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solidpixel merged 2 commits into from
Mar 14, 2025
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Add big-endian build docs #559

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Add BE build docs
solidpixel Mar 14, 2025
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15 changes: 9 additions & 6 deletions Docs/Building-BE.md
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Original file line number Diff line number Diff line change
Expand Up @@ -8,9 +8,9 @@ distributions still support BE platforms.

Even though Arm64 can run in a BE mode, it's now very rare in practice. It's no
longer supported out of the box in the latest Arm upstream compiler releases,
and getting hold of a sysroot is increasingly painful. To test BE builds I
and getting hold of a sysroot is increasingly difficult. To test BE builds, I
therefore cross-compile Linux builds for MIPS64 and use `qemu-user` to run
them. This doesn't use a real sysroot, so everything must be compiled with
them. This doesn't use a real sysroot, and so everything must be compiled with
`-static` linkage.

## Host software
Expand All @@ -32,9 +32,9 @@ sudo ln -s /usr/mips64-linux-gnuabi64 /etc/qemu-binfmt/mips64

## CMake toolchain file

Cross-compiling needs an correctly configured CMake, and the easiest way to
Cross-compiling needs a correctly configured CMake, and the easiest way to
do this consistently is to use a toolchain file. Create a `CMake-BE.toolchain`
file with the following content in the root of the project:
file in the root of the project, with the following content:

```
# Operating system
Expand Down Expand Up @@ -65,15 +65,18 @@ set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
## Build astcenc

Building uses CMake as normal, with the additional specification of the
toolchain file to configure the build for cross-compilation.
toolchain file to configure the build for cross-compilation. We don't have any
SIMD implementations for big-endian architectures so these builds must compile
for the reference C SIMD implementation, `ASTCENC_ISA_NONE`.

```
cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=../ -DASTCENC_ISA_NONE=ON -DCMAKE_TOOLCHAIN_FILE=../CMake-BE.toolchain ..
```

## Run astcenc

The cross-compiled `astcenc` binary runs as normal, and can access host files, but must run through QEMU to do the instruction-set translation.
The cross-compiled `astcenc` binary runs as normal, and can access host files,
but must run through QEMU to do the instruction set translation.

```
qemu-mips64 ./bin/astcenc-none ...
Expand Down