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[PATCH 2/2] z80-elf: support complex relocation symbols

Jan Beulich jbeulich@suse.com
Tue Oct 28 09:11:18 GMT 2025 
On 27.10.2025 23:37, H. Peter Anvin wrote:
> On 2025-10-26 15:06, Maciej W. Rozycki wrote:
>> On Sun, 26 Oct 2025, H. Peter Anvin wrote:
>>
>>>>  Possibly, though as usually with BFD I suspect there's a catch; also I 
>>>> guess a lot of complication in the MIPS backend comes from the use of said 
>>>> odd n64 encoding (triple relocs in a single Elf64_Rela entry).
>>>
>>> I have done it as a prototype, it is trivial, at least for i386. No problems
>>> at all.
>>>
>>> It is literally a matter of moving the zeroing of a variable out of a loop.
>>
>>  Does it work as expected, i.e. identical output section contents, when 
>> you link to a srec output (such as with `ld --oformat=srec ...')?
>>
> 
> I just tried it, and it does not; it errors out:
> 
> /opt/z80/bin/z80-none-elf-ld: expreloc.o: in function `_start':
> (.text+0x1): undefined reference to
> `*:s15:CONSOLE_COLUMNS:+:s12:CONSOLE_ROWS:#ffffffff'
> /opt/z80/bin/z80-none-elf-ld: (.text+0x5): undefined reference to
> `-:s3:foo:s11:__IY_BASE__'
> /opt/z80/bin/z80-none-elf-ld: (.text+0x7): undefined reference to
> `+:s5:pizza:*:s15:CONSOLE_COLUMNS:+:s12:CONSOLE_ROWS:#ffffffff'
> /opt/z80/bin/z80-none-elf-ld: (.text+0xa): undefined reference to
> `+:s5:pizza:s13:CONSOLE_BYTES'
> /opt/z80/bin/z80-none-elf-ld: (.text+0x16): undefined reference to
> `+:+:s5:pizza:*:#00000002:s15:CONSOLE_COLUMNS:<<:+:s12:CONSOLE_ROWS:#ffffffff:#00000002'
> 
> Linking to ELF and then using objcopy to srec works correctly, even with stock
> binutils ld (no modifications whatsoever).
> 
> There are , in fact, no R_RELC anywhere in the object file. The relocations
> are all R_Z80_* but of course the type is set to SHT_RELC.
> 
> Relocation section '.rela.text' at offset 0x270 contains 7 entries:
>  Offset     Info    Type            Sym.Value  Sym. Name + Addend
> 00000001  00000c04 R_Z80_16          00000000   *:s15:CONSOLE_COL[...] + 0
> 00000005  00000d02 R_Z80_8_DIS       00000000   -:s3:foo:s11:__IY[...] + 0
> 00000007  00000e04 R_Z80_16          00000000   +:s5:pizza:*:s15:[...] + 0
> 0000000a  00000f04 R_Z80_16          00000000   +:s5:pizza:s13:CO[...] + 0
> 0000000d  00000a04 R_Z80_16          00000000   pizza + 730
> 00000010  00000b04 R_Z80_16          00000000   CONSOLE_BYTES + 0
> 00000016  00001004 R_Z80_16          00000000   +:+:s5:pizza:*:#0[...] + 0

Hmm, same for the MeP testcase. Things appear to be working from STT_RELC /
STT_SRELC, as checked for by elf_link_input_bfd(). Which then also explains
why things don't work when linking to other than an ELF output. Another
example where logic solely depending on input properties is wrongly tied
to the output format (just very recently I fixed a similar issue in section
merging). Of course the symbol _types_ wouldn't be representable in non-
ELF output; perhaps those symbols then may simply need dropping. (I'm not
sure they're overly useful in an ELF executable's static symbol table
either.)

Interestingly in objdump's symbol table output I can't spot any notion of
STT_RELC / STT_SRELC (or even STT_TLS) at all, so the connection became
apparent to me only when using my own dumping tool.

Jan
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