[libc] Add a library of low level utils.

[sivachandra]

• clang-format.

[abrachet]

Do these all belong in a linux specific directory? Wouldn't the two which aren't x86 specific be fine to put into libc/src/__support/?

Also, we should be weary of LTO inlining. I'm not entirely sure of the details here or how to force the linker to not inline these functions. It would certainly break all of these so it's worth looking into.

[sivachandra]

I did not finish this patch, but wrote just enough to make it understandable so that the main discussion about sanitizer instrumentation can proceed smoothly.

In D78611#1996187, @abrachet wrote:

Do these all belong in a linux specific directory? Wouldn't the two which aren't x86 specific be fine to put into libc/src/__support/?

The __builtin* functions are really clang/gcc specific. That is why I put them in a linux specific directory. May be in future they have to be grouped differently.

Also, we should be weary of LTO inlining. I'm not entirely sure of the details here or how to force the linker to not inline these functions. It would certainly break all of these so it's worth looking into.

Thanks for bringing this up. So yes, we need to add the noinline attribute to guarantee that these functions don't get inlined even under LTO. Will do this in the next update.

libc/config/linux/platform_lowlevel.cpp

13

Add noinline attribute.

libc/config/linux/x86_64/machine_lowlevel.cpp

13

Add noinline attribute.

libc/config/linux/CMakeLists.txt

 add_gen_header(
   linux_syscall_h
   DEF_FILE syscall.h.def
   GEN_HDR syscall.h
   PARAMS
     inline_syscalls=${LIBC_TARGET_MACHINE}/syscall.h.inc
   DATA_FILES
     ${LIBC_TARGET_MACHINE}/syscall.h.inc
   DEPENDS
     libc.src.__support.common
 )
 
+add_object_library(
+  lowlevel_utils
+  SRCS
+    ${LIBC_TARGET_MACHINE}/machine_lowlevel.cpp
+    platform_lowlevel.cpp
+  COMPILE_OPTIONS
+    # Some of the implementations assume presence of the frame
+    # pointer.
+    -fno-omit-frame-pointer
+)
+
 add_subdirectory(x86_64)

libc/config/linux/platform_lowlevel.h.inc

+//===-- Lowlevel Linux utilities --------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, 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
+//
+//===----------------------------------------------------------------------===//
+
+%%begin()
+
+#include <stdint.h>
+
+namespace __llvm_libc {
+
+static __attribute__((always_inline)) uintptr_t get_current_bp() {
+  return reinterpret_cast<uintptr_t>(__builtin_frame_address(0));
+}
+
+} // namespace llvm_libc

libc/config/linux/platform_lowlevel.cpp

+//===-- Implementation of machine independent low level utils -------------===//
+//
+// Part of the LLVM Project, 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
+//
+//===----------------------------------------------------------------------===//
+
+#include <stdint.h>
+
+namespace __llvm_libc {
+
+uintptr_t get_current_pc() {
+  return reinterpret_cast<uintptr_t>(
+      __builtin_extract_return_addr(__builtin_return_address(0)));
+}
+
+} // namespace __llvm_libc

libc/config/linux/x86_64/machine_lowlevel.cpp

+//===-- Implementation of x86_64 specific low level utils -----------------===//
+//
+// Part of the LLVM Project, 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
+//
+//===----------------------------------------------------------------------===//
+
+#include <stdint.h>
+
+namespace __llvm_libc {
+
+uintptr_t get_current_sp() {
+  uintptr_t *bp = reinterpret_cast<uintptr_t *>(__builtin_frame_address(0));
+  // If compiled with frame pointer, then the x86_64 ABI says ...
+  return reinterpret_cast<uintptr_t>(bp + 2);
+}
+
+} // namespace __llvm_libc

libc/src/CMakeLists.txt

+add_subdirectory(__support)
+
 add_subdirectory(assert)
 add_subdirectory(errno)
 add_subdirectory(math)
 add_subdirectory(signal)
 add_subdirectory(stdio)
 add_subdirectory(stdlib)
 add_subdirectory(string)
 # TODO: Add this target conditional to the target OS.
 add_subdirectory(sys)
 add_subdirectory(threads)
 add_subdirectory(unistd)
-
-add_subdirectory(__support)

libc/src/__support/CMakeLists.txt

 add_gen_header(
   common
   DEF_FILE common.h.def
   PARAMS
     platform_defs=../../config/${LIBC_TARGET_OS}/platfrom_defs.h.inc
   GEN_HDR common.h
   DATA_FILES
     ../../config/${LIBC_TARGET_OS}/platfrom_defs.h.inc
 )
+
+add_gen_header(
+  lowlevel_utils
+  DEF_FILE
+    lowlevel_utils.h.def
+  PARAMS
+    platform_lowlevel=../../config/${LIBC_TARGET_OS}/platform_lowlevel.h.inc
+  GEN_HDR
+    lowlevel_utils.h
+  DATA_FILES
+    ../../config/${LIBC_TARGET_OS}/platform_lowlevel.h.inc
+)

libc/src/__support/lowlevel_utils.h.def

+//===-- Platform independent lowlevel utils -------------------------------===//
+//
+// Part of the LLVM Project, 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
+//
+//===----------------------------------------------------------------------===//
+
+#include <stdint.h>
+
+namespace __llvm_libc {
+
+uintptr_t get_current_pc();
+uintptr_t get_current_sp();
+
+} // namespace __llvm_libc
+
+%%include_file(${platform_lowlevel})