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

Message ID 20210720144458.367954-1-ben.dooks@codethink.co.uk (mailing list archive)
State New, archived
Headers show
Series [v2] riscv: add as-options for modules with assembly compontents | expand

Commit Message

Ben Dooks July 20, 2021, 2:44 p.m. UTC
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@codethink.co.uk>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
---
 arch/riscv/Makefile | 1 +
 1 file changed, 1 insertion(+)

Comments

Ben Dooks Aug. 10, 2021, 8:49 a.m. UTC | #1
On 20/07/2021 15:44, Ben Dooks wrote:
> 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

Just wanted to check v2 is fine for merging, and if so when is that
likely to be?
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Patch

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