NE10 Assembly File Syntax Errors with AARCH64 GCC Assembler
The core issue revolves around the failure to build NE10 library assembly files for the ARM Cortex-A53 processor using the AARCH64 GCC assembler in a QNX 7.0.4 environment. The specific error occurs during the assembly phase, where the AARCH64 GCC assembler encounters an unrecognized character, the ‘@’ symbol, which is used as a comment delimiter in the NE10 assembly files. This error is indicative of a syntax incompatibility between the assembly code and the AARCH64 GCC assembler’s expected syntax. The NE10 library, designed for ARM NEON optimizations, contains hand-written assembly files that use ‘@’ for comments, a convention common in ARM assembly but not recognized by the AARCH64 GCC assembler in this context.
The Cortex-A53 processor, part of the ARMv8-A architecture, supports both AARCH32 and AARCH64 execution states. The AARCH64 state introduces a new instruction set and assembly syntax, which differs from the traditional ARM assembly syntax used in AARCH32. The NE10 library, while optimized for ARM NEON, may not fully account for the syntactic differences between AARCH32 and AARCH64 assembly, leading to build failures when targeting AARCH64. The QNX 7.0.4 operating system, being a real-time OS, imposes additional constraints on the build environment, further complicating the porting process.
The error message, "junk at end of line, first unrecognized character is ‘@’", specifically points to the assembler’s inability to parse the ‘@’ symbol as a comment delimiter. This suggests that the AARCH64 GCC assembler expects a different syntax for comments, likely the ‘//’ or ‘/* */’ style used in C/C++, rather than the ‘@’ symbol traditionally used in ARM assembly. This discrepancy highlights a fundamental mismatch between the assembly code’s syntax and the assembler’s expectations, necessitating a thorough review and modification of the assembly files to ensure compatibility with the AARCH64 GCC assembler.
AARCH64 GCC Assembler Syntax Incompatibility and NE10 Assembly Conventions
The root cause of the build error lies in the syntax incompatibility between the NE10 assembly files and the AARCH64 GCC assembler. The NE10 library, originally designed for ARMv7-A and ARMv8-A architectures, uses the ‘@’ symbol to denote comments in its assembly files. This convention is consistent with the ARM assembly language syntax used in AARCH32, where ‘@’ is a valid comment delimiter. However, the AARCH64 GCC assembler, which is based on the GNU assembler (GAS), does not recognize ‘@’ as a comment delimiter. Instead, it expects comments to be marked using the ‘//’ or ‘/* */’ syntax, similar to C/C++.
The AARCH64 GCC assembler’s syntax requirements are stricter compared to the ARM assembler used in AARCH32. This strictness is partly due to the AARCH64 instruction set’s design, which introduces new instructions and syntax rules that differ from AARCH32. The AARCH64 GCC assembler is designed to enforce these new rules, ensuring that the generated machine code is valid for the AARCH64 execution state. As a result, any deviation from the expected syntax, such as the use of ‘@’ for comments, results in an error.
Another contributing factor is the QNX 7.0.4 build environment, which may have specific requirements or constraints that further complicate the assembly process. QNX, being a real-time operating system, often requires custom toolchains and build configurations to ensure that the resulting binaries are optimized for real-time performance. These customizations can introduce additional layers of complexity, making it more challenging to resolve syntax incompatibilities between the assembly code and the assembler.
The NE10 library’s assembly files are hand-optimized for ARM NEON, a SIMD (Single Instruction, Multiple Data) extension that accelerates multimedia and signal processing tasks. These optimizations are critical for achieving high performance on ARM processors, but they also make the assembly code more sensitive to syntax changes. Any modification to the assembly files must be done carefully to preserve the optimizations while ensuring compatibility with the AARCH64 GCC assembler.
Modifying NE10 Assembly Files for AARCH64 GCC Assembler Compatibility
To resolve the build errors, the NE10 assembly files must be modified to replace the ‘@’ comment delimiter with a syntax that is recognized by the AARCH64 GCC assembler. This involves systematically reviewing each assembly file and replacing all instances of ‘@’ with ‘//’ or ‘/* */’. The process requires a deep understanding of both the ARM assembly language and the AARCH64 instruction set to ensure that the modifications do not introduce new errors or degrade performance.
The first step is to identify all assembly files in the NE10 library that use the ‘@’ symbol for comments. This can be done using a combination of grep and sed commands in a Unix-like environment. For example, the following command can be used to search for all instances of ‘@’ in the assembly files:
grep -r '@' modules/math/
Once the problematic lines are identified, the next step is to replace the ‘@’ symbol with the appropriate comment delimiter. This can be done using a script or manually, depending on the number of files and lines involved. For example, the following sed command can be used to replace ‘@’ with ‘//’ in a single file:
sed -i 's/@/\/\//g' modules/math/NE10_add.neon.s
After modifying the assembly files, the next step is to rebuild the NE10 library using the AARCH64 GCC assembler. This involves configuring the build environment to use the correct toolchain and ensuring that all dependencies are properly resolved. The build process should be closely monitored to verify that the modifications have resolved the syntax errors and that the library is successfully built.
In addition to modifying the comment syntax, it may also be necessary to review other aspects of the assembly code to ensure compatibility with the AARCH64 GCC assembler. This includes checking for any AARCH32-specific instructions or syntax that may not be supported in AARCH64. Any such instances should be replaced with their AARCH64 equivalents, if available, or with alternative code that achieves the same functionality.
Finally, it is important to test the modified NE10 library to ensure that it performs as expected on the target hardware. This involves running the library’s test suite and any application-specific tests to verify that the optimizations and functionality are preserved. Any performance regressions or functional issues should be investigated and addressed as needed.
In conclusion, resolving the NE10 assembly build errors for the ARM Cortex-A53 processor in a QNX 7.0.4 environment requires a thorough understanding of both the ARM assembly language and the AARCH64 instruction set. By carefully modifying the assembly files to replace the ‘@’ comment delimiter with a syntax recognized by the AARCH64 GCC assembler, and by ensuring that all other aspects of the code are compatible with AARCH64, it is possible to successfully build the NE10 library and leverage its optimizations for high-performance multimedia and signal processing tasks.
