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 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) /* * 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)) +endif + # $(srctree)/$(src) for including checkin headers from generated source files # $(objtree)/$(obj) for including generated headers from checkin source files ifeq ($(KBUILD_EXTMOD),)
