From 5febf432df1cfa5b25d99b54c32103fafbdd0eb9 Mon Sep 17 00:00:00 2001 From: Miguel Ojeda Date: Sun, 16 Aug 2026 15:32:33 +0200 Subject: kbuild: rust: keep Rust objects out of Clang LTO with inline helpers Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit `objtool` errors such as: vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a: can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd The reason is that in such builds, the Clang invocation that compiles the combined Rust plus helpers bitcode emits LLVM bitcode (again) -- the final code generation happens in the linker's LTO step, which the `-mllvm` trap options passed to Clang do not reach. This, in turn, means that unreachable traps are missing, and the impossible paths do not merely fallthrough to the next symbol, but past the end of their own section, since LTO builds place each function in its own section. Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always emits machine code directly, with the traps in place. Assisted-by: LLM Cc: Gary Guo Cc: Boqun Feng Cc: Alice Ryhl Cc: Matthew Maurer Cc: Josh Poimboeuf Cc: Peter Zijlstra Cc: stable@vger.kernel.org Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust") Acked-by: Gary Guo Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org Signed-off-by: Miguel Ojeda --- samples/bpf/tracex3.bpf.c | 100 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 100 insertions(+) create mode 100644 samples/bpf/tracex3.bpf.c (limited to 'samples/bpf/tracex3.bpf.c') diff --git a/samples/bpf/tracex3.bpf.c b/samples/bpf/tracex3.bpf.c new file mode 100644 index 000000000..41f37966f --- /dev/null +++ b/samples/bpf/tracex3.bpf.c @@ -0,0 +1,100 @@ +/* Copyright (c) 2013-2015 PLUMgrid, http://plumgrid.com + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of version 2 of the GNU General Public + * License as published by the Free Software Foundation. + */ +#include "vmlinux.h" +#include +#include +#include + +struct start_key { + dev_t dev; + u32 _pad; + sector_t sector; +}; + +struct { + __uint(type, BPF_MAP_TYPE_HASH); + __type(key, long); + __type(value, u64); + __uint(max_entries, 4096); +} my_map SEC(".maps"); + +/* from /sys/kernel/tracing/events/block/block_io_start/format */ +SEC("tracepoint/block/block_io_start") +int bpf_prog1(struct trace_event_raw_block_rq *ctx) +{ + u64 val = bpf_ktime_get_ns(); + struct start_key key = { + .dev = ctx->dev, + .sector = ctx->sector + }; + + bpf_map_update_elem(&my_map, &key, &val, BPF_ANY); + return 0; +} + +static unsigned int log2l(unsigned long long n) +{ +#define S(k) if (n >= (1ull << k)) { i += k; n >>= k; } + int i = -(n == 0); + S(32); S(16); S(8); S(4); S(2); S(1); + return i; +#undef S +} + +#define SLOTS 100 + +struct { + __uint(type, BPF_MAP_TYPE_PERCPU_ARRAY); + __uint(key_size, sizeof(u32)); + __uint(value_size, sizeof(u64)); + __uint(max_entries, SLOTS); +} lat_map SEC(".maps"); + +/* from /sys/kernel/tracing/events/block/block_io_done/format */ +SEC("tracepoint/block/block_io_done") +int bpf_prog2(struct trace_event_raw_block_rq *ctx) +{ + struct start_key key = { + .dev = ctx->dev, + .sector = ctx->sector + }; + + u64 *value, l, base; + u32 index; + + value = bpf_map_lookup_elem(&my_map, &key); + if (!value) + return 0; + + u64 cur_time = bpf_ktime_get_ns(); + u64 delta = cur_time - *value; + + bpf_map_delete_elem(&my_map, &key); + + /* the lines below are computing index = log10(delta)*10 + * using integer arithmetic + * index = 29 ~ 1 usec + * index = 59 ~ 1 msec + * index = 89 ~ 1 sec + * index = 99 ~ 10sec or more + * log10(x)*10 = log2(x)*10/log2(10) = log2(x)*3 + */ + l = log2l(delta); + base = 1ll << l; + index = (l * 64 + (delta - base) * 64 / base) * 3 / 64; + + if (index >= SLOTS) + index = SLOTS - 1; + + value = bpf_map_lookup_elem(&lat_map, &index); + if (value) + *value += 1; + + return 0; +} +char _license[] SEC("license") = "GPL"; +u32 _version SEC("version") = LINUX_VERSION_CODE; -- cgit v1.3.1