Migrating code to object (from faerie) (#1848)

* Using the "object" library everywhere in wasmtime.
* scroll_derive

crates/obj/src/module.rs

@@ -3,24 +3,44 @@ use crate::data_segment::{declare_data_segment, emit_data_segment};
 use crate::function::{declare_functions, emit_functions};
 use crate::table::{declare_table, emit_table};
 use anyhow::Result;
-use faerie::{Artifact, Decl, Link};
+use object::write::{Object, Relocation, StandardSection, Symbol, SymbolSection};
+use object::{RelocationEncoding, RelocationKind, SymbolFlags, SymbolKind, SymbolScope};
 use wasmtime_environ::isa::TargetFrontendConfig;
 use wasmtime_environ::{Compilation, DataInitializer, Module, Relocations};
 
 fn emit_vmcontext_init(
-    obj: &mut Artifact,
+    obj: &mut Object,
     module: &Module,
     target_config: &TargetFrontendConfig,
 ) -> Result<()> {
     let (data, table_relocs) = layout_vmcontext(module, target_config);
-    obj.declare_with("_vmcontext_init", Decl::data().global(), data.to_vec())?;
+    let symbol_id = obj.add_symbol(Symbol {
+        name: "_vmcontext_init".as_bytes().to_vec(),
+        value: 0,
+        size: 0,
+        kind: SymbolKind::Data,
+        scope: SymbolScope::Linkage,
+        weak: false,
+        section: SymbolSection::Undefined,
+        flags: SymbolFlags::None,
+    });
+    let section_id = obj.section_id(StandardSection::Data);
+    let section_offset = obj.add_symbol_data(symbol_id, section_id, &data, 1);
+
     for reloc in table_relocs.iter() {
         let target_name = format!("_table_{}", reloc.index);
-        obj.link(Link {
-            from: "_vmcontext_init",
-            to: &target_name,
-            at: reloc.offset as u64,
-        })?;
+        let target_symbol = obj.symbol_id(target_name.as_bytes()).unwrap();
+        obj.add_relocation(
+            section_id,
+            Relocation {
+                offset: section_offset + reloc.offset as u64,
+                size: 64, // FIXME for all targets
+                kind: RelocationKind::Absolute,
+                encoding: RelocationEncoding::Generic,
+                symbol: target_symbol,
+                addend: 0,
+            },
+        )?;
     }
     Ok(())
 }
@@ -28,7 +48,7 @@ fn emit_vmcontext_init(
 /// Emits a module that has been emitted with the `wasmtime-environ` environment
 /// implementation to a native object file.
 pub fn emit_module(
-    obj: &mut Artifact,
+    obj: &mut Object,
     module: &Module,
     compilation: &Compilation,
     relocations: &Relocations,