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Alternative to D125036. Implement R_RISCV_ALIGN relaxation so that we can handle -mrelax object files (i.e. -mno-relax is no longer needed) and creates a framework for future relaxation. `relaxAux` is placed in a union with InputSectionBase::jumpInstrMod, storing auxiliary information for relaxation. In the first pass, `relaxAux` is allocated. The main data structure is `relocDeltas`: when referencing `relocations[i]`, the actual offset is `r_offset - (i ? relocDeltas[i-1] : 0)`. `relaxOnce` performs one relaxation pass. It computes `relocDeltas` for all text section. Then, adjust st_value/st_size for symbols relative to this section based on `SymbolAnchor`. `bytesDropped` is set so that `assignAddresses` knows that the size has changed. Run `relaxOnce` in the `finalizeAddressDependentContent` loop to wait for convergence of text sections and other address dependent sections (e.g. SHT_RELR). Note: extrating `relaxOnce` into a separate loop works for many cases but has issues in some linker script edge cases. After convergence, compute section contents: shrink the NOP sequence of each R_RISCV_ALIGN as appropriate. Instead of deleting bytes, we run a sequence of memcpy on the content delimitered by relocation locations. For R_RISCV_ALIGN let the next memcpy skip the desired number of bytes. Section content computation is parallelizable, but let's ensure the implementation is mature before optimizations. Technically we can save a copy if we interleave some code with `OutputSection::writeTo`, but let's not pollute the generic code (we don't have templated relocation resolving, so using conditions can impose overhead to non-RISCV.) Tested: `make ARCH=riscv CROSS_COMPILE=riscv64-linux-gnu- LLVM=1 defconfig all` built Linux kernel using -mrelax is bootable. FreeBSD RISCV64 system using -mrelax is bootable. bash/curl/firefox/libevent/vim/tmux using -mrelax works. Differential Revision: https://reviews.llvm.org/D127581
LLVM Linker (lld)
This directory and its subdirectories contain source code for the LLVM Linker, a modular cross platform linker which is built as part of the LLVM compiler infrastructure project.
lld is open source software. You may freely distribute it under the terms of the license agreement found in LICENSE.txt.
Benchmarking
In order to make sure various developers can evaluate patches over the same tests, we create a collection of self contained programs.
It is hosted at https://s3-us-west-2.amazonaws.com/linker-tests/lld-speed-test.tar.xz
The current sha256 is 10eec685463d5a8bbf08d77f4ca96282161d396c65bd97dc99dbde644a31610f.