Merge pull request #17815 from Luukdegram/wasm-no-entry

wasm-linker: implement `-fno-entry` and correctly pass `--shared` and `--pie` when given

1 files changed, 54 insertions, 3 deletions

diff --git a/src/main.zig b/src/main.zig
index 385067f703..eb613a65f2 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -519,7 +519,9 @@ const usage_build_generic =
     \\  --dynamic-linker [path]        Set the dynamic interpreter path (usually ld.so)
     \\  --sysroot [path]               Set the system root directory (usually /)
     \\  --version [ver]                Dynamic library semver
-    \\  --entry [name]                 Set the entrypoint symbol name
+    \\  -fentry                        Enable entry point with default symbol name
+    \\  -fentry=[name]                 Override the entry point symbol name
+    \\  -fno-entry                     Do not output any entry point
     \\  --force_undefined [name]       Specify the symbol must be defined for the link to succeed
     \\  -fsoname[=name]                Override the default SONAME value
     \\  -fno-soname                    Disable emitting a SONAME
@@ -845,6 +847,7 @@ fn buildOutputType(
     var linker_import_symbols: bool = false;
     var linker_import_table: bool = false;
     var linker_export_table: bool = false;
+    var linker_force_entry: ?bool = null;
     var linker_initial_memory: ?u64 = null;
     var linker_max_memory: ?u64 = null;
     var linker_shared_memory: bool = false;
@@ -1081,8 +1084,8 @@ fn buildOutputType(
                         subsystem = try parseSubSystem(args_iter.nextOrFatal());
                     } else if (mem.eql(u8, arg, "-O")) {
                         optimize_mode_string = args_iter.nextOrFatal();
-                    } else if (mem.eql(u8, arg, "--entry")) {
-                        entry = args_iter.nextOrFatal();
+                    } else if (mem.startsWith(u8, arg, "-fentry=")) {
+                        entry = arg["-fentry=".len..];
                     } else if (mem.eql(u8, arg, "--force_undefined")) {
                         try force_undefined_symbols.put(gpa, args_iter.nextOrFatal(), {});
                     } else if (mem.eql(u8, arg, "--stack")) {
@@ -1513,6 +1516,10 @@ fn buildOutputType(
                         }
                     } else if (mem.eql(u8, arg, "--import-memory")) {
                         linker_import_memory = true;
+                    } else if (mem.eql(u8, arg, "-fentry")) {
+                        linker_force_entry = true;
+                    } else if (mem.eql(u8, arg, "-fno-entry")) {
+                        linker_force_entry = false;
                     } else if (mem.eql(u8, arg, "--export-memory")) {
                         linker_export_memory = true;
                     } else if (mem.eql(u8, arg, "--import-symbols")) {
@@ -2144,6 +2151,8 @@ fn buildOutputType(
                     linker_import_table = true;
                 } else if (mem.eql(u8, arg, "--export-table")) {
                     linker_export_table = true;
+                } else if (mem.eql(u8, arg, "--no-entry")) {
+                    linker_force_entry = false;
                 } else if (mem.eql(u8, arg, "--initial-memory")) {
                     const next_arg = linker_args_it.nextOrFatal();
                     linker_initial_memory = std.fmt.parseUnsigned(u32, eatIntPrefix(next_arg, 16), 16) catch |err| {
@@ -2606,6 +2615,23 @@ fn buildOutputType(
             link_libcpp = true;
     }
 
+    if (linker_force_entry) |force| {
+        if (!force) {
+            entry = null;
+        } else if (entry == null and output_mode == .Exe) {
+            entry = switch (target_info.target.ofmt) {
+                .coff => "wWinMainCRTStartup",
+                .macho => "_main",
+                .elf, .plan9 => "_start",
+                .wasm => defaultWasmEntryName(wasi_exec_model),
+                else => |tag| fatal("No default entry point available for output format {s}", .{@tagName(tag)}),
+            };
+        }
+    } else if (entry == null and target_info.target.isWasm() and output_mode == .Exe) {
+        // For WebAssembly the compiler defaults to setting the entry name when no flags are set.
+        entry = defaultWasmEntryName(wasi_exec_model);
+    }
+
     if (target_info.target.ofmt == .coff) {
         // Now that we know the target supports resources,
         // we can add the res files as link objects.
@@ -2628,6 +2654,23 @@ fn buildOutputType(
         if (single_threaded == null) {
             single_threaded = true;
         }
+        if (link_mode) |mode| {
+            if (mode == .Dynamic) {
+                if (linker_export_memory != null and linker_export_memory.?) {
+                    fatal("flags '-dynamic' and '--export-memory' are incompatible", .{});
+                }
+                // User did not supply `--export-memory` which is incompatible with -dynamic, therefore
+                // set the flag to false to ensure it does not get enabled by default.
+                linker_export_memory = false;
+            }
+        }
+        if (wasi_exec_model != null and wasi_exec_model.? == .reactor) {
+            if (entry) |entry_name| {
+                if (!mem.eql(u8, "_initialize", entry_name)) {
+                    fatal("the entry symbol of the reactor model must be '_initialize', but found '{s}'", .{entry_name});
+                }
+            }
+        }
         if (linker_shared_memory) {
             if (output_mode == .Obj) {
                 fatal("shared memory is not allowed in object files", .{});
@@ -7225,3 +7268,11 @@ fn createDependenciesModule(
     try main_mod.deps.put(arena, "@dependencies", deps_mod);
     return deps_mod;
 }
+
+fn defaultWasmEntryName(exec_model: ?std.builtin.WasiExecModel) []const u8 {
+    const model = exec_model orelse .command;
+    if (model == .reactor) {
+        return "_initialize";
+    }
+    return "_start";
+}