On Fri, Apr 14, 2023 at 10:12:55AM -0700, Josh Poimboeuf wrote: > On Fri, Apr 14, 2023 at 10:53:03AM +0100, Mark Rutland wrote: > > > Currently proposed topics follow. The list is open though and more will > > > be added during the regular Call for Topics. > > > > > > - klp-convert (as means to fix CET IBT limitations) and its > > > upstreamability > > > - shadow variables, global state transition > > > - kselftests and the future direction of development > > > - arm64 live patching > > > > I'm happy to talk about the kernel-side of arm64 live patching; it'd be good to > > get in contact with anyone looking at the arm64 userspace side (e.g. > > klp-convert). > > klp-convert is still considered experimental. FYI here's a pull request > which adds arm64 support to kpatch-build: > > https://github.com/dynup/kpatch/pull/1302 Ah; I'm clearly not familiar with the userspace side at all! > > I have some topics which overlap between live-patching and general toolchain > > bits and pieces, and I'm not sure if they'd be best suited here or in a > > toolchain track, e.g. > > > > * How to avoid/minimize the need to reverse-engineer control flow for things > > like ORC generation. > > > > On the arm64 side we're pretty averse to doing this to generate metadata for > > unwinding (and we might not need to), but there are things objtool does today > > that requires awareness of control-flow (e.g. forward-edge checks for noinstr > > safety). > > > > Hopefully without a flamewar about DWARF... > > If objtool is going to be doing control-flow anyway then it could just > validate DWARF/SFrame. Then everybody's happy? > > > * Better compiler support for noinstr and similar properties. > > > > For example, noinstr functions are currently all noinline, and we can't > > inline a noinstr function into a noinstr function, leading to a painful mix > > of noinstr and __always_inline. Having a mechanism to allow noinstr code to > > be inlined into other noinstr code would be nice. > > Can you elaborate? Why can't noinstr inline noinstr? (that's a > mouthful) > > Is it because of potential cloning caused by IPA optimizations? Today, noinstr is marks as noinline: | /* Section for code which can't be instrumented at all */ | #define __noinstr_section(section) \ | noinline notrace __attribute((__section__(section))) \ | __no_kcsan __no_sanitize_address __no_profile __no_sanitize_coverage \ | __no_sanitize_memory | | #define noinstr __noinstr_section(".noinstr.text") My understnading is that without that, a noinstr function *could* get inlined into an instrumentable function and get instrumented (e.g. in the case of a static noinstr function with a single caller). > > Likewise, whether we could somehow get compile-time warnings about unintended > > calls from instrumentable code from noinstr code. > > > > * How is this going to work with rust? > > > > It's not clear to me whether/how things like ftrace, RELIABLE_STACKTRACE, and > > live-patching are going to work with rust. > > Not to mention how objtool will react to compiled rust code (has it > already been tried?) I have no idea :) Thanks, Mark
