Problem:

When cross-compiling aws-lc-sys for aarch64-unknown-linux-gnu target, the build fails with an error indicating that __ARM_ARCH is not defined during ARM assembly file compilation. The error occurs in aws-lc/include/openssl/asm_base.h:77 when compiling ARM assembly files (e.g., arm/aes/aes-xts-dec.S). This issue has been confirmed in both v0.36.0 and v0.37.0 (latest as of Jan 23, 2026).

Error Message:

error: #error "ARM assembler must define __ARM_ARCH"
 #error "ARM assembler must define __ARM_ARCH"
  ^

Reproduction Steps:

1. Set up cross-compilation environment for aarch64-unknown-linux-gnu (e.g., using maturin-action with manylinux Docker containers)
2. Build a Rust project that depends on aws-lc-sys = "0.37.0" (or 0.36.0)
3. The build fails during ARM assembly compilation phase with the __ARM_ARCH error

Environment:

• Build tool: maturin-action (using manylinux Docker containers)
• CI/CD: GitHub Actions
• Docker platform: linux/arm64 (for aarch64 target)

Relevant details

AWS-LC for Rust versions or commit: aws-lc-sys = "0.36.0" (tested, has the issue), aws-lc-sys = "0.37.0" (latest as of Jan 23, 2026, tested and confirmed same issue), aws-lc-rs = "1.15.4" (direct dependency)

System information:

• CPU architecture: x86-64 (host), aarch64 (target)
• CPU name: GitHub Actions runner (x86_64 host)
• OS: Ubuntu 22.04 (host), Linux (target - aarch64-unknown-linux-gnu)

Build log:

• The log tells compiler and version.

warning: aws-lc-sys@0.37.0: In file included from /root/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/aws-lc-sys-0.37.0/aws-lc/third_party/s2n-bignum/s2n-bignum-to-be-imported/arm/aes/aes-xts-dec.S:4:0:
warning: aws-lc-sys@0.37.0: /root/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/aws-lc-sys-0.37.0/aws-lc/include/openssl/asm_base.h:77:2: error: #error "ARM assembler must define __ARM_ARCH"
warning: aws-lc-sys@0.37.0:  #error "ARM assembler must define __ARM_ARCH"
warning: aws-lc-sys@0.37.0:   ^
error: failed to run custom build command for `aws-lc-sys v0.37.0`

Caused by:
  process didn't exit successfully: `/home/runner/work/aerospike-client-python-async/aerospike-client-python-async/target/release/build/aws-lc-sys-0b48bad560a68ec3/build-script-main` (exit status: 1)

Cross-compiler information:

• Compiler: aarch64-unknown-linux-gnu-gcc
• Target: aarch64-unknown-linux-gnu
• Host: x86_64-unknown-linux-gnu
• Rust version: 1.90.0

Build Configuration:
We're using the following environment variables to force pre-generated bindings:

AWS_LC_SYS_CMAKE_BUILDER=0
AWS_LC_SYS_EXTERNAL_BINDGEN=0
AWS_LC_SYS_NO_PREGENERATED_SRC=0

What We've Tried:

1. Tested aws-lc-sys 0.36.0 - confirmed __ARM_ARCH issue
2. Tested aws-lc-sys 0.37.0 (released Jan 23, 2026 with aws-lc-rs v1.15.4) - same __ARM_ARCH issue persists
3. Set environment variables to force pre-generated bindings (AWS_LC_SYS_CMAKE_BUILDER=0, AWS_LC_SYS_EXTERNAL_BINDGEN=0, AWS_LC_SYS_NO_PREGENERATED_SRC=0)
4. Attempted to use aws-lc-rs with bindgen feature, but this forced bindgen for all targets (including x86_64 with pre-generated bindings), requiring libclang which isn't available in manylinux Docker containers
5. AWS_LC_SYS_NO_ASM only works for debug builds, not release builds

Expected Behavior:
The build should succeed for aarch64-unknown-linux-gnu target, as this platform is listed as having pre-generated bindings available according to the platform support documentation.

Actual Behavior:
The build fails during ARM assembly compilation because the cross-compiler (aarch64-unknown-linux-gnu-gcc) doesn't properly define __ARM_ARCH when compiling ARM assembly files (.S files). This occurs during the AWS-LC C library compilation phase, not during Rust binding generation.

Related Issues:

• cross-rs/cross#1689 - Similar ARM cross-compilation issues with aws-lc-sys (bindgen-related)
• aws-lc-rs#762 - Failed build for aarch64_unknown_linux_musl
• aws-lc-rs#635 - aarch64-linux-android cross-compilation failure

Workaround:
Currently, we've disabled aarch64-unknown-linux-gnu builds in our CI until this issue is resolved. We're only building for x86_64-unknown-linux-gnu and i686-unknown-linux-gnu targets.