On Tue, Oct 26, 2021 at 02:01:32PM +0200, Peter Zijlstra wrote: > Hi, > > These patches rewrite the way retpolines are rewritten. Currently objtool emits > alternative entries for most retpoline calls. However trying to extend that led > to trouble (ELF files are horrid). > > Therefore completely overhaul this and have objtool emit a .retpoline_sites > section that lists all compiler generated retpoline thunk calls. Then the > kernel can do with them as it pleases. > > Notably it will: > > - rewrite them to indirect instructions for !RETPOLINE > - rewrite them to lfence; indirect; for RETPOLINE_AMD, > where size allows (boo clang!) > > Specifically, the !RETPOLINE case can now also deal with the clang-special > conditional-indirect-tail-call: > > Jcc __x86_indirect_thunk_\reg. > > Finally, also update the x86 BPF jit to catch up to recent times and do these > same things. > > All this should help improve performance by removing an indirection. > > Patches can (soon) be found here: > > git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git objtool/core > > Changes since v2: > > - rewrite the __x86_indirect_thunk_array[] stuff again > - rewrite the retpoline,amd rewrite logic, it now also supports > rewriting the Jcc case, if the original instruction is long enough, but > more importantly, it's simpler code. > - bpf label simplification patch > - random assorted cleanups > - actually managed to get bpf selftests working Good stuff! Acked-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> -- Josh
