[Crash-utility] Re: [PATCH] symbols: redetermine the end of kernel range for in_ksymbol_range

Date: Wed, 26 Feb 2025 17:51:21 +1300 From: Tao Liu <ltao(a)redhat.com&gt; Subject: [Crash-utility] [PATCH] symbols: redetermine the end of kernel range for in_ksymbol_range To: devel(a)lists.crash-utility.osci.io Cc: k-hagio-ab(a)nec.com, Tao Liu <ltao(a)redhat.com&gt; Message-ID: <20250226045121.16717-1-ltao(a)redhat.com&gt; Content-Type: text/plain; charset="US-ASCII"; x-default=true For in_ksymbol_range(), it determine the kernel range by st->symtable[0].value as the start and st->symtable[st->symcnt-1].value as the end, this however, implies the last element is in the kernel range. In most cases it was correct, but it is no longer valid with the kernel commit [1]. The xen_elfnote_phys32_entry_value introduced by [1], is beyound the kernel range(doesn't belong to any kernel section), thus doesn't get relocated by relocate(). So in order to have a correct in_ksymbol_range(), we need to eliminate those symbols.

Without the patch: crash> sym schedule ffffffff973ffb30 (T) schedule /root/linux-6.14-rc3/kernel/sched/core.c: 6848 crash> sym 0xffffffff973ffb30 sym: invalid address: 0xffffffff973ffb30 With the patch: crash> sym schedule ffffffff973ffb30 (T) schedule /root/linux-6.14-rc3/kernel/sched/core.c: 6848 crash> sym 0xffffffff973ffb30 ffffffff973ffb30 (T) schedule /root/linux-6.14-rc3/kernel/sched/core.c: 6848 [1]: https://github.com/torvalds/linux/commit/223abe96ac0d227b22d48ab447dd9384... Signed-off-by: Tao Liu <ltao(a)redhat.com&gt; --- v2 -> v1: In fact the gnu_qsort() does sort the symbols with no problem, unlike the root cause described in v1. It's because xen_elfnote_phys32_entry_value doesn't belong to any kernel section, so the symval >= st->first_section_start && symval <= st->last_section_end check will not success in relocate(), so the symbol is not relocated. But I'm not sure if xen_elfnote_phys32_entry_value should be relocated or not, it looks to be an absoluate symbol to me, but the code comment is not very clear... v1 patch: https://www.mail-archive.com/devel@lists.crash-utility.osci.io/msg01373.html v1 discussion: https://www.mail-archive.com/devel@lists.crash-utility.osci.io/msg01378.html --- --- symbols.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/symbols.c b/symbols.c index 6385d02..edbafa4 100644 --- a/symbols.c +++ b/symbols.c @@ -5443,8 +5443,14 @@ old_module: int in_ksymbol_range(ulong value) { + int i; + for (i = st->symcnt-1; i >= 0; i--) { + if (!strstr(st->symtable[i].name, "xen_elfnote")) + break; + } + if ((value >= st->symtable[0].value) && - (value <= st->symtable[st->symcnt-1].value)) { + (value <= st->symtable[i].value)) { if ((st->flags & PERCPU_SYMS) && (value < st->first_ksymbol)) return FALSE; else -- 2.47.0