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| 1 | +/* |
| 2 | + * Copyright (c) Meta Platforms, Inc. and affiliates. |
| 3 | + * |
| 4 | + * This source code is licensed under the MIT license found in the |
| 5 | + * LICENSE file in the root directory of this source tree. |
| 6 | + */ |
| 7 | + |
| 8 | +use core::iter::Iterator; |
| 9 | +use std::sync::atomic::AtomicUsize; |
| 10 | +use std::sync::atomic::Ordering; |
| 11 | + |
| 12 | +use cpython::*; |
| 13 | +use evalframe_sys::EvalFrameMode; |
| 14 | + |
| 15 | +/// IP (PC) Offset in Sapling_PyEvalFrame after the `call ...`. |
| 16 | +static OFFSET_IP: AtomicUsize = AtomicUsize::new(0); |
| 17 | + |
| 18 | +/// SP Offset to get the Python frame object. |
| 19 | +static OFFSET_SP: AtomicUsize = AtomicUsize::new(0); |
| 20 | + |
| 21 | +/// Attempt to get the IP and SP offsets. |
| 22 | +pub fn get_offsets() -> Option<(usize, usize)> { |
| 23 | + // Unsupported Python version (Python C API)? |
| 24 | + if !evalframe_sys::resolve_frame_is_supported() { |
| 25 | + return None; |
| 26 | + } |
| 27 | + |
| 28 | + let gil = Python::acquire_gil(); |
| 29 | + let py = gil.python(); |
| 30 | + |
| 31 | + // Use probe mode to track last_frame for offset detection. |
| 32 | + unsafe { evalframe_sys::set_mode(EvalFrameMode::Probe) }; |
| 33 | + |
| 34 | + let m = PyModule::new(py, "probe").ok()?; |
| 35 | + m.add(py, "examine_backtrace", py_fn!(py, examine_backtrace())) |
| 36 | + .ok()?; |
| 37 | + |
| 38 | + let code = r#" |
| 39 | +def call_native_examine_backtrace(): |
| 40 | + examine_backtrace() |
| 41 | +call_native_examine_backtrace() |
| 42 | +"#; |
| 43 | + py.run(code, Some(&m.dict(py)), None).ok()?; |
| 44 | + |
| 45 | + let offset_ip = OFFSET_IP.load(Ordering::Acquire); |
| 46 | + let offset_sp = OFFSET_SP.load(Ordering::Acquire); |
| 47 | + if offset_ip > 0 { |
| 48 | + Some((offset_ip, offset_sp)) |
| 49 | + } else { |
| 50 | + None |
| 51 | + } |
| 52 | +} |
| 53 | + |
| 54 | +/// Attempt to set OFFSET_IP and OFFSET_SP. |
| 55 | +/// Intended to be called from a pure Python function. |
| 56 | +fn examine_backtrace(_py: Python) -> PyResult<Option<bool>> { |
| 57 | + backtrace::trace(|frame| { |
| 58 | + let ip = frame.ip() as usize; |
| 59 | + let start = evalframe_sys::sapling_py_eval_frame_addr(); |
| 60 | + // How many bytes the `Sapling_PyEvalFrame` function has at most? |
| 61 | + const CODE_SIZE_THRESHOLD: usize = 64; |
| 62 | + // How many bytes the `Sapling_PyEvalFrame` stack might be at most? |
| 63 | + const STACK_SIZE_THRESHOLD: usize = 48; |
| 64 | + if ip >= start && ip <= start + CODE_SIZE_THRESHOLD { |
| 65 | + let sp = frame.sp() as usize; |
| 66 | + let last_frame = evalframe_sys::get_last_frame(); |
| 67 | + |
| 68 | + // Try "known" SP offsets first. This reduces issues reading "bad" offsets. |
| 69 | + let sp_offset_hints: &[usize] = if cfg!(all( |
| 70 | + any(target_os = "linux", target_os = "macos"), |
| 71 | + any(target_arch = "x86_64", target_arch = "aarch64"), |
| 72 | + )) { |
| 73 | + // x86_64 |
| 74 | + // Sapling_PyEvalFrame(PyThreadState* tstate, PyFrameObject* f, int exc) |
| 75 | + // (lldb) disassemble -n Sapling_PyEvalFrame |
| 76 | + // <+0>: pushq %rbp |
| 77 | + // <+1>: movq %rsp, %rbp ; FP |
| 78 | + // <+4>: subq $0x20, %rsp ; SP = FP - 0x20 |
| 79 | + // <+8>: movq %rdi, -0x18(%rbp) |
| 80 | + // <+12>: movq %rsi, -0x10(%rbp) ; PyFrame f at FP - 0x10 or SP + 0x10 |
| 81 | + // <+16>: movl %edx, -0x4(%rbp) |
| 82 | + // <+19>: movq -0x18(%rbp), %rdi |
| 83 | + // <+23>: movq -0x10(%rbp), %rsi |
| 84 | + // <+27>: movl -0x4(%rbp), %edx |
| 85 | + // <+30>: callq 0x8d4eb0 ; symbol stub for: _PyEval_EvalFrameDefault |
| 86 | + // <+35>: addq $0x20, %rsp |
| 87 | + // <+39>: popq %rbp |
| 88 | + // <+40>: retq |
| 89 | + // |
| 90 | + // x86_64 with FCF protection: |
| 91 | + // <+0>: endbr64 |
| 92 | + // <+4>: pushq %rbp |
| 93 | + // <+5>: movq %rsp, %rbp |
| 94 | + // <+8>: subq $0x20, %rsp |
| 95 | + // <+12>: movq %rdi, -0x8(%rbp) |
| 96 | + // <+16>: movq %rsi, -0x10(%rbp) ; PyFrame f at SP + 0x10 |
| 97 | + // <+20>: movl %edx, -0x14(%rbp) |
| 98 | + // <+23>: movl -0x14(%rbp), %edx |
| 99 | + // <+26>: movq -0x10(%rbp), %rcx |
| 100 | + // <+30>: movq -0x8(%rbp), %rax |
| 101 | + // <+34>: movq %rcx, %rsi |
| 102 | + // <+37>: movq %rax, %rdi |
| 103 | + // <+40>: callq 0x4e5e0b0 ; symbol stub for: _PyEval_EvalFrameDefault |
| 104 | + // <+45>: leave |
| 105 | + // <+46>: retq |
| 106 | + // |
| 107 | + // aarch64 |
| 108 | + // <+0>: sub sp, sp, #0x30 |
| 109 | + // <+4>: stp x29, x30, [sp, #0x20] |
| 110 | + // <+8>: add x29, sp, #0x20 ; FP (x29) = SP + 0x20 |
| 111 | + // <+12>: stur x0, [x29, #-0x8] ; x0 is 1st arg (tstate) |
| 112 | + // <+16>: str x1, [sp, #0x10] ; x1 is 2nd arg (f), at SP + 0x10 |
| 113 | + // <+20>: str w2, [sp, #0xc] |
| 114 | + // <+24>: ldur x0, [x29, #-0x8] |
| 115 | + // <+28>: ldr x1, [sp, #0x10] |
| 116 | + // <+32>: ldr w2, [sp, #0xc] |
| 117 | + // <+36>: bl 0x102c76340 ; symbol stub for: _PyEval_EvalFrameDefault |
| 118 | + // <+40>: ldp x29, x30, [sp, #0x20] |
| 119 | + // <+44>: add sp, sp, #0x30 |
| 120 | + // <+48>: ret |
| 121 | + &[0x10] |
| 122 | + } else if cfg!(all( |
| 123 | + target_os = "windows", |
| 124 | + target_env = "msvc", |
| 125 | + target_arch = "x86_64" |
| 126 | + )) { |
| 127 | + // <+0>: pushq %rbp |
| 128 | + // <+1>: subq $0x40, %rsp |
| 129 | + // <+5>: leaq 0x40(%rsp), %rbp ; FP = SP + 0x40 |
| 130 | + // <+10>: movl %r8d, -0x4(%rbp) |
| 131 | + // <+14>: movq %rdx, -0x18(%rbp) ; rdx is 2nd arg. FP - 0x18 = SP + 0x28 |
| 132 | + // <+18>: movq %rcx, -0x10(%rbp) |
| 133 | + // <+22>: movl -0x4(%rbp), %r8d |
| 134 | + // <+26>: movq -0x18(%rbp), %rdx |
| 135 | + // <+30>: movq -0x10(%rbp), %rcx |
| 136 | + // <+34>: callq *0x517e830(%rip) |
| 137 | + // <+40>: nop |
| 138 | + // <+41>: addq $0x40, %rsp |
| 139 | + // <+45>: popq %rbp |
| 140 | + // <+46>: retq |
| 141 | + &[0x28] |
| 142 | + } else { |
| 143 | + // Unsupported OS or arch. |
| 144 | + &[] |
| 145 | + }; |
| 146 | + |
| 147 | + for sp_offset in sp_offset_hints |
| 148 | + .iter() |
| 149 | + .copied() |
| 150 | + .chain((0..=STACK_SIZE_THRESHOLD).step_by(std::mem::size_of::<usize>())) |
| 151 | + { |
| 152 | + let frame_ptr: *const *mut libc::c_void = (sp + sp_offset) as *const _; |
| 153 | + let frame: *mut libc::c_void = unsafe { *frame_ptr }; |
| 154 | + if frame as usize == last_frame { |
| 155 | + // Got the SP offset and IP offset. |
| 156 | + OFFSET_IP.store(ip - start, Ordering::Release); |
| 157 | + OFFSET_SP.store(sp_offset, Ordering::Release); |
| 158 | + return false; |
| 159 | + } |
| 160 | + } |
| 161 | + } |
| 162 | + // Not Sapling_PyEvalFrame. Check the next frame. |
| 163 | + true |
| 164 | + }); |
| 165 | + Ok(None) |
| 166 | +} |
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