44df171a10
The llvm patch [1] enabled opaque pointer which caused selftest 'exhandler' failure. ... ; work = task->task_works; 7: (79) r1 = *(u64 *)(r6 +2120) ; R1_w=ptr_callback_head(off=0,imm=0) R6_w=ptr_task_struct(off=0,imm=0) ; func = work->func; 8: (79) r2 = *(u64 *)(r1 +8) ; R1_w=ptr_callback_head(off=0,imm=0) R2_w=scalar() ; if (!work && !func) 9: (4f) r1 |= r2 math between ptr_ pointer and register with unbounded min value is not allowed below is insn 10 and 11 10: (55) if r1 != 0 goto +5 11: (18) r1 = 0 ll ... In llvm, the code generation of 'r1 |= r2' happened in codegen selectiondag phase due to difference of opaque pointer vs. non-opaque pointer. Without [1], the related code looks like: r2 = *(u64 *)(r6 + 2120) r1 = *(u64 *)(r2 + 8) if r2 != 0 goto +6 <LBB0_4> if r1 != 0 goto +5 <LBB0_4> r1 = 0 ll ... I haven't found a good way in llvm to fix this issue. So let us workaround the problem first so bpf CI won't be blocked. [1] https://reviews.llvm.org/D123300 Signed-off-by: Yonghong Song <yhs@fb.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20220419050900.3136024-1-yhs@fb.com
55 lines
1.5 KiB
C
55 lines
1.5 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/* Copyright (c) 2021, Oracle and/or its affiliates. */
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#include "vmlinux.h"
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#include <bpf/bpf_helpers.h>
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#include <bpf/bpf_tracing.h>
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#include <bpf/bpf_core_read.h>
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#define barrier_var(var) asm volatile("" : "=r"(var) : "0"(var))
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char _license[] SEC("license") = "GPL";
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unsigned int exception_triggered;
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int test_pid;
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/* TRACE_EVENT(task_newtask,
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* TP_PROTO(struct task_struct *p, u64 clone_flags)
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*/
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SEC("tp_btf/task_newtask")
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int BPF_PROG(trace_task_newtask, struct task_struct *task, u64 clone_flags)
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{
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int pid = bpf_get_current_pid_tgid() >> 32;
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struct callback_head *work;
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void *func;
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if (test_pid != pid)
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return 0;
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/* To verify we hit an exception we dereference task->task_works->func.
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* If task work has been added,
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* - task->task_works is non-NULL; and
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* - task->task_works->func is non-NULL also (the callback function
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* must be specified for the task work.
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*
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* However, for a newly-created task, task->task_works is NULLed,
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* so we know the exception handler triggered if task_works is
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* NULL and func is NULL.
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*/
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work = task->task_works;
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func = work->func;
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/* Currently verifier will fail for `btf_ptr |= btf_ptr` * instruction.
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* To workaround the issue, use barrier_var() and rewrite as below to
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* prevent compiler from generating verifier-unfriendly code.
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*/
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barrier_var(work);
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if (work)
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return 0;
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barrier_var(func);
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if (func)
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return 0;
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exception_triggered++;
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return 0;
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}
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