How to define a linker symbol in llvm? - llvm

Question

I would like to add a linker symbol in an llvm pass that I can access later in a linker script.
For example, to show what I'd like to see in the resulting object file, here is an assembly file that creates a linker symbol with a given value.
$ cat sym.s
asdf = 0x1234
.global asdf
$ clang -c sym.s && readelf --symbols sym.o
Symbol table '.symtab' contains 2 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND
1: 0000000000001234 0 NOTYPE GLOBAL DEFAULT ABS asdf
I could not see how to do this in the llvm library (c++ api), as I do not see how to interact with the symbol table given a handle to a Module when my pass is called via runOnModule(Module &M).
I'm not even sure the correct way to do this from an llvm source file.
Here is my best attempt exploring in that direction
$ cat attempt.ll
target triple = "x86_64-pc-linux-gnu"
#asdf = global i8 1234, !absolute_symbol !0
!0 = !{ i64 1234, i64 1234 }
$ clang -c attempt.ll && readelf --symbols attempt.o
Symbol table '.symtab' contains 3 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND
1: 0000000000000000 0 FILE LOCAL DEFAULT ABS attempt.ll
2: 0000000000000000 1 OBJECT GLOBAL DEFAULT 3 asdf
The !absolute_symbol does not actually create an absolute symbol in the object file. It instead still creates a variable (of size 1 in this case), and apparently the variable (not the symbol) has an associated value. So this way of approaching it may be a dead end.
So getting back on track:
How to I add a symbol given a handle to an llvm::Module?