kernel.git/tools/lib/bpf/bpf_core_read.h, branch master

bpf: Fix uninitialized values in BPF_{CORE,PROBE}_READ

2025-05-05T21:20:28Z

With the latest LLVM bpf selftests build will fail with the following error message: progs/profiler.inc.h:710:31: error: default initialization of an object of type 'typeof ((parent_task)->real_cred->uid.val)' (aka 'const unsigned int') leaves the object uninitialized and is incompatible with C++ [-Werror,-Wdefault-const-init-unsafe] 710 | proc_exec_data->parent_uid = BPF_CORE_READ(parent_task, real_cred, uid.val); | ^ tools/testing/selftests/bpf/tools/include/bpf/bpf_core_read.h:520:35: note: expanded from macro 'BPF_CORE_READ' 520 | ___type((src), a, ##__VA_ARGS__) __r; \ | ^ This happens because BPF_CORE_READ (and other macro) declare the variable __r using the ___type macro which can inherit const modifier from intermediate types. Fix this by using __typeof_unqual__, when supported. (And when it is not supported, the problem shouldn't appear, as older compilers haven't complained.) Fixes: 792001f4f7aa ("libbpf: Add user-space variants of BPF_CORE_READ() family of macros") Fixes: a4b09a9ef945 ("libbpf: Add non-CO-RE variants of BPF_CORE_READ() macro family") Signed-off-by: Anton Protopopov Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20250502193031.3522715-1-a.s.protopopov@gmail.com

bpf: Avoid uninitialized value in BPF_CORE_READ_BITFIELD

2024-05-08T22:00:55Z

[Changes from V1: - Use a default branch in the switch statement to initialize `val'.] GCC warns that `val' may be used uninitialized in the BPF_CRE_READ_BITFIELD macro, defined in bpf_core_read.h as: [...] unsigned long long val; \ [...] \ switch (__CORE_RELO(s, field, BYTE_SIZE)) { \ case 1: val = *(const unsigned char *)p; break; \ case 2: val = *(const unsigned short *)p; break; \ case 4: val = *(const unsigned int *)p; break; \ case 8: val = *(const unsigned long long *)p; break; \ } \ [...] val; \ } \ This patch adds a default entry in the switch statement that sets `val' to zero in order to avoid the warning, and random values to be used in case __builtin_preserve_field_info returns unexpected values for BPF_FIELD_BYTE_SIZE. Tested in bpf-next master. No regressions. Signed-off-by: Jose E. Marchesi Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20240508101313.16662-1-jose.marchesi@oracle.com

libbpf: Use local bpf_helpers.h include

2024-04-02T16:28:34Z

Commit 20d59ee55172fdf6 ("libbpf: add bpf_core_cast() macro") added a bpf_helpers include in bpf_core_read.h as a system include. Usually, the includes are local, though, like in bpf_tracing.h. This commit adjusts the include to be local as well. Signed-off-by: Tobias Böhm Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/q5d5bgc6vty2fmaazd5e73efd6f5bhiru2le6fxn43vkw45bls@fhlw2s5ootdb

libbpf: Add support to GCC in CORE macro definitions

2024-02-13T19:28:12Z

Due to internal differences between LLVM and GCC the current implementation for the CO-RE macros does not fit GCC parser, as it will optimize those expressions even before those would be accessible by the BPF backend. As examples, the following would be optimized out with the original definitions: - As enums are converted to their integer representation during parsing, the IR would not know how to distinguish an integer constant from an actual enum value. - Types need to be kept as temporary variables, as the existing type casts of the 0 address (as expanded for LLVM), are optimized away by the GCC C parser, never really reaching GCCs IR. Although, the macros appear to add extra complexity, the expanded code is removed from the compilation flow very early in the compilation process, not really affecting the quality of the generated assembly. Signed-off-by: Cupertino Miranda Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20240213173543.1397708-1-cupertino.miranda@oracle.com

libbpf: add bpf_core_cast() macro

2024-01-30T23:55:50Z

Add bpf_core_cast() macro that wraps bpf_rdonly_cast() kfunc. It's more ergonomic than kfunc, as it automatically extracts btf_id with bpf_core_type_id_kernel(), and works with type names. It also casts result to (T *) pointer. See the definition of the macro, it's self-explanatory. libbpf declares bpf_rdonly_cast() extern as __weak __ksym and should be safe to not conflict with other possible declarations in user code. But we do have a conflict with current BPF selftests that declare their externs with first argument as `void *obj`, while libbpf opts into more permissive `const void *obj`. This causes conflict, so we fix up BPF selftests uses in the same patch. Acked-by: Eduard Zingerman Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/r/20240130212023.183765-2-andrii@kernel.org Signed-off-by: Martin KaFai Lau

libbpf: Correct bpf_core_read.h comment wrt bpf_core_relo struct

2024-01-24T04:29:57Z

Past commit ([0]) removed the last vestiges of struct bpf_field_reloc, it's called struct bpf_core_relo now. [0] 28b93c64499a ("libbpf: Clean up and improve CO-RE reloc logging") Signed-off-by: Dima Tisnek Signed-off-by: Andrii Nakryiko Acked-by: Yonghong Song Link: https://lore.kernel.org/bpf/20240121060126.15650-1-dimaqq@gmail.com

libbpf: Add BPF_CORE_WRITE_BITFIELD() macro

2023-12-13T23:42:19Z

=== Motivation === Similar to reading from CO-RE bitfields, we need a CO-RE aware bitfield writing wrapper to make the verifier happy. Two alternatives to this approach are: 1. Use the upcoming `preserve_static_offset` [0] attribute to disable CO-RE on specific structs. 2. Use broader byte-sized writes to write to bitfields. (1) is a bit hard to use. It requires specific and not-very-obvious annotations to bpftool generated vmlinux.h. It's also not generally available in released LLVM versions yet. (2) makes the code quite hard to read and write. And especially if BPF_CORE_READ_BITFIELD() is already being used, it makes more sense to to have an inverse helper for writing. === Implementation details === Since the logic is a bit non-obvious, I thought it would be helpful to explain exactly what's going on. To start, it helps by explaining what LSHIFT_U64 (lshift) and RSHIFT_U64 (rshift) is designed to mean. Consider the core of the BPF_CORE_READ_BITFIELD() algorithm: val <<= __CORE_RELO(s, field, LSHIFT_U64); val = val >> __CORE_RELO(s, field, RSHIFT_U64); Basically what happens is we lshift to clear the non-relevant (blank) higher order bits. Then we rshift to bring the relevant bits (bitfield) down to LSB position (while also clearing blank lower order bits). To illustrate: Start: ........XXX...... Lshift: XXX......00000000 Rshift: 00000000000000XXX where `.` means blank bit, `0` means 0 bit, and `X` means bitfield bit. After the two operations, the bitfield is ready to be interpreted as a regular integer. Next, we want to build an alternative (but more helpful) mental model on lshift and rshift. That is, to consider: * rshift as the total number of blank bits in the u64 * lshift as number of blank bits left of the bitfield in the u64 Take a moment to consider why that is true by consulting the above diagram. With this insight, we can now define the following relationship: bitfield _ | | 0.....00XXX0...00 | | | | |______| | | lshift | | |____| (rshift - lshift) That is, we know the number of higher order blank bits is just lshift. And the number of lower order blank bits is (rshift - lshift). Finally, we can examine the core of the write side algorithm: mask = (~0ULL << rshift) >> lshift; // 1 val = (val & ~mask) | ((nval << rpad) & mask); // 2 1. Compute a mask where the set bits are the bitfield bits. The first left shift zeros out exactly the number of blank bits, leaving a bitfield sized set of 1s. The subsequent right shift inserts the correct amount of higher order blank bits. 2. On the left of the `|`, mask out the bitfield bits. This creates 0s where the new bitfield bits will go. On the right of the `|`, bring nval into the correct bit position and mask out any bits that fall outside of the bitfield. Finally, by bor'ing the two halves, we get the final set of bits to write back. [0]: https://reviews.llvm.org/D133361 Co-developed-by: Eduard Zingerman Signed-off-by: Eduard Zingerman Co-developed-by: Jonathan Lemon Signed-off-by: Jonathan Lemon Acked-by: Andrii Nakryiko Signed-off-by: Daniel Xu Link: https://lore.kernel.org/r/4d3dd215a4fd57d980733886f9c11a45e1a9adf3.1702325874.git.dxu@dxuuu.xyz Signed-off-by: Martin KaFai Lau

libbpf: Fix BPF_PROBE_READ{_STR}_INTO() on s390x

2023-01-28T20:45:14Z

BPF_PROBE_READ_INTO() and BPF_PROBE_READ_STR_INTO() should map to bpf_probe_read() and bpf_probe_read_str() respectively in order to work correctly on architectures with !ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE. Signed-off-by: Ilya Leoshkevich Link: https://lore.kernel.org/r/20230128000650.1516334-24-iii@linux.ibm.com Signed-off-by: Alexei Starovoitov

libbpf: add bpf_core_type_matches() helper macro

2022-07-06T04:15:19Z

This patch finalizes support for the proposed type match relation in libbpf by adding bpf_core_type_matches() macro which emits TYPE_MATCH relocation. Clang support for this relocation was added in [0]. [0] https://reviews.llvm.org/D126838 Signed-off-by: Daniel Müller ¬ Signed-off-by: Andrii Nakryiko ¬ Link: https://lore.kernel.org/bpf/20220628160127.607834-7-deso@posteo.net¬

bpf: Introduce TYPE_MATCH related constants/macros

2022-07-06T03:24:12Z

In order to provide type match support we require a new type of relocation which, in turn, requires toolchain support. Recent LLVM/Clang versions support a new value for the last argument to the __builtin_preserve_type_info builtin, for example. With this change we introduce the necessary constants into relevant header files, mirroring what the compiler may support. Signed-off-by: Daniel Müller Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20220628160127.607834-2-deso@posteo.net