Em Wed, Jul 05, 2023 at 05:00:40AM +0300, Vitaly Chikunov escreveu:
> Hi,
>
> 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 :-)
> 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.
- 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;
