From 241180216f92c86f833910d73e1c86f54ae940e4 Mon Sep 17 00:00:00 2001
From: Luuk de Gram <luuk@degram.dev>
Date: Fri, 27 May 2022 19:31:34 +0200
Subject: [PATCH] wasm-linker: Parse object file from the archive

Rather than finding the original object file, we seekTo to the
object file's position within the archive file, and from there open
a new file handle. This file handle is passed to the `Object` parser
which will create the object.
---
 src/link/Wasm/Archive.zig | 15 ++++++++-------
 src/link/Wasm/Object.zig  |  7 ++++---
 2 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/src/link/Wasm/Archive.zig b/src/link/Wasm/Archive.zig
index 9169a7effa..e214d1b124 100644
--- a/src/link/Wasm/Archive.zig
+++ b/src/link/Wasm/Archive.zig
@@ -181,6 +181,8 @@ pub fn parseObject(self: Archive, allocator: Allocator, file_offset: u32) !Objec
     try self.file.seekTo(file_offset);
     const reader = self.file.reader();
     const header = try reader.readStruct(ar_hdr);
+    const current_offset = try self.file.getPos();
+    try self.file.seekTo(0);
 
     if (!mem.eql(u8, &header.ar_fmag, ARFMAG)) {
         log.err("invalid header delimiter: expected '{s}', found '{s}'", .{ ARFMAG, header.ar_fmag });
@@ -191,16 +193,15 @@ pub fn parseObject(self: Archive, allocator: Allocator, file_offset: u32) !Objec
     defer allocator.free(object_name);
 
     const name = name: {
-        if (object_name.len == 0) {
-            break :name try std.fmt.allocPrint(allocator, "{s}.o", .{self.name});
-        }
-        const base_path = std.fs.path.dirname(self.name);
-        break :name try std.fmt.allocPrint(allocator, "{s}/{s}.o", .{ base_path, object_name });
+        var buffer: [std.fs.MAX_PATH_BYTES]u8 = undefined;
+        const path = try std.os.realpath(self.name, &buffer);
+        break :name try std.fmt.allocPrint(allocator, "{s}({s})", .{ path, object_name });
     };
+    defer allocator.free(name);
 
-    log.debug(" parsing object file '{s}' from archive\n", .{name});
-    const object_file = try std.fs.cwd().openFile(name, .{});
+    const object_file = try std.fs.cwd().openFile(self.name, .{});
     errdefer object_file.close();
 
+    try object_file.seekTo(current_offset);
     return Object.create(allocator, object_file, name);
 }
diff --git a/src/link/Wasm/Object.zig b/src/link/Wasm/Object.zig
index 6fa451af09..9dba838d27 100644
--- a/src/link/Wasm/Object.zig
+++ b/src/link/Wasm/Object.zig
@@ -68,7 +68,7 @@ string_table: Wasm.StringTable = .{},
 const RelocatableData = struct {
     /// The type of the relocatable data
     type: enum { data, code, custom },
-    /// Pointer to the data of the segment, where it's length is written to `size`
+    /// Pointer to the data of the segment, where its length is written to `size`
     data: [*]u8,
     /// The size in bytes of the data representing the segment within the section
     size: u32,
@@ -105,10 +105,10 @@ pub const InitError = error{NotObjectFile} || ParseError || std.fs.File.ReadErro
 
 /// Initializes a new `Object` from a wasm object file.
 /// This also parses and verifies the object file.
-pub fn create(gpa: Allocator, file: std.fs.File, path: []const u8) InitError!Object {
+pub fn create(gpa: Allocator, file: std.fs.File, name: []const u8) InitError!Object {
     var object: Object = .{
         .file = file,
-        .name = path,
+        .name = try gpa.dupe(u8, name),
     };
 
     var is_object_file: bool = false;
@@ -154,6 +154,7 @@ pub fn deinit(self: *Object, gpa: Allocator) void {
     }
     gpa.free(self.relocatable_data);
     self.string_table.deinit(gpa);
+    gpa.free(self.name);
     self.* = undefined;
 }