Commit `bddf138e72`

Luuk de Gram <luuk@degram.dev>

2023-03-08 06:27:03

wasm-link: fix storing decls in the right segment

When a decl is `undefined` is must be stored in the data segment when the build mode is safe. For unsafe optimize modes, it must be stored in the bss segment instead. For mutable decls where the atom contains all zeroes, it must always be stored in the bss segment. All other values will result in the atom being stored in the data segment.

master

1 parent c31007b

Changed files (1)

src

link

Wasm.zig

@@ -2828,22 +2828,31 @@ pub fn flushModule(wasm: *Wasm, comp: *Compilation, prog_node: *std.Progress.Nod
             const decl = mod.declPtr(entry.key_ptr.*);
             if (decl.isExtern()) continue;
             const atom_index = entry.value_ptr.*;
+            const atom = wasm.getAtomPtr(atom_index);
             if (decl.ty.zigTypeTag() == .Fn) {
                 try wasm.parseAtom(atom_index, .function);
             } else if (decl.getVariable()) |variable| {
                 if (!variable.is_mutable) {
                     try wasm.parseAtom(atom_index, .{ .data = .read_only });
                 } else if (variable.init.isUndefDeep()) {
-                    try wasm.parseAtom(atom_index, .{ .data = .uninitialized });
+                    // for safe build modes, we store the atom in the data segment,
+                    // whereas for unsafe build modes we store it in bss.
+                    const is_initialized = wasm.base.options.optimize_mode == .Debug or
+                        wasm.base.options.optimize_mode == .ReleaseSafe;
+                    try wasm.parseAtom(atom_index, .{ .data = if (is_initialized) .initialized else .uninitialized });
                 } else {
-                    try wasm.parseAtom(atom_index, .{ .data = .initialized });
+                    // when the decl is all zeroes, we store the atom in the bss segment,
+                    // in all other cases it will be in the data segment.
+                    const is_zeroes = for (atom.code.items) |byte| {
+                        if (byte != 0) break false;
+                    } else true;
+                    try wasm.parseAtom(atom_index, .{ .data = if (is_zeroes) .uninitialized else .initialized });
                 }
             } else {
                 try wasm.parseAtom(atom_index, .{ .data = .read_only });
             }
 
             // also parse atoms for a decl's locals
-            const atom = wasm.getAtomPtr(atom_index);
             for (atom.locals.items) |local_atom_index| {
                 try wasm.parseAtom(local_atom_index, .{ .data = .read_only });
             }

Commit bddf138e72

Commit `bddf138e72`