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Add initial big-endian support #1812

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11df93a
configure: Add --with-endian option
djtodoro Aug 14, 2024
c9d6ddc
linux-headers: Ensure proper endianess
djtodoro Aug 14, 2024
6355cfd
README: Add BE instructions
djtodoro Aug 14, 2024
e01382e
configure: Fix glibc multilib build on BE platforms
aleksapaunovic-htec Dec 4, 2025
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6 changes: 5 additions & 1 deletion Makefile.in
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Original file line number Diff line number Diff line change
Expand Up @@ -84,7 +84,11 @@ ifneq ($(XLEN),32)
XLEN := 64
endif

make_tuple = riscv$(1)-unknown-$(2)
ifeq (@endian@,big)
ENDIAN_POSTFIX := be
endif

make_tuple = riscv$(1)$(ENDIAN_POSTFIX)-unknown-$(2)
LINUX_TUPLE ?= $(call make_tuple,$(XLEN),linux-gnu)
NEWLIB_TUPLE ?= $(call make_tuple,$(XLEN),elf)
MUSL_TUPLE ?= $(call make_tuple,$(XLEN),linux-musl)
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9 changes: 9 additions & 0 deletions README.md
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Expand Up @@ -111,6 +111,15 @@ This option only takes effect for the GNU toolchain.
The toolchain has an option `--enable-strip` to control strip of host binaries,
strip is disabled by default.

### Big Endian configuration

To build either cross-compiler with support for big endian targets, run the following command:

```
./configure --prefix=/opt/riscv --with-endian=big
make (target)
```

### Troubleshooting Build Problems

Builds work best if installing into an empty directory. If you build a
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23 changes: 22 additions & 1 deletion configure
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Expand Up @@ -641,6 +641,7 @@ configure_host
target_cxxflags
target_cflags
cmodel
endian
gcc_checking
musl_multilib_names
newlib_multilib_names
Expand Down Expand Up @@ -730,6 +731,7 @@ with_multilib_generator
with_extra_multilib_test
enable_gcc_checking
with_cmodel
with_endian
with_target_cflags
with_target_cxxflags
with_host
Expand Down Expand Up @@ -1426,6 +1428,7 @@ Optional Packages:
--with-extra-multilib-test="rv64gcv-lp64;rv64gcv_zba-lp64"
--with-cmodel Select the code model to use when building libc and
libgcc [--with-cmodel=medlow]
--with-endian Select the target endianess [--with-endian=little]
--with-target-cflags Add extra target flags for C for library code
--with-target-cxxflags Add extra target flags for C++ for library code
--with-host=x86_64-w64-mingw32
Expand Down Expand Up @@ -4080,6 +4083,19 @@ WITH_SIM=$with_sim
WITH_LANGUAGES=$with_languages


# Check whether --with-endian was given.
if test "${with_endian+set}" = set; then :
withval=$with_endian;
fi

if test "x$with_endian" != x; then :
endian=$with_endian

else
endian=little

fi

# Check whether --enable-multilib was given.
if test ${enable_multilib+y}
then :
Expand Down Expand Up @@ -4138,7 +4154,12 @@ fi

if test "x$enable_multilib" = xyes
then :
glibc_multilib_names="rv32imac-ilp32 rv32gc-ilp32d rv64imac-lp64 rv64gc-lp64d rv64gcv-lp64d"
glibc_multilib_names="rv32imac-ilp32 rv32gc-ilp32d rv64imac-lp64 rv64gc-lp64d"
# Vector extension is currently not supported on Big-endian systems.
if test "x$endian" = xlittle
then :
glibc_multilib_names+=" rv64gcv-lp64d"
fi

else $as_nop
glibc_multilib_names="$with_arch-$with_abi"
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4 changes: 4 additions & 0 deletions configure.ac
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Expand Up @@ -188,6 +188,10 @@ AS_IF([test "x$with_cmodel" != xno],
[AC_SUBST(cmodel, -mcmodel=$with_cmodel)],
[AC_SUBST(cmodel, -mcmodel=medlow)])

AS_IF([test "x$with_endian" != x],
[AC_SUBST(endian, endian=$with_endian)],
[AC_SUBST(endian, endian=little)])

AC_ARG_WITH(target_cflags,
[AS_HELP_STRING([--with-target-cflags],
[Add extra target flags for C for library code])],
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4 changes: 4 additions & 0 deletions linux-headers/include/asm/byteorder.h
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Expand Up @@ -7,6 +7,10 @@
#ifndef _ASM_RISCV_BYTEORDER_H
#define _ASM_RISCV_BYTEORDER_H

#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
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@cmuellner cmuellner Dec 18, 2025

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All linux headers are copied without modification as we don't want downstream changes here.
If we add such non-upstream changes, then there is a risk of breaking the BE build each time we update the linux headers.

#include <linux/byteorder/little_endian.h>
#else
#include <linux/byteorder/big_endian.h>
#endif

#endif /* _ASM_RISCV_BYTEORDER_H */