rustc: Introduce ABI versioning so we can change value representations without breaking the compiler

mk/rt.mk

@@ -26,6 +26,7 @@ RUNTIME_CS := rt/sync/timer.cpp \
               rt/rust_shape.cpp \
               rt/rust_obstack.cpp \
               rt/rust_gc.cpp \
+              rt/rust_abi.cpp \
               rt/memory_region.cpp \
               rt/test/rust_test_harness.cpp \
               rt/test/rust_test_runtime.cpp \

src/comp/back/abi.rs

@@ -112,6 +112,8 @@ const ivec_heap_elt_elems: uint = 1u;
 
 const worst_case_glue_call_args: int = 7;
 
+const abi_version: uint = 1u;
+
 fn memcpy_glue_name() -> str { ret "rust_memcpy_glue"; }
 
 fn bzero_glue_name() -> str { ret "rust_bzero_glue"; }

src/comp/middle/shape.rs

@@ -84,15 +84,20 @@ fn eq_res_info(a: &res_info, b: &res_info) -> bool {
     ret a.did.crate == b.did.crate && a.did.node == b.did.node && a.t == b.t;
 }
 
-fn mk_global(ccx: &@crate_ctxt, name: &str, llval: ValueRef) -> ValueRef {
+fn mk_global(ccx: &@crate_ctxt, name: &str, llval: ValueRef,
+             internal: bool) -> ValueRef {
     let llglobal =
         lib::llvm::llvm::LLVMAddGlobal(ccx.llmod, val_ty(llval),
                                        str::buf(name));
     lib::llvm::llvm::LLVMSetInitializer(llglobal, llval);
     lib::llvm::llvm::LLVMSetGlobalConstant(llglobal, True);
-    lib::llvm::llvm::LLVMSetLinkage(llglobal,
-                                    lib::llvm::LLVMInternalLinkage as
-                                        lib::llvm::llvm::Linkage);
+
+    if (internal) {
+        lib::llvm::llvm::LLVMSetLinkage(llglobal,
+                                        lib::llvm::LLVMInternalLinkage as
+                                            lib::llvm::llvm::Linkage);
+    }
+
     ret llglobal;
 }
 
@@ -510,7 +515,7 @@ fn gen_tag_shapes(ccx: &@crate_ctxt) -> ValueRef {
     header += data;
     header += lv_table;
 
-    ret mk_global(ccx, "tag_shapes", C_bytes(header));
+    ret mk_global(ccx, "tag_shapes", C_bytes(header), true);
 }
 
 fn gen_resource_shapes(ccx: &@crate_ctxt) -> ValueRef {
@@ -523,7 +528,7 @@ fn gen_resource_shapes(ccx: &@crate_ctxt) -> ValueRef {
         i += 1u;
     }
 
-    ret mk_global(ccx, "resource_shapes", C_struct(dtors));
+    ret mk_global(ccx, "resource_shapes", C_struct(dtors), true);
 }
 
 fn gen_shape_tables(ccx: &@crate_ctxt) {

src/comp/middle/trans.rs

@@ -6926,6 +6926,12 @@ fn write_metadata(cx: &@crate_ctxt, crate: &@ast::crate) {
     llvm::LLVMSetInitializer(llvm_used, C_array(t_ptr_i8, [llglobal]));
 }
 
+// Writes the current ABI version into the crate.
+fn write_abi_version(ccx: &@crate_ctxt) {
+    shape::mk_global(ccx, "rust_abi_version", C_uint(abi::abi_version),
+                     false);
+}
+
 fn trans_crate(sess: &session::session, crate: &@ast::crate, tcx: &ty::ctxt,
                output: &str, amap: &ast_map::map) -> ModuleRef {
     let llmod =
@@ -7001,6 +7007,7 @@ fn trans_crate(sess: &session::session, crate: &@ast::crate, tcx: &ty::ctxt,
     create_crate_map(ccx);
     emit_tydescs(ccx);
     shape::gen_shape_tables(ccx);
+    write_abi_version(ccx);
 
     // Translate the metadata.
     write_metadata(cx.ccx, crate);

src/rt/rust_abi.cpp

@@ -0,0 +1,10 @@
+#include <cstdlib>
+#include <stdint.h>
+#include "rust_abi.h"
+
+weak_symbol<uint32_t> abi_version("rust_abi_version");
+
+uint32_t get_abi_version() {
+    return (*abi_version == NULL) ? 0 : **abi_version;
+}
+

src/rt/rust_abi.h

@@ -1,6 +1,8 @@
 #ifndef RUST_ABI_H
 #define RUST_ABI_H
 
+#include <cstdlib>
+
 #ifdef __WIN32__
 #include <windows.h>
 #else
@@ -34,5 +36,7 @@ public:
     T *&operator*() { fill(); return data; }
 };
 
+uint32_t get_abi_version();
+
 #endif