[Bug ld/31220] New: [RISC-V] Fix relaxation of calls to addresses above 0xFFFF800

[davidegrayson at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=31220

            Bug ID: 31220
           Summary: [RISC-V] Fix relaxation of calls to addresses above
                    0xFFFF800
           Product: binutils
           Version: 2.42 (HEAD)
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: ld
          Assignee: unassigned at sourceware dot org
          Reporter: davidegrayson at gmail dot com
  Target Milestone: ---

Created attachment 15288
  --> https://sourceware.org/bugzilla/attachment.cgi?id=15288&action=edit
Patch that fixes the bug

I want to put a ROM in the top 2 KiB of the address space on a 32-bit RISC-V
system, since calls to that region can be implemented with a single JAL
instruction.  However, I noticed that the GNU linker was failing to implement
that relaxation.  The small attached patch fixes the problem.

In case anyone wants to reproduce the issue, use this linker script and
assembly file:

----

MEMORY
{
  ROM : ORIGIN = 0x10000000, LENGTH = 64K
}
SECTIONS
{
  .text : { *(.text) } >ROM
}
abs_func1 = 0x7FC;
abs_func2 = 0xFFFFF800;

-----

.text
.global start
start: call abs_func1
call2: call abs_func2

-----

Then run these commands:

riscv64-unknown-elf-as -march=rv32i -mabi=ilp32 test.s -o test.o
riscv64-unknown-elf-ld --relax -m elf32lriscv -T test.ld test.o -o test.elf
riscv64-unknown-elf-objdump -d test.elf

Observe that the second call is implemented with an "AUIPC" and "JALR"
instruction instead of a single "JALR" instruction, like the first one.

Please let me know if you want any more info or changes.  Thanks!

-- 
You are receiving this mail because:
You are on the CC list for the bug.