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

H. Peter Anvin hpa@zytor.com
Mon Oct 27 22:37:30 GMT 2025 
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

I have attached a tarball with assembly source, object output, linker output,
readelf output, and disassembly of the post-link ELF file.

	-hpa



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