link: give executable bit to wasm executables sometimes

Give +x to the .wasm file if it is an executable and the OS is WASI.
Some systems may be configured to execute such binaries directly. Even
if that is not the case, it means we will get "exec format error" when
trying to run it rather than "access denied", and then can react to that
in the same way as trying to run an ELF file from a foreign CPU
architecture.

This is part of the strategy to unify RunStep and EmulatableRunStep.

1 files changed, 27 insertions, 5 deletions

diff --git a/src/link/Wasm.zig b/src/link/Wasm.zig
index 00a52177f7..74525138a1 100644
--- a/src/link/Wasm.zig
+++ b/src/link/Wasm.zig
@@ -345,7 +345,17 @@ pub fn openPath(allocator: Allocator, sub_path: []const u8, options: link.Option
     }
 
     // TODO: read the file and keep valid parts instead of truncating
-    const file = try options.emit.?.directory.handle.createFile(sub_path, .{ .truncate = true, .read = true });
+    const file = try options.emit.?.directory.handle.createFile(sub_path, .{
+        .truncate = true,
+        .read = true,
+        .mode = if (fs.has_executable_bit)
+            if (options.target.os.tag == .wasi and options.output_mode == .Exe)
+                fs.File.default_mode | 0b001_000_000
+            else
+                fs.File.default_mode
+        else
+            0,
+    });
     wasm_bin.base.file = file;
     wasm_bin.name = sub_path;
 
@@ -3750,10 +3760,7 @@ fn linkWithLLD(wasm: *Wasm, comp: *Compilation, prog_node: *std.Progress.Node) !
         if (wasm.base.options.import_symbols) {
             try argv.append("--allow-undefined");
         }
-        try argv.appendSlice(&[_][]const u8{
-            "-o",
-            full_out_path,
-        });
+        try argv.appendSlice(&.{ "-o", full_out_path });
 
         if (target.cpu.arch == .wasm64) {
             try argv.append("-mwasm64");
@@ -3889,6 +3896,21 @@ fn linkWithLLD(wasm: *Wasm, comp: *Compilation, prog_node: *std.Progress.Node) !
                 }
             }
         }
+
+        // Give +x to the .wasm file if it is an executable and the OS is WASI.
+        // Some systems may be configured to execute such binaries directly. Even if that
+        // is not the case, it means we will get "exec format error" when trying to run
+        // it, and then can react to that in the same way as trying to run an ELF file
+        // from a foreign CPU architecture.
+        if (fs.has_executable_bit and target.os.tag == .wasi and
+            wasm.base.options.output_mode == .Exe)
+        {
+            // TODO: what's our strategy for reporting linker errors from this function?
+            // report a nice error here with the file path if it fails instead of
+            // just returning the error code.
+            // chmod does not interact with umask, so we use a conservative -rwxr--r-- here.
+            try std.os.fchmodat(fs.cwd().fd, full_out_path, 0o744, 0);
+        }
     }
 
     if (!wasm.base.options.disable_lld_caching) {