From 4d8fc6d43831f81ed107da94fe68f10158f7aa6f Mon Sep 17 00:00:00 2001 From: Andrii Nakryiko Date: Wed, 6 Nov 2019 12:15:00 -0800 Subject: [PATCH] libbpf: Simplify BPF_CORE_READ_BITFIELD_PROBED usage Streamline BPF_CORE_READ_BITFIELD_PROBED interface to follow BPF_CORE_READ_BITFIELD (direct) and BPF_CORE_READ, in general, i.e., just return read result or 0, if underlying bpf_probe_read() failed. In practice, real applications rarely check bpf_probe_read() result, because it has to always work or otherwise it's a bug. So propagating internal bpf_probe_read() error from this macro hurts usability without providing real benefits in practice. This patch fixes the issue and simplifies usage, noticeable even in selftest itself. Signed-off-by: Andrii Nakryiko Signed-off-by: Alexei Starovoitov Acked-by: Yonghong Song Link: https://lore.kernel.org/bpf/20191106201500.2582438-1-andriin@fb.com --- src/bpf_core_read.h | 27 +++++++++++---------------- 1 file changed, 11 insertions(+), 16 deletions(-) diff --git a/src/bpf_core_read.h b/src/bpf_core_read.h index 11461b2..7009dc9 100644 --- a/src/bpf_core_read.h +++ b/src/bpf_core_read.h @@ -39,32 +39,27 @@ enum bpf_field_info_kind { #endif /* - * Extract bitfield, identified by src->field, and put its value into u64 - * *res. All this is done in relocatable manner, so bitfield changes such as + * Extract bitfield, identified by s->field, and return its value as u64. + * All this is done in relocatable manner, so bitfield changes such as * signedness, bit size, offset changes, this will be handled automatically. * This version of macro is using bpf_probe_read() to read underlying integer * storage. Macro functions as an expression and its return type is * bpf_probe_read()'s return value: 0, on success, <0 on error. */ -#define BPF_CORE_READ_BITFIELD_PROBED(src, field, res) ({ \ - unsigned long long val; \ +#define BPF_CORE_READ_BITFIELD_PROBED(s, field) ({ \ + unsigned long long val = 0; \ \ - *res = 0; \ - val = __CORE_BITFIELD_PROBE_READ(res, src, field); \ - if (!val) { \ - *res <<= __CORE_RELO(src, field, LSHIFT_U64); \ - val = __CORE_RELO(src, field, RSHIFT_U64); \ - if (__CORE_RELO(src, field, SIGNED)) \ - *res = ((long long)*res) >> val; \ - else \ - *res = ((unsigned long long)*res) >> val; \ - val = 0; \ - } \ + __CORE_BITFIELD_PROBE_READ(&val, s, field); \ + val <<= __CORE_RELO(s, field, LSHIFT_U64); \ + if (__CORE_RELO(s, field, SIGNED)) \ + val = ((long long)val) >> __CORE_RELO(s, field, RSHIFT_U64); \ + else \ + val = val >> __CORE_RELO(s, field, RSHIFT_U64); \ val; \ }) /* - * Extract bitfield, identified by src->field, and return its value as u64. + * Extract bitfield, identified by s->field, and return its value as u64. * This version of macro is using direct memory reads and should be used from * BPF program types that support such functionality (e.g., typed raw * tracepoints).