Merge tag 'bpf-next-6.13' of git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next

Pull bpf updates from Alexei Starovoitov:

 - Add BPF uprobe session support (Jiri Olsa)

 - Optimize uprobe performance (Andrii Nakryiko)

 - Add bpf_fastcall support to helpers and kfuncs (Eduard Zingerman)

 - Avoid calling free_htab_elem() under hash map bucket lock (Hou Tao)

 - Prevent tailcall infinite loop caused by freplace (Leon Hwang)

 - Mark raw_tracepoint arguments as nullable (Kumar Kartikeya Dwivedi)

 - Introduce uptr support in the task local storage map (Martin KaFai
   Lau)

 - Stringify errno log messages in libbpf (Mykyta Yatsenko)

 - Add kmem_cache BPF iterator for perf's lock profiling (Namhyung Kim)

 - Support BPF objects of either endianness in libbpf (Tony Ambardar)

 - Add ksym to struct_ops trampoline to fix stack trace (Xu Kuohai)

 - Introduce private stack for eligible BPF programs (Yonghong Song)

 - Migrate samples/bpf tests to selftests/bpf test_progs (Daniel T. Lee)

 - Migrate test_sock to selftests/bpf test_progs (Jordan Rife)

* tag 'bpf-next-6.13' of git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next: (152 commits)
  libbpf: Change hash_combine parameters from long to unsigned long
  selftests/bpf: Fix build error with llvm 19
  libbpf: Fix memory leak in bpf_program__attach_uprobe_multi
  bpf: use common instruction history across all states
  bpf: Add necessary migrate_disable to range_tree.
  bpf: Do not alloc arena on unsupported arches
  selftests/bpf: Set test path for token/obj_priv_implicit_token_envvar
  selftests/bpf: Add a test for arena range tree algorithm
  bpf: Introduce range_tree data structure and use it in bpf arena
  samples/bpf: Remove unused variable in xdp2skb_meta_kern.c
  samples/bpf: Remove unused variables in tc_l2_redirect_kern.c
  bpftool: Cast variable `var` to long long
  bpf, x86: Propagate tailcall info only for subprogs
  bpf: Add kernel symbol for struct_ops trampoline
  bpf: Use function pointers count as struct_ops links count
  bpf: Remove unused member rcu from bpf_struct_ops_map
  selftests/bpf: Add struct_ops prog private stack tests
  bpf: Support private stack for struct_ops progs
  selftests/bpf: Add tracing prog private stack tests
  bpf, x86: Support private stack in jit
  ...

2 files changed, 78 insertions, 3 deletions

diff --git a/Documentation/bpf/btf.rst b/Documentation/bpf/btf.rst
index 93060283b6fd..2478cef758f8 100644
--- a/Documentation/bpf/btf.rst
+++ b/Documentation/bpf/btf.rst
@@ -835,7 +835,7 @@ section named by ``btf_ext_info_sec->sec_name_off``.
 See :ref:`Documentation/bpf/llvm_reloc.rst <btf-co-re-relocations>`
 for more information on CO-RE relocations.
 
-4.2 .BTF_ids section
+4.3 .BTF_ids section
 --------------------
 
 The .BTF_ids section encodes BTF ID values that are used within the kernel.
@@ -896,6 +896,81 @@ and is used as a filter when resolving the BTF ID value.
 All the BTF ID lists and sets are compiled in the .BTF_ids section and
 resolved during the linking phase of kernel build by ``resolve_btfids`` tool.
 
+4.4 .BTF.base section
+---------------------
+Split BTF - where the .BTF section only contains types not in the associated
+base .BTF section - is an extremely efficient way to encode type information
+for kernel modules, since they generally consist of a few module-specific
+types along with a large set of shared kernel types. The former are encoded
+in split BTF, while the latter are encoded in base BTF, resulting in more
+compact representations. A type in split BTF that refers to a type in
+base BTF refers to it using its base BTF ID, and split BTF IDs start
+at last_base_BTF_ID + 1.
+
+The downside of this approach however is that this makes the split BTF
+somewhat brittle - when the base BTF changes, base BTF ID references are
+no longer valid and the split BTF itself becomes useless. The role of the
+.BTF.base section is to make split BTF more resilient for cases where
+the base BTF may change, as is the case for kernel modules not built every
+time the kernel is for example. .BTF.base contains named base types; INTs,
+FLOATs, STRUCTs, UNIONs, ENUM[64]s and FWDs. INTs and FLOATs are fully
+described in .BTF.base sections, while composite types like structs
+and unions are not fully defined - the .BTF.base type simply serves as
+a description of the type the split BTF referred to, so structs/unions
+have 0 members in the .BTF.base section. ENUM[64]s are similarly recorded
+with 0 members. Any other types are added to the split BTF. This
+distillation process then leaves us with a .BTF.base section with
+such minimal descriptions of base types and .BTF split section which refers
+to those base types. Later, we can relocate the split BTF using both the
+information stored in the .BTF.base section and the new .BTF base; the type
+information in the .BTF.base section allows us to update the split BTF
+references to point at the corresponding new base BTF IDs.
+
+BTF relocation happens on kernel module load when a kernel module has a
+.BTF.base section, and libbpf also provides a btf__relocate() API to
+accomplish this.
+
+As an example consider the following base BTF::
+
+      [1] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED
+      [2] STRUCT 'foo' size=8 vlen=2
+              'f1' type_id=1 bits_offset=0
+              'f2' type_id=1 bits_offset=32
+
+...and associated split BTF::
+
+      [3] PTR '(anon)' type_id=2
+
+i.e. split BTF describes a pointer to struct foo { int f1; int f2 };
+
+.BTF.base will consist of::
+
+      [1] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED
+      [2] STRUCT 'foo' size=8 vlen=0
+
+If we relocate the split BTF later using the following new base BTF::
+
+      [1] INT 'long unsigned int' size=8 bits_offset=0 nr_bits=64 encoding=(none)
+      [2] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED
+      [3] STRUCT 'foo' size=8 vlen=2
+              'f1' type_id=2 bits_offset=0
+              'f2' type_id=2 bits_offset=32
+
+...we can use our .BTF.base description to know that the split BTF reference
+is to struct foo, and relocation results in new split BTF::
+
+      [4] PTR '(anon)' type_id=3
+
+Note that we had to update BTF ID and start BTF ID for the split BTF.
+
+So we see how .BTF.base plays the role of facilitating later relocation,
+leading to more resilient split BTF.
+
+.BTF.base sections will be generated automatically for out-of-tree kernel module
+builds - i.e. where KBUILD_EXTMOD is set (as it would be for "make M=path/2/mod"
+cases). .BTF.base generation requires pahole support for the "distilled_base"
+BTF feature; this is available in pahole v1.28 and later.
+
 5. Using BTF
 ============
 
diff --git a/Documentation/bpf/verifier.rst b/Documentation/bpf/verifier.rst
index d23761540002..95e6f80a407e 100644
--- a/Documentation/bpf/verifier.rst
+++ b/Documentation/bpf/verifier.rst
@@ -507,7 +507,7 @@ Notes:
   from the parent state to the current state.
 
 * Details about REG_LIVE_READ32 are omitted.
-  
+
 * Function ``propagate_liveness()`` (see section :ref:`read_marks_for_cache_hits`)
   might override the first parent link. Please refer to the comments in the
   ``propagate_liveness()`` and ``mark_reg_read()`` source code for further
@@ -571,7 +571,7 @@ works::
   are considered equivalent.
 
 .. _read_marks_for_cache_hits:
-  
+
 Read marks propagation for cache hits
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~