Initial reorg.

This is largely the same as #305, but updated for the current tree.

crates/obj/src/context.rs

@@ -0,0 +1,93 @@
+#![allow(clippy::cast_ptr_alignment)]
+
+use alloc::boxed::Box;
+use alloc::vec::Vec;
+use core::ptr;
+use cranelift_codegen::isa::TargetFrontendConfig;
+use cranelift_entity::EntityRef;
+use cranelift_wasm::GlobalInit;
+use std::collections::hash_map::Entry;
+use std::collections::HashMap;
+use wasmtime_environ::{Module, TargetSharedSignatureIndex, VMOffsets};
+
+pub struct TableRelocation {
+    pub index: usize,
+    pub offset: usize,
+}
+
+pub fn layout_vmcontext(
+    module: &Module,
+    target_config: &TargetFrontendConfig,
+) -> (Box<[u8]>, Box<[TableRelocation]>) {
+    let ofs = VMOffsets::new(target_config.pointer_bytes(), &module);
+    let out_len = ofs.size_of_vmctx() as usize;
+    let mut out = vec![0; out_len];
+
+    // Assign unique indicies to unique signatures.
+    let mut signature_registry = HashMap::new();
+    let mut signature_registry_len = signature_registry.len();
+    for (index, sig) in module.signatures.iter() {
+        let offset = ofs.vmctx_vmshared_signature_id(index) as usize;
+        let target_index = match signature_registry.entry(sig) {
+            Entry::Occupied(o) => *o.get(),
+            Entry::Vacant(v) => {
+                assert!(signature_registry_len <= ::core::u32::MAX as usize);
+                let id = TargetSharedSignatureIndex::new(signature_registry_len as u32);
+                signature_registry_len += 1;
+                *v.insert(id)
+            }
+        };
+        unsafe {
+            let to = out.as_mut_ptr().add(offset) as *mut TargetSharedSignatureIndex;
+            ptr::write(to, target_index);
+        }
+    }
+
+    let num_tables_imports = module.imported_tables.len();
+    let mut table_relocs = Vec::with_capacity(module.table_plans.len() - num_tables_imports);
+    for (index, table) in module.table_plans.iter().skip(num_tables_imports) {
+        let def_index = module.defined_table_index(index).unwrap();
+        let offset = ofs.vmctx_vmtable_definition(def_index) as usize;
+        let current_elements = table.table.minimum;
+        unsafe {
+            assert_eq!(
+                ::std::mem::size_of::<u32>() as u8,
+                ofs.size_of_vmtable_definition_current_elements(),
+                "vmtable_definition_current_elements expected to be u32"
+            );
+            let to = out
+                .as_mut_ptr()
+                .add(offset)
+                .add(ofs.vmtable_definition_current_elements() as usize);
+            ptr::write(to as *mut u32, current_elements);
+        }
+        table_relocs.push(TableRelocation {
+            index: def_index.index(),
+            offset,
+        });
+    }
+
+    let num_globals_imports = module.imported_globals.len();
+    for (index, global) in module.globals.iter().skip(num_globals_imports) {
+        let def_index = module.defined_global_index(index).unwrap();
+        let offset = ofs.vmctx_vmglobal_definition(def_index) as usize;
+        let to = unsafe { out.as_mut_ptr().add(offset) };
+        match global.initializer {
+            GlobalInit::I32Const(x) => unsafe {
+                ptr::write(to as *mut i32, x);
+            },
+            GlobalInit::I64Const(x) => unsafe {
+                ptr::write(to as *mut i64, x);
+            },
+            GlobalInit::F32Const(x) => unsafe {
+                ptr::write(to as *mut u32, x);
+            },
+            GlobalInit::F64Const(x) => unsafe {
+                ptr::write(to as *mut u64, x);
+            },
+            _ => panic!("unsupported global type"),
+        }
+    }
+
+    (out.into_boxed_slice(), table_relocs.into_boxed_slice())
+}