On Tue, Jul 28, 2026 at 5:58 PM Vasily Gorbik <[email protected]> wrote:
> So I do not think -mrecord-mcount Rust support is only needed for > s390. The Rust build path needs an equivalent of -mrecord-mcount when > FTRACE_MCOUNT_USE_CC is selected. And additionally an equivalent of > -mnop-mcount for s390 (this is debatable, we could check if this brings > us much or we could drop it). Right, as background, the llvm x86 maintainer were uninterested in supporting these options [1] when I created the PR. I think the argument is roughly that these options are bespoke features for building this project. mrecordmcount already does that, independent of the compiler. I think some llvm maintainers hold the opinion that patchable-function-entries is already a sufficient replacement for fentry. Digging through commit history, the answer is unsurprisingly that using recordmcount is slower. It's certainly more convenient to have the compiler record them. [1] https://github.com/llvm/llvm-project/pull/184641
