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145 lines
3.9 KiB
Markdown
145 lines
3.9 KiB
Markdown
# Biscuit: RISC-V Runtime Code Generation Library
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*RISC it for the biscuit*
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## About
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An experimental runtime code generator for RISC-V.
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This allows for runtime code generation of RISC-V instructions. Similar
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to how [Xbyak](https://github.com/herumi/xbyak) allows for runtime code generation of x86 instructions.
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## Implemented ISA Features
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Includes both 32-bit and 64-bit instructions in the following:
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| Feature | Version |
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|:----------|:-------:|
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| A | 2.1 |
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| B | 1.0 |
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| C | 2.0 |
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| D | 2.2 |
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| F | 2.2 |
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| H | 1.0 RC |
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| K | 1.0.1 |
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| M | 2.0 |
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| N | 1.1 |
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| Q | 2.2 |
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| RV32I | 2.1 |
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| RV64I | 2.1 |
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| S | 1.12 |
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| V | 1.0 |
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| Sstc | 0.5.4 |
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| Zfh | 1.0 |
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| Zfhmin | 1.0 |
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| Zicbom | 1.0 |
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| Zicbop | 1.0 |
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| Zicboz | 1.0 |
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| Zicsr | 2.0 |
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| Zifencei | 2.0 |
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| Zihintntl | 0.2 |
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Note that usually only extensions considered ratified will be implemented
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as non-ratified documents are considerably more likely to have
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large changes made to them, which makes maintaining instruction
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APIs a little annoying.
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## Dependencies
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Biscuit requires no external dependencies for its library other than the C++ standard library.
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The tests, however, use the Catch2 testing library. This is included in tree so there's no need
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to worry about installing it yourself if you wish to run said tests.
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## Building Biscuit
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1. Generate the build files for the project with CMake
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2. Hit the build button in your IDE of choice, or run the relevant console command to build for the CMake generator you've chosen.
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3. Done.
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## Running Tests
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1. Generate the build files for the project with CMake
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2. Build the tests
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3. Run the test executable directly, or enter `ctest` into your terminal.
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## License
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The library is licensed under the MIT license.
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While it's not a requirement whatsoever, it'd be pretty neat if you told me that you found the library useful :-)
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## Example
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The following is an adapted equivalent of the `strlen` implementation within the RISC-V bit manipulation extension specification.
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For brevity, it has been condensed to only handle little-endian platforms.
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```cpp
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// We prepare some contiguous buffer and give the pointer to the beginning
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// of the data and the total size of the buffer in bytes to the assembler.
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void strlen_example(uint8_t* buffer, size_t buffer_size) {
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using namespace biscuit;
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constexpr int ptrlog = 3;
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constexpr int szreg = 8;
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Assembler as(buffer, buffer_size);
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Label done;
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Label loop;
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as.ANDI(a3, a0, szreg - 1); // Offset
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as.ANDI(a1, a0, 0xFF8); // Align pointer
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as.LI(a4, szreg);
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as.SUB(a4, a4, a3); // XLEN - offset
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as.SLLI(a3, a3, ptrlog); // offset * 8
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as.LD(a2, 0, a1); // Chunk
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//
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// Shift the partial/unaligned chunk we loaded to remove the bytes
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// from before the start of the string, adding NUL bytes at the end.
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//
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as.SRL(a2, a2, a3); // chunk >> (offset * 8)
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as.ORCB(a2, a2);
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as.NOT(a2, a2);
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// Non-NUL bytes in the string have been expanded to 0x00, while
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// NUL bytes have become 0xff. Search for the first set bit
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// (corresponding to a NUL byte in the original chunk).
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as.CTZ(a2, a2);
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// The first chunk is special: compare against the number of valid
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// bytes in this chunk.
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as.SRLI(a0, a2, 3);
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as.BGTU(a4, a0, &done);
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as.ADDI(a3, a1, szreg);
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as.LI(a4, -1);
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// Our critical loop is 4 instructions and processes data in 4 byte
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// or 8 byte chunks.
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as.Bind(&loop);
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as.LD(a2, szreg, a1);
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as.ADDI(a1, a1, szreg);
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as.ORCB(a2, a2);
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as.BEQ(a2, a4, &loop);
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as.NOT(a2, a2);
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as.CTZ(a2, a2);
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as.SUB(a1, a1, a3);
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as.ADD(a0, a0, a1);
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as.SRLI(a2, a2, 3);
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as.ADD(a0, a0, a2);
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as.Bind(&done);
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as.RET();
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}
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```
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