On 25/04/2025 15:50, Alexei Starovoitov wrote: > Hi All, > > Looks like pahole fails to deduplicate BTF when kernel and > kernel module are built with gcc-14. > I see this issue with various kernel .config-s on bpf and > bpf-next trees. > I tried pahole 1.28 and the latest master. Same issues. > > BTF in bpf_testmod.ko built with gcc-14 has 2849 types. > When built with gcc-13 it has 454 types. > So something is confusing dedup logic. > Would be great if dedup experts can take a look, > since this dedup issue is breaking a lot of selftests/bpf. > > Also vmlinux.h generated out of the kernel compiled with gcc-13 > and out of the kernel compiled with gcc-14 shows these differences: > > --- vmlinux13.h 2025-04-24 21:33:50.556884372 -0700 > +++ vmlinux14.h 2025-04-24 21:39:10.310488992 -0700 > @@ -148815,7 +148815,6 @@ > extern int hid_bpf_input_report(struct hid_bpf_ctx *ctx, enum > hid_report_type type, u8 *buf, const size_t buf__sz) __weak __ksym; > extern void hid_bpf_release_context(struct hid_bpf_ctx *ctx) __weak __ksym; > extern int hid_bpf_try_input_report(struct hid_bpf_ctx *ctx, enum > hid_report_type type, u8 *buf, const size_t buf__sz) __weak __ksym; > -extern bool scx_bpf_consume(u64 dsq_id) __weak __ksym; > extern int scx_bpf_cpu_node(s32 cpu) __weak __ksym; > extern struct rq *scx_bpf_cpu_rq(s32 cpu) __weak __ksym; > extern u32 scx_bpf_cpuperf_cap(s32 cpu) __weak __ksym; > @@ -148825,12 +148824,8 @@ > extern void scx_bpf_destroy_dsq(u64 dsq_id) __weak __ksym; > extern void scx_bpf_dispatch(struct task_struct *p, u64 dsq_id, u64 > slice, u64 enq_flags) __weak __ksym; > extern void scx_bpf_dispatch_cancel(void) __weak __ksym; > -extern bool scx_bpf_dispatch_from_dsq(struct bpf_iter_scx_dsq > *it__iter, struct task_struct *p, u64 dsq_id, u64 enq_flags) __weak > __ksym; > -extern void scx_bpf_dispatch_from_dsq_set_slice(struct > bpf_iter_scx_dsq *it__iter, u64 slice) __weak __ksym; > extern void scx_bpf_dispatch_from_dsq_set_vtime(struct > bpf_iter_scx_dsq *it__iter, u64 vtime) __weak __ksym; > extern u32 scx_bpf_dispatch_nr_slots(void) __weak __ksym; > -extern void scx_bpf_dispatch_vtime(struct task_struct *p, u64 dsq_id, > u64 slice, u64 vtime, u64 enq_flags) __weak __ksym; > -extern bool scx_bpf_dispatch_vtime_from_dsq(struct bpf_iter_scx_dsq > *it__iter, struct task_struct *p, u64 dsq_id, u64 enq_flags) __weak > __ksym; > extern void scx_bpf_dsq_insert(struct task_struct *p, u64 dsq_id, u64 > slice, u64 enq_flags) __weak __ksym; > extern void scx_bpf_dsq_insert_vtime(struct task_struct *p, u64 > dsq_id, u64 slice, u64 vtime, u64 enq_flags) __weak __ksym; > extern bool scx_bpf_dsq_move(struct bpf_iter_scx_dsq *it__iter, > struct task_struct *p, u64 dsq_id, u64 enq_flags) __weak __ksym; > > gcc-14's kernel is clearly wrong. > These 5 kfuncs still exist in the kernel. > I manually checked there is no if __GNUC__ > 13 in the code. > Also: > nm bld/vmlinux|grep -w scx_bpf_consume > ffffffff8159d4b0 T scx_bpf_consume > ffffffff8120ea81 t scx_bpf_consume.cold > > I suspect the second issue is not related to the dedup problem. > All 5 missing kfuncs have ".cold" optimized bodies. > But ".cold" maybe a red herring, since > nm bld/vmlinux|grep -w scx_bpf_dispatch > ffffffff8159d020 T scx_bpf_dispatch > ffffffff8120ea0f t scx_bpf_dispatch.cold > but this kfunc is present in vmlinux14.h > > If it makes a difference I have these configs: > # CONFIG_DEBUG_INFO_DWARF4 is not set > # CONFIG_DEBUG_INFO_DWARF5 is not set > # CONFIG_DEBUG_INFO_REDUCED is not set > CONFIG_DEBUG_INFO_COMPRESSED_NONE=y > # CONFIG_DEBUG_INFO_COMPRESSED_ZLIB is not set > # CONFIG_DEBUG_INFO_SPLIT is not set > CONFIG_DEBUG_INFO_BTF=y > CONFIG_PAHOLE_HAS_SPLIT_BTF=y > CONFIG_DEBUG_INFO_BTF_MODULES=y thanks for the report! I've just reproduced this now with gcc 14; my initial theory was it might be DWARF5-related, but dedup issues occur for modules with CONFIG_DEBUG_INFO_DWARF4=y also. I'm seeing task_struct duplicates in module BTF among other things, so I will try and dig further and report back when I find something. Like you I suspect the issues with missing kfuncs are different; may be an issue with our logic handling inconsistent functions getting confused by the .cold components. But right now understanding dedup issues is the top priority. Alan
