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!
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