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Computer Enhance Part 3.8 Homework -- Linking Directly to ASM (on macOS/arm64)
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| // @NOTE(BDJ): Resources: | |
| // - ARM ABI: https://github.com/ARM-software/abi-aa (see "Procedure Call Standard for the Arm 64-bit Architecture") | |
| // - Apple's ARM64 ABI: https://developer.apple.com/documentation/xcode/writing-arm64-code-for-apple-platforms | |
| // - ARM instruction reference: https://developer.arm.com/documentation/dui0802/b/A64-General-Instructions | |
| // - clang/GNU assembler syntax reference: https://developer.arm.com/documentation/100068/0622/Migrating-from-armasm-to-the-armclang-Integrated-Assembler/Overview-of-differences-between-armasm-and-GNU-syntax-assembly-code | |
| // | |
| // There are a few minor assembler syntax differences compared to NASM: | |
| // | |
| // - all label names have to be unique--including loop labels | |
| // - no leading `.` in front of labels | |
| // - `global` -> `.global` | |
| // - `section .text` -> `.text` | |
| // - the end of an assembly file is marked with `.end` | |
| // - conventionally ARM assembly files have a `.s` file extension | |
| // | |
| // To satisfy Apple's ARM64 toolchain and ABI, we also need to: | |
| // | |
| // - prepend global symbol names with an underscore | |
| // - align the first instruction in a function to an 8-byte boundary (using `.balign`) | |
| .global _MOVAllBytesASM | |
| .global _NOPAllBytesASM | |
| .global _CMPAllBytesASM | |
| .global _DECAllBytesASM | |
| .text | |
| // @NOTE(BDJ): On ARM64, the first 8 parameters to a function are passed | |
| // in registers x0-x7. x9-x15 are available as temporary registers. So-- | |
| // | |
| // x0 holds the count | |
| // x1 holds the base data pointer | |
| .balign 8 | |
| _MOVAllBytesASM: | |
| eor x9, x9, x9 | |
| loop_mov: | |
| strb w9, [x1, x9] | |
| add x9, x9, #1 | |
| cmp x9, x0 | |
| b.lo loop_mov | |
| ret | |
| // @NOTE(BDJ): There is no variable-length `nop` instruction in ARM64. But there are SOME variable-length instructions! | |
| .balign 8 | |
| _NOPAllBytesASM: | |
| eor x9, x9, x9 | |
| loop_nop: | |
| nop | |
| add x9, x9, #1 | |
| cmp x9, x0 | |
| b.lo loop_nop | |
| ret | |
| .balign 8 | |
| _CMPAllBytesASM: | |
| eor x9, x9, x9 | |
| loop_cmp: | |
| add x9, x9, #1 | |
| cmp x9, x0 | |
| b.lo loop_cmp | |
| ret | |
| .balign 8 | |
| _DECAllBytesASM: | |
| loop_sub: | |
| sub x0, x0, #1 | |
| cbnz x0, loop_sub | |
| ret | |
| .end |
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| // @NOTE(BDJ): Build steps: | |
| // - Assemble: clang -arch arm64 -g -o arm64_assembly.o -c arm64_assembly.s | |
| // - Archive: ar rcs libarm64_assembly.a arm64_assembly.o | |
| // - Compile+Link: clang -L. -larm64_assembly test.c -o test | |
| // | |
| // Debug with Xcode or lldb as usual. In Xcode, be sure to check the menu option | |
| // Debug >> Debug Workflow >> "Always Show Disassembly". Hold down the Control key | |
| // when debugging to step by assembly instruction. | |
| typedef int s32; | |
| typedef unsigned char u8; | |
| typedef unsigned long long u64; | |
| extern void MOVAllBytesASM( u64 count, u8 *data ); | |
| extern void NOPAllBytesASM( u64 count ); | |
| extern void CMPAllBytesASM( u64 count ); | |
| extern void DECAllBytesASM( u64 count ); | |
| s32 main (s32 argument_count, char const* arguments[]) { | |
| u8 buffer[ 1 << 16 ] = {0}; | |
| MOVAllBytesASM( sizeof(buffer), buffer ); | |
| NOPAllBytesASM( sizeof(buffer) ); | |
| CMPAllBytesASM( sizeof(buffer) ); | |
| DECAllBytesASM( sizeof(buffer) ); | |
| return 0; | |
| } |
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There are numerical local labels. You jump to them providing direction
f- for forward,b- for backward. You can have multiple of them in one file and they'd better be used in macro.https://developer.arm.com/documentation/100068/0618/Migrating-from-armasm-to-the-armclang-Integrated-Assembler/Numeric-local-labels?lang=en