On 12 Jan 2022, Luis Chamberlain stated: > On Thu, Dec 16, 2021 at 08:19:12PM +0000, Nick Alcock wrote: >> /proc/kallsyms is very useful for tracers and other tools that need to >> map kernel symbols to addresses. >> >> It would be useful > > It took me digging on archives to see to *who* this is useful to. > The short answer seeme to be dtrace. Can you work on getting use > of this for something (I don't know, maybe kernelshark?) that does > not taint the kernel? Last I checked using dtrace on linux taints the > kernel. It hasn't tainted the kernel for at least four years :) v1 (with a kernel module) has been GPLv2 since 2017; v2 is pure-BPF and has no DTrace-specific kernel modules, just using some new things we have to add to the kernel, most of which seem plausibly useful to others too (kallmodsyms, waitfd pro tem until pidfd supports ptracers, and CTF). This is not a DTrace-specific feature in any case: all my submissions have noted that it seems likely to be useful to anyone who wants a stable reference to modules that doesn't change whenever the kernel config changes, which probably means most tracers with support for kernel modules which implement anything like a programming language. > Without valid upstream users I see no need to add more complexity to the > kernel. And complexity added by tainting modules or not upstream modules We don't need any of those any more :) Even CTF is now generated by GCC (once GCC 12 is released) and deduplicated by GNU ld: the CTF patch will be only a few hundred lines long once GCC 12 is out and I drop the DWARF->CTF translator. > Without a valid non-taining user being made very clear with a value-add, > I will have to ignore this. I hope this gives you a reason to not ignore it! Have some links: DTrace v1 (maintenance mode, fairly hefty GPL kernel module, UPL userspace; fully-functional including fbt, kernel side will shrink): https://github.com/oracle/dtrace-linux-kernel v1/5.15 https://github.com/oracle/dtrace-utils 1.x-branch-dev DTrace v2 based on BPF, in progress, some features still missing (UPL userspace and a few GPL kernel patches, including this one: needs a BPF cross-compiler, which is a new GCC 12 target): https://github.com/oracle/dtrace-linux-kernel v2/5.14.9 https://github.com/oracle/dtrace-utils 2.0-branch (I'm going to respin all of these kernel branches against 5.17-rc once the merge window closes, and bring the things both kernel trees have in common into sync. I'll drop you a line once that's done.) Config-wise both of these need kernels with CONFIG_KALLMODSYMS, CONFIG_WAITFD and CONFIG_CTF turned on, and a kernel built with a 'make ctf' done after 'make', and the kernel source tree available when DTrace proper is built. -- NULL && (void)
