elf: resolve and write objects to file

src/arch/x86_64/Emit.zig

@@ -45,7 +45,7 @@ pub fn emitMir(emit: *Emit) Error!void {
                     // Add relocation to the decl.
                     const atom_ptr = elf_file.symbol(symbol.atom_index).atom(elf_file).?;
                     try atom_ptr.addReloc(elf_file, .{
-                        .r_offset = end_offset,
+                        .r_offset = end_offset - 4,
                         .r_info = (@as(u64, @intCast(symbol.sym_index)) << 32) | std.elf.R_X86_64_PLT32,
                         .r_addend = -4,
                     });

src/link/Elf.zig

@@ -1072,6 +1072,7 @@ pub fn flushModule(self: *Elf, comp: *Compilation, prog_node: *std.Progress.Node
             try self.base.file.?.pwriteAll(code, file_offset);
         }
     }
+    try self.writeObjects();
 
     try self.updateSymtabSize();
     try self.writeSymtab();
@@ -1414,6 +1415,13 @@ fn allocateObjects(self: *Elf) !void {
             try atom_ptr.allocate(self);
         }
 
+        for (object.locals()) |local_index| {
+            const local = self.symbol(local_index);
+            const atom_ptr = local.atom(self) orelse continue;
+            if (!atom_ptr.alive) continue;
+            local.value = atom_ptr.value;
+        }
+
         for (object.globals()) |global_index| {
             const global = self.symbol(global_index);
             if (global.file_index == index) {
@@ -1423,6 +1431,26 @@ fn allocateObjects(self: *Elf) !void {
     }
 }
 
+fn writeObjects(self: *Elf) !void {
+    const gpa = self.base.allocator;
+
+    for (self.objects.items) |index| {
+        const object = self.file(index).?.object;
+        for (object.atoms.items) |atom_index| {
+            const atom_ptr = self.atom(atom_index) orelse continue;
+            if (!atom_ptr.alive) continue;
+
+            const shdr = &self.shdrs.items[atom_ptr.output_section_index];
+            const file_offset = shdr.sh_offset + atom_ptr.value - shdr.sh_addr;
+            const code = try atom_ptr.codeInObjectUncompressAlloc(self);
+            defer gpa.free(code);
+
+            try atom_ptr.resolveRelocs(self, code);
+            try self.base.file.?.pwriteAll(code, file_offset);
+        }
+    }
+}
+
 fn linkWithLLD(self: *Elf, comp: *Compilation, prog_node: *std.Progress.Node) !void {
     const tracy = trace(@src());
     defer tracy.end();

src/link/Elf/Atom.zig

@@ -67,12 +67,13 @@ pub fn codeInObjectUncompressAlloc(self: Atom, elf_file: *Elf) ![]u8 {
         switch (chdr.ch_type) {
             .ZLIB => {
                 var stream = std.io.fixedBufferStream(data[@sizeOf(elf.Elf64_Chdr)..]);
-                var zlib_stream = try std.compress.zlib.decompressStream(gpa, stream.reader());
+                var zlib_stream = std.compress.zlib.decompressStream(gpa, stream.reader()) catch
+                    return error.InputOutput;
                 defer zlib_stream.deinit();
                 const decomp = try gpa.alloc(u8, chdr.ch_size);
-                const nread = try zlib_stream.reader().readAll(decomp);
+                const nread = zlib_stream.reader().readAll(decomp) catch return error.InputOutput;
                 if (nread != decomp.len) {
-                    return error.Io;
+                    return error.InputOutput;
                 }
                 return decomp;
             },
@@ -366,6 +367,7 @@ pub fn scanRelocs(self: Atom, elf_file: *Elf) !void {
 pub fn resolveRelocs(self: Atom, elf_file: *Elf, code: []u8) !void {
     relocs_log.debug("0x{x}: {s}", .{ self.value, self.name(elf_file) });
 
+    const file_ptr = elf_file.file(self.file_index).?;
     var stream = std.io.fixedBufferStream(code);
     const cwriter = stream.writer();
 
@@ -373,7 +375,11 @@ pub fn resolveRelocs(self: Atom, elf_file: *Elf, code: []u8) !void {
         const r_type = rel.r_type();
         if (r_type == elf.R_X86_64_NONE) continue;
 
-        const target = elf_file.symbol(rel.r_sym());
+        const target = switch (file_ptr) {
+            .zig_module => elf_file.symbol(rel.r_sym()),
+            .object => |x| elf_file.symbol(x.symbols.items[rel.r_sym()]),
+            else => unreachable,
+        };
 
         // We will use equation format to resolve relocations:
         // https://intezer.com/blog/malware-analysis/executable-and-linkable-format-101-part-3-relocations/
@@ -414,9 +420,17 @@ pub fn resolveRelocs(self: Atom, elf_file: *Elf, code: []u8) !void {
 
         switch (rel.r_type()) {
             elf.R_X86_64_NONE => unreachable,
+
             elf.R_X86_64_64 => try cwriter.writeIntLittle(i64, S + A),
-            elf.R_X86_64_PLT32 => try cwriter.writeIntLittle(i32, @as(i32, @intCast(S + A - P))),
-            else => @panic("TODO"),
+
+            elf.R_X86_64_PLT32,
+            elf.R_X86_64_PC32,
+            => try cwriter.writeIntLittle(i32, @as(i32, @intCast(S + A - P))),
+
+            else => {
+                log.err("TODO: unhandled relocation type {}", .{fmtRelocType(rel.r_type())});
+                @panic("TODO unhandled relocation type");
+            },
         }
     }
 }

src/link/Elf/Object.zig

@@ -270,6 +270,10 @@ fn initSymtab(self: *Object, elf_file: *Elf) !void {
         sym_ptr.esym_index = @as(u32, @intCast(i));
         sym_ptr.atom_index = if (sym.st_shndx == elf.SHN_ABS) 0 else self.atoms.items[sym.st_shndx];
         sym_ptr.file_index = self.index;
+        sym_ptr.output_section_index = if (sym_ptr.atom(elf_file)) |atom_ptr|
+            atom_ptr.output_section_index
+        else
+            0;
     }
 
     for (self.symtab[first_global..]) |sym| {