From e475ddb08e4bb3bacbc50bdd26fa83f579783dbb Mon Sep 17 00:00:00 2001
From: Luuk de Gram <luuk@degram.dev>
Date: Sun, 1 Jan 2023 17:10:51 +0100
Subject: wasm-linker: export symbols by virtual address

When exporting a data symbol, generate a regular global and use
the data symbol's virtual addres as the value (init) of the global.
---
 src/link/Wasm/Atom.zig | 42 ++++++++++++++++++------------------------
 1 file changed, 18 insertions(+), 24 deletions(-)

(limited to 'src/link/Wasm/Atom.zig')

diff --git a/src/link/Wasm/Atom.zig b/src/link/Wasm/Atom.zig
index eb3a31b8a0..de9cefebdc 100644
--- a/src/link/Wasm/Atom.zig
+++ b/src/link/Wasm/Atom.zig
@@ -90,24 +90,26 @@ pub fn getFirst(atom: *Atom) *Atom {
     return tmp;
 }
 
-/// Unlike `getFirst` this returns the first `*Atom` that was
-/// produced from Zig code, rather than an object file.
-/// This is useful for debug sections where we want to extend
-/// the bytes, and don't want to overwrite existing Atoms.
-pub fn getFirstZigAtom(atom: *Atom) *Atom {
-    if (atom.file == null) return atom;
-    var tmp = atom;
-    return while (tmp.prev) |prev| {
-        if (prev.file == null) break prev;
-        tmp = prev;
-    } else unreachable; // must allocate an Atom first!
-}
-
 /// Returns the location of the symbol that represents this `Atom`
 pub fn symbolLoc(atom: Atom) Wasm.SymbolLoc {
     return .{ .file = atom.file, .index = atom.sym_index };
 }
 
+/// Returns the virtual address of the `Atom`. This is the address starting
+/// from the first entry within a section.
+pub fn getVA(atom: Atom, wasm: *const Wasm, symbol: *const Symbol) u32 {
+    if (symbol.tag == .function) return atom.offset;
+    std.debug.assert(symbol.tag == .data);
+    const merge_segment = wasm.base.options.output_mode != .Obj;
+    const segment_info = if (atom.file) |object_index| blk: {
+        break :blk wasm.objects.items[object_index].segment_info;
+    } else wasm.segment_info.values();
+    const segment_name = segment_info[symbol.index].outputName(merge_segment);
+    const segment_index = wasm.data_segments.get(segment_name).?;
+    const segment = wasm.segments.items[segment_index];
+    return segment.offset + atom.offset;
+}
+
 /// Resolves the relocations within the atom, writing the new value
 /// at the calculated offset.
 pub fn resolveRelocs(atom: *Atom, wasm_bin: *const Wasm) void {
@@ -159,7 +161,7 @@ pub fn resolveRelocs(atom: *Atom, wasm_bin: *const Wasm) void {
 /// The final value must be casted to the correct size.
 fn relocationValue(atom: Atom, relocation: types.Relocation, wasm_bin: *const Wasm) u64 {
     const target_loc = (Wasm.SymbolLoc{ .file = atom.file, .index = relocation.index }).finalLoc(wasm_bin);
-    const symbol = target_loc.getSymbol(wasm_bin).*;
+    const symbol = target_loc.getSymbol(wasm_bin);
     switch (relocation.relocation_type) {
         .R_WASM_FUNCTION_INDEX_LEB => return symbol.index,
         .R_WASM_TABLE_NUMBER_LEB => return symbol.index,
@@ -190,17 +192,9 @@ fn relocationValue(atom: Atom, relocation: types.Relocation, wasm_bin: *const Wa
             if (symbol.isUndefined()) {
                 return 0;
             }
-
-            const merge_segment = wasm_bin.base.options.output_mode != .Obj;
             const target_atom = wasm_bin.symbol_atom.get(target_loc).?;
-            const segment_info = if (target_atom.file) |object_index| blk: {
-                break :blk wasm_bin.objects.items[object_index].segment_info;
-            } else wasm_bin.segment_info.values();
-            const segment_name = segment_info[symbol.index].outputName(merge_segment);
-            const segment_index = wasm_bin.data_segments.get(segment_name).?;
-            const segment = wasm_bin.segments.items[segment_index];
-            const rel_value = @intCast(i32, target_atom.offset + segment.offset) + relocation.addend;
-            return @intCast(u32, rel_value);
+            const va = @intCast(i32, target_atom.getVA(wasm_bin, symbol));
+            return @intCast(u32, va + relocation.addend);
         },
         .R_WASM_EVENT_INDEX_LEB => return symbol.index,
         .R_WASM_SECTION_OFFSET_I32 => {
-- 
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