[libc][bazel] Mark all libc public functions to have "default" visibility.

[sivachandra]

Summary

For the bazel build, we also build all source files with
-fvisibility=hidden.

[gchatelet]

libc/src/__support/common.h

25

Since we're carefully defining it in the build system I think it makes sense to err if the attribute is not defined otherwise it's complicated to reason about it and debug.

#error make sure that LLVM_LIBC_FUNCTION_ATTR is defined in either CMake of Bazel configuration

Then we'd need the same logic in CMake.

utils/bazel/llvm-project-overlay/libc/libc_build_rules.bzl

51

Thx!

81

This should be a defines attribute I think (and above as well)
https://bazel.build/reference/be/c-cpp#cc_binary.defines

[sivachandra]

• Confine the change to bazel.
• Use local_defines instead of copts to pass preprocessor defines.

[sivachandra]

PTAL

libc/src/__support/common.h

25

I removed this change now - we will keep the definition of the macro up to the individual build system. The "default" visibility thing is now added only for Bazel.

utils/bazel/llvm-project-overlay/libc/libc_build_rules.bzl

81

I moved all preprocessor defines to local_defines now.

libc/src/__support/common.h

 #ifndef unlikely
 #define unlikely(x) __builtin_expect(x, 0)
 #endif
 #ifndef UNUSED
 #define UNUSED __attribute__((unused))
 #endif
 
 #ifndef LLVM_LIBC_FUNCTION_ATTR
-#define LLVM_LIBC_FUNCTION_ATTR
+#define LLVM_LIBC_FUNCTION_ATTR __attribute__((visibility("default")))
 #endif
 
 // We use OpenMP to declare these functions on the device.
 #define STR(X) #X
 #define LLVM_LIBC_DECLARE_DEVICE(name)                                         \
   _Pragma(STR(omp declare target to(name) device_type(nohost)))
 
 // GPU targets do not support aliasing and must be declared on the device.

utils/bazel/llvm-project-overlay/libc/BUILD.bazel

 # This file is licensed under the Apache License v2.0 with LLVM Exceptions.
 # See https://llvm.org/LICENSE.txt for license information.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 # LLVM libc project.
-load(":libc_build_rules.bzl", "libc_function", "libc_math_function")
+load(":libc_build_rules.bzl", "libc_function", "libc_math_function",
+     "libc_support_library")
 load(":platforms.bzl", "PLATFORM_CPU_ARM64", "PLATFORM_CPU_X86_64")
 load("@bazel_skylib//lib:selects.bzl", "selects")
 load("@bazel_skylib//rules:common_settings.bzl", "string_flag")
 
 package(
     default_visibility = ["//visibility:public"],
     features = ["-use_header_modules"],
 )

 # paths of the kind "../../" to other libc targets.
 cc_library(
     name = "libc_root",
     includes = ["."],
 )
 
 ############################## Support libraries #############################
 
-cc_library(
+libc_support_library(
     name = "__support_common",
     hdrs = [
         "src/__support/architectures.h",
         "src/__support/common.h",
         "src/__support/endian.h",
         "src/__support/sanitizer.h",
     ],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_cpp_array",
     hdrs = ["src/__support/CPP/array.h"],
     deps = [":libc_root"],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_cpp_bit",
     hdrs = ["src/__support/CPP/bit.h"],
     deps = [":libc_root"],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_cpp_bitset",
     hdrs = ["src/__support/CPP/bitset.h"],
     deps = [":libc_root"],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_cpp_cstddef",
     hdrs = ["src/__support/CPP/cstddef.h"],
     deps = [
         "__support_cpp_type_traits",
         ":libc_root",
     ],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_cpp_functional",
     hdrs = ["src/__support/CPP/functional.h"],
     deps = [":libc_root"],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_cpp_limits",
     hdrs = ["src/__support/CPP/limits.h"],
     deps = [":libc_root"],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_cpp_optional",
     hdrs = ["src/__support/CPP/optional.h"],
     deps = [":libc_root"],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_cpp_span",
     hdrs = ["src/__support/CPP/span.h"],
     deps = [
         "__support_cpp_array",
         "__support_cpp_type_traits",
         ":libc_root",
     ],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_cpp_string_view",
     hdrs = ["src/__support/CPP/string_view.h"],
     deps = [":libc_root"],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_cpp_type_traits",
     hdrs = ["src/__support/CPP/type_traits.h"],
     deps = [":libc_root"],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_cpp_utility",
     hdrs = ["src/__support/CPP/utility.h"],
     deps = [
         ":__support_cpp_type_traits",
         ":libc_root",
     ],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_cpp_vector",
     hdrs = ["src/__support/CPP/vector.h"],
     deps = [":libc_root"],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_cpp_atomic",
     hdrs = ["src/__support/CPP/atomic.h"],
     deps = [
         ":__support_cpp_type_traits",
         ":libc_root",
     ],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_number_pair",
     hdrs = ["src/__support/number_pair.h"],
     deps = [
         "__support_cpp_type_traits",
         "__support_named_pair",
         ":libc_root",
     ],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_integer_utils",
     hdrs = ["src/__support/integer_utils.h"],
     deps = [
         "__support_builtin_wrappers",
         "__support_cpp_type_traits",
         "__support_number_pair",
         ":libc_root",
     ],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_uint",
     hdrs = ["src/__support/UInt.h"],
     deps = [
         "__support_builtin_wrappers",
         "__support_cpp_array",
         "__support_cpp_limits",
         "__support_cpp_optional",
         "__support_cpp_type_traits",
         "__support_integer_utils",
         "__support_number_pair",
         ":libc_root",
     ],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_uint128",
     hdrs = ["src/__support/UInt128.h"],
     deps = [
         ":__support_uint",
         ":libc_root",
     ],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_integer_operations",
     hdrs = ["src/__support/integer_operations.h"],
     deps = [":__support_cpp_type_traits"],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_ctype_utils",
     hdrs = ["src/__support/ctype_utils.h"],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_str_to_integer",
     hdrs = ["src/__support/str_to_integer.h"],
     deps = [
         ":__support_cpp_limits",
         ":__support_ctype_utils",
     ],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_fputil_basic_operations",
     hdrs = ["src/__support/FPUtil/BasicOperations.h"],
     deps = [
         ":__support_cpp_type_traits",
         ":__support_fputil_fp_bits",
         ":libc_root",
     ],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_named_pair",
     hdrs = ["src/__support/named_pair.h"],
     deps = [":libc_root"],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_builtin_wrappers",
     hdrs = ["src/__support/builtin_wrappers.h"],
     deps = [
         ":__support_cpp_type_traits",
         ":__support_named_pair",
         ":libc_root",
     ],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_fputil_division_and_remainder_operations",
     hdrs = ["src/__support/FPUtil/DivisionAndRemainderOperations.h"],
     deps = [
         ":__support_cpp_type_traits",
         ":__support_fputil_fp_bits",
         ":__support_fputil_manipulation_functions",
         ":__support_fputil_normal_float",
         ":libc_root",
     ],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_fputil_except_value_utils",
     hdrs = ["src/__support/FPUtil/except_value_utils.h"],
     deps = [
         ":__support_cpp_optional",
         ":__support_fputil_fenv_impl",
         ":__support_fputil_fp_bits",
         ":libc_root",
     ],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_fputil_fenv_impl",
     hdrs = ["src/__support/FPUtil/FEnvImpl.h"],
     textual_hdrs = [
         "src/__support/FPUtil/x86_64/FEnvImpl.h",
         "src/__support/FPUtil/aarch64/FEnvImpl.h",
         "src/__support/FPUtil/aarch64/fenv_darwin_impl.h",
     ],
     deps = [
         ":__support_common",
         ":__support_fputil_fp_bits",
         ":libc_root",
     ],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_fputil_float_properties",
     hdrs = ["src/__support/FPUtil/FloatProperties.h"],
     deps = [
         ":__support_fputil_platform_defs",
         ":__support_uint128",
         ":libc_root",
     ],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_fputil_fp_bits",
     hdrs = ["src/__support/FPUtil/FPBits.h"],
     textual_hdrs = ["src/__support/FPUtil/x86_64/LongDoubleBits.h"],
     deps = [
         ":__support_builtin_wrappers",
         ":__support_common",
         ":__support_cpp_bit",
         ":__support_cpp_type_traits",
         ":__support_fputil_float_properties",
         ":__support_fputil_platform_defs",
         ":__support_uint128",
         ":libc_root",
     ],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_fputil_hypot",
     hdrs = ["src/__support/FPUtil/Hypot.h"],
     deps = [
         ":__support_builtin_wrappers",
         ":__support_cpp_bit",
         ":__support_cpp_type_traits",
         ":__support_fputil_basic_operations",
         ":__support_fputil_fenv_impl",
         ":__support_fputil_fp_bits",
         ":__support_uint128",
         ":libc_root",
     ],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_fputil_manipulation_functions",
     hdrs = ["src/__support/FPUtil/ManipulationFunctions.h"],
     textual_hdrs = ["src/__support/FPUtil/x86_64/NextAfterLongDouble.h"],
     deps = [
         ":__support_common",
         ":__support_cpp_bit",
         ":__support_cpp_type_traits",
         ":__support_fputil_fp_bits",
         ":__support_fputil_nearest_integer_operations",
         ":__support_fputil_normal_float",
         ":__support_fputil_platform_defs",
         ":__support_uint128",
         ":libc_root",
     ],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_fputil_nearest_integer_operations",
     hdrs = ["src/__support/FPUtil/NearestIntegerOperations.h"],
     deps = [
         ":__support_cpp_type_traits",
         ":__support_fputil_fenv_impl",
         ":__support_fputil_fp_bits",
         ":libc_root",
     ],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_fputil_normal_float",
     hdrs = ["src/__support/FPUtil/NormalFloat.h"],
     deps = [
         ":__support_cpp_type_traits",
         ":__support_fputil_fp_bits",
         ":libc_root",
     ],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_fputil_platform_defs",
     hdrs = ["src/__support/FPUtil/PlatformDefs.h"],
     deps = [
         ":__support_common",
         ":libc_root",
     ],
 )
 
 sqrt_common_hdrs = [
     "src/__support/FPUtil/sqrt.h",
     "src/__support/FPUtil/generic/sqrt.h",
     "src/__support/FPUtil/generic/sqrt_80_bit_long_double.h",
 ]
 
 sqrt_hdrs = selects.with_or({
     "//conditions:default": sqrt_common_hdrs,
     PLATFORM_CPU_X86_64: sqrt_common_hdrs + [
         "src/__support/FPUtil/x86_64/sqrt.h",
     ],
     PLATFORM_CPU_ARM64: sqrt_common_hdrs + [
         "src/__support/FPUtil/aarch64/sqrt.h",
     ],
 })
 
-cc_library(
+libc_support_library(
     name = "__support_fputil_sqrt",
     hdrs = sqrt_hdrs,
     deps = [
         ":__support_builtin_wrappers",
         ":__support_common",
         ":__support_cpp_bit",
         ":__support_cpp_type_traits",
         ":__support_fputil_fenv_impl",
fma_common_hdrs = [
     "src/__support/FPUtil/generic/FMA.h",
 ]
 
 fma_platform_hdrs = [
     "src/__support/FPUtil/x86_64/FMA.h",
     "src/__support/FPUtil/aarch64/FMA.h",
 ]
 
-cc_library(
+libc_support_library(
     name = "__support_fputil_fma",
     hdrs = fma_common_hdrs,
     # These are conditionally included and will #error out if the platform
     # doesn't support FMA, so they can't be compiled on their own.
     textual_hdrs = fma_platform_hdrs,
     deps = [
         ":__support_builtin_wrappers",
         ":__support_common",
         ":__support_cpp_bit",
         ":__support_cpp_type_traits",
         ":__support_fputil_fenv_impl",
         ":__support_fputil_float_properties",
         ":__support_fputil_fp_bits",
         ":__support_uint128",
         ":libc_root",
     ],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_fputil_multiply_add",
     hdrs = [
         "src/__support/FPUtil/multiply_add.h",
     ],
     deps = [
         ":__support_common",
         ":__support_fputil_fma",
     ],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_fputil_polyeval",
     hdrs = [
         "src/__support/FPUtil/PolyEval.h",
     ],
     deps = [
         ":__support_fputil_multiply_add",
     ],
 )
 
 nearest_integer_common_hdrs = [
     "src/__support/FPUtil/nearest_integer.h",
 ]
 
 nearest_integer_platform_hdrs = [
     "src/__support/FPUtil/x86_64/nearest_integer.h",
     "src/__support/FPUtil/aarch64/nearest_integer.h",
 ]
 
-cc_library(
+libc_support_library(
     name = "__support_fputil_nearest_integer",
     hdrs = nearest_integer_common_hdrs,
     # These are conditionally included and will #error out if the platform
     # doesn't support rounding instructions, so they can't be compiled on their
     # own.
     textual_hdrs = nearest_integer_platform_hdrs,
     deps = [
         ":__support_common",
         ":libc_root",
     ],
 )
 
-cc_library(
+libc_support_library(
     name = "__support_osutil",
     hdrs = ["src/__support/OSUtil/syscall.h"],
     textual_hdrs = [
         "src/__support/OSUtil/linux/syscall.h",
         "src/__support/OSUtil/linux/aarch64/syscall.h",
         "src/__support/OSUtil/linux/x86_64/syscall.h",
     ],
     deps = [
libc_function(
     deps = [
         ":__support_common",
         ":__support_fputil_fenv_impl",
     ],
 )
 
 ################################ math targets ################################
 
-cc_library(
+libc_support_library(
     name = "math_utils",
     srcs = ["src/math/generic/math_utils.cpp"],
     hdrs = ["src/math/generic/math_utils.h"],
     deps = [
         "__support_cpp_bit",
         "__support_cpp_type_traits",
         ":__support_common",
         ":libc_root",
     ],
 )
 
-cc_library(
+libc_support_library(
     name = "common_constants",
     srcs = ["src/math/generic/common_constants.cpp"],
     hdrs = ["src/math/generic/common_constants.h"],
     deps = [
         ":libc_root",
     ],
 )
 
-cc_library(
+libc_support_library(
     name = "range_reduction",
     hdrs = [
         "src/math/generic/range_reduction.h",
         "src/math/generic/range_reduction_fma.h",
     ],
     deps = [
         ":__support_fputil_fma",
         ":__support_fputil_fp_bits",
         ":__support_fputil_multiply_add",
         ":__support_fputil_nearest_integer",
         ":libc_root",
     ],
 )
 
-cc_library(
+libc_support_library(
     name = "sincosf_utils",
     hdrs = ["src/math/generic/sincosf_utils.h"],
     deps = [
         ":__support_common",
         ":__support_fputil_fp_bits",
         ":__support_fputil_polyeval",
         ":libc_root",
         ":range_reduction",

 
 no_sanitize_features = [
     "-asan",
     "-msan",
     "-tsan",
     "-ubsan",
 ]
 
-cc_library(
+libc_support_library(
     name = "string_memory_utils",
     hdrs = [
         "src/string/memory_utils/op_aarch64.h",
         "src/string/memory_utils/op_builtin.h",
         "src/string/memory_utils/op_generic.h",
         "src/string/memory_utils/op_x86.h",
         "src/string/memory_utils/utils.h",
     ],
deps = [
         ":__support_cpp_array",
         ":__support_cpp_bit",
         ":__support_cpp_cstddef",
         ":__support_cpp_type_traits",
         ":libc_root",
     ],
 )
 
-cc_library(
+libc_support_library(
     name = "string_utils",
     hdrs = ["src/string/string_utils.h"],
     deps = [
         ":__support_common",
         ":__support_cpp_bitset",
         ":libc_root",
         ":string_memory_utils",
     ],

utils/bazel/llvm-project-overlay/libc/libc_build_rules.bzl

 # This file is licensed under the Apache License v2.0 with LLVM Exceptions.
 # See https://llvm.org/LICENSE.txt for license information.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 """LLVM libc starlark rules for building individual functions."""
 
 load(":platforms.bzl", "PLATFORM_CPU_ARM64", "PLATFORM_CPU_X86_64")
 load("@bazel_skylib//lib:selects.bzl", "selects")
 
 LIBC_ROOT_TARGET = ":libc_root"
 INTERNAL_SUFFIX = ".__internal__"
 
+def _libc_library(name, copts = None, **kwargs):
+    """Internal macro to serve as a base for all other libc library rules.
+
+    Args:
+      name: Target name.
+      copts: The special compiler options for the target.
+      **kwargs: All other attributes relevant for the cc_library rule.
+    """
+    copts = copts or []
+    # We want all libc sources to be compiled with "hidden" visibility.
+    # The public symbols will be given "default" visibility explicitly.
+    # See src/__support/common.h for more information.
+    copts.append("-fvisibility=hidden")
+    native.cc_library(
+        name = name,
+        copts = copts,
+        linkstatic = 1,
+        **kwargs
+    )
+
+# A convenience var which should be used to list all libc support libraries.
+# Any library which does not define a public function should be listed with
+# libc_support_library.
+libc_support_library = _libc_library
+
 def libc_function(name, srcs, weak = False, deps = None, copts = None, **kwargs):
     """Add target for a libc function.
 
     The libc function is eventually available as a cc_library target by name
     "name". LLVM libc implementations of libc functions are in C++. So, this
     rule internally generates a C wrapper for the C++ implementation and adds
     it to the source list of the cc_library. This way, the C++ implementation
     and the C wrapper are both available in the cc_library.
 
     Args:
       name: Target name. It is normally the name of the function this target is
             for.
       srcs: The .cpp files which contain the function implementation.
-      weak: Whether the symbol is marked weak.
+      weak: Make the symbol corresponding to the libc function "weak".
       deps: The list of target dependencies if any.
       copts: The list of options to add to the C++ compilation command.
       **kwargs: Other attributes relevant for a cc_library. For example, deps.
     """
     deps = deps or []
     deps.append(LIBC_ROOT_TARGET)
     copts = copts or []
     copts.append("-O3")
native.cc_library(
         copts = copts,
         linkstatic = 1,
         **kwargs
     )
 
     # This second target is the llvm libc C function.
     copts.append("-DLLVM_LIBC_PUBLIC_PACKAGING")
     if weak:
-        copts.append("-DLLVM_LIBC_FUNCTION_ATTR=__attribute__((weak))")
-    native.cc_library(
+        # We want weak libc functions to also have default visibility. So,
+        # we will add the weak as well as the default visibility attribute.
+        weak_attr = "__attribute__((weak))"
+        default_vis = "__attribute__((visibility(\"default\")))"
+        copts.append("-DLLVM_LIBC_FUNCTION_ATTR='%s %s'" % (weak_attr, default_vis))
+    _libc_library(
         name = name,
         srcs = srcs,
         deps = deps,
         copts = copts,
-        linkstatic = 1,
         **kwargs
     )
 
 def libc_math_function(
         name,
         specializations = None,
         additional_deps = None):
     """Add a target for a math function.