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/filetests/src/test_binemit.rs

@@ -5,8 +5,7 @@
 
 use crate::match_directive::match_directive;
 use crate::subtest::{Context, SubTest, SubtestResult};
-use cranelift_codegen::binemit;
-use cranelift_codegen::binemit::{CodeSink, RegDiversions};
+use cranelift_codegen::binemit::{self, CodeInfo, CodeSink, RegDiversions};
 use cranelift_codegen::dbg::DisplayList;
 use cranelift_codegen::ir;
 use cranelift_codegen::ir::entities::AnyEntity;
@@ -96,9 +95,12 @@ impl binemit::CodeSink for TextSink {
         write!(self.text, "{} ", code).unwrap();
     }
 
-    fn begin_rodata(&mut self) {
+    fn begin_jumptables(&mut self) {
         self.code_size = self.offset
     }
+
+    fn begin_rodata(&mut self) {}
+    fn end_codegen(&mut self) {}
 }
 
 impl SubTest for TestBinEmit {
@@ -164,7 +166,7 @@ impl SubTest for TestBinEmit {
         }
 
         // Relax branches and compute EBB offsets based on the encodings.
-        let code_size = binemit::relax_branches(&mut func, isa)
+        let CodeInfo { total_size, .. } = binemit::relax_branches(&mut func, isa)
             .map_err(|e| pretty_error(&func, context.isa, e))?;
 
         // Collect all of the 'bin:' directives on instructions.
@@ -288,7 +290,7 @@ impl SubTest for TestBinEmit {
             }
         }
 
-        sink.begin_rodata();
+        sink.begin_jumptables();
 
         for (jt, jt_data) in func.jump_tables.iter() {
             let jt_offset = func.jt_offsets[jt];
@@ -298,10 +300,15 @@ impl SubTest for TestBinEmit {
             }
         }
 
-        if sink.offset != code_size {
+        sink.begin_rodata();
+        // TODO: Read-only (constant pool) data.
+
+        sink.end_codegen();
+
+        if sink.offset != total_size {
             return Err(format!(
                 "Expected code size {}, got {}",
-                code_size, sink.offset
+                total_size, sink.offset
             ));
         }
 

cranelift/filetests/src/test_compile.rs

@@ -4,8 +4,9 @@
 
 use crate::subtest::{run_filecheck, Context, SubTest, SubtestResult};
 use cranelift_codegen;
+use cranelift_codegen::binemit::{self, CodeInfo};
+use cranelift_codegen::ir;
 use cranelift_codegen::print_errors::pretty_error;
-use cranelift_codegen::{binemit, ir};
 use cranelift_reader::TestCommand;
 use log::info;
 use std::borrow::Cow;
@@ -38,13 +39,13 @@ impl SubTest for TestCompile {
         let isa = context.isa.expect("compile needs an ISA");
         let mut comp_ctx = cranelift_codegen::Context::for_function(func.into_owned());
 
-        let code_size = comp_ctx
+        let CodeInfo { total_size, .. } = comp_ctx
             .compile(isa)
             .map_err(|e| pretty_error(&comp_ctx.func, context.isa, e))?;
 
         info!(
             "Generated {} bytes of code:\n{}",
-            code_size,
+            total_size,
             comp_ctx.func.display(isa)
         );
 
@@ -56,10 +57,10 @@ impl SubTest for TestCompile {
             &mut sink,
         );
 
-        if sink.offset != code_size {
+        if sink.offset != total_size {
             return Err(format!(
                 "Expected code size {}, got {}",
-                code_size, sink.offset
+                total_size, sink.offset
             ));
         }
 
@@ -105,5 +106,7 @@ impl binemit::CodeSink for SizeSink {
     }
     fn reloc_jt(&mut self, _reloc: binemit::Reloc, _jt: ir::JumpTable) {}
     fn trap(&mut self, _code: ir::TrapCode, _srcloc: ir::SourceLoc) {}
+    fn begin_jumptables(&mut self) {}
     fn begin_rodata(&mut self) {}
+    fn end_codegen(&mut self) {}
 }