wasmtime_cranelift/debug/transform/
synthetic.rs

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
use gimli::write::{
    AttributeValue, LineProgram, Reference, StringTable, Unit, UnitEntryId, UnitId, UnitTable,
};
use wasmtime_environ::StaticModuleIndex;
use wasmtime_versioned_export_macros::versioned_stringify_ident;

use crate::debug::{Compilation, ModuleMemoryOffset};

/// Internal Wasm utility types DIEs such as WebAssemblyPtr and WasmtimeVMContext.
///
/// For unwrapping Wasm pointer, the WasmtimeVMContext has the `set()` method
/// that allows to control current Wasm memory to inspect.
/// Notice that "wasmtime_set_vmctx_memory" is an external/builtin subprogram
/// that is not part of Wasm code.
///
/// This CU is currently per-module since VMContext memory structure is per-module;
/// some of the contained types could be made global (per-Compilation).
pub struct ModuleSyntheticUnit {
    unit_id: UnitId,
    vmctx_ptr_die_id: UnitEntryId,
    wasm_ptr_die_id: UnitEntryId,
}

macro_rules! add_tag {
    ($unit:ident, $parent_id:ident, $tag:expr => $die:ident as $die_id:ident { $($a:path = $v:expr),* }) => {
        let $die_id = $unit.add($parent_id, $tag);
        let $die = $unit.get_mut($die_id);
        $( $die.set($a, $v); )*
    };
}

impl ModuleSyntheticUnit {
    pub fn new(
        module: StaticModuleIndex,
        compilation: &Compilation<'_>,
        encoding: gimli::Encoding,
        out_units: &mut UnitTable,
        out_strings: &mut StringTable,
    ) -> Self {
        let unit_id = Self::create_unit(encoding, out_units, out_strings);
        let unit = out_units.get_mut(unit_id);
        let vmctx_ptr_die_id = Self::create_vmctx_ptr_die(module, compilation, unit, out_strings);
        let wasm_ptr_die_id = Self::create_wasm_ptr_die(unit, out_strings);

        Self {
            unit_id,
            vmctx_ptr_die_id,
            wasm_ptr_die_id,
        }
    }

    pub fn vmctx_ptr_die_ref(&self) -> Reference {
        Reference::Entry(self.unit_id, self.vmctx_ptr_die_id)
    }

    pub fn wasm_ptr_die_ref(&self) -> Reference {
        Reference::Entry(self.unit_id, self.wasm_ptr_die_id)
    }

    fn create_unit(
        encoding: gimli::Encoding,
        out_units: &mut UnitTable,
        out_strings: &mut StringTable,
    ) -> UnitId {
        let unit_id = out_units.add(Unit::new(encoding, LineProgram::none()));
        let unit = out_units.get_mut(unit_id);
        let unit_die = unit.get_mut(unit.root());
        unit_die.set(
            gimli::DW_AT_name,
            AttributeValue::StringRef(out_strings.add("WasmtimeModuleSyntheticUnit")),
        );
        unit_id
    }

    fn create_vmctx_ptr_die(
        module: StaticModuleIndex,
        compilation: &Compilation<'_>,
        unit: &mut Unit,
        out_strings: &mut StringTable,
    ) -> UnitEntryId {
        // Build DW_TAG_base_type for Wasm byte:
        //  .. DW_AT_name = u8
        //  .. DW_AT_encoding = DW_ATE_unsigned
        //  .. DW_AT_byte_size = 1
        let root_id = unit.root();
        add_tag!(unit, root_id, gimli::DW_TAG_base_type => memory_byte_die as memory_byte_die_id {
            gimli::DW_AT_name = AttributeValue::StringRef(out_strings.add("u8")),
            gimli::DW_AT_encoding = AttributeValue::Encoding(gimli::DW_ATE_unsigned),
            gimli::DW_AT_byte_size = AttributeValue::Data1(1)
        });

        // Build DW_TAG_pointer_type that references Wasm bytes:
        //  .. DW_AT_name = "u8*"
        //  .. DW_AT_type = <memory_byte_die>
        add_tag!(unit, root_id, gimli::DW_TAG_pointer_type => memory_bytes_die as memory_bytes_die_id {
            gimli::DW_AT_name = AttributeValue::StringRef(out_strings.add("u8*")),
            gimli::DW_AT_type = AttributeValue::UnitRef(memory_byte_die_id)
        });

        // Create artificial VMContext type and its reference for convenience viewing
        // its fields (such as memory ref) in a debugger. Build DW_TAG_structure_type:
        //   .. DW_AT_name = "WasmtimeVMContext"
        let vmctx_die_id = unit.add(root_id, gimli::DW_TAG_structure_type);
        let vmctx_die = unit.get_mut(vmctx_die_id);
        vmctx_die.set(
            gimli::DW_AT_name,
            AttributeValue::StringRef(out_strings.add("WasmtimeVMContext")),
        );

        // TODO multiple memories
        match compilation.module_memory_offsets[module] {
            ModuleMemoryOffset::Defined(memory_offset) => {
                // The context has defined memory: extend the WasmtimeVMContext size
                // past the "memory" field.
                const MEMORY_FIELD_SIZE_PLUS_PADDING: u32 = 8;
                vmctx_die.set(
                    gimli::DW_AT_byte_size,
                    AttributeValue::Data4(memory_offset + MEMORY_FIELD_SIZE_PLUS_PADDING),
                );

                // Define the "memory" field which is a direct pointer to allocated Wasm memory.
                // Build DW_TAG_member:
                //  .. DW_AT_name = "memory"
                //  .. DW_AT_type = <memory_bytes_die>
                //  .. DW_AT_data_member_location = `memory_offset`
                add_tag!(unit, vmctx_die_id, gimli::DW_TAG_member => m_die as m_die_id {
                    gimli::DW_AT_name = AttributeValue::StringRef(out_strings.add("memory")),
                    gimli::DW_AT_type = AttributeValue::UnitRef(memory_bytes_die_id),
                    gimli::DW_AT_data_member_location = AttributeValue::Udata(memory_offset as u64)
                });
            }
            ModuleMemoryOffset::Imported { .. } => {
                // TODO implement convenience pointer to and additional types for VMMemoryImport.
            }
            ModuleMemoryOffset::None => (),
        }

        // Build DW_TAG_pointer_type for `WasmtimeVMContext*`:
        //  .. DW_AT_name = "WasmtimeVMContext*"
        //  .. DW_AT_type = <vmctx_die>
        add_tag!(unit, root_id, gimli::DW_TAG_pointer_type => vmctx_ptr_die as vmctx_ptr_die_id {
            gimli::DW_AT_name = AttributeValue::StringRef(out_strings.add("WasmtimeVMContext*")),
            gimli::DW_AT_type = AttributeValue::UnitRef(vmctx_die_id)
        });

        // Build vmctx_die's DW_TAG_subprogram for `set` method:
        //  .. DW_AT_linkage_name = "wasmtime_set_vmctx_memory"
        //  .. DW_AT_name = "set"
        //  .. DW_TAG_formal_parameter
        //  ..  .. DW_AT_type = <vmctx_ptr_die>
        //  ..  .. DW_AT_artificial = 1
        add_tag!(unit, vmctx_die_id, gimli::DW_TAG_subprogram => vmctx_set as vmctx_set_id {
            gimli::DW_AT_linkage_name = AttributeValue::StringRef(out_strings.add(versioned_stringify_ident!(wasmtime_set_vmctx_memory))),
            gimli::DW_AT_name = AttributeValue::StringRef(out_strings.add("set"))
        });
        add_tag!(unit, vmctx_set_id, gimli::DW_TAG_formal_parameter => vmctx_set_this_param as vmctx_set_this_param_id {
            gimli::DW_AT_type = AttributeValue::UnitRef(vmctx_ptr_die_id),
            gimli::DW_AT_artificial = AttributeValue::Flag(true)
        });

        vmctx_ptr_die_id
    }

    fn create_wasm_ptr_die(unit: &mut Unit, out_strings: &mut StringTable) -> UnitEntryId {
        // Build DW_TAG_base_type for generic `WebAssemblyPtr`.
        //  .. DW_AT_name = "WebAssemblyPtr"
        //  .. DW_AT_byte_size = 4
        //  .. DW_AT_encoding = DW_ATE_unsigned
        const WASM_PTR_LEN: u8 = 4;
        let root_id = unit.root();
        add_tag!(unit, root_id, gimli::DW_TAG_base_type => wp_die as wp_die_id {
            gimli::DW_AT_name = AttributeValue::StringRef(out_strings.add("WebAssemblyPtr")),
            gimli::DW_AT_byte_size = AttributeValue::Data1(WASM_PTR_LEN),
            gimli::DW_AT_encoding = AttributeValue::Encoding(gimli::DW_ATE_unsigned)
        });

        wp_die_id
    }
}