lld: allow for entrypoint symbol name to be set

This commit enables for the entrypoint symbol to be set when linking ELF
or WebAssembly modules with lld using the Zig compiler.

7 files changed, 30 insertions, 0 deletions

diff --git a/src/Compilation.zig b/src/Compilation.zig
index c21bf71326..2c64657903 100644
--- a/src/Compilation.zig
+++ b/src/Compilation.zig
@@ -791,6 +791,7 @@ pub const InitOptions = struct {
     /// infinite recursion.
     skip_linker_dependencies: bool = false,
     parent_compilation_link_libc: bool = false,
+    entry: ?[]const u8 = null,
     stack_size_override: ?u64 = null,
     image_base_override: ?u64 = null,
     self_exe_path: ?[]const u8 = null,
@@ -1572,6 +1573,7 @@ pub fn create(gpa: Allocator, options: InitOptions) !*Compilation {
             .linker_optimization = linker_optimization,
             .major_subsystem_version = options.major_subsystem_version,
             .minor_subsystem_version = options.minor_subsystem_version,
+            .entry = options.entry,
             .stack_size_override = options.stack_size_override,
             .image_base_override = options.image_base_override,
             .include_compiler_rt = include_compiler_rt,
diff --git a/src/link.zig b/src/link.zig
index 3dc75c77e8..916dea0429 100644
--- a/src/link.zig
+++ b/src/link.zig
@@ -84,6 +84,7 @@ pub const Options = struct {
     /// the binary file does not already have such a section.
     program_code_size_hint: u64 = 256 * 1024,
     entry_addr: ?u64 = null,
+    entry: ?[]const u8,
     stack_size_override: ?u64,
     image_base_override: ?u64,
     cache_mode: CacheMode,
diff --git a/src/link/Coff.zig b/src/link/Coff.zig
index 26b8c78a28..b6ae8abcb1 100644
--- a/src/link/Coff.zig
+++ b/src/link/Coff.zig
@@ -951,6 +951,7 @@ fn linkWithLLD(self: *Coff, comp: *Compilation) !void {
             _ = try man.addFile(key.status.success.object_path, null);
         }
         try man.addOptionalFile(module_obj_path);
+        man.hash.addOptionalBytes(self.base.options.entry);
         man.hash.addOptional(self.base.options.stack_size_override);
         man.hash.addOptional(self.base.options.image_base_override);
         man.hash.addListOfBytes(self.base.options.lib_dirs);
diff --git a/src/link/Elf.zig b/src/link/Elf.zig
index d0f9d7851d..d675833ef2 100644
--- a/src/link/Elf.zig
+++ b/src/link/Elf.zig
@@ -1396,6 +1396,7 @@ fn linkWithLLD(self: *Elf, comp: *Compilation) !void {
 
         // We can skip hashing libc and libc++ components that we are in charge of building from Zig
         // installation sources because they are always a product of the compiler version + target information.
+        man.hash.addOptionalBytes(self.base.options.entry);
         man.hash.add(stack_size);
         man.hash.addOptional(self.base.options.image_base_override);
         man.hash.add(gc_sections);
@@ -1518,6 +1519,11 @@ fn linkWithLLD(self: *Elf, comp: *Compilation) !void {
             self.base.options.linker_optimization,
         }));
 
+        if (self.base.options.entry) |entry| {
+            try argv.append("--entry");
+            try argv.append(entry);
+        }
+
         if (self.base.options.output_mode == .Exe) {
             try argv.append("-z");
             try argv.append(try std.fmt.allocPrint(arena, "stack-size={d}", .{stack_size}));
diff --git a/src/link/MachO.zig b/src/link/MachO.zig
index 6335151bef..eaeb5265eb 100644
--- a/src/link/MachO.zig
+++ b/src/link/MachO.zig
@@ -509,6 +509,7 @@ pub fn flushModule(self: *MachO, comp: *Compilation) !void {
         try man.addOptionalFile(module_obj_path);
         // We can skip hashing libc and libc++ components that we are in charge of building from Zig
         // installation sources because they are always a product of the compiler version + target information.
+        man.hash.addOptionalBytes(self.base.options.entry);
         man.hash.add(stack_size);
         man.hash.addListOfBytes(self.base.options.lib_dirs);
         man.hash.addListOfBytes(self.base.options.framework_dirs);
diff --git a/src/link/Wasm.zig b/src/link/Wasm.zig
index 34723cdb27..e9ebb669fe 100644
--- a/src/link/Wasm.zig
+++ b/src/link/Wasm.zig
@@ -1137,6 +1137,7 @@ fn linkWithLLD(self: *Wasm, comp: *Compilation) !void {
         }
         try man.addOptionalFile(module_obj_path);
         try man.addOptionalFile(compiler_rt_path);
+        man.hash.addOptionalBytes(self.base.options.entry);
         man.hash.addOptional(self.base.options.stack_size_override);
         man.hash.add(self.base.options.import_memory);
         man.hash.add(self.base.options.import_table);
@@ -1295,6 +1296,11 @@ fn linkWithLLD(self: *Wasm, comp: *Compilation) !void {
             }
         }
 
+        if (self.base.options.entry) |entry| {
+            try argv.append("--entry");
+            try argv.append(entry);
+        }
+
         if (self.base.options.output_mode == .Exe) {
             // Increase the default stack size to a more reasonable value of 1MB instead of
             // the default of 1 Wasm page being 64KB, unless overridden by the user.
diff --git a/src/main.zig b/src/main.zig
index c924b14b69..3561315989 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -400,6 +400,7 @@ 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
     \\  -fsoname[=name]                Override the default SONAME value
     \\  -fno-soname                    Disable emitting a SONAME
     \\  -fLLD                          Force using LLD as the linker
@@ -647,6 +648,7 @@ fn buildOutputType(
     var linker_optimization: ?u8 = null;
     var test_evented_io = false;
     var test_no_exec = false;
+    var entry: ?[]const u8 = null;
     var stack_size_override: ?u64 = null;
     var image_base_override: ?u64 = null;
     var use_llvm: ?bool = null;
@@ -847,6 +849,10 @@ fn buildOutputType(
                         if (i + 1 >= args.len) fatal("expected parameter after {s}", .{arg});
                         i += 1;
                         optimize_mode_string = args[i];
+                    } else if (mem.eql(u8, arg, "--entry")) {
+                        if (i + 1 >= args.len) fatal("expected parameter after {s}", .{arg});
+                        i += 1;
+                        entry = args[i];
                     } else if (mem.eql(u8, arg, "--stack")) {
                         if (i + 1 >= args.len) fatal("expected parameter after {s}", .{arg});
                         i += 1;
@@ -1624,6 +1630,12 @@ fn buildOutputType(
                         fatal("unable to parse '{s}': {s}", .{ arg, @errorName(err) });
                     };
                     have_version = true;
+                } else if (mem.eql(u8, arg, "-e") or mem.eql(u8, arg, "--entry")) {
+                    i += 1;
+                    if (i >= linker_args.items.len) {
+                        fatal("expected linker arg after '{s}'", .{arg});
+                    }
+                    entry = linker_args.items[i];
                 } else if (mem.eql(u8, arg, "--stack")) {
                     i += 1;
                     if (i >= linker_args.items.len) {
@@ -2500,6 +2512,7 @@ fn buildOutputType(
         .minor_subsystem_version = minor_subsystem_version,
         .link_eh_frame_hdr = link_eh_frame_hdr,
         .link_emit_relocs = link_emit_relocs,
+        .entry = entry,
         .stack_size_override = stack_size_override,
         .image_base_override = image_base_override,
         .strip = strip,