On Fri, Dec 27, 2024 at 11:19 AM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > > On Thu, 26 Dec 2024 15:01:07 -0800 > Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > > On Thu, 26 Dec 2024 at 13:49, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > > > > > > But then, when the linker removes these functions because they were > > > overridden, the code does not disappear, leaving the pointers in the > > > __mcount_loc locations. > > > > This seems entirely unrelated to weak functions, and will be true for > > any other "linker removed it" (which can happen for other reasons > > too). > > > > So your "fix" seems to be hacking around a symptom. > > Yeah, that's why this was just a POC. > > > > > And honestly, the kallsyms argument seems bogus too. The problem with > > kallsyms is that it looks up the size the wrong way. Making up new > > function names doesn't fix the problem, it - once again - just hacks > > around the symptom of doing something wrong. > > > > Christ, kallsyms looking at nm output and going by "next symbol" was > > always bogus, but I think that's how the old a.out format worked > > originally. > > > > But "nm" literally takes a "-S" argument. We just don't use it. > > > > So I think the fix is literally to just make kallsysms have the size > > data. Of course, very annoyingly out /proc/kallsyms file format also > > tracks the (legacy) nm output that doesn't have size information. > > > > But I do think that if you hit real problems, you need to fix the > > *source* of the issue, not add another ugly hack around things. > > So basically the real solution is to fix kallsyms to know about the end > of functions. Peter Zijlstra mentioned that before, but it would take a > bit more work and understanding of kallsyms to fix it properly. > > I'm fine not doing the hack and hopefully one day someone will have the > time to fix kallsyms. This was just something I could do quickly, > knowing it is mostly keeping with the status quo and not actually > fixing the root of the issue. I also needed to refresh my ELF parsing > abilities ;-) > > I may take a look at kallsyms internals. I have some spare time before > the new year to try and work on things I don't normally get time to > work on. > > -- Steve So, does the kallsyms patch set from Zheng Yejian fix the issues? It was a long time ago that I reviewed his v1. I need to take a look if we decide to go with that approach. -- Best Regards Masahiro Yamada
