Record information about sections of emitted code+data.

The result of the emitter is a vector of bytes holding machine code,
jump tables, and (in the future) other read-only data.  Some clients,
notably Firefox's Wasm compiler, needs to separate the machine code
from the data in order to insert more code directly after the code
generated by Cranelift.

To make such separation possible, we record more information about the
emitted bytes: the sizes of each of the sections of code, jump tables,
and read-only data, as well as the locations within the code that
reference (PC-relatively) the jump tables and read-only data.

cranelift/faerie/src/backend.rs

@@ -138,9 +138,9 @@ impl Backend for FaerieBackend {
         name: &str,
         ctx: &cranelift_codegen::Context,
         namespace: &ModuleNamespace<Self>,
-        code_size: u32,
+        total_size: u32,
     ) -> ModuleResult<FaerieCompiledFunction> {
-        let mut code: Vec<u8> = vec![0; code_size as usize];
+        let mut code: Vec<u8> = vec![0; total_size as usize];
 
         // Non-lexical lifetimes would obviate the braces here.
         {
@@ -153,7 +153,7 @@ impl Backend for FaerieBackend {
             };
 
             if let Some(ref mut trap_manifest) = self.trap_manifest {
-                let mut trap_sink = FaerieTrapSink::new(name, code_size);
+                let mut trap_sink = FaerieTrapSink::new(name, total_size);
                 unsafe {
                     ctx.emit_to_memory(
                         &*self.isa,