https://sourceware.org/bugzilla/show_bug.cgi?id=18009
Bug ID: 18009
Summary: LDR macro on arm can't generate relative address
Product: binutils
Version: 2.25
Status: NEW
Severity: normal
Priority: P2
Component: gas
Assignee: unassigned at sourceware dot org
Reporter: goswin-v-b at web dot de
The arm assembly has a LDR macro to load constants:
ldr r0, =symbol
This works for symbols (or constants, but that isn't the use case I want) in
the same file and section and also for symbols in other sections or files. For
external symbols it generates an R_ARM_ABS32 linker reference in the next
literals block and adds PC relative addressing to load that.
One can also generate a R_ARM_REL32 linker reference writing
1: .word symbol - 1b
This correctly stores the relative (to the 1 label) offset of the symbol and
fills that in at link time (and generates a .rel.dyn entry for shared code).
What does not work is writing
1: ldr r0, =(symbol - 1b)
boot.S:49: Error: constant expression expected -- `ldr r0,=(symbol-1b)'
this works fine with clangs internal assembler and should work here too. There
seems to be no other way to add a R_ARM_REL32 linker reference to the literals
block and load that into a register.
An alternate this could be something like
ldr r0, [pc, =symbol]
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