When the ELF Note does not contain CPU registers,
attempting to retrieve online CPU registers will cause a crash.

After:
CPU 6:
help: registers not collected for cpu 6
...

Signed-off-by: Guanyou.Chen <chenguanyou@xiaomi.com>
---
 netdump.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/netdump.c b/netdump.c
index 8ea5159..435793b 100644
--- a/netdump.c
+++ b/netdump.c
@@ -2780,6 +2780,10 @@ display_regs_from_elf_notes(int cpu, FILE *ofp)
                nd->nt_prstatus_percpu[cpu];
        else
                    note64 = (Elf64_Nhdr *)nd->nt_prstatus;
+       if (!note64) {
+           error(INFO, "registers not collected for cpu %d\n", cpu);
+           return;
+       }
        len = sizeof(Elf64_Nhdr);
        len = roundup(len + note64->n_namesz, 4);
        len = roundup(len + note64->n_descsz, 4);
@@ -2820,6 +2824,10 @@ display_regs_from_elf_notes(int cpu, FILE *ofp)
                nd->nt_prstatus_percpu[cpu];
        else
                    note32 = (Elf32_Nhdr *)nd->nt_prstatus;
+       if (!note32) {
+           error(INFO, "registers not collected for cpu %d\n", cpu);
+           return;
+       }
        len = sizeof(Elf32_Nhdr);
        len = roundup(len + note32->n_namesz, 4);
        len = roundup(len + note32->n_descsz, 4);

@@ -2857,6 +2865,10 @@ display_regs_from_elf_notes(int cpu, FILE *ofp)
        else
            note64 = (Elf64_Nhdr *)nd->nt_prstatus;

+       if (!note64) {
+           error(INFO, "registers not collected for cpu %d\n", cpu);
+           return;
+       }
        prs = (struct ppc64_elf_prstatus *)
            ((char *)note64 + sizeof(Elf64_Nhdr) + note64->n_namesz);
        prs = (struct ppc64_elf_prstatus *)roundup((ulong)prs, 4);
@@ -2903,6 +2915,10 @@ display_regs_from_elf_notes(int cpu, FILE *ofp)
                nd->nt_prstatus_percpu[cpu];
        else
                    note64 = (Elf64_Nhdr *)nd->nt_prstatus;
+       if (!note64) {
+           error(INFO, "registers not collected for cpu %d\n", cpu);
+           return;
+       }
        len = sizeof(Elf64_Nhdr);
        len = roundup(len + note64->n_namesz, 4);
        len = roundup(len + note64->n_descsz, 4);
--
2.34.1

Guanyou.

Thanks