Implement `getrandom` function for linux targets.

[michaelrj]

Overall this patch is almost there, it just needs a couple more mechanical things since it adds a new header. Specifically, you should add the header definition to spec/linux.td. You can look at how HeaderSpecs are defined in spec/stdc.td, I would recommend looking at the one for string.h as an example, or feel free to reach out if you need help figuring it out.

libc/include/CMakeLists.txt

237

you need to add this target to include/llvm-libc-macros/CMakeLists.txt (it should be the same as the others in there) as well as the cmake file in the linux subfolder.

libc/src/sys/CMakeLists.txt

8

nit: please fix

libc/src/sys/random/getrandom.h

2–3

nit: this should all be on one line

libc/src/sys/random/linux/CMakeLists.txt

13

nit: please fix

libc/src/sys/random/linux/getrandom.cpp

22

if there's only one possible syscall, we usually don't bother with checking if it's defined, since the compiler will do that for us.

libc/test/src/sys/random/linux/getrandom_test.cpp

48

nit: please fix

[SchrodingerZhu]

• address code reviews:
  • add getrandom to linux specification
  • add sys/random.h to header target
  • random format bits

[sivachandra]

Thanks for the patch and working through all the details. Overall LGTM but needs one code policy related change.

libc/include/llvm-libc-macros/linux/sys-random-macros.h

16

An empty line between 15 and 16?

libc/test/src/sys/random/linux/getrandom_test.cpp

6

We don't include C++ headers from unit tests. Also, for functions like fabs, we use internal functions. So:

1. Either add M_PI definition to math.h or use a constant for this test.
2. Instead of ::fabs, use __llvm_libc::fabs.

[SchrodingerZhu]

• address code reviews
  • add blank lines in headers
  • use internal math functions in test
  • let getrandom_test depend on lib.src.math.fabs
• additional fix
  • fix wrong names in macro headers (rename STAT to RANDOM)

[SchrodingerZhu]

is this patch ready for merge?

[sivachandra]

Yes.

[SchrodingerZhu]

@michaelrj would you please consider merging this or give more instructions on updating this?
I see that some syscall related changes may have already made this patch incompatible. I am worried that it will become even harder to keep track given the active development of libc.

[sivachandra]

Hi, if you can update after rebasing, I can submit the patch for you.

[michaelrj]

I've left two comments for things to fix, and once you fix those I'll approve the patch and one of us will land it.

libc/spec/linux.td

132–133

you need to add SysRandom to this list, preferably right after SysMMan.

libc/src/sys/random/linux/getrandom.cpp

22

this needs to be syscall_impl

[SchrodingerZhu]

• rebase to main
• address code reviews:
  • use syscall_impl instead
  • add SysRandom to linux spec file

[michaelrj]

Approved with one last nit

libc/src/sys/CMakeLists.txt

8

nit: please fix

[SchrodingerZhu]

• address code review: add blank line to CMakeLists.txt

libc/config/linux/x86_64/entrypoints.txt

set(TARGET_LIBC_ENTRYPOINTS
 
     # sys/mman.h entrypoints
     libc.src.sys.mman.madvise
     libc.src.sys.mman.mmap
     libc.src.sys.mman.mprotect
     libc.src.sys.mman.munmap
     libc.src.sys.mman.posix_madvise
 
+    # sys/random.h entrypoints
+    libc.src.sys.random.getrandom
+
     # sys/resource.h entrypoints
     libc.src.sys.resource.getrlimit
     libc.src.sys.resource.setrlimit
 
     # sys/sendfile entrypoints
     libc.src.sys.sendfile.sendfile
 
     # sys/stat.h entrypoints

libc/config/linux/x86_64/headers.txt

 set(TARGET_PUBLIC_HEADERS
     libc.include.assert_h
     libc.include.ctype
     libc.include.errno
     libc.include.fenv
     libc.include.inttypes
     libc.include.math
     libc.include.pthread
     libc.include.sched
     libc.include.signal
     libc.include.stdio
     libc.include.stdlib
     libc.include.string
     libc.include.sys_mman
+    libc.include.sys_random
     libc.include.sys_syscall
     libc.include.threads
     libc.include.time
     libc.include.unistd
 )

libc/include/CMakeLists.txt

add_gen_header(
   DEPENDS
     .llvm_libc_common_h
     .llvm-libc-types.off_t
     .llvm-libc-types.ssize_t
     .llvm-libc-macros.sys_mman_macros
 )
 
 add_gen_header(
+  sys_random
+  DEF_FILE sys/random.h.def
+  GEN_HDR sys/random.h
+  DEPENDS
+    .llvm_libc_common_h
+    .llvm-libc-macros.sys_random_macros
+    .llvm-libc-types.ssize_t
+    .llvm-libc-types.size_t
+)
+
+add_gen_header(
   sys_resource
   DEF_FILE sys/resource.h.def
   GEN_HDR sys/resource.h
   DEPENDS
     .llvm_libc_common_h
     .llvm-libc-macros.sys_resource_macros
     .llvm-libc-types.rlim_t
     .llvm-libc-types.struct_rlimit

libc/include/llvm-libc-macros/CMakeLists.txt

add_header(
   sys_mman_macros
   HDR
     sys-mman-macros.h
   DEPENDS
     .linux.sys_mman_macros
 )
 
 add_header(
+  sys_random_macros
+  HDR
+    sys-random-macros.h
+  DEPENDS
+    .linux.sys_random_macros
+)
+
+add_header(
   sys_resource_macros
   HDR
     sys-resource-macros.h
   DEPENDS
     .linux.sys_resource_macros
 )
 
 add_header(

libc/include/llvm-libc-macros/linux/CMakeLists.txt

 
 add_header(
   sys_mman_macros
   HDR
     sys-mman-macros.h
 )
 
 add_header(
-  sys_stat_macros
+  sys_random_macros
   HDR
-    sys-stat-macros.h
+    sys-random-macros.h
 )
 
 add_header(
   sys_wait_macros
   HDR
     sys-wait-macros.h
 )
 
 add_header(
   time_macros
   HDR
     time-macros.h
 )
 
 add_header(
   sys_resource_macros
   HDR
     sys-resource-macros.h
 )
 
 add_header(
+  sys_stat_macros
+  HDR
+    sys-stat-macros.h
+)
+
+add_header(
   unistd_macros
   HDR
     unistd-macros.h
 )
 
 add_header(
   signal_macros
   HDR
     signal-macros.h
 )

libc/include/llvm-libc-macros/linux/sys-random-macros.h

+//===-- Definition of macros from sys/random.h ----------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef __LLVM_LIBC_MACROS_LINUX_SYS_RANDOM_MACROS_H
+#define __LLVM_LIBC_MACROS_LINUX_SYS_RANDOM_MACROS_H
+
+// Getrandom flags
+#define GRND_RANDOM 0x0001
+#define GRND_NONBLOCK 0x0002
+#define GRND_INSECURE 0x0004
+
+#endif // __LLVM_LIBC_MACROS_LINUX_SYS_RANDOM_MACROS_H

libc/include/llvm-libc-macros/sys-random-macros.h

+//===-- Macros defined in sys/random.h header file ------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef __LLVM_LIBC_MACROS_SYS_RANDOM_MACROS_H
+#define __LLVM_LIBC_MACROS_SYS_RANDOM_MACROS_H
+
+#ifdef __unix__
+#include "linux/sys-random-macros.h"
+#endif
+
+#endif // __LLVM_LIBC_MACROS_SYS_RANDOM_MACROS_H

libc/include/sys/random.h.def

+//===-- Linux sys/random.h ------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SYS_RANDOM_H
+#define LLVM_LIBC_SYS_RANDOM_H
+
+#include <__llvm-libc-common.h>
+
+#include <llvm-libc-macros/sys-random-macros.h>
+
+%%public_api()
+
+#endif // LLVM_LIBC_SYS_RANDOM_H

libc/spec/linux.td

HeaderSpec Errno = HeaderSpec<
       ]
   >;
 
   HeaderSpec SysMMan = HeaderSpec<
       "sys/mman.h",
       [Macro<"MAP_ANONYMOUS">]
   >;
 
+  HeaderSpec SysRandom = HeaderSpec<
+      "sys/random.h",
+      [
+        Macro<"GRND_RANDOM">,
+        Macro<"GRND_NONBLOCK">,
+        Macro<"GRND_INSECURE">,
+      ],
+      [], // Types
+      [], // Enumerations
+      [
+        FunctionSpec<
+          "getrandom",
+          RetValSpec<SSizeTType>,
+          [
+            ArgSpec<VoidPtr>,
+            ArgSpec<SizeTType>,
+            ArgSpec<UnsignedIntType>
+          ]
+        >,
+      ]
+  >;
+
   HeaderSpec Signal = HeaderSpec<
       "signal.h",
       [
         Macro<"NSIG">,
 
         Macro<"SIGHUP">,
         Macro<"SIGINT">,
         Macro<"SIGQUIT">,
HeaderSpec Signal = HeaderSpec<
         Macro<"SIGPWR">,
         Macro<"SIGSYS">,
         Macro<"SIGUNUSED">,
       ]
   >;
 
   let Headers = [
     Errno,
     SysMMan,
+    SysRandom,
     Signal,
   ];
 }

libc/src/sys/CMakeLists.txt

 add_subdirectory(mman)
+add_subdirectory(random)
 add_subdirectory(resource)
 add_subdirectory(sendfile)
 add_subdirectory(stat)
 add_subdirectory(utsname)
 add_subdirectory(wait)

libc/src/sys/random/CMakeLists.txt

+if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
+  add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
+endif()
+
+add_entrypoint_object(
+  getrandom
+  ALIAS
+  DEPENDS
+    .${LIBC_TARGET_OS}.getrandom
+)

libc/src/sys/random/getrandom.h

+//===-- Implementation header for getrandom ----------------------*- 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_SYS_RANDOM_GETRANDOM_H
+#define LLVM_LIBC_SRC_SYS_RANDOM_GETRANDOM_H
+
+#include <sys/types.h>
+
+namespace __llvm_libc {
+
+ssize_t getrandom(void *buf, size_t buflen, unsigned int flags);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_SYS_RANDOM_GETRANDOM_H

libc/src/sys/random/linux/CMakeLists.txt

+add_entrypoint_object(
+  getrandom
+  SRCS
+    getrandom.cpp
+  HDRS
+    ../getrandom.h
+  DEPENDS
+    libc.include.sys_random
+    libc.include.sys_syscall
+    libc.src.__support.OSUtil.osutil
+    libc.src.errno.errno
+)

libc/src/sys/random/linux/getrandom.cpp

+//===-- Linux implementation of getrandom ---------------------------------===//
+//
+// 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 "src/sys/random/getrandom.h"
+
+#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+#include "src/__support/common.h"
+
+#include <errno.h>
+#include <sys/syscall.h> // For syscall numbers.
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(ssize_t, getrandom,
+                   (void *buf, size_t buflen, unsigned int flags)) {
+  long ret = __llvm_libc::syscall_impl(SYS_getrandom, buf, buflen, flags);
+  if (ret < 0) {
+    errno = -ret;
+    return -1;
+  }
+  return 0;
+}
+
+} // namespace __llvm_libc

libc/test/src/sys/CMakeLists.txt

 add_subdirectory(mman)
+add_subdirectory(random)
 add_subdirectory(resource)
 add_subdirectory(sendfile)
 add_subdirectory(stat)
 add_subdirectory(utsname)
 add_subdirectory(wait)

libc/test/src/sys/random/CMakeLists.txt

+if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
+  add_subdirectory(${LIBC_TARGET_OS})
+endif()

libc/test/src/sys/random/linux/CMakeLists.txt

+add_libc_testsuite(libc_sys_random_unittests)
+
+add_libc_unittest(
+  getrandom_test
+  SUITE
+    libc_sys_random_unittests
+  SRCS
+    getrandom_test.cpp
+  DEPENDS
+    libc.include.errno
+    libc.include.math
+    libc.include.sys_random
+    libc.src.errno.errno
+    libc.src.math.fabs
+    libc.src.sys.random.getrandom
+    libc.test.errno_setter_matcher
+)

libc/test/src/sys/random/linux/getrandom_test.cpp

+#include "src/math/fabs.h"
+#include "src/sys/random/getrandom.h"
+#include "test/ErrnoSetterMatcher.h"
+#include "utils/UnitTest/Test.h"
+
+TEST(LlvmLibcGetRandomTest, InvalidFlag) {
+  using __llvm_libc::testing::ErrnoSetterMatcher::Fails;
+  static constexpr size_t SIZE = 256;
+  char data[SIZE];
+  errno = 0;
+  ASSERT_THAT(__llvm_libc::getrandom(data, SIZE, -1), Fails(EINVAL));
+  errno = 0;
+}
+
+TEST(LlvmLibcGetRandomTest, InvalidBuffer) {
+  using __llvm_libc::testing::ErrnoSetterMatcher::Fails;
+
+  errno = 0;
+  ASSERT_THAT(__llvm_libc::getrandom(nullptr, 65536, 0), Fails(EFAULT));
+  errno = 0;
+}
+
+TEST(LlvmLibcGetRandomTest, PiEstimation) {
+  static constexpr size_t LIMIT = 10000000;
+  static constexpr double PI = 3.14159265358979;
+
+  auto generator = []() {
+    uint16_t data;
+    __llvm_libc::getrandom(&data, sizeof(data), 0);
+    return data;
+  };
+
+  auto sample = [&]() {
+    auto x = static_cast<double>(generator()) / 65536.0;
+    auto y = static_cast<double>(generator()) / 65536.0;
+    return x * x + y * y < 1.0;
+  };
+
+  double counter = 0;
+  for (size_t i = 0; i < LIMIT; ++i) {
+    if (sample()) {
+      counter += 1.0;
+    }
+  }
+  counter = counter / LIMIT * 4.0;
+  ASSERT_TRUE(__llvm_libc::fabs(counter - PI) < 0.1);
+}