression, though I have trouble finding any U.S. case law to that effect. (Personally, that makes me a bit uneasy: for instance, if the copyrighted spec lists the file sections in a certain order, and your implementation happens to output them in the same order even if it doesn't have to, then have you infringed on the owner's copyright of that particular arrangement?) Meanwhile, they could have gotten a patent on (some parts of) the format, but that doesn't seem to be the case here.
  - Veserv 2y ago
    The rule in general (not just for software) is that patents are for functional elements where as copyrights are for non-functional elements; they are exclusive, a element can only be patentable or copyrightable, not both. If it is necessary for operation or inter-operation [1] then they can probably not enforce copyright or trademark. [1] https://en.wikipedia.org/wiki/Sega_v._Accolade https://en.wikipedia.org/wiki/Sega_v._Accolade
    - LegionMammal978 2y ago
      Sure, but usually in any file format, an encoder has some choice in how to produce its output, with no functional difference either way. For instance, different PNG encoders might include the necessary chunks in a different order in the file. And my concern is that some such choices, if they align with choices described in the copyrighted spec, might be protectable as a creative arrangement or similar. (E.g., a spec might list the chunks in such an order that their names form a creative acronym.) Of course, the defense against this would be to scramble (or normalize) all non-functional choices compared to anything in the spec. But you have to be careful to make sure there's nothing left of the spec's non-functional influence. At least Oracle v. Google appears to provide some ammunition here in favor of implementers: the court found the transformative use in that case enough to trump even the byte-for-byte copying of the API signatures. So perhaps interoperability could similarly trump such non-functional copying from the spec. But overall, it's still on shakier ground than I'd like.
  - MaskRay 2y ago
    I feel that The SCO Group's role in the evolution of the System V ABI seems to have been more of a curator/editor than an innovator, inheriting the System V ABI from previous entities. Given that the Tool Interface Standard (TIS) Committee has essentially released the ELF-related chapters into the public domain, and others have made changes, it's unclear what specific rights The SCO Group (and now Xinuos) could claim to reserve. (That said, their maintenance work needs to be remembered.)
- vintagedave 2y ago
  It's concerning that a huge open source ecosystem like Linux depends on a closed specification. That is, I read it as that the spec cannot be continued, developed, and evolved or republished without full redefinition and respecification. Has anyone looked at creating a new object format for Linux? A non-open spec seems a minor issue, really, in an era when we put binary blobs in the kernel (hi Nvidia.) But the more decades I work in closed source, the more I value open source, and believe keeping _everything_ open.
  - yjftsjthsd-h 2y ago
    I wouldn't think you'd need to create a new format, just write up a spec of what all available FOSS implementations are actually doing and agree that that's the standard going forward. Between Linux/*BSD/illumos you should be able to pretty completely describe all currently-active uses of ELF. (Of course this assumes that doing this is sufficient to make it legally not derived from the original spec as far as copyright law cares about, which is beyond my non-lawyer ability to be that confident in.)
    - skissane 2y ago
      > Between Linux/*BSD/illumos you should be able to pretty completely describe all currently-active uses of ELF. OpenVMS uses ELF too. Rather niche proprietary OS but still maintained and in production use. (Not a new thing with x86-64 port, ELF was adopted during the Alpha to Iranian transition.) As do many RTOS (both open source and proprietary)
      - Iwan-Zotow 2y ago
        To WHAT transition?
        yjftsjthsd-h 2y ago
        Lol. Although, Itanium does have an entertaining history of having caused a lot of positive changes even though it crashed and burned itself - it's where we got UEFI, and apparently a good time for some OSs to pick up ELF.
jcranmer 2y ago
One of the things I've been (very slowly) putting together is a master list of all the references one needs to build a compiler toolchain--such as processor ISA manuals, ABI specifications, language standards, even things like IEEE 754 or DWARF. While IEEE 754 is an issue because it's not freely available for most people, the only document that has truly stumped me is the ELF specification. From your blog post, it seems like my failure to find the most up-to-date specification is simply because one doesn't exist.
- marssaxman 2y ago
  Are you familiar with the OSDev wiki? Perhaps their list of links will be helpful: https://wiki.osdev.org/ELF#External_Links https://wiki.osdev.org/ELF#External_Links
  - jcranmer 2y ago
    That wiki's list of links isn't always the most up-to-date.
    - marssaxman 2y ago
      How often does anyone change the ELF file format, though? No matter; but that's the most up-to-date list of references I know about.
      - jcranmer 2y ago
        The ELF format isn't the one that I'm the most concerned about, but for example compressed sections were updated in the past decade. The ABI for x86-64 is out-of-date (actually, the site it links to is now a 404, but my recollection was that was a version around 2013)--missing things like _Float16 rules, DWARF register naming for AMX and APX registers, microarchitecture levels, new relocation types,
        khuey 2y ago
        The up to date ABI for x86-64 lives at https://gitlab.com/x86-psABIs/x86-64-ABI https://gitlab.com/x86-psABIs/x86-64-ABI
WalterBright 2y ago
The first thing I do when porting to a new platform is build an object file format pretty-printer. It's the only way to figure out how it really works. The written specifications for them are often a bit of a fairy tale. The real specification is whatever the local C compiler generates. The other gatekeeper is what the linker will accept. That can sometimes be a nightmare.
- rvbissell 2y ago
  Do you have any examples of the pretty-printing that you've generated?
  - WalterBright 2y ago
    I never got around to open sourcing them. But here's part of a dump of a .o file: Section 14 .eh_frame PROGBITS,ALLOC,SIZE=0x0030(48),OFFSET=0x0040,ALIGN=8 offset = 00000000, length = 0x0014(20) CIE_id = 00000000 version = 1 augmentation = 'zR' code_alignment_factor = 1 data_alignment_factor = -8 return_address_register = 16 Augmentation_Length = 1 Address pointer encoding = DW_EH_PE_pcrel|sdata4 DW_CFA_def_cfa reg = 7, off = 00000008 DW_CFA_offset_10 off = 1 DW_CFA_nop DW_CFA_nop offset = 00000018, length = 0x0014(20) CIE_pointer = 0000001c offset 00000000 augmentation = 'zR' PC_Begin = 0 PC_Range = 6 Augmentation_Length = 0 DW_CFA_nop DW_CFA_nop DW_CFA_nop DW_CFA_nop DW_CFA_nop DW_CFA_nop DW_CFA_nop 0040: 14 0 0 0 0 0 0 0 1 7a 52 0 1 78 10 1 .........zR..x.. 0050: 1b c 7 8 90 1 0 0 14 0 0 0 1c 0 0 0 ................ 0060: 0 0 0 0 6 0 0 0 0 0 0 0 0 0 0 0 ................ Section 15 .data._D16TypeInfo_S3__C1S6__initZ PROGBITS,WRITE,ALLOC,SIZE=0x0090(144),OFFSET=0x0070,ALIGN=16 0070: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ................ 0080: 7 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ................ 0090: 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ................ 00a0: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ................ 00b0: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ................ 00c0: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ................ 00d0: 0 0 0 0 0 0 0 0 4 0 0 0 0 0 0 0 ................ 00e0: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ................ 00f0: 0 0 0 0 0 0 0 0 53 33 5f 5f 43 31 53 0 ........S3__C1S. Section 16 .rela.data._D16TypeInfo_S3__C1S6__initZ RELA,ENTRIES=3,OFFSET=0x06A4,ALIGN=8,LINK=8,INFO=15 0 offset=00000000 addend=0000000000000000 type=R_X86_64_64 sym=24 sym="_D15TypeInfo_Struct6__vtblZ" 1 offset=00000018 addend=0000000000000088 type=R_X86_64_64 sym=21 sym="_D16TypeInfo_S3__C1S6__initZ" 2 offset=00000070 addend=0000000000000000 type=R_X86_64_64 sym=25 sym="_D10TypeInfo_i6__initZ" Section 17 .bss.__bzeroBytes NOBITS,WRITE,ALLOC,SIZE=0x0080(128),OFFSET=0x0100,ALIGN=16 Section 18 .group GROUP,ENTRIES=2,OFFSET=0x0100,ALIGN=4,LINK=8,INFO=23 0100: 1 0 0 0 13 0 0 0 ........ Section 19 .text.test PROGBITS,ALLOC,EXEC,GROUP,SIZE=0x0008(8),OFFSET=0x0108,ALIGN=4 0108: b8 4 0 0 0 c3 0 0 ........
trws 2y ago
I fell very far down this rabbit hole trying to figure out the history of library link orders and symbol resolution. One fun outcome of which was finding that the first ever public release of a manpage for ld.so on Linux listed RPATH as deprecated. Finding mailing lists from before the source ware transition is hard, some of it exists if you follow the path back to the Solaris forums, but only some. I’ll look through my archives for the features you listed, but I don’t think I uncovered anything about them specifically. Good luck!
- MaskRay 2y ago
  https://www.sco.com/developers/gabi/latest/revision.html https://www.sco.com/developers/gabi/latest/revision.html specifies > Second draft published May 3, 1999. > ... > New dynamic section tags DT_RUNPATH and DT_FLAGS added. Dynamic section tag DT_RPATH moved to level 2. In glibc, DT_RPATH and DT_RUNPATH have different semantics regarding precedence related to LD_LIBRARY_PATH. In FreeBSD rtld and musl, DT_RPATH and DT_RUNPATH are equivallent.
IAmLiterallyAB 2y ago
Just want to say, your blog has been a godsend for understanding the weird quirks of linking and ABI stuff. Thank you.

Joker_vD 2y ago

> How does the ABI end up being “All rights reserved” by SCO? Text of the spec is copyrighted by the SCO, they did not put it in public domain. That's what "All rights reserved" was intended to mean even though this phrase has not been meaning anything since 2000.

LegionMammal978 2y ago
Yeah, it's not like they could copyright the ELF format anyway, only that particular description, or any particular implementation they had. Pretty much everyone seems to agree that file formats themselves aren't copyrightable expression, though I have trouble finding any U.S. case law to that effect. (Personally, that makes me a bit uneasy: for instance, if the copyrighted spec lists the file sections in a certain order, and your implementation happens to output them in the same order even if it doesn't have to, then have you infringed on the owner's copyright of that particular arrangement?) Meanwhile, they could have gotten a patent on (some parts of) the format, but that doesn't seem to be the case here.
- Veserv 2y ago
  The rule in general (not just for software) is that patents are for functional elements where as copyrights are for non-functional elements; they are exclusive, a element can only be patentable or copyrightable, not both. If it is necessary for operation or inter-operation [1] then they can probably not enforce copyright or trademark. [1] https://en.wikipedia.org/wiki/Sega_v._Accolade https://en.wikipedia.org/wiki/Sega_v._Accolade
  - LegionMammal978 2y ago
    Sure, but usually in any file format, an encoder has some choice in how to produce its output, with no functional difference either way. For instance, different PNG encoders might include the necessary chunks in a different order in the file. And my concern is that some such choices, if they align with choices described in the copyrighted spec, might be protectable as a creative arrangement or similar. (E.g., a spec might list the chunks in such an order that their names form a creative acronym.) Of course, the defense against this would be to scramble (or normalize) all non-functional choices compared to anything in the spec. But you have to be careful to make sure there's nothing left of the spec's non-functional influence. At least Oracle v. Google appears to provide some ammunition here in favor of implementers: the court found the transformative use in that case enough to trump even the byte-for-byte copying of the API signatures. So perhaps interoperability could similarly trump such non-functional copying from the spec. But overall, it's still on shakier ground than I'd like.
- MaskRay 2y ago
  I feel that The SCO Group's role in the evolution of the System V ABI seems to have been more of a curator/editor than an innovator, inheriting the System V ABI from previous entities. Given that the Tool Interface Standard (TIS) Committee has essentially released the ELF-related chapters into the public domain, and others have made changes, it's unclear what specific rights The SCO Group (and now Xinuos) could claim to reserve. (That said, their maintenance work needs to be remembered.)
vintagedave 2y ago
It's concerning that a huge open source ecosystem like Linux depends on a closed specification. That is, I read it as that the spec cannot be continued, developed, and evolved or republished without full redefinition and respecification. Has anyone looked at creating a new object format for Linux? A non-open spec seems a minor issue, really, in an era when we put binary blobs in the kernel (hi Nvidia.) But the more decades I work in closed source, the more I value open source, and believe keeping _everything_ open.
- yjftsjthsd-h 2y ago
  I wouldn't think you'd need to create a new format, just write up a spec of what all available FOSS implementations are actually doing and agree that that's the standard going forward. Between Linux/*BSD/illumos you should be able to pretty completely describe all currently-active uses of ELF. (Of course this assumes that doing this is sufficient to make it legally not derived from the original spec as far as copyright law cares about, which is beyond my non-lawyer ability to be that confident in.)
  - skissane 2y ago
    > Between Linux/*BSD/illumos you should be able to pretty completely describe all currently-active uses of ELF. OpenVMS uses ELF too. Rather niche proprietary OS but still maintained and in production use. (Not a new thing with x86-64 port, ELF was adopted during the Alpha to Iranian transition.) As do many RTOS (both open source and proprietary)
    - Iwan-Zotow 2y ago
      To WHAT transition?
      - yjftsjthsd-h 2y ago
        Lol. Although, Itanium does have an entertaining history of having caused a lot of positive changes even though it crashed and burned itself - it's where we got UEFI, and apparently a good time for some OSs to pick up ELF.

jcranmer 2y ago

One of the things I've been (very slowly) putting together is a master list of all the references one needs to build a compiler toolchain--such as processor ISA manuals, ABI specifications, language standards, even things like IEEE 754 or DWARF. While IEEE 754 is an issue because it's not freely available for most people, the only document that has truly stumped me is the ELF specification. From your blog post, it seems like my failure to find the most up-to-date specification is simply because one doesn't exist.

marssaxman 2y ago
Are you familiar with the OSDev wiki? Perhaps their list of links will be helpful: https://wiki.osdev.org/ELF#External_Links https://wiki.osdev.org/ELF#External_Links
- jcranmer 2y ago
  That wiki's list of links isn't always the most up-to-date.
  - marssaxman 2y ago
    How often does anyone change the ELF file format, though? No matter; but that's the most up-to-date list of references I know about.
    - jcranmer 2y ago
      The ELF format isn't the one that I'm the most concerned about, but for example compressed sections were updated in the past decade. The ABI for x86-64 is out-of-date (actually, the site it links to is now a 404, but my recollection was that was a version around 2013)--missing things like _Float16 rules, DWARF register naming for AMX and APX registers, microarchitecture levels, new relocation types,
      - khuey 2y ago
        The up to date ABI for x86-64 lives at https://gitlab.com/x86-psABIs/x86-64-ABI https://gitlab.com/x86-psABIs/x86-64-ABI

WalterBright 2y ago

The first thing I do when porting to a new platform is build an object file format pretty-printer. It's the only way to figure out how it really works. The written specifications for them are often a bit of a fairy tale. The real specification is whatever the local C compiler generates. The other gatekeeper is what the linker will accept. That can sometimes be a nightmare.

rvbissell 2y ago
Do you have any examples of the pretty-printing that you've generated?
- WalterBright 2y ago
  I never got around to open sourcing them. But here's part of a dump of a .o file: Section 14 .eh_frame PROGBITS,ALLOC,SIZE=0x0030(48),OFFSET=0x0040,ALIGN=8 offset = 00000000, length = 0x0014(20) CIE_id = 00000000 version = 1 augmentation = 'zR' code_alignment_factor = 1 data_alignment_factor = -8 return_address_register = 16 Augmentation_Length = 1 Address pointer encoding = DW_EH_PE_pcrel|sdata4 DW_CFA_def_cfa reg = 7, off = 00000008 DW_CFA_offset_10 off = 1 DW_CFA_nop DW_CFA_nop offset = 00000018, length = 0x0014(20) CIE_pointer = 0000001c offset 00000000 augmentation = 'zR' PC_Begin = 0 PC_Range = 6 Augmentation_Length = 0 DW_CFA_nop DW_CFA_nop DW_CFA_nop DW_CFA_nop DW_CFA_nop DW_CFA_nop DW_CFA_nop 0040: 14 0 0 0 0 0 0 0 1 7a 52 0 1 78 10 1 .........zR..x.. 0050: 1b c 7 8 90 1 0 0 14 0 0 0 1c 0 0 0 ................ 0060: 0 0 0 0 6 0 0 0 0 0 0 0 0 0 0 0 ................ Section 15 .data._D16TypeInfo_S3__C1S6__initZ PROGBITS,WRITE,ALLOC,SIZE=0x0090(144),OFFSET=0x0070,ALIGN=16 0070: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ................ 0080: 7 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ................ 0090: 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ................ 00a0: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ................ 00b0: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ................ 00c0: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ................ 00d0: 0 0 0 0 0 0 0 0 4 0 0 0 0 0 0 0 ................ 00e0: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ................ 00f0: 0 0 0 0 0 0 0 0 53 33 5f 5f 43 31 53 0 ........S3__C1S. Section 16 .rela.data._D16TypeInfo_S3__C1S6__initZ RELA,ENTRIES=3,OFFSET=0x06A4,ALIGN=8,LINK=8,INFO=15 0 offset=00000000 addend=0000000000000000 type=R_X86_64_64 sym=24 sym="_D15TypeInfo_Struct6__vtblZ" 1 offset=00000018 addend=0000000000000088 type=R_X86_64_64 sym=21 sym="_D16TypeInfo_S3__C1S6__initZ" 2 offset=00000070 addend=0000000000000000 type=R_X86_64_64 sym=25 sym="_D10TypeInfo_i6__initZ" Section 17 .bss.__bzeroBytes NOBITS,WRITE,ALLOC,SIZE=0x0080(128),OFFSET=0x0100,ALIGN=16 Section 18 .group GROUP,ENTRIES=2,OFFSET=0x0100,ALIGN=4,LINK=8,INFO=23 0100: 1 0 0 0 13 0 0 0 ........ Section 19 .text.test PROGBITS,ALLOC,EXEC,GROUP,SIZE=0x0008(8),OFFSET=0x0108,ALIGN=4 0108: b8 4 0 0 0 c3 0 0 ........

trws 2y ago

I fell very far down this rabbit hole trying to figure out the history of library link orders and symbol resolution. One fun outcome of which was finding that the first ever public release of a manpage for ld.so on Linux listed RPATH as deprecated. Finding mailing lists from before the source ware transition is hard, some of it exists if you follow the path back to the Solaris forums, but only some. I’ll look through my archives for the features you listed, but I don’t think I uncovered anything about them specifically. Good luck!

MaskRay 2y ago
https://www.sco.com/developers/gabi/latest/revision.html https://www.sco.com/developers/gabi/latest/revision.html specifies > Second draft published May 3, 1999. > ... > New dynamic section tags DT_RUNPATH and DT_FLAGS added. Dynamic section tag DT_RPATH moved to level 2. In glibc, DT_RPATH and DT_RUNPATH have different semantics regarding precedence related to LD_LIBRARY_PATH. In FreeBSD rtld and musl, DT_RPATH and DT_RUNPATH are equivallent.

IAmLiterallyAB 2y ago

Just want to say, your blog has been a godsend for understanding the weird quirks of linking and ABI stuff. Thank you.