On Fri, Mar 8, 2024 at 2:48 PM Fangrui Song <mask...@google.com> wrote: > > On ELF64, it looks like BFD uses 8-byte alignment for compressed > `.debug_*` sections while gold/lld/mold use 1-byte alignment. I do not > know how the Solaris linker sets the alignment. > > The specification's wording makes me confused whether it really > requires 8-byte alignment, even if a non-packed `Elf64_Chdr` surely > requires 8.
Since compressed sections begin with a compression header structure that identifies the compression algorithm, compressed sections must be aligned to the alignment of the compression header. I don't think there is any ambiguity here. > > The sh_size and sh_addralign fields of the section header for a compressed > > section reflect the requirements of the compressed section. > > There are many `.debug_*` sections. So avoiding some alignment padding > seems a very natural extension (a DWARF v5 -gsplit-dwarf relocatable > file has ~10 `.debug_*` sections), even if the specification doesn't > allow it with a very strict interpretation... > > (Off-topic: I wonder whether ELF control structures should use > unaligned LEB128 more. REL/RELA can naturally be replaced with a > LEB128 one similar to wasm.) > > On Fri, Mar 8, 2024 at 1:57 PM Ian Lance Taylor <i...@golang.org> wrote: > > > > Reportedly when lld compresses debug sections, it fails to set the > > alignment of the compressed section such that the compressed header > > can be read directly. To me this seems like a bug in lld. However, > > libbacktrace needs to work around it. This patch, originally by the > > GitHub user ubyte, does that. Bootstrapped and tested on > > x86_64-pc-linux-gnu. Committed to mainline. > > > > Ian > > > > * elf.c (elf_uncompress_chdr): Don't assume compressed section is > > aligned. > > > > -- > 宋方睿 -- H.J.
