Arnaldo,
On Mon, Jul 10, 2023 at 10:42:43AM -0300, Arnaldo Carvalho de Melo wrote:
> Em Wed, Jul 05, 2023 at 05:00:40AM +0300, Vitaly Chikunov escreveu:
> >
> > After updating Dwarves to v1.25 we are getting SIGSEGV while building
> > kernel on 32-bit x86 architecture. It looks like this:
>
> 128 cores, 32-bit system? Interesting :-)
This is just AMD Zen in 32-bit personality.
>
> > BTF .btf.vmlinux.bin.o
> > scripts/link-vmlinux.sh: line 111: 395728 Segmentation fault LLVM_OBJCOPY="${OBJCOPY}" ${PAHOLE} -J ${PAHOLE_FLAGS} ${1}
> > LD .tmp_vmlinux.kallsyms1
> > NM .tmp_vmlinux.kallsyms1.syms
> > KSYMS .tmp_vmlinux.kallsyms1.S
> > AS .tmp_vmlinux.kallsyms1.S
> > LD .tmp_vmlinux.kallsyms2
> > NM .tmp_vmlinux.kallsyms2.syms
> > KSYMS .tmp_vmlinux.kallsyms2.S
> > AS .tmp_vmlinux.kallsyms2.S
> > LD vmlinux
> > BTFIDS vmlinux
> > libbpf: failed to find '.BTF' ELF section in vmlinux
> > FAILED: load BTF from vmlinux: No data available
> >
> > What crashes is this command:
> >
> > pahole -J --btf_gen_floats -j --lang_exclude=rust .tmp_vmlinux.btf
> >
> > I found that cause of the crash is that build box having 128 cores. By
> > experiment I found that with -j81 pahole works OK, but with -j82 or
> > greater it crashes.
> >
> > $ gdb -q --args pahole -J --btf_gen_floats -j111 --lang_exclude=rust .tmp_vmlinux.btf
> > Thread 15 "pahole" received signal SIGSEGV, Segmentation fault.
> > [Switching to Thread 0xda5ffb40 (LWP 3102466)]
> > 0xf7f3c944 in btf_encoder__btf (encoder=0x0) at /usr/src/debug/dwarves-1.25/btf_encoder.c:1890
> > 1890 return encoder->btf;
> > (gdb) bt
> > #0 0xf7f3c944 in btf_encoder__btf (encoder=0x0) at /usr/src/debug/dwarves-1.25/btf_encoder.c:1890
> > #1 0x5655c25d in pahole_stealer (cu=0xd9a01f80, conf_load=0x565640c0 <conf_load>, thr_data=0x56567c18) at /usr/src/debug/dwarves-1.25/pahole.c:3100
> > #2 0xf7f452d7 in cu__finalize (cu=cu@entry=0xd9a01f80, conf=0x565640c0 <conf_load>, thr_data=thr_data@entry=0x56567c18)
> > at /usr/src/debug/dwarves-1.25/dwarf_loader.c:3001
> > #3 0xf7f4541d in cus__finalize (thr_data=0x56567c18, conf=<optimized out>, cu=0xd9a01f80, cus=0x565651c0) at /usr/src/debug/dwarves-1.25/dwarf_loader.c:3008
> > #4 dwarf_cus__create_and_process_cu (dcus=dcus@entry=0xffffd19c, cu_die=cu_die@entry=0xda5ff38c, pointer_size=<optimized out>, thr_data=0x56567c18)
> > at /usr/src/debug/dwarves-1.25/dwarf_loader.c:3207
> > #5 0xf7f461af in dwarf_cus__process_cu_thread (arg=0xffffcbf8) at /usr/src/debug/dwarves-1.25/dwarf_loader.c:3250
> > #6 0xf7db4258 in start_thread (arg=<optimized out>) at pthread_create.c:444
> > #7 0xf7e3a878 in clone3 () from /lib/libc.so.6
> > (gdb) p encoder
> > $1 = (struct btf_encoder *) 0x0
> > (gdb) f 1
> > #1 0x5655c25d in pahole_stealer (cu=0xd9a01f80, conf_load=0x565640c0 <conf_load>, thr_data=0x56567c18) at /usr/src/debug/dwarves-1.25/pahole.c:3100
> > 3100 thread->btf = btf_encoder__btf(thread->encoder);
> > (gdb) list -2
> > 3093 thread->encoder =
> > 3094 btf_encoder__new(cu, detached_btf_filename,
> > 3095 NULL,
> > 3096 skip_encoding_btf_vars,
> > 3097 btf_encode_force,
> > 3098 btf_gen_floats,
> > 3099 global_verbose);
> > 3100 thread->btf = btf_encoder__btf(thread->encoder);
> > 3101 }
> > 3102 encoder = thread->encoder;
> >
> > I think that return value of btf_encoder__new is not checked. But did
> > not investigate further why is this happening. It would be great to have
> > this fixed.
>
> Can you try with this minimal patch? Maybe we can with some more work
> auto-limit the number of threads or make the threads without a
> btf_encoder be processed at the end, reusing the main btf_encoder, but
> this first patch would at least help diagnosing the problem more
> quickly.
With this patch applied and run on 20 core:
builder@i586:kernel-source-6.3$ pahole -J --btf_gen_floats -j111 --lang_exclude=rust .tmp_vmlinux.btf
Not enough memory to instantiate new BTF encoder.
HINT: Maybe reduce the -j/--jobs command line value?.
... 40 times this message ....
Not enough memory to instantiate new BTF encoder.
HINT: Maybe reduce the -j/--jobs command line value?.
builder@i586:kernel-source-6.3$ echo $?
0
Thanks,
>
> - Arnaldo
>
> diff --git a/pahole.c b/pahole.c
> index e843999fde2a8a37..887b3403dcff18c0 100644
> --- a/pahole.c
> +++ b/pahole.c
> @@ -3097,6 +3097,15 @@ static enum load_steal_kind pahole_stealer(struct cu *cu,
> btf_encode_force,
> btf_gen_floats,
> global_verbose);
> + if (thread->encoder == NULL) {
> + fprintf(stderr, "Not enough memory to instantiate new BTF encoder.\n");
> +
> + if (conf_load->nr_jobs > 1)
> + fprintf(stderr, "HINT: Maybe reduce the -j/--jobs command line value?.\n");
> +
> + ret = LSK__STOP_LOADING;
> + goto out_btf;
> + }
> thread->btf = btf_encoder__btf(thread->encoder);
> }
> encoder = thread->encoder;
