[PATCH v4 bpf-next 0/7] kbuild, bpf: Support inline info in BTF

[Alan Maguire <alan.maguire@oracle.com>]

If CONFIG_DEBUG_INFO_BTF_INLINE=y|m, add the "inline" BTF feature
and encode inline site info in BTF alongside standard BTF data.
resolve_btfids will then partition into non- and inline-related
info and split BTF will be used to store inline info in a
.BTF.inline section in vmlinux and modules.  For
CONFIG_DEBUG_INFO_BTF=m, vmlinux inline info will be stored
in btf_vmlinux_inline.ko and will be loaded on-demand if used
via /sys/kernel/btf/vmlinux.inline.  A .BTF.inline.link section
in vmlinux stores the module name, the SHA of the BTF and the
size so that even without loading the kernel can size the
sysfs representation correctly.  This approach is based on [1]
and the .BTF.inline.link section is modeled on .GNU_debuglink.

Because a module can be built with .BTF.base to allow for
BTF relocation, its inline info needs to be relocated also
so a bit more work needs to be done to handle this.

Patches 1, 2 add resolve_btfids support to partition BTF
into .BTF and .BTF.inline and to support populating
a BTF link section for BTF_INLINE=m.  Patch 3 handles
vmlinux.inline exposure in sysfs.  Patch 4 does prep
work for relocation needed in patch 5 prior to exposing
relocated BTF in sysfs, and patches 6 and 7 test BTF
sysfs representations and inline validity using
bpf_testmod respectively.

To generate inline info the latest pahole is needed [2].

Inline info for vmlinux can be quite large ~10Mb for
over 600,000 inline sites in the kernel, so

CONFIG_DEBUG_INFO_BTF_INLINE=m

is recommended; this brings the on-disk size down below
4Mb for a gzip-compressed btf_vmlinux_inline.ko.

Changes since v3 [3]:

- Retain original BTF in resolve_btfids and be careful about
  free order (bots, patch 1)
- Add more failure diagnostics to patching of BTF links
  (bots, patch 2)
- Guard vmallocs for zero-sized inline data (bots, patch 3)
- Fix potential NULL pointer BTF deref (bots, patch 5)
- Fix up leaks in sysfs test (bots, patch 6)
- Fix up tests to use kallsyms lookup directly, and improve
  validation of location info (bots, patch 7)

Changes since v2 [4]

 - Delivered the libbpf, bpftool parts are prerequisites
 - Switched to using Eduard's neater BTF partitioning approach which
   is fully in resolve_btfids instead of libbpf (Eduard, patch 1)
 - Supports mmap()ed vmlinux.inline (Alexei, patch 3, test patch 7)
 - Moved to using .BTF.inline.link to store inline BTF size
   which avoids need to switch to using kernfs; also allows us
   to SHA-verify BTF inline info

[1] https://lore.kernel.org/bpf/20260925224229.1850-1-wanjay@amazon.com/
[2] https://git.kernel.org/pub/scm/devel/pahole/pahole.git/
[3] https://lore.kernel.org/bpf/20261003194323.817885-1-alan.maguire@oracle.com/
[4] https://lore.kernel.org/bpf/20260901165757.801449-1-alan.maguire@oracle.com/

Alan Maguire (6):
  resolve_btfids: Populate BTF link section
  kbuild, btf: Expose vmlinux inline BTF through sysfs
  btf: Preserve string relocation maps for split BTF
  btf: Relocate and expose module inline BTF
  selftests/bpf: Test BTF sysfs inline representations
  selftests/bpf: Add a test verifying inline information

Eduard Zingerman (1):
  resolve_btfids: Build separate main and inline BTF objects

 .gitignore                                    |   1 +
 Makefile                                      |   1 +
 include/asm-generic/vmlinux.lds.h             |  31 ++
 include/linux/btf.h                           |  42 +-
 include/linux/module.h                        |   4 +
 kernel/bpf/Makefile                           |   1 +
 kernel/bpf/btf.c                              | 397 +++++++++++++---
 kernel/bpf/btf_vmlinux_inline.c               |  29 ++
 kernel/bpf/sysfs_btf.c                        | 149 +++++-
 kernel/module/main.c                          |   7 +
 lib/Kconfig.debug                             |  18 +
 scripts/Makefile.btf                          |   7 +
 scripts/gen-btf.sh                            |  31 +-
 scripts/link-vmlinux.sh                       |   8 +-
 scripts/package/kernel.spec                   |  10 +-
 tools/bpf/resolve_btfids/Build                |   1 +
 tools/bpf/resolve_btfids/btf_colors.c         | 145 ++++++
 tools/bpf/resolve_btfids/btf_colors.h         |  24 +
 tools/bpf/resolve_btfids/main.c               | 427 +++++++++++++++++-
 tools/lib/bpf/btf.c                           |   2 +-
 tools/lib/bpf/btf_relocate.c                  |   7 +-
 tools/lib/bpf/libbpf_internal.h               |   3 +-
 tools/testing/selftests/bpf/Makefile          |   4 +-
 .../selftests/bpf/prog_tests/btf_inline.c     | 113 +++++
 .../selftests/bpf/prog_tests/btf_sysfs.c      |  87 +++-
 .../selftests/bpf/test_kmods/bpf_testmod.c    |  11 +-
 tools/testing/selftests/bpf/trace_helpers.c   |  20 +
 tools/testing/selftests/bpf/trace_helpers.h   |   1 +
 tools/testing/selftests/hid/Makefile          |   2 +
 29 files changed, 1455 insertions(+), 128 deletions(-)
 create mode 100644 kernel/bpf/btf_vmlinux_inline.c
 create mode 100644 tools/bpf/resolve_btfids/btf_colors.c
 create mode 100644 tools/bpf/resolve_btfids/btf_colors.h
 create mode 100644 tools/testing/selftests/bpf/prog_tests/btf_inline.c

-- 
2.43.5