[libc] Add Initial Support for Signals

[abrachet]

Summary

This patch adds signal support on Linux. The current implementation gets the SIG* macros and types like sigset_t from <linux/signals.h>

This patch also adds raise(3), and internal routines block_all_signals and restore_signals

[gchatelet]

libc/src/signal/linux/signal.h

25

Let's wait for D74530 to be in.

[abrachet]

Use new syscall from D74530

[abrachet]

Add missing include guards in src/signal/linux/signal.h

[MaskRay]

libc/config/linux/api.td

144

What is it 64?

[MaskRay]

libc/spec/linux.td

117

Signal,

libc/spec/stdc.td

198

,

[MaskRay]

libc/config/linux/api.td

144

65 may be a reasonable choice for most architectures.

MIPS may require 129. A MIPS signal mask contains 128 bits.

The Linux uapi may be stuck with #define SIGRTMAX _NSIG but a libc should not replicate that (mistake). A libc should have SIGRTMAX-1 == _NSIG, though SIGRTMAX is not necessarily a constant.

[abrachet]

libc/config/linux/api.td

144

Good catch.

My /usr/include/x86_64-linux-gnu/asm/signal.h has:

#define NSIG		32
typedef unsigned long sigset_t;
// ... further down
#define SIGRTMIN	32
#define SIGRTMAX	_NSIG

This is where I am currently getting sigset_t and NSIG. Should we not rely on this header then and define these our self? I do want to use this include to give me sigset_t, struct sigaction, because I think this lessens the burden on us. I would want to hear your thoughts on how difficult (or easy) it is to maintain portability between architectures without using the Linux headers.

65 may be a reasonable choice for most architectures.

MIPS may require 129. A MIPS signal mask contains 128 bits.

We already have x86_64 specific directory, for header gen config here, it shouldn't be a big problem to make NSIG platform dependent, I'm happy to do it in this patch, if we step away from using <linux/signal.h>

[sivachandra]

libc/config/linux/api.td

144

Though I accepted, I was not sure about employing this pattern here. I am guilty of setting an example with this pattern and I think I did not get it correct entirely.

We should strive to use platform headers if available and avoid copying them into the libc tree. Considering that we are keeping the platform specific definitions open anyway (as in, one can add them to the signal.h.in file in this case), we are not really blocking any platform which wants such definitions from a libc.

Which means, we should not need to list these macros at all in this file (and also the sigset_t type).

libc/src/signal/linux/signal.h

23

I should have pointed this out earlier: this is x86/x86_64 specific. I am OK for now as it would cause a compilation error for other architectures where sigset_t is not of an integer type. We can fix it then unless you want to fix it now.

[abrachet]

• Remove macros we can get from linux/sginals.h
• Add internal wrapper type to make it easier to deal with non integer sigset_t in the future.

[abrachet]

libc/config/linux/api.td

144

I've removed those macros, except for SIG_BLOCK and friends because those are not defined in the linux headers. Are we happy with it like this?

libc/src/signal/linux/signal.h

23

I think this wrapper type is a good solution for when we need to deal with such sigset_t's.

[sivachandra]

libc/config/linux/api.td

144

On my machine, I do get SIG_BLOCK and friends from the linux headers. They are defined in asm-generic/signal-defs.h, which is included by asm/signal.h, which is included by linux/signal.h.

libc/src/signal/linux/signal.h

23

As long as it does not need a big surgery to extend, I am OK. I do not have any strong opinion here. Essentially because I have not worked on any other arch.

[abrachet]

Remove unnecessary DefineIfNot<"SIG_BLOCK", "0"> and friends from config/linux/api.td

[abrachet]

libc/config/linux/api.td

144

Indeed, good catch.

libc/src/signal/linux/signal.h

23

I feel the same way. I think that I should be able to keep any big changes inside Sigset in the future.

[gchatelet]

libc/src/signal/linux/raise.cpp

19

This is yielding an unused variable error

[abrachet]

libc/src/signal/linux/raise.cpp

19

Fixed. Thanks!

libc/config/linux/api.td

let TypeDeclarations = [
     OffT,
   ];
 
   let Functions = [
     "mmap",
     "munmap",
   ];
 }
+
+def SignalAPI : PublicAPI<"signal.h"> {
+  let Macros = [
+    MacroDefineIfNot<"SIG_BLOCK", "0">,
+    MacroDefineIfNot<"SIG_UNBLOCK", "1">,
+    MacroDefineIfNot<"SIG_SETMASK", "2">,
+  ];
+
+  let TypeDeclarations = [
+    SizeT, // This is needed by <linux/signal.h>.
+  ];
+
+  let Functions = [
+    "raise",
+  ];
+}

libc/config/linux/signal.h.in

+//===---------------- Linux specific signal.h definitions -----------------===//
+//
+// 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 <linux/signal.h>

libc/include/CMakeLists.txt

add_gen_header(
   DEF_FILE errno.h.def
   PARAMS
     platform_errno=../config/${LIBC_TARGET_OS}/errno.h.in
   GEN_HDR errno.h
   DATA_FILES
     ../config/${LIBC_TARGET_OS}/errno.h.in
 )
 
+add_gen_header(
+  signal_h
+  DEF_FILE signal.h.def
+  PARAMS
+    platform_signal=../config/${LIBC_TARGET_OS}/signal.h.in
+  GEN_HDR signal.h
+  DATA_FILES
+    ../config/${LIBC_TARGET_OS}/signal.h.in
+)
+
 # TODO: Not all platforms will have a include/sys directory. Add the sys
 # directory and the targets for sys/*.h files conditional to the OS requiring
 # them.
 file(MAKE_DIRECTORY "sys")
 
 add_gen_header(
   sys_mman_h
   DEF_FILE sys/mman.h.def

libc/include/signal.h.def

+//===---------------- C standard library header signal.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_SIGNAL_H
+#define LLVM_LIBC_SIGNAL_H
+
+#include <__llvm-libc-common.h>
+
+%%public_api()
+
+%%include_file(${platform_signal})
+
+#endif // LLVM_LIBC_SIGNAL_H

libc/lib/CMakeLists.txt

 
 add_entrypoint_library(
   llvmlibc
   DEPENDS
     # errno.h entrypoints
     __errno_location
 
     # string.h entrypoints
     strcpy
     strcat
 
     # sys/mman.h entrypoints
     mmap
     munmap
+
+    # signal.h entrypoints
+    raise
 )
 
 add_entrypoint_library(
   llvmlibm
   DEPENDS
     # math.h entrypoints
     round
 )
 
 add_redirector_library(
   llvmlibc_redirectors
   DEPENDS
     round_redirector
 )

libc/spec/linux.td

def Linux : StandardSpec<"Linux"> {
 
   HeaderSpec SysMMan = HeaderSpec<
       "sys/mman.h",
       [Macro<"MAP_ANONYMOUS">],
       [], // Types
       []  // Functions
   >;
 
+  HeaderSpec Signal = HeaderSpec<
+      "signal.h",
+      [
+        Macro<"NSIG">,
+
+        Macro<"SIGHUP">,
+        Macro<"SIGINT">,
+        Macro<"SIGQUIT">,
+        Macro<"SIGILL">,
+        Macro<"SIGTRAP">,
+        Macro<"SIGABRT">,
+        Macro<"SIGIOT">,
+        Macro<"SIGBUS">,
+        Macro<"SIGFPE">,
+        Macro<"SIGKILL">,
+        Macro<"SIGUSR1">,
+        Macro<"SIGSEGV">,
+        Macro<"SIGUSR2">,
+        Macro<"SIGPIPE">,
+        Macro<"SIGALRM">,
+        Macro<"SIGTERM">,
+        Macro<"SIGSTKFLT">,
+        Macro<"SIGCHLD">,
+        Macro<"SIGCONT">,
+        Macro<"SIGSTOP">,
+        Macro<"SIGTSTP">,
+        Macro<"SIGTTIN">,
+        Macro<"SIGTTOU">,
+        Macro<"SIGURG">,
+        Macro<"SIGXCPU">,
+        Macro<"SIGXFSZ">,
+        Macro<"SIGVTALRM">,
+        Macro<"SIGPROF">,
+        Macro<"SIGWINCH">,
+        Macro<"SIGIO">,
+        Macro<"SIGPOLL">,
+        Macro<"SIGPWR">,
+        Macro<"SIGSYS">,
+        Macro<"SIGUNUSED">,
+      ],
+      [], // Types
+      []  // Functions
+  >;
+
   let Headers = [
     Errno,
     SysMMan,
+    Signal,
   ];
 }

libc/spec/stdc.td

HeaderSpec Errno = HeaderSpec<
         Macro<"EDOM">,
         Macro<"EILSEQ">,
         Macro<"ERANGE">,
       ],
       [], // Types
       []  // Functions
   >;
 
+  HeaderSpec Signal = HeaderSpec<
+      "signal.h",
+      [
+        Macro<"SIG_BLOCK">,
+        Macro<"SIG_UNBLOCK">,
+        Macro<"SIG_SETMASK">,
+
+        Macro<"SIGABRT">,
+        Macro<"SIGFPE">,
+        Macro<"SIGILL">,
+        Macro<"SIGINT">,
+        Macro<"SIGSEGV">,
+        Macro<"SIGTERM">
+      ],
+      [
+        NamedType<"sigset_t">,
+        SizeTType,
+      ],
+      [
+        FunctionSpec<"raise", RetValSpec<IntType>, [ArgSpec<IntType>]>,
+      ]
+  >;
+
   let Headers = [
     Errno,
     Math,
     String,
     StdIO,
+    Signal,
   ];
 }

libc/src/CMakeLists.txt

 add_subdirectory(errno)
 add_subdirectory(math)
+add_subdirectory(signal)
 add_subdirectory(string)
 # TODO: Add this target conditional to the target OS.
 add_subdirectory(sys)
 
 add_subdirectory(__support)

libc/src/signal/CMakeLists.txt

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

libc/src/signal/linux/CMakeLists.txt

+
+add_entrypoint_object(
+  raise
+  SRCS
+    raise.cpp
+  HDRS
+    signal.h
+    ../raise.h
+  DEPENDS
+    sys_syscall_h
+    linux_syscall_h
+    __errno_location
+    signal_h
+)

libc/src/signal/linux/raise.cpp

+//===------------------ Linux implementation of signal --------------------===//
+//
+// 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/signal/raise.h"
+#include "src/signal/linux/signal.h"
+
+#include "src/__support/common.h"
+
+namespace __llvm_libc {
+
+int LLVM_LIBC_ENTRYPOINT(raise)(int sig) {
+  __llvm_libc::Sigset sigset;
+  int got = __llvm_libc::block_all_signals(sigset);
+  long pid = __llvm_libc::syscall(SYS_getpid);
+  long tid = __llvm_libc::syscall(SYS_gettid);
+  int ret = __llvm_libc::syscall(SYS_tgkill, pid, tid, sig);
+  __llvm_libc::restore_signals(sigset);
+  return ret;
+}
+
+} // namespace __llvm_libc

libc/src/signal/linux/signal.h

+//===----------------- Internal header for Linux signals ------------------===//
+//
+// 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_SIGNAL_LINUX_SIGNAL_H
+#define LLVM_LIBC_SRC_SIGNAL_LINUX_SIGNAL_H
+
+#include "config/linux/syscall.h" // For internal syscall function.
+#include "include/sys/syscall.h"  // For syscall numbers.
+
+#include "include/signal.h"
+
+static_assert(sizeof(sigset_t) * 8 >= NSIG, "sigset_t cannot hold all signals");
+
+namespace __llvm_libc {
+
+// Using this internally defined type will make it easier in the future to port
+// to different architectures.
+struct Sigset {
+  sigset_t nativeSigset;
+
+  constexpr static Sigset fullset() { return {-1UL}; }
+
+  operator sigset_t() const { return nativeSigset; }
+};
+
+constexpr static Sigset all = Sigset::fullset();
+
+static inline int block_all_signals(Sigset &set) {
+  sigset_t nativeSigset = all;
+  sigset_t oldSet = set;
+  return __llvm_libc::syscall(SYS_rt_sigprocmask, SIG_BLOCK, &nativeSigset,
+                              &oldSet, sizeof(sigset_t));
+}
+
+static inline int restore_signals(const Sigset &set) {
+  sigset_t nativeSigset = set;
+  return __llvm_libc::syscall(SYS_rt_sigprocmask, SIG_SETMASK,
+                              &nativeSigset, nullptr,
+                              sizeof(sigset_t));
+}
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_SIGNAL_LINUX_SIGNAL_H

libc/src/signal/raise.h

+//===------------- Implementation header for raise function ------ *-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_SIGNAL_RAISE_H
+#define LLVM_LIBC_SRC_SIGNAL_RAISE_H
+
+#include "include/signal.h"
+
+namespace __llvm_libc {
+
+int raise(int sig);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_SIGNAL_RAISE_H

libc/test/src/CMakeLists.txt

 add_subdirectory(errno)
+add_subdirectory(signal)
 add_subdirectory(string)
 add_subdirectory(sys)

libc/test/src/signal/CMakeLists.txt

+add_libc_testsuite(libc_signal_unittests)
+
+add_libc_unittest(
+  raise_test
+  SUITE
+    libc_signal_unittests
+  SRCS
+    raise_test.cpp
+  DEPENDS
+    raise
+    signal_h
+)

libc/test/src/signal/raise_test.cpp

+//===----------------------- Unittests for raise --------------------------===//
+//
+// 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 "include/signal.h"
+#include "src/signal/raise.h"
+#include "utils/UnitTest/Test.h"
+
+TEST(SignalTest, Raise) {
+  // SIGCONT is ingored unless stopped, so we can use it to check the return
+  // value of raise without needing to block.
+  EXPECT_EQ(__llvm_libc::raise(SIGCONT), 0);
+}