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| 1 | +//! Tempo precompile coverage feedback for coverage-guided fuzzing. |
| 2 | +//! |
| 3 | +//! Provides SanitizerCoverage callbacks and a thread-local coverage map pointer |
| 4 | +//! that can be set by the fuzzing executor to collect edge coverage from Tempo precompile code. |
| 5 | +
|
| 6 | +use std::cell::Cell; |
| 7 | +use std::sync::atomic::{AtomicU32, Ordering}; |
| 8 | + |
| 9 | +pub const COVERAGE_MAP_SIZE: usize = 65536; |
| 10 | + |
| 11 | +thread_local! { |
| 12 | + static COVERAGE_MAP_PTR: Cell<*mut u8> = const { Cell::new(std::ptr::null_mut()) }; |
| 13 | + static COVERAGE_MAP_LEN: Cell<usize> = const { Cell::new(0) }; |
| 14 | +} |
| 15 | + |
| 16 | +pub fn set_coverage_map(ptr: *mut u8, len: usize) { |
| 17 | + COVERAGE_MAP_PTR.with(|c| c.set(ptr)); |
| 18 | + COVERAGE_MAP_LEN.with(|c| c.set(len)); |
| 19 | +} |
| 20 | + |
| 21 | +pub fn clear_coverage_map() { |
| 22 | + COVERAGE_MAP_PTR.with(|c| c.set(std::ptr::null_mut())); |
| 23 | + COVERAGE_MAP_LEN.with(|c| c.set(0)); |
| 24 | +} |
| 25 | + |
| 26 | +pub fn is_active() -> bool { |
| 27 | + COVERAGE_MAP_PTR.with(|c| !c.get().is_null()) |
| 28 | +} |
| 29 | + |
| 30 | +pub struct CoverageMapGuard; |
| 31 | + |
| 32 | +impl CoverageMapGuard { |
| 33 | + pub fn new(ptr: *mut u8, len: usize) -> Self { |
| 34 | + set_coverage_map(ptr, len); |
| 35 | + Self |
| 36 | + } |
| 37 | +} |
| 38 | + |
| 39 | +impl Drop for CoverageMapGuard { |
| 40 | + fn drop(&mut self) { |
| 41 | + clear_coverage_map(); |
| 42 | + } |
| 43 | +} |
| 44 | + |
| 45 | +#[inline(always)] |
| 46 | +pub fn record_hit(guard_id: u32) { |
| 47 | + COVERAGE_MAP_PTR.with(|ptr_cell| { |
| 48 | + let ptr = ptr_cell.get(); |
| 49 | + if ptr.is_null() { |
| 50 | + return; |
| 51 | + } |
| 52 | + COVERAGE_MAP_LEN.with(|len_cell| { |
| 53 | + let len = len_cell.get(); |
| 54 | + let idx = guard_id as usize % len; |
| 55 | + unsafe { |
| 56 | + let slot = ptr.add(idx); |
| 57 | + *slot = (*slot).wrapping_add(1); |
| 58 | + } |
| 59 | + }); |
| 60 | + }); |
| 61 | +} |
| 62 | + |
| 63 | +static GUARD_COUNTER: AtomicU32 = AtomicU32::new(1); |
| 64 | + |
| 65 | +/// # Safety |
| 66 | +/// |
| 67 | +/// Called by the LLVM SanitizerCoverage runtime at startup. `[start, stop)` must be a valid |
| 68 | +/// range of mutable `u32` guard slots allocated by the compiler for the current DSO. |
| 69 | +#[unsafe(no_mangle)] |
| 70 | +pub unsafe extern "C" fn __sanitizer_cov_trace_pc_guard_init(mut start: *mut u32, stop: *mut u32) { |
| 71 | + while start < stop { |
| 72 | + let id = GUARD_COUNTER.fetch_add(1, Ordering::Relaxed); |
| 73 | + unsafe { |
| 74 | + *start = id; |
| 75 | + start = start.add(1); |
| 76 | + } |
| 77 | + } |
| 78 | +} |
| 79 | + |
| 80 | +/// # Safety |
| 81 | +/// |
| 82 | +/// Called by the LLVM SanitizerCoverage runtime at every instrumented CFG edge. |
| 83 | +/// `guard` must point to a valid `u32` guard slot initialized by `__sanitizer_cov_trace_pc_guard_init`. |
| 84 | +#[unsafe(no_mangle)] |
| 85 | +pub unsafe extern "C" fn __sanitizer_cov_trace_pc_guard(guard: *mut u32) { |
| 86 | + let id = unsafe { *guard }; |
| 87 | + if id == 0 { |
| 88 | + return; |
| 89 | + } |
| 90 | + record_hit(id); |
| 91 | +} |
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