https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114060
Bug ID: 114060
Summary: asm constraints getting GOT address for ARM/FDPIC look
wrong
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libgcc
Assignee: unassigned at gcc dot gnu.org
Reporter: bugdal at aerifal dot cx
Target Milestone: ---
Reading the code added for unwind-pe.h for FDPIC, I came across the ARM
implementation that uses FDPIC_REGNUM as an input constraint to __asm to get
the GOT register value. As I understand it, this is not correct, as there is no
contract that this register permanently hold the GOT address for the executing
code; it's just a hidden argument register for making function calls, which the
callee can throw away if it does not need to access the GOT or any global data,
or spill and reload.
To reliably get the GOT register, I think you need to make an actual external
call to an asm function that movs the GOT register to the return-value register
and returns.
