https://sourceware.org/bugzilla/show_bug.cgi?id=32196
--- Comment #6 from Fangrui Song <maskray at sourceware dot org> ---
We should revisit the resolution to PR25551 and PR32196.
I raised PR25551 due to an unneeded .symtab entry .Lprintk$local .
The resolution changed R_X86_64_PLT32 to R_X86_64_PC32, which is less
desirable, and required an amendment for this issue.
PLT32 is a branch relocation type, which means the symbol address is
insignificant (similar to R_AARCH64_CALL26 / R_PPC64_REL24).
In a modified large code model, we could instruct the linker to create a range
extension thunk if the target symbol is out of reach of +-2GiB.
.section .init.text,"ax",@progbits
call .Lprintk$local
# -- End function
.text
.globl printk # -- Begin function printk
.type printk,@function
printk: # @printk
.Lprintk$local:
ret
Using PC32 means the symbol address is significant, and we cannot safely
redirect the relocation (without disassembling the instruction) to a thunk.
For this assembly sequence, LLVM integrated assembler generates the desired
R_X86_64_PLT32 relocation referencing .text - 4, which allows range extension
thunks.
(Meta Platforms engineers want to implement range extension thunks for
https://groups.google.com/g/x86-64-abi/c/RsJDf06xMJ0
I mentioned that "we should have at least some basic agreement on x86-64-abi
(gitlab.com/x86-psABIs/x86-64-ABI) before moving in this direction - and I
recalled this gas issue.)
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