Commit 2ae2ac33d9

Luuk de Gram <luuk@degram.dev>
2022-05-04 21:25:33
wasm: Emit debug sections
This commit adds the ability to emit the following debug sections: .debug_info .debug_abbrev .debug_line .debug_str Line information and files are now being loaded correctly by browser debuggers.
1 parent 9b6b703
Changed files (3)
src/link/Wasm/Atom.zig
@@ -90,15 +90,6 @@ pub fn getFirst(self: *Atom) *Atom {
     return tmp;
 }
 
-/// Returns the atom for the given `symbol_index`.
-/// This can be either the `Atom` itself, or one of its locals.
-pub fn symbolAtom(self: *Atom, symbol_index: u32) *Atom {
-    if (self.sym_index == symbol_index) return self;
-    return for (self.locals.items) |*local_atom| {
-        if (local_atom.sym_index == symbol_index) break local_atom;
-    } else unreachable; // Used a symbol index not present in this atom or its children.
-}
-
 /// Returns the location of the symbol that represents this `Atom`
 pub fn symbolLoc(self: Atom) Wasm.SymbolLoc {
     return .{ .file = self.file, .index = self.sym_index };
src/link/Dwarf.zig
@@ -963,21 +963,18 @@ pub fn commitDeclState(
                     const wasm_file = file.cast(File.Wasm).?;
                     const segment_index = try wasm_file.getDebugLineIndex();
                     const segment = &wasm_file.segments.items[segment_index];
-                    const debug_atom = wasm_file.atoms.get(segment_index).?;
+                    const debug_line = &wasm_file.debug_line;
                     if (needed_size != segment.size) {
                         log.debug(" needed size does not equal allocated size: {d}", .{needed_size});
                         if (needed_size > segment.size) {
-                            log.debug("  allocating {d} bytes for debug line information", .{needed_size - segment.size});
-                            try debug_atom.code.resize(self.allocator, needed_size);
-                            std.mem.set(u8, debug_atom.code.items[segment.size..], 0);
+                            log.debug("  allocating {d} bytes for 'debug line' information", .{needed_size - segment.size});
+                            try debug_line.resize(self.allocator, needed_size);
+                            mem.set(u8, debug_line.items[segment.size..], 0);
                         }
-                        debug_atom.size = needed_size;
                         segment.size = needed_size;
                     }
-                    // since we can tighly pack the debug lines, wasm does not require
-                    // us to pad with Nops.
                     const offset = segment.offset + src_fn.off;
-                    std.mem.copy(u8, debug_atom.code.items[offset..], dbg_line_buffer.items);
+                    mem.copy(u8, debug_line.items[offset..], dbg_line_buffer.items);
                 },
                 else => unreachable,
             }
@@ -1116,7 +1113,9 @@ fn updateDeclDebugInfoAllocation(self: *Dwarf, file: *File, atom: *Atom, len: u3
                         const file_pos = debug_info_sect.offset + atom.off;
                         try pwriteDbgInfoNops(d_sym.file, file_pos, 0, &[0]u8{}, atom.len, false);
                     },
-                    .wasm => {},
+                    .wasm => {
+                        log.debug(" todo: updateDeclDebugInfoAllocation for Wasm: {d}", .{atom.len});
+                    },
                     else => unreachable,
                 }
                 // TODO Look at the free list before appending at the end.
@@ -1241,6 +1240,23 @@ fn writeDeclDebugInfo(self: *Dwarf, file: *File, atom: *Atom, dbg_info_buf: []co
                 trailing_zero,
             );
         },
+        .wasm => {
+            const wasm_file = file.cast(File.Wasm).?;
+            const segment_index = try wasm_file.getDebugInfoIndex();
+            const segment = &wasm_file.segments.items[segment_index];
+            const debug_info = &wasm_file.debug_info;
+            if (needed_size != segment.size) {
+                log.debug(" needed size does not equal allocated size: {d}", .{needed_size});
+                if (needed_size > segment.size) {
+                    log.debug("  allocating {d} bytes for 'debug info' information", .{needed_size - segment.size});
+                    try debug_info.resize(self.allocator, needed_size);
+                    mem.set(u8, debug_info.items[segment.size..], 0);
+                }
+                segment.size = needed_size;
+            }
+            const offset = segment.offset + atom.off;
+            mem.copy(u8, debug_info.items[offset..], dbg_info_buf);
+        },
         else => unreachable,
     }
 }
@@ -1279,8 +1295,7 @@ pub fn updateDeclLineNumber(self: *Dwarf, file: *File, decl: *const Module.Decl)
             const segment_index = wasm_file.getDebugLineIndex() catch unreachable;
             const segment = wasm_file.segments.items[segment_index];
             const offset = segment.offset + decl.fn_link.wasm.src_fn.off + self.getRelocDbgLineOff();
-            const debug_atom = wasm_file.atoms.get(segment_index).?;
-            std.mem.copy(u8, debug_atom.code.items[offset..], &data);
+            mem.copy(u8, wasm_file.debug_line.items[offset..], &data);
         },
         else => unreachable,
     }
@@ -1514,6 +1529,11 @@ pub fn writeDbgAbbrev(self: *Dwarf, file: *File) !void {
             const file_pos = debug_abbrev_sect.offset + abbrev_offset;
             try d_sym.file.pwriteAll(&abbrev_buf, file_pos);
         },
+        .wasm => {
+            const wasm_file = file.cast(File.Wasm).?;
+            try wasm_file.debug_abbrev.resize(wasm_file.base.allocator, needed_size);
+            mem.copy(u8, wasm_file.debug_abbrev.items, &abbrev_buf);
+        },
         else => unreachable,
     }
 }
@@ -1621,6 +1641,10 @@ pub fn writeDbgInfoHeader(self: *Dwarf, file: *File, module: *Module, low_pc: u6
             const file_pos = debug_info_sect.offset;
             try pwriteDbgInfoNops(d_sym.file, file_pos, 0, di_buf.items, jmp_amt, false);
         },
+        .wasm => {
+            const wasm_file = file.cast(File.Wasm).?;
+            mem.copy(u8, wasm_file.debug_info.items, di_buf.items);
+        },
         else => unreachable,
     }
 }
@@ -2004,6 +2028,10 @@ pub fn writeDbgLineHeader(self: *Dwarf, file: *File, module: *Module) !void {
             const file_pos = debug_line_sect.offset;
             try pwriteDbgLineNops(d_sym.file, file_pos, 0, di_buf.items, jmp_amt);
         },
+        .wasm => {
+            const wasm_file = file.cast(File.Wasm).?;
+            mem.copy(u8, wasm_file.debug_line.items, di_buf.items);
+        },
         else => unreachable,
     }
 }
@@ -2127,6 +2155,8 @@ pub fn flushModule(self: *Dwarf, file: *File, module: *Module) !void {
                     const debug_info_sect = &dwarf_segment.sections.items[d_sym.debug_info_section_index.?];
                     break :blk debug_info_sect.offset;
                 },
+                // for wasm, the offset is always 0 as we write to memory first
+                .wasm => break :blk @as(u32, 0),
                 else => unreachable,
             }
         };
@@ -2145,6 +2175,10 @@ pub fn flushModule(self: *Dwarf, file: *File, module: *Module) !void {
                     const d_sym = &macho_file.d_sym.?;
                     try d_sym.file.pwriteAll(&buf, file_pos + reloc.atom.off + reloc.offset);
                 },
+                .wasm => {
+                    const wasm_file = file.cast(File.Wasm).?;
+                    mem.copy(u8, wasm_file.debug_info.items[reloc.atom.off + reloc.offset ..], &buf);
+                },
                 else => unreachable,
             }
         }
src/link/Wasm.zig
@@ -90,6 +90,14 @@ string_table: StringTable = .{},
 /// Debug information for wasm
 dwarf: ?Dwarf = null,
 
+// *debug information* //
+/// Contains all bytes for the '.debug_info' section
+debug_info: std.ArrayListUnmanaged(u8) = .{},
+/// Contains all bytes for the '.debug_line' section
+debug_line: std.ArrayListUnmanaged(u8) = .{},
+/// Contains all bytes for the '.debug_abbrev' section
+debug_abbrev: std.ArrayListUnmanaged(u8) = .{},
+
 // Output sections
 /// Output type section
 func_types: std.ArrayListUnmanaged(wasm.Type) = .{},
@@ -501,6 +509,10 @@ pub fn deinit(self: *Wasm) void {
     if (self.dwarf) |*dwarf| {
         dwarf.deinit();
     }
+
+    self.debug_info.deinit(gpa);
+    self.debug_line.deinit(gpa);
+    self.debug_abbrev.deinit(gpa);
 }
 
 pub fn allocateDeclIndexes(self: *Wasm, decl_index: Module.Decl.Index) !void {
@@ -576,7 +588,9 @@ pub fn updateFunc(self: *Wasm, mod: *Module, func: *Module.Fn, air: Air, livenes
             &self.base,
             mod,
             decl,
-            // Actual value will be written after relocation
+            // Actual value will be written after relocation.
+            // For Wasm, this is the offset relative to the code section
+            // which isn't known until flush().
             0,
             code.len,
             &decl_state.?,
@@ -1016,10 +1030,12 @@ fn parseAtom(self: *Wasm, atom: *Atom, kind: Kind) !void {
                 // segment indexes can be off by 1 due to also containing a segment
                 // for the code section, so we must check if the existing segment
                 // is larger than that of the code section, and substract the index by 1 in such case.
-                const info_add = if (self.code_section_index) |idx| blk: {
+                var info_add = if (self.code_section_index) |idx| blk: {
                     if (idx < index) break :blk @as(u32, 1);
                     break :blk 0;
                 } else @as(u32, 0);
+                if (self.debug_info_index != null) info_add += 1;
+                if (self.debug_line_index != null) info_add += 1;
                 symbol.index = index - info_add;
                 // segment info already exists, so free its memory
                 self.base.allocator.free(segment_name);
@@ -1320,11 +1336,8 @@ fn setupMemory(self: *Wasm) !void {
     }
 
     var offset: u32 = @intCast(u32, memory_ptr);
-    for (self.segments.items) |*segment, i| {
-        // skip 'code' segments
-        if (self.code_section_index) |index| {
-            if (index == i) continue;
-        }
+    for (self.data_segments.values()) |segment_index| {
+        const segment = &self.segments.items[segment_index];
         memory_ptr = std.mem.alignForwardGeneric(u64, memory_ptr, segment.alignment);
         memory_ptr += segment.size;
         segment.offset = offset;
@@ -1588,6 +1601,7 @@ fn resetState(self: *Wasm) void {
     self.symbol_atom.clearRetainingCapacity();
     self.code_section_index = null;
     self.debug_info_index = null;
+    self.debug_line_index = null;
 }
 
 pub fn flush(self: *Wasm, comp: *Compilation, prog_node: *std.Progress.Node) !void {
@@ -2016,10 +2030,43 @@ pub fn flushModule(self: *Wasm, comp: *Compilation, prog_node: *std.Progress.Nod
             try self.emitDataRelocations(file, arena, data_index, symbol_table);
         }
     } else if (!self.base.options.strip) {
+        if (self.dwarf) |*dwarf| {
+            if (self.debug_info_index != null) {
+                _ = dwarf;
+                try dwarf.writeDbgAbbrev(&self.base);
+                try dwarf.writeDbgInfoHeader(&self.base, mod, 0, 0);
+                try dwarf.writeDbgLineHeader(&self.base, mod);
+
+                try emitDebugSection(file, self.debug_info.items, ".debug_info");
+                try emitDebugSection(file, self.debug_abbrev.items, ".debug_abbrev"); // TODO
+                try emitDebugSection(file, self.debug_line.items, ".debug_line");
+                try emitDebugSection(file, dwarf.strtab.items, ".debug_str");
+            }
+        }
         try self.emitNameSection(file, arena);
     }
 }
 
+fn emitDebugSection(file: fs.File, data: []const u8, name: []const u8) !void {
+    const header_offset = try reserveCustomSectionHeader(file);
+    const writer = file.writer();
+    try leb.writeULEB128(writer, @intCast(u32, name.len));
+    try writer.writeAll(name);
+
+    try file.writevAll(&[_]std.os.iovec_const{.{
+        .iov_base = data.ptr,
+        .iov_len = data.len,
+    }});
+    const start = header_offset + 6 + name.len + getULEB128Size(@intCast(u32, name.len));
+    log.debug("Emit debug section: '{s}' start=0x{x:0>8} end=0x{x:0>8}", .{ name, start, start + data.len });
+
+    try writeCustomSectionHeader(
+        file,
+        header_offset,
+        @intCast(u32, (try file.getPos()) - header_offset - 6),
+    );
+}
+
 fn emitNameSection(self: *Wasm, file: fs.File, arena: Allocator) !void {
     const Name = struct {
         index: u32,