CLI: add support for -fno-builtin

src/Compilation.zig

@@ -825,6 +825,7 @@ pub const InitOptions = struct {
     rdynamic: bool = false,
     strip: bool = false,
     function_sections: bool = false,
+    no_builtin: bool = false,
     is_native_os: bool,
     is_native_abi: bool,
     time_report: bool = false,
@@ -1351,6 +1352,7 @@ pub fn create(gpa: Allocator, options: InitOptions) !*Compilation {
         cache.hash.add(omit_frame_pointer);
         cache.hash.add(link_mode);
         cache.hash.add(options.function_sections);
+        cache.hash.add(options.no_builtin);
         cache.hash.add(strip);
         cache.hash.add(link_libc);
         cache.hash.add(link_libcpp);
@@ -1682,6 +1684,7 @@ pub fn create(gpa: Allocator, options: InitOptions) !*Compilation {
             .is_native_os = options.is_native_os,
             .is_native_abi = options.is_native_abi,
             .function_sections = options.function_sections,
+            .no_builtin = options.no_builtin,
             .allow_shlib_undefined = options.linker_allow_shlib_undefined,
             .bind_global_refs_locally = options.linker_bind_global_refs_locally orelse false,
             .import_memory = options.linker_import_memory orelse false,
@@ -3925,6 +3928,10 @@ pub fn addCCArgs(
         try argv.append("-ffunction-sections");
     }
 
+    if (comp.bin_file.options.no_builtin) {
+        try argv.append("-fno-builtin");
+    }
+
     if (comp.bin_file.options.link_libcpp) {
         const libcxx_include_path = try std.fs.path.join(arena, &[_][]const u8{
             comp.zig_lib_directory.path.?, "libcxx", "include",
@@ -4997,6 +5004,7 @@ fn buildOutputFromZig(
         .optimize_mode = comp.compilerRtOptMode(),
         .link_mode = .Static,
         .function_sections = true,
+        .no_builtin = true,
         .want_sanitize_c = false,
         .want_stack_check = false,
         .want_red_zone = comp.bin_file.options.red_zone,

src/clang_options_data.zig

@@ -2529,7 +2529,14 @@ flagpd1("fborland-extensions"),
 flagpd1("fbounds-check"),
 sepd1("fbracket-depth"),
 flagpd1("fbranch-count-reg"),
-flagpd1("fbuiltin"),
+.{
+    .name = "fbuiltin",
+    .syntax = .flag,
+    .zig_equivalent = .builtin,
+    .pd1 = true,
+    .pd2 = false,
+    .psl = false,
+},
 flagpd1("fbuiltin-module-map"),
 flagpd1("fcall-saved-x10"),
 flagpd1("fcall-saved-x11"),
@@ -2925,7 +2932,14 @@ flagpd1("fno-blocks"),
 flagpd1("fno-borland-extensions"),
 flagpd1("fno-bounds-check"),
 flagpd1("fno-branch-count-reg"),
-flagpd1("fno-builtin"),
+.{
+    .name = "fno-builtin",
+    .syntax = .flag,
+    .zig_equivalent = .no_builtin,
+    .pd1 = true,
+    .pd2 = false,
+    .psl = false,
+},
 flagpd1("fno-caller-saves"),
 .{
     .name = "fno-caret-diagnostics",

src/codegen/llvm.zig

@@ -2347,7 +2347,9 @@ pub const DeclGen = struct {
         if (comp.unwind_tables) {
             dg.addFnAttr(llvm_fn, "uwtable");
         }
-        if (comp.bin_file.options.skip_linker_dependencies) {
+        if (comp.bin_file.options.skip_linker_dependencies or
+            comp.bin_file.options.no_builtin)
+        {
             // The intent here is for compiler-rt and libc functions to not generate
             // infinite recursion. For example, if we are compiling the memcpy function,
             // and llvm detects that the body is equivalent to memcpy, it may replace the

src/link.zig

@@ -108,6 +108,7 @@ pub const Options = struct {
     link_libcpp: bool,
     link_libunwind: bool,
     function_sections: bool,
+    no_builtin: bool,
     eh_frame_hdr: bool,
     emit_relocs: bool,
     rdynamic: bool,

src/main.zig

@@ -381,6 +381,10 @@ const usage_build_generic =
     \\  -fno-stage1               Prevent using bootstrap compiler as the codegen backend
     \\  -fsingle-threaded         Code assumes there is only one thread
     \\  -fno-single-threaded      Code may not assume there is only one thread
+    \\  -fbuiltin                 Enable implicit builtin knowledge of functions
+    \\  -fno-builtin              Disable implicit builtin knowledge of functions
+    \\  -ffunction-sections       Places each function in a separate section
+    \\  -fno-function-sections    All functions go into same section
     \\  --strip                   Omit debug symbols
     \\  -ofmt=[mode]              Override target object format
     \\    elf                     Executable and Linking Format
@@ -398,7 +402,6 @@ const usage_build_generic =
     \\  -D[macro]=[value]         Define C [macro] to [value] (1 if [value] omitted)
     \\  --libc [file]             Provide a file which specifies libc paths
     \\  -cflags [flags] --        Set extra flags for the next positional C source files
-    \\  -ffunction-sections       Places each function in a separate section
     \\
     \\Link Options:
     \\  -l[lib], --library [lib]       Link against system library (only if actually used)
@@ -604,6 +607,7 @@ fn buildOutputType(
     var compatibility_version: ?std.builtin.Version = null;
     var strip = false;
     var function_sections = false;
+    var no_builtin = false;
     var watch = false;
     var debug_compile_errors = false;
     var verbose_link = std.process.hasEnvVarConstant("ZIG_VERBOSE_LINK");
@@ -1241,6 +1245,12 @@ fn buildOutputType(
                         single_threaded = false;
                     } else if (mem.eql(u8, arg, "-ffunction-sections")) {
                         function_sections = true;
+                    } else if (mem.eql(u8, arg, "-fno-function-sections")) {
+                        function_sections = false;
+                    } else if (mem.eql(u8, arg, "-fbuiltin")) {
+                        no_builtin = false;
+                    } else if (mem.eql(u8, arg, "-fno-builtin")) {
+                        no_builtin = true;
                     } else if (mem.eql(u8, arg, "--eh-frame-hdr")) {
                         link_eh_frame_hdr = true;
                     } else if (mem.eql(u8, arg, "--emit-relocs")) {
@@ -1464,6 +1474,8 @@ fn buildOutputType(
                     .no_omit_frame_pointer => omit_frame_pointer = false,
                     .function_sections => function_sections = true,
                     .no_function_sections => function_sections = false,
+                    .builtin => no_builtin = false,
+                    .no_builtin => no_builtin = true,
                     .color_diagnostics => color = .on,
                     .no_color_diagnostics => color = .off,
                     .stack_check => want_stack_check = true,
@@ -2847,6 +2859,7 @@ fn buildOutputType(
         .strip = strip,
         .single_threaded = single_threaded,
         .function_sections = function_sections,
+        .no_builtin = no_builtin,
         .self_exe_path = self_exe_path,
         .thread_pool = &thread_pool,
         .clang_passthrough_mode = clang_passthrough_mode,
@@ -4572,6 +4585,8 @@ pub const ClangArgIterator = struct {
         no_omit_frame_pointer,
         function_sections,
         no_function_sections,
+        builtin,
+        no_builtin,
         color_diagnostics,
         no_color_diagnostics,
         stack_check,

tools/update_clang_options.zig

@@ -320,6 +320,14 @@ const known_options = [_]KnownOpt{
         .name = "fno-function-sections",
         .ident = "no_function_sections",
     },
+    .{
+        .name = "fbuiltin",
+        .ident = "builtin",
+    },
+    .{
+        .name = "fno-builtin",
+        .ident = "no_builtin",
+    },
     .{
         .name = "fcolor-diagnostics",
         .ident = "color_diagnostics",