Add big-endian build option for riscv

Add big-endian build option for riscv

[Ben Dooks]

Add the option to allow building a RISC-V system big-endian.

This has been tested against our big-endian qemu/cva6 system
and is the minimal base to allow a system to run big-endian.

We don't yet address IO endian which has been an interesting
issue, as some code seems to assume big-endian means big-endian
IO.

[PATCH v2 1/2] riscv: add build support for big-endian

[Ben Dooks]

Add support to build code big-endian if the board supports
it. Updates the makefile to pass the correct compiler and
elf flags.

Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
---
v2:
- fixed issue with big v little endian build (+typos)
---
 arch/riscv/config.mk | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/arch/riscv/config.mk b/arch/riscv/config.mk
index 9f16dda92a0..eddd6a3b9a2 100644
--- a/arch/riscv/config.mk
+++ b/arch/riscv/config.mk
@@ -10,19 +10,29 @@
 # Rick Chen, Andes Technology Corporation <rick@andestech.com>
 #
 
-32bit-emul		:= elf32lriscv
-64bit-emul		:= elf64lriscv
+ifdef CONFIG_SYS_BIG_ENDIAN
+small-endian		:= b
+large-endian		:= big
+PLATFORM_CPPFLAGS       += -mbig-endian
+KBUILD_LDFLAGS          += -mbig-endian
+else
+small-endian		:= l
+large-endian		:= little
+endif
+
+32bit-emul		:= elf32$(small-endian)riscv
+64bit-emul		:= elf64$(small-endian)riscv
 
 ifdef CONFIG_32BIT
 KBUILD_LDFLAGS		+= -m $(32bit-emul)
 EFI_LDS			:= elf_riscv32_efi.lds
-PLATFORM_ELFFLAGS	+= -B riscv -O elf32-littleriscv
+PLATFORM_ELFFLAGS	+= -B riscv -O elf32-$(large-endian)riscv
 endif
 
 ifdef CONFIG_64BIT
 KBUILD_LDFLAGS		+= -m $(64bit-emul)
 EFI_LDS			:= elf_riscv64_efi.lds
-PLATFORM_ELFFLAGS	+= -B riscv -O elf64-littleriscv
+PLATFORM_ELFFLAGS	+= -B riscv -O elf64-$(large-endian)riscv
 endif
 
 PLATFORM_CPPFLAGS	+= -ffixed-x3 -fpic
-- 
2.37.2.352.g3c44437643

[PATCH v2 2/2] riscv: byteorder: add test for big-endian

[Ben Dooks]

Test for big-endian either via __RISCVEB__ which migth be
rather old, or check the BYTE_ORDER if the compiler defines
it (which should be any modern gcc like v12)

Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
---
 arch/riscv/include/asm/byteorder.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/riscv/include/asm/byteorder.h b/arch/riscv/include/asm/byteorder.h
index d26ac5688fa..3140c1f585e 100644
--- a/arch/riscv/include/asm/byteorder.h
+++ b/arch/riscv/include/asm/byteorder.h
@@ -26,7 +26,7 @@
 #  define __SWAB_64_THRU_32__
 #endif
 
-#ifdef __RISCVEB__
+#if  defined(__RISCVEB__) || (defined(__BYTE_ORDER__) && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__)
 #include <linux/byteorder/big_endian.h>
 #else
 #include <linux/byteorder/little_endian.h>
-- 
2.37.2.352.g3c44437643

Re: [PATCH v2 1/2] riscv: add build support for big-endian

[Tom Rini]

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On Fri, Jun 13, 2025 at 05:12:57PM +0100, Ben Dooks wrote:

> Add support to build code big-endian if the board supports
> it. Updates the makefile to pass the correct compiler and
> elf flags.
> 
> Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>

Reviewed-by: Tom Rini <trini@konsulko.com>

-- 
Tom

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Re: [PATCH v2 2/2] riscv: byteorder: add test for big-endian

[Leo Liang]

On Fri, Jun 13, 2025 at 05:12:58PM +0100, Ben Dooks wrote:
> Test for big-endian either via __RISCVEB__ which migth be
> rather old, or check the BYTE_ORDER if the compiler defines
> it (which should be any modern gcc like v12)
> 
> Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
> ---
>  arch/riscv/include/asm/byteorder.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Acked-by: Leo Yu-Chi Liang <ycliang@andestech.com>