On Thu, Sep 14, 2023 at 5:17 PM Jiri Olsa <olsajiri@xxxxxxxxx> wrote: > > On Fri, Sep 08, 2023 at 10:15:35PM +0200, Jiri Olsa wrote: > > On Fri, Sep 08, 2023 at 10:14:56AM -0700, Nick Desaulniers wrote: > > > Thanks for the patch! > > > > > > + Marcus > > > > > > Marcus can you please test the below patch and provide your tested-by > > > and reported-by tags? > > > > > > On Fri, Sep 8, 2023 at 4:47 AM Jiri Olsa <olsajiri@xxxxxxxxx> wrote: > > > > > > > > On Thu, Sep 07, 2023 at 10:33:00PM +0200, Jiri Olsa wrote: > > > > > On Thu, Sep 07, 2023 at 12:01:18PM -0700, Nick Desaulniers wrote: > > > > > > So we've got a curious report recently: > > > > > > https://github.com/ClangBuiltLinux/linux/issues/1913 > > > > > > > > > > > > ld.lld: error: ld-temp.o <inline asm>:14577:1: symbol > > > > > > '__BTF_ID__struct__cgroup__624' is already defined > > > > > > __BTF_ID__struct__cgroup__624: > > > > > > ^ > > > > > > > > > > > > It's been hard to pin down a SHA and .config to reproduce this, but > > > > > > looking at the definition of BTF_ID's usage of __ID's usage of > > > > > > __COUNTER__, and the two statements: > > > > > > > > > > > > kernel/bpf/helpers.c:2460:BTF_ID(struct, cgroup) > > > > > > kernel/bpf/verifier.c:5075:BTF_ID(struct, cgroup) > > > > > > > > > > > > Is it possible that __COUNTER__ could evaluate to the same value > > > > > > across 2 different translation units, leading to a name collision like > > > > > > the above? > > > > > > > > > > hum, that probably the case, I see same counter values at different > > > > > __BTF_ID_ symbols: > > > > > > > > > > ffffffff833fe540 r __BTF_ID__struct__bpf_bloom_filter__380 > > > > > ffffffff833fe548 r __BTF_ID__struct__bpf_queue_stack__380 > > > > > ffffffff833fe578 r __BTF_ID__struct__cgroup__380 > > > > > > > > > > perhaps we were just lucky not to hit that :-\ > > > > > > > > > > > > > > > > > looking at another usage of BTF_ID other than struct > > > > > > cgroup;kernel/bpf/helpers.c:2461:BTF_ID(func, bpf_cgroup_release) > > > > > > is only defined in one translation unit > > > > > > > > > > > > Should one of those two `BTF_ID(struct, cgroup)` be removed? Is there > > > > > > some other way we can avoid these collisions in the future? > > > > > > > > > > need to find some way to make the symbol unique, will check > > > > > > > > the change below uses object's path as the __BTF_ID_.. symbol suffix to make > > > > it unique > > > > > > > > I'm still looking, but can't think of a better way so far, perhaps somebody > > > > will have better idea > > > > > > Another good approach; I had simply added __LINE__ into the paste. > > > https://github.com/ClangBuiltLinux/linux/issues/1913#issuecomment-1710794319 > > > Which just makes the probability of this occurring again smaller, but > > > still non-zero. > > > > yes, there's still possibility of the match > > > > > > > > + Masahiro for thoughts on the invocation of echo and base32. Looks > > > like base32 is part of coreutils. Kind of strange that coreutils isn't > > > listed in Documentation/process/changes.rst. Would adding the usage > > > of base32 add a new dependency on coreutils? > > > > > > > > > > > jirka > > > > > > > > > > > > --- > > > > diff --git a/include/linux/btf_ids.h b/include/linux/btf_ids.h > > > > index a3462a9b8e18..564953f9cbc7 100644 > > > > --- a/include/linux/btf_ids.h > > > > +++ b/include/linux/btf_ids.h > > > > @@ -49,7 +49,7 @@ word \ > > > > ____BTF_ID(symbol, word) > > > > > > > > #define __ID(prefix) \ > > > > - __PASTE(prefix, __COUNTER__) > > > > + __PASTE(__PASTE(prefix, __COUNTER__), BTF_ID_BASE) > > > > > > Do we still need __COUNTER__ if we're now using BTF_ID_BASE? > > > > yes we still need that because we could have same __BTF_ID__... > > symbol used multiple times within same object, and that's where > > __COUNTER__ makes the difference > > > > > > > > > > > > > /* > > > > * The BTF_ID defines unique symbol for each ID pointing > > > > diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib > > > > index 68d0134bdbf9..2ef8b2798be0 100644 > > > > --- a/scripts/Makefile.lib > > > > +++ b/scripts/Makefile.lib > > > > @@ -200,6 +200,10 @@ _c_flags += $(if $(patsubst n%,, \ > > > > -D__KCSAN_INSTRUMENT_BARRIERS__) > > > > endif > > > > > > > > +ifeq ($(CONFIG_DEBUG_INFO_BTF),y) > > > > +_c_flags += -DBTF_ID_BASE=$(subst =,,$(shell echo -n $(modfile) | base32 -w0)) > > > > > > `man 1 base32` shows it can just read a file. Could the above be: > > > > > > _c_flags += -DBTF_ID_BASE=$(subst =,,$(shell base32 -w0 $(modfile))) > > > > > > ? (untested) > > > > > > Also, the output of > > > > > > $ base32 -w0 Documentation/process/changes.rst > > > > > > is 24456 characters. This is going to blow up symbol tables. I > > > suppose ELF probably has some length limit on symbol names, too. I > > > was nervous about my approaching appending __LINE__. > > > > > > Perhaps pipe the output to `head -c <n bytes>`? > > > > so the change is about adding unique id that's basically path of > > the object stored in base32 so it could be used as symbol, so we > > don't really need to read the actual file > > > > the problem is when BTF_ID definition like: > > > > BTF_ID(struct, cgroup) > > > > translates in 2 separate objects into same symbol name because of > > the matching __COUNTER__ macro values (like 380 below) > > > > __BTF_ID__struct__cgroup__380 > > > > this change just adds unique id of the path name at the end of the > > symbol with: > > > > echo -n 'kernel/bpf/helpers' | base32 -w0 --> NNSXE3TFNQXWE4DGF5UGK3DQMVZHG > > > > so the symbol looks like: > > > > __BTF_ID__struct__cgroup__380NNSXE3TFNQXWE4DGF5UGK3DQMVZHG > > > > and is unique over the sources > > > > but I still hope we could come up with some better solution ;-) > > so far the only better solution I could come up with is to use > cksum (also from coreutils) instead of base32, which makes the > BTF_ID_BASE value compact > > I'll run test to find out how much it hurts the build time > > jirka Seems a bad idea to me. It would fork a new shell and chsum for all files, while only a few of them need it. Better to consult BTF forks. -- Best Regards Masahiro Yamada
