linux-kernel - [PATCH] [PATCH v2] riscv: add as-options for modules with assembly compontents

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Message-Id: <20220529152200.609809-1-ben.dooks@codethink.co.uk>
Date:   Sun, 29 May 2022 16:22:00 +0100
From:   Ben Dooks <ben.dooks@...ethink.co.uk>
To:     linux-kernel@...ts.codethink.co.uk, linux-riscv@...ts.infradead.org
Cc:     palmer@...belt.com, aou@...s.berkeley.edu,
        linux-kernel@...r.kernel.org,
        Ben Dooks <ben.dooks@...ethink.co.uk>,
        Bin Meng <bmeng.cn@...il.com>
Subject: [PATCH] [PATCH v2] riscv: add as-options for modules with assembly compontents

When trying to load modules built for RISC-V which include assembly files
the kernel loader errors with "unexpected relocation type 'R_RISCV_ALIGN'"
due to R_RISCV_ALIGN relocations being generated by the assembler.

The R_RISCV_ALIGN relocations can be removed at the expense of code space
by adding -mno-relax to gcc and as.  In commit 7a8e7da42250138
("RISC-V: Fixes to module loading") -mno-relax is added to the build
variable KBUILD_CFLAGS_MODULE. See [1] for more info.

The issue is that when kbuild builds a .S file, it invokes gcc with
the -mno-relax flag, but this is not being passed through to the
assembler. Adding -Wa,-mno-relax to KBUILD_AFLAGS_MODULE ensures that
the assembler is invoked correctly. This may have now been fixed in
gcc[2] and this addition should not stop newer gcc and as from working.

[1] https://github.com/riscv/riscv-elf-psabi-doc/issues/183
[2] https://github.com/gcc-mirror/gcc/commit/3b0a7d624e64eeb81e4d5e8c62c46d86ef521857

Notes:

Signed-off-by: Ben Dooks <ben.dooks@...ethink.co.uk>
Reviewed-by: Bin Meng <bmeng.cn@...il.com>
---
 arch/riscv/Makefile | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index 1f5c03082976..fca40511a8c6 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -60,6 +60,7 @@ ifeq ($(CONFIG_PERF_EVENTS),y)
 endif

 KBUILD_CFLAGS_MODULE += $(call cc-option,-mno-relax)
+KBUILD_AFLAGS_MODULE += $(call as-option,-Wa$(comma)-mno-relax)

 # GCC versions that support the "-mstrict-align" option default to allowing
 # unaligned accesses.  While unaligned accesses are explicitly allowed in the
-- 
2.35.1