[PATCH v2][makedumpfile 00/14] btf/kallsyms based eppic extension for mm page filtering
Tao Liu
ltao at redhat.com
Fri Nov 28 00:10:01 PST 2025
Hi Kazu,
On Fri, Nov 28, 2025 at 9:04 PM HAGIO KAZUHITO(萩尾 一仁)
<k-hagio-ab at nec.com> wrote:
>
> On 2025/11/24 13:46, Tao Liu wrote:
> > Kindly ping... Any comments on this?
>
> Hi Tao,
>
> I'm sorry for the delay. I think I can look into this next month.
No worries, please take your time :)
Thanks,
Tao Liu
>
> Thanks,
> Kazu
>
> >
> > Thanks,
> > Tao Liu
> >
> > On Tue, Oct 21, 2025 at 11:24 AM Tao Liu <ltao at redhat.com> wrote:
> >>
> >> A) This patchset will introduce the following features to makedumpfile:
> >>
> >> 1) Enable eppic script for memory pages filtering.
> >> 2) Enable btf and kallsyms for symbol type and address resolving.
> >>
> >> B) The purpose of the features are:
> >>
> >> 1) Currently makedumpfile filters mm pages based on page flags, because flags
> >> can help to determine one page's usage. But this page-flag-checking method
> >> lacks of flexibility in certain cases, e.g. if we want to filter those mm
> >> pages occupied by GPU during vmcore dumping due to:
> >>
> >> a) GPU may be taking a large memory and contains sensitive data;
> >> b) GPU mm pages have no relations to kernel crash and useless for vmcore
> >> analysis.
> >>
> >> But there is no GPU mm page specific flags, and apparently we don't need
> >> to create one just for kdump use. A programmable filtering tool is more
> >> suitable for such cases. In addition, different GPU vendors may use
> >> different ways for mm pages allocating, programmable filtering is better
> >> than hard coding these GPU specific logics into makedumpfile in this case.
> >>
> >> 2) Currently makedumpfile already contains a programmable filtering tool, aka
> >> eppic script, which allows user to write customized code for data erasing.
> >> However it has the following drawbacks:
> >>
> >> a) cannot do mm page filtering.
> >> b) need to access to debuginfo of both kernel and modules, which is not
> >> applicable in the 2nd kernel.
> >> c) Poor performance, making vmcore dumping time unacceptable (See
> >> the following performance testing).
> >>
> >> makedumpfile need to resolve the dwarf data from debuginfo, to get symbols
> >> types and addresses. In recent kernel there are dwarf alternatives such
> >> as btf/kallsyms which can be used for this purpose. And btf/kallsyms info
> >> are already packed within vmcore, so we can use it directly.
> >>
> >> With these, this patchset introduces an upgraded eppic, which is based on
> >> btf/kallsyms symbol resolving, and is programmable for mm page filtering.
> >> The following info shows its usage and performance, please note the tests
> >> are performed in 1st kernel:
> >>
> >> $ time ./makedumpfile -d 31 -l /var/crash/127.0.0.1-2025-06-10-18\:03\:12/vmcore
> >> /tmp/dwarf.out -x /lib/debug/lib/modules/6.11.8-300.fc41.x86_64/vmlinux
> >> --eppic eppic_scripts/filter_amdgpu_mm_pages.c
> >> real 14m6.894s
> >> user 4m16.900s
> >> sys 9m44.695s
> >>
> >> $ time ./makedumpfile -d 31 -l /var/crash/127.0.0.1-2025-06-10-18\:03\:12/vmcore
> >> /tmp/btf.out --eppic eppic_scripts/filter_amdgpu_mm_pages.c
> >> real 0m10.672s
> >> user 0m9.270s
> >> sys 0m1.130s
> >>
> >> -rw------- 1 root root 367475074 Jun 10 18:06 btf.out
> >> -rw------- 1 root root 367475074 Jun 10 21:05 dwarf.out
> >> -rw-rw-rw- 1 root root 387181418 Jun 10 18:03 /var/crash/127.0.0.1-2025-06-10-18:03:12/vmcore
> >>
> >> C) Discussion:
> >>
> >> 1) GPU types: Currently only tested with amdgpu's mm page filtering, others
> >> are not tested.
> >> 2) OS: The code can work on rhel-10+/rhel9.5+ on x86_64/arm64/s390/ppc64.
> >> Others are not tested.
> >>
> >> D) Testing:
> >>
> >> 1) If you don't want to create your vmcore, you can find a vmcore which I
> >> created with amdgpu mm pages unfiltered [1], the amdgpu mm pages are
> >> allocated by program [2]. You can use the vmcore in 1st kernel to filter
> >> the amdgpu mm pages by the previous performance testing cmdline. To
> >> verify the pages are filtered in crash:
> >>
> >> Unfiltered:
> >> crash> search -c "!QAZXSW@#EDC"
> >> ffff96b7fa800000: !QAZXSW@#EDCXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
> >> ffff96b87c800000: !QAZXSW@#EDCXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
> >> crash> rd ffff96b7fa800000
> >> ffff96b7fa800000: 405753585a415121 !QAZXSW@
> >> crash> rd ffff96b87c800000
> >> ffff96b87c800000: 405753585a415121 !QAZXSW@
> >>
> >> Filtered:
> >> crash> search -c "!QAZXSW@#EDC"
> >> crash> rd ffff96b7fa800000
> >> rd: page excluded: kernel virtual address: ffff96b7fa800000 type: "64-bit KVADDR"
> >> crash> rd ffff96b87c800000
> >> rd: page excluded: kernel virtual address: ffff96b87c800000 type: "64-bit KVADDR"
> >>
> >> 2) You can use eppic_scripts/print_all_vma.c against an ordinary vmcore to
> >> test only btf/kallsyms functions by output all VMAs if no amdgpu
> >> vmcores/machine avaliable.
> >>
> >> [1]: https://people.redhat.com/~ltao/core/
> >> [2]: https://gist.github.com/liutgnu/a8cbce1c666452f1530e1410d1f352df
> >>
> >> v2 -> v1:
> >>
> >> 1) Moved maple tree related code(for VMA iteration) into eppic script, so we
> >> don't need to port maple tree code to makedumpfile.
> >>
> >> 2) Reorganized the patchset as follows:
> >>
> >> --- <common modification> ---
> >> 1.Add page filtering function
> >> 2.Supporting main() as the entry of eppic script
> >>
> >> --- <dwarf related modification> ---
> >> 3.dwarf_info: Support kernel address randomization
> >> 4.dwarf_info: Fix a infinite recursion bug for rust
> >> 5.eppic dwarf: support anonymous structs member resolving
> >> 6.Enable page filtering for dwarf eppic
> >>
> >> --- <btf & kallsyms related modification> ---
> >> 7.Implement kernel kallsyms resolving
> >> 8.Implement kernel btf resolving
> >> 9.Implement kernel module's kallsyms resolving
> >> 10.Implement kernel module's btf resolving
> >> 11.Export necessary btf/kallsyms functions to eppic extension
> >> 12.Enable page filtering for btf/kallsyms eppic
> >> 13.Docs: Update eppic related entries
> >>
> >> --- <only for test purpose, don't merge> ---
> >> 14.Introducing 2 eppic scripts to test the dwarf/btf eppic extension
> >>
> >> The modification on dwarf is primary for comparision purpose, that
> >> for the same eppic program, mm page filtering should get exact same
> >> outputs for dwarf & kallsyms/btf based approaches. If outputs unmatch,
> >> this indicates bugs. In fact, we will never take dwarf mm pages filtering
> >> in real use, due to its poor performance as well as inaccessibility
> >> of debuginfo during kdump in 2nd kernel. So patch 3/4/5 won't affect
> >> the function of btf/kallsyms eppic mm page filtering, but there are
> >> functions shared in patch 6, so it is a must-have one. Patch 14 is
> >> only for test purpose, to demonstrate how to write eppic script for
> >> mm page filtering, so it isn't a must-have patch.
> >>
> >> Please note, in patch 14, I have deliberately converted all array
> >> operation into pointer operation, e.g. modified "node->slot[i]" into
> >> "*((unsigned long *)&(node->slot) + i)". This is because there are
> >> bugs for array operation support in extension_eppic.c. I didn't have
> >> effort to test and fix them all because as I mentioned previously,
> >> mm page filtering in dwarf side is only for comparision and will
> >> never be used in real use. There is no such issue for kallsyms/btf
> >> eppic side.
> >>
> >> 3) Since we ported maple tree code to eppic script, several bugs found
> >> both for eppic library & eppic btf support. Please use master branch
> >> of eppic library to co-compile with this patchset.
> >>
> >> Tao Liu (14):
> >> Add page filtering function
> >> Supporting main() as the entry of eppic script
> >> dwarf_info: Support kernel address randomization
> >> dwarf_info: Fix a infinite recursion bug for rust
> >> eppic dwarf: support anonymous structs member resolving
> >> Enable page filtering for dwarf eppic
> >> Implement kernel kallsyms resolving
> >> Implement kernel btf resolving
> >> Implement kernel module's kallsyms resolving
> >> Implement kernel module's btf resolving
> >> Export necessary btf/kallsyms functions to eppic extension
> >> Enable page filtering for btf/kallsyms eppic
> >> Docs: Update eppic related entries
> >> Introducing 2 eppic scripts to test the dwarf/btf eppic extension
> >>
> >> Makefile | 6 +-
> >> btf.c | 919 +++++++++++++++++++++++++
> >> btf.h | 177 +++++
> >> dwarf_info.c | 7 +
> >> eppic_scripts/filter_amdgpu_mm_pages.c | 255 +++++++
> >> eppic_scripts/print_all_vma.c | 239 +++++++
> >> erase_info.c | 120 +++-
> >> erase_info.h | 19 +
> >> extension_btf.c | 258 +++++++
> >> extension_eppic.c | 106 ++-
> >> extension_eppic.h | 6 +-
> >> kallsyms.c | 392 +++++++++++
> >> kallsyms.h | 41 ++
> >> makedumpfile.8.in | 24 +-
> >> makedumpfile.c | 21 +-
> >> makedumpfile.h | 11 +
> >> print_info.c | 11 +-
> >> 17 files changed, 2550 insertions(+), 62 deletions(-)
> >> create mode 100644 btf.c
> >> create mode 100644 btf.h
> >> create mode 100644 eppic_scripts/filter_amdgpu_mm_pages.c
> >> create mode 100644 eppic_scripts/print_all_vma.c
> >> create mode 100644 extension_btf.c
> >> create mode 100644 kallsyms.c
> >> create mode 100644 kallsyms.h
> >>
> >> --
> >> 2.47.0
> >>
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