This is a followup question to What do %pcrel_hi and %pcrel_lo actually do?. I’m writing a simple Risc-V linker, and I’m trying to understand how, given an R_RISCV_PCREL_LO12I relocation, the symbol of the corresponding R_RISCV_PCREL_HI20 relocation is found.

For concreteness, here is a RiscV instruction sequence, with relocations interleaved:

1: auipc x10,%pcrel_hi(some_symbol)
      R_RISCV_PCREL_HI20   some_symbol
   lw    x11,%pcrel_lo(1b)(x10)
      R_RISCV_PCREL_LO20I  1b    // symbol refers to the auipc instruction above.

Imagine what the linker does when encountering the ...LO12I relocation.
For this particular relocation type, it looks up the symbol 1b, which gives it the location
of the auipc instruction. However, the linker also needs the symbol some_symbol associated
with the auipc instruction. As far as I can tell, there is no direct way to
find that some_symbol. The reason is that the ELF spec as far as I’m able to tell
doesn’t provide a mapping symbol => relocations_using_that_symbol.
We only have a relocation => symbol mapping.

There must be a function which, given a symbol (like 1b) from a ...LO12I relocation,
yields the corresponding ...HI20 relocation. How is this function typically
implemented? Does the linker need to build a special table of R_RISCV_PCREL_HI20
relocations, indexed by symbols? Or is there a more clever way of locating, for a
given ...LO12I relocation, the corresponding ...HI20 relocation?