[libc] Re-enable functions from signal.h and re-enable abort.

[sivachandra]

Summary

They were disabled because we were including linux/signal.h from our
signal.h. Linux's signal.h is not designed to be included from user
programs as it causes a lot of non-standard name pollution. Also, it is
not self-contained. This change defines types and macros relevant for
signal related syscalls within libc's headers and removes inclusion of
Linux headers.

This patch enables the funtions only for x86_64. They will be enabled
for aarch64 also in a follow up patch after testing.

[abrachet]

libc/include/llvm-libc-macros/signal-macros.h

12–14

Should this be __linux__?

libc/include/llvm-libc-types/siginfo_t.h

3

This got moved to the next line

28

FWIW, this looks like it's architecture dependent. Admittedly I don't remember the story about why we moved away from using Linux headers. It might be nice to leave around something like

#if ! (defined(LLVM_LIBC_ARCH_X86_64) || defined(LLVM_LIBC_ARCH_AARCH64))
#error "this siginfo may not be valid for your architecture"
#endif

Though I have no strong preference because it looks like only mips and ia64 have other implementations of this type

libc/include/llvm-libc-types/struct_sigaction.h

22

Should this be __linux__? From looking at various other man pages (and your comment right bellow) this is seemingly only on Linux.

[sivachandra]

Address comments.

[sivachandra]

libc/include/llvm-libc-macros/signal-macros.h

12–14

I don't remember why we started doing #ifdef __unix__ - I have changed to __linux__ now. I will cleanup other instances in a different change.

libc/include/llvm-libc-types/siginfo_t.h

28

About Linux headers, tl;dr - they lead to name pollution in user programs.

About making this struct target specific or excluding it, I think we can do it when we have an example to deal with.

libc/config/linux/api.td

 def SysMManAPI : PublicAPI<"sys/mman.h"> {
   let Types = ["off_t", "size_t"];
   let Macros = [
   ];
 
 }
 
 def SignalAPI : PublicAPI<"signal.h"> {
-  let Types = ["struct sigaction", "__sighandler_t"];
+  let Types = ["sigset_t", "struct sigaction", "union sigval", "siginfo_t"];
 }
 
 def ThreadsAPI : PublicAPI<"threads.h"> {
   let Macros = [
     SimpleMacroDef<"ONCE_FLAG_INIT", "{0}">,
   ];
 
   let Types = [

libc/config/linux/x86_64/entrypoints.txt

list(APPEND TARGET_LIBC_ENTRYPOINTS
     libc.src.stdio.fprintf
     libc.src.stdio.printf
     libc.src.stdio.puts
     libc.src.stdio.stderr
     libc.src.stdio.stdout
 
     # stdlib.h entrypoints
     libc.src.stdlib._Exit
+    libc.src.stdlib.abort
     libc.src.stdlib.atexit
     libc.src.stdlib.exit
     libc.src.stdlib.getenv
 
     # signal.h entrypoints
-    # TODO: Enable signal.h entrypoints after fixing signal.h
-    # libc.src.signal.raise
-    # libc.src.signal.sigaction
-    # libc.src.signal.sigdelset
-    # libc.src.signal.sigaddset
-    # libc.src.signal.sigemptyset
-    # libc.src.signal.sigprocmask
-    # libc.src.signal.sigfillset
-    # libc.src.signal.signal
+    libc.src.signal.raise
+    libc.src.signal.sigaction
+    libc.src.signal.sigdelset
+    libc.src.signal.sigaddset
+    libc.src.signal.sigemptyset
+    libc.src.signal.sigprocmask
+    libc.src.signal.sigfillset
+    libc.src.signal.signal
 
     # threads.h entrypoints
     libc.src.threads.call_once
     libc.src.threads.cnd_broadcast
     libc.src.threads.cnd_destroy
     libc.src.threads.cnd_init
     libc.src.threads.cnd_signal
     libc.src.threads.cnd_wait

libc/include/CMakeLists.txt

add_gen_header(
   signal
   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
   DEPENDS
+    .llvm-libc-macros.signal_macros
     .llvm-libc-types.struct_sigaction
     .llvm-libc-types.__sighandler_t
+    .llvm-libc-types.sigset_t
 )
 
 add_gen_header(
   stdio
   DEF_FILE stdio.h.def
   GEN_HDR stdio.h
   DEPENDS
     .llvm_libc_common_h

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

 
 add_header(
   file_seek_macros
   HDR
     file-seek-macros.h
 )
 
 add_header(
+  signal_macros
+  HDR
+    signal-macros.h
+  DEPENDS
+    .linux.signal_macros
+)
+
+add_header(
   sys_stat_macros
   HDR
     sys-stat-macros.h
   DEPENDS
     .linux.sys_stat_macros
 )
 
 add_header(

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

HDR
     sys-resource-macros.h
 )
 
 add_header(
   unistd_macros
   HDR
     unistd-macros.h
 )
+
+add_header(
+  signal_macros
+  HDR
+    signal-macros.h
+)

libc/include/llvm-libc-macros/linux/signal-macros.h

+//===-- Definition of Linux signal number macros --------------------------===//
+//
+// 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_SIGNUM_MACROS_H
+#define __LLVM_LIBC_MACROS_LINUX_SIGNUM_MACROS_H
+
+#define SIGHUP 1
+#define SIGINT 2
+#define SIGQUIT 3
+#define SIGILL 4
+#define SIGTRAP 5
+#define SIGABRT 6
+#define SIGIOT 6
+#define SIGBUS 7
+#define SIGFPE 8
+#define SIGKILL 9
+#define SIGUSR1 10
+#define SIGSEGV 11
+#define SIGUSR2 12
+#define SIGPIPE 13
+#define SIGALRM 14
+#define SIGTERM 15
+#define SIGSTKFLT 16
+#define SIGCHLD 17
+#define SIGCONT 18
+#define SIGSTOP 19
+#define SIGTSTP 20
+#define SIGTTIN 21
+#define SIGTTOU 22
+#define SIGURG 23
+#define SIGXCPU 24
+#define SIGXFSZ 25
+#define SIGVTALRM 26
+#define SIGPROF 27
+#define SIGWINCH 28
+#define SIGIO 29
+#define SIGPOLL SIGIO
+#define SIGPWR 30
+#define SIGSYS 31
+
+// Max signal number
+#define NSIG 64
+
+// SIGRTMIN is current set to the minimum usable from user mode programs. If
+// the libc itself uses some of these signal numbers for private operations,
+// then it has to be adjusted in future to reflect that.
+#define SIGRTMIN 32
+
+#define SIGRTMAX NSIG
+
+// The kernel sigset is stored as an array of long values. Each bit of this
+// array corresponds to a signal, adjusted by 1. That is, bit 0 corresponds
+// to signal number 1, bit 1 corresponds to signal number 2 and so on. The
+// below macro denotes the size of that array (in number of long words and
+// not bytes).
+#define __NSIGSET_WORDS (NSIG / (sizeof(unsigned long) * 8))
+
+#define SIG_BLOCK 0   // For blocking signals
+#define SIG_UNBLOCK 1 // For unblocking signals
+#define SIG_SETMASK 2 // For setting signal mask
+
+// Flag values to be used for setting sigaction.sa_flags.
+#define SA_NOCLDSTOP 0x00000001
+#define SA_NOCLDWAIT 0x00000002
+#define SA_SIGINFO 0x00000004
+#define SA_RESTART 0x10000000
+#define SA_RESTORER 0x04000000
+
+#define SIG_DFL ((__sighandler_t)0)
+#define SIG_IGN ((__sighandler_t)1)
+#define SIG_ERR ((__sighandler_t)-1)
+
+#endif // __LLVM_LIBC_MACROS_LINUX_SIGNUM_MACROS_H

libc/include/llvm-libc-macros/signal-macros.h

-//===-- C standard library header signal.h --------------------------------===//
+//===-- Definition of signal number macros --------------------------------===//
 //
 // 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
+#ifndef __LLVM_LIBC_MACROS_SIGNUM_MACROS_H
+#define __LLVM_LIBC_MACROS_SIGNUM_MACROS_H
 
-#include <__llvm-libc-common.h>
+#ifdef __linux__
+#include "linux/signal-macros.h"
+#endif
 
-#define __need_size_t
-#include <stddef.h>
-
-%%include_file(${platform_signal})
-
-%%public_api()
-
-#endif // LLVM_LIBC_SIGNAL_H
+#endif // __LLVM_LIBC_MACROS_SIGNUM_MACROS_H

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

 add_header(pthread_mutex_t HDR pthread_mutex_t.h DEPENDS .__futex_word .__mutex_type)
 add_header(pthread_t HDR pthread_t.h DEPENDS .__thread_type)
 add_header(pthread_mutexattr_t HDR pthread_mutexattr_t.h)
 add_header(pthread_once_t HDR pthread_once_t.h DEPENDS .__futex_word)
 add_header(rlim_t HDR rlim_t.h)
 add_header(struct_rlimit HDR struct_rlimit.h DEPENDS .rlim_t)
 add_header(ssize_t HDR ssize_t.h)
 add_header(struct_dirent HDR struct_dirent.h DEPENDS .ino_t .off_t)
-add_header(struct_sigaction HDR struct_sigaction.h)
+add_header(union_sigval HDR union_sigval.h)
+add_header(siginfo_t HDR siginfo_t.h DEPENDS .union_sigval .pid_t .uid_t)
+add_header(sigset_t HDR sigset_t.h DEPENDS libc.include.llvm-libc-macros.signal_macros)
+add_header(struct_sigaction HDR struct_sigaction.h DEPENDS .sigset_t .siginfo_t)
 add_header(time_t HDR time_t.h)
 add_header(struct_timespec HDR struct_timespec.h DEPENDS .time_t)
 add_header(
   struct_stat
   HDR struct_stat.h
   DEPENDS
     .dev_t .ino_t .mode_t .nlink_t .uid_t .gid_t .off_t .struct_timespec
     .blksize_t .blkcnt_t
 )
 add_header(struct_tm HDR struct_tm.h)
 add_header(struct_utsname HDR struct_utsname.h)
 add_header(thrd_start_t HDR thrd_start_t.h)
 add_header(thrd_t HDR thrd_t.h DEPENDS .__thread_type)
 add_header(tss_t HDR tss_t.h)
 add_header(tss_dtor_t HDR tss_dtor_t.h)
 add_header(__atexithandler_t HDR __atexithandler_t.h)

libc/include/llvm-libc-types/siginfo_t.h

+//===-- Definition of siginfo_t type --------------------------------------===//
+//
+// 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_TYPES_SIGINFO_T_H__
+#define __LLVM_LIBC_TYPES_SIGINFO_T_H__
+
+#include <llvm-libc-types/pid_t.h>
+#include <llvm-libc-types/uid_t.h>
+#include <llvm-libc-types/union_sigval.h>
+
+typedef struct {
+  int si_signo;
+  int si_code;
+  int si_errno;
+  pid_t si_pid;
+  uid_t si_uid;
+  void *si_addr;
+  int si_status;
+  long si_band;
+  union sigval si_value;
+} siginfo_t;
+
+#endif // __LLVM_LIBC_TYPES_SIGINFO_T_H__

libc/include/llvm-libc-types/sigset_t.h

+//===-- Definition of sigset_t type ---------------------------------------===//
+//
+// 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_TYPES_SIGSET_T_H__
+#define __LLVM_LIBC_TYPES_SIGSET_T_H__
+
+#include <llvm-libc-macros/signal-macros.h>
+
+// This definition can be adjusted/specialized for different targets and
+// platforms as necessary. This definition works for Linux on most targets.
+typedef struct {
+  unsigned long __signals[__NSIGSET_WORDS];
+} sigset_t;
+
+#endif // __LLVM_LIBC_TYPES_SIGSET_T_H__

libc/include/llvm-libc-types/struct_sigaction.h

 //===-- Definition of struct __sigaction ----------------------------------===//
 //
 // 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_TYPES_SIGACTION_H__
 #define __LLVM_LIBC_TYPES_SIGACTION_H__
 
-struct __sigaction {
+#include <llvm-libc-types/siginfo_t.h>
+#include <llvm-libc-types/sigset_t.h>
+
+struct sigaction {
   union {
     void (*sa_handler)(int);
-    void (*sa_action)(int, siginfo_t *, void *);
+    void (*sa_sigaction)(int, siginfo_t *, void *);
   };
   sigset_t sa_mask;
   int sa_flags;
+#ifdef __linux__
+  // This field is present on linux for most targets.
   void (*sa_restorer)(void);
+#endif
 };
 
+typedef void (*__sighandler_t)(int);
+
 #endif // __LLVM_LIBC_TYPES_SIGACTION_H__

libc/include/llvm-libc-types/union_sigval.h

-//===-- C standard library header signal.h --------------------------------===//
+//===-- Definition of type union sigval -----------------------------------===//
 //
 // 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
+#ifndef __LLVM_LIBC_TYPES_UNION_SIGVAL_H__
+#define __LLVM_LIBC_TYPES_UNION_SIGVAL_H__
 
-#include <__llvm-libc-common.h>
+union sigval {
+  int sival_int;
+  void *sival_ptr;
+};
 
-#define __need_size_t
-#include <stddef.h>
-
-%%include_file(${platform_signal})
-
-%%public_api()
-
-#endif // LLVM_LIBC_SIGNAL_H
+#endif // __LLVM_LIBC_TYPES_UNION_SIGVAL_H__

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>
 
 #define __need_size_t
 #include <stddef.h>
 
-%%include_file(${platform_signal})
+#include <llvm-libc-macros/signal-macros.h>
 
 %%public_api()
 
 #endif // LLVM_LIBC_SIGNAL_H

libc/spec/posix.td

 def SigSetType : NamedType<"sigset_t">;
 def SigSetPtrType : PtrType<SigSetType>;
 def ConstSigSetPtrType : ConstType<SigSetPtrType>;
 def RestrictedSigSetType : RestrictedPtrType<SigSetType>;
 def ConstRestrictedSigSetType : ConstType<RestrictedSigSetType>;
 
+def SigInfoType : NamedType<"siginfo_t">;
+def UnionSigVal : NamedType<"union sigval">;
+
 def StructSigaction : NamedType<"struct sigaction">;
 def StructSigactionPtr : PtrType<StructSigaction>;
 def ConstStructSigactionPtr : ConstType<StructSigactionPtr>;
 def RestrictedStructSigactionPtr : RestrictedPtrType<StructSigaction>;
 def ConstRestrictedStructSigactionPtr : ConstType<RestrictedStructSigactionPtr>;
 
 def PThreadStartT : NamedType<"__pthread_start_t">;
 def PThreadTSSDtorT : NamedType<"__pthread_tss_dtor_t">;
HeaderSpec SysMMan = HeaderSpec<
         >,
       ]
   >;
 
   HeaderSpec Signal = HeaderSpec<
       "signal.h",
       [], // Macros
       [
+        SigInfoType,
         SigSetType,
         StructSigaction,
+        UnionSigVal,
       ],
       [], // Enumerations
       [
         FunctionSpec<
           "sigaction",
           RetValSpec<IntType>,
           [ArgSpec<IntType>,
            ArgSpec<ConstRestrictedStructSigactionPtr>,

libc/src/CMakeLists.txt

 
 if(NOT LLVM_LIBC_FULL_BUILD)
   return()
 endif()
 
 # The signal API is currently disabled as signal.h is incorrect.
 # since assert uses the signal API, we disable assert also.
 # add_subdirectory(assert)
-# add_subdirectory(signal)
+add_subdirectory(signal)
 add_subdirectory(threads)
 add_subdirectory(time)

libc/src/signal/linux/CMakeLists.txt

+add_header_library(
+  signal_utils
+  HDRS
+    signal_utils.h
+  DEPENDS
+    libc.include.sys_syscall
+    libc.src.__support.OSUtil.osutil
+)
 
 add_entrypoint_object(
   raise
   SRCS
     raise.cpp
   HDRS
-    signal.h
     ../raise.h
   DEPENDS
+    .signal_utils
     libc.include.signal
     libc.include.sys_syscall
     libc.src.__support.OSUtil.osutil
 )
 
 add_object_library(
   __restore
   SRCS
DEPENDS
     libc.src.__support.OSUtil.osutil
 )
 
 add_entrypoint_object(
   sigaction
   SRCS
     sigaction.cpp
   HDRS
-    signal.h
     ../sigaction.h
   DEPENDS
     .__restore
     libc.include.signal
     libc.include.sys_syscall
     libc.src.__support.OSUtil.osutil
     libc.src.errno.errno
 )
 
 add_entrypoint_object(
   sigprocmask
   SRCS
     sigprocmask.cpp
   HDRS
-    signal.h
     ../sigprocmask.h
   DEPENDS
+    .signal_utils
     libc.include.signal
     libc.include.sys_syscall
     libc.src.__support.OSUtil.osutil
     libc.src.errno.errno
 )
 
 add_entrypoint_object(
   sigemptyset
   SRCS
     sigemptyset.cpp
   HDRS
-    signal.h
     ../sigemptyset.h
   DEPENDS
+    .signal_utils
     libc.include.errno
     libc.include.signal
     libc.src.errno.errno
 )
 
 add_entrypoint_object(
   sigaddset
   SRCS
     sigaddset.cpp
   HDRS
-    signal.h
     ../sigaddset.h
   DEPENDS
+    .signal_utils
     libc.include.errno
     libc.include.signal
     libc.src.errno.errno
 )
 
 add_entrypoint_object(
   signal
   SRCS
     signal.cpp
   HDRS
-    signal.h
     ../signal.h
   DEPENDS
     .sigaction
     libc.include.signal
 )
 
 add_entrypoint_object(
   sigfillset
   SRCS
     sigfillset.cpp
   HDRS
-    signal.h
     ../sigfillset.h
   DEPENDS
+    .signal_utils
     libc.include.errno
     libc.include.signal
     libc.src.errno.errno
 )
 
 add_entrypoint_object(
   sigdelset
   SRCS
     sigdelset.cpp
   HDRS
-    signal.h
     ../sigdelset.h
   DEPENDS
+    .signal_utils
     libc.include.errno
     libc.include.signal
     libc.src.errno.errno
 )

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/signal/linux/signal_utils.h"
 
 #include "src/__support/common.h"
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(int, raise, (int sig)) {
-  __llvm_libc::Sigset sigset;
-  __llvm_libc::block_all_signals(sigset);
+  ::sigset_t sigset;
+  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);
+  restore_signals(sigset);
   return ret;
 }
 
 } // namespace __llvm_libc

libc/src/signal/linux/sigaction.cpp

 //===-- Linux implementation of sigaction ---------------------------------===//
 //
 // 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
 //
 //===----------------------------------------------------------------------===//
 
-#define __LLVM_LIBC_INTERNAL_SIGACTION
 #include "src/signal/sigaction.h"
-#include "src/errno/llvmlibc_errno.h"
-#include "src/signal/linux/signal.h"
+#include "src/signal/linux/signal_utils.h"
 
 #include "src/__support/common.h"
 
+#include <errno.h>
+#include <signal.h>
+
 namespace __llvm_libc {
 
 // TOOD: Some architectures will have their signal trampoline functions in the
 // vdso, use those when available.
 
 extern "C" void __restore_rt();
 
-template <typename T, typename V>
-static void copy_sigaction(T &dest, const V &source) {
-  dest.sa_handler = source.sa_handler;
-  dest.sa_mask = source.sa_mask;
-  dest.sa_flags = source.sa_flags;
-  dest.sa_restorer = source.sa_restorer;
-}
-
 LLVM_LIBC_FUNCTION(int, sigaction,
-                   (int signal, const struct __sigaction *__restrict libc_new,
-                    struct __sigaction *__restrict libc_old)) {
-  struct sigaction kernel_new;
+                   (int signal, const struct sigaction *__restrict libc_new,
+                    struct sigaction *__restrict libc_old)) {
+  KernelSigaction kernel_new;
   if (libc_new) {
-    copy_sigaction(kernel_new, *libc_new);
+    kernel_new = *libc_new;
     if (!(kernel_new.sa_flags & SA_RESTORER)) {
       kernel_new.sa_flags |= SA_RESTORER;
       kernel_new.sa_restorer = __restore_rt;
     }
   }
 
-  struct sigaction kernel_old;
+  KernelSigaction kernel_old;
   int ret = syscall(SYS_rt_sigaction, signal, libc_new ? &kernel_new : nullptr,
                     libc_old ? &kernel_old : nullptr, sizeof(sigset_t));
   if (ret) {
-    llvmlibc_errno = -ret;
+    errno = -ret;
     return -1;
   }
 
   if (libc_old)
-    copy_sigaction(*libc_old, kernel_old);
+    *libc_old = kernel_old;
   return 0;
 }
 
 } // namespace __llvm_libc

libc/src/signal/linux/sigaddset.cpp

 //===-- Linux implementation of sigaddset ---------------------------------===//
 //
 // 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/sigaddset.h"
-#include "include/errno.h" // For E* macros.
-#include "src/errno/llvmlibc_errno.h"
-#include "src/signal/linux/signal.h"
-
 #include "src/__support/common.h"
+#include "src/signal/linux/signal_utils.h"
+
+#include <errno.h>
+#include <signal.h>
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(int, sigaddset, (sigset_t * set, int signum)) {
-  if (!set || (unsigned)(signum - 1) >= (8 * sizeof(sigset_t))) {
-    llvmlibc_errno = EINVAL;
-    return -1;
-  }
-  auto *sigset = reinterpret_cast<__llvm_libc::Sigset *>(set);
-  sigset->addset(signum);
+  if (set != nullptr && add_signal(*set, signum))
     return 0;
+  errno = EINVAL;
+  return -1;
 }
 
 } // namespace __llvm_libc

libc/src/signal/linux/sigdelset.cpp

 //===-- Linux implementation of sigdelset ---------------------------------===//
 //
 // 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/sigdelset.h"
-#include "include/errno.h"
-#include "src/errno/llvmlibc_errno.h"
-#include "src/signal/linux/signal.h"
-
 #include "src/__support/common.h"
+#include "src/signal/linux/signal_utils.h"
+
+#include <errno.h>
+#include <signal.h>
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(int, sigdelset, (sigset_t * set, int signum)) {
-  if (!set || (unsigned)(signum - 1) >= (8 * sizeof(sigset_t))) {
-    llvmlibc_errno = EINVAL;
-    return -1;
-  }
-  auto *sigset = reinterpret_cast<__llvm_libc::Sigset *>(set);
-  sigset->delset(signum);
+  if (set != nullptr && delete_signal(*set, signum))
     return 0;
+  errno = EINVAL;
+  return -1;
 }
 
 } // namespace __llvm_libc

libc/src/signal/linux/sigemptyset.cpp

 //===-- Linux implementation of sigemptyset -------------------------------===//
 //
 // 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/sigemptyset.h"
-#include "include/errno.h" // For E* macros.
-#include "src/errno/llvmlibc_errno.h"
-#include "src/signal/linux/signal.h"
+#include "src/signal/linux/signal_utils.h"
 
 #include "src/__support/common.h"
 
+#include <errno.h>
+#include <signal.h>
+
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(int, sigemptyset, (sigset_t * set)) {
   if (!set) {
-    llvmlibc_errno = EINVAL;
+    errno = EINVAL;
     return -1;
   }
-  *set = __llvm_libc::Sigset::empty_set();
+  *set = empty_set();
   return 0;
 }
 
 } // namespace __llvm_libc

libc/src/signal/linux/sigfillset.cpp

 //===-- Linux implementation of sigfillset --------------------------------===//
 //
 // 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/sigfillset.h"
-#include "include/errno.h"
-#include "src/errno/llvmlibc_errno.h"
-#include "src/signal/linux/signal.h"
-
 #include "src/__support/common.h"
+#include "src/signal/linux/signal_utils.h"
+
+#include <errno.h>
+#include <signal.h>
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(int, sigfillset, (sigset_t * set)) {
   if (!set) {
-    llvmlibc_errno = EINVAL;
+    errno = EINVAL;
     return -1;
   }
-  auto *sigset = reinterpret_cast<__llvm_libc::Sigset *>(set);
-  *sigset = __llvm_libc::Sigset::fullset();
+  *set = full_set();
   return 0;
 }
 
 } // namespace __llvm_libc

libc/src/signal/linux/signal.h

-//===-- Internal header for Linux signals -----------------------*- 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_LINUX_SIGNAL_H
-#define LLVM_LIBC_SRC_SIGNAL_LINUX_SIGNAL_H
-
-#include "include/sys/syscall.h"          // For syscall numbers.
-#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
-
-#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 native_sigset;
-
-  constexpr static Sigset fullset() { return {-1UL}; }
-  constexpr static Sigset empty_set() { return {0}; }
-
-  constexpr void addset(int signal) { native_sigset |= (1L << (signal - 1)); }
-
-  constexpr void delset(int signal) { native_sigset &= ~(1L << (signal - 1)); }
-
-  operator sigset_t() const { return native_sigset; }
-};
-
-constexpr static Sigset ALL = Sigset::fullset();
-
-static inline int block_all_signals(Sigset &set) {
-  sigset_t native_sigset = ALL;
-  sigset_t old_set = set;
-  int ret = __llvm_libc::syscall(SYS_rt_sigprocmask, SIG_BLOCK, &native_sigset,
-                                 &old_set, sizeof(sigset_t));
-  set = {old_set};
-  return ret;
-}
-
-static inline int restore_signals(const Sigset &set) {
-  sigset_t native_sigset = set;
-  return __llvm_libc::syscall(SYS_rt_sigprocmask, SIG_SETMASK, &native_sigset,
-                              nullptr, sizeof(sigset_t));
-}
-
-} // namespace __llvm_libc
-
-#endif // LLVM_LIBC_SRC_SIGNAL_LINUX_SIGNAL_H

libc/src/signal/linux/signal.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
 //
 //===----------------------------------------------------------------------===//
 
-#define __LLVM_LIBC_INTERNAL_SIGACTION
 #include "src/signal/signal.h"
 #include "src/signal/sigaction.h"
 
 #include "src/__support/common.h"
 
+#include <signal.h>
+
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(sighandler_t, signal, (int signum, sighandler_t handler)) {
-  struct __sigaction action, old;
+  struct sigaction action, old;
   action.sa_handler = handler;
   action.sa_flags = SA_RESTART;
   // Errno will already be set so no need to worry about changing errno here.
   return __llvm_libc::sigaction(signum, &action, &old) == -1 ? SIG_ERR
                                                              : old.sa_handler;
 }
 
 } // namespace __llvm_libc

libc/src/signal/linux/signal_utils.h

+//===-- Internal header for Linux signals -----------------------*- 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_LINUX_SIGNAL_UTILS_H
+#define LLVM_LIBC_SRC_SIGNAL_LINUX_SIGNAL_UTILS_H
+
+#include "include/sys/syscall.h"          // For syscall numbers.
+#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+
+#include <signal.h>
+#include <stddef.h>
+
+namespace __llvm_libc {
+
+// The POSIX definition of struct sigaction and the sigaction data structure
+// expected by the rt_sigaction syscall differ in their definition. So, we
+// define the equivalent of the what the kernel expects to help with making
+// the rt_sigaction syscall.
+//
+// NOTE: Though the kernel definition does not have a union to include the
+// handler taking siginfo_t * argument, one can set sa_handler to sa_sigaction
+// if SA_SIGINFO is set in sa_flags.
+struct KernelSigaction {
+  using HandlerType = void(int);
+  using SiginfoHandlerType = void(int, siginfo_t *, void *);
+
+  KernelSigaction &operator=(const struct sigaction &sa) {
+    sa_flags = sa.sa_flags;
+    sa_restorer = sa.sa_restorer;
+    sa_mask = sa.sa_mask;
+    if (sa_flags & SA_SIGINFO) {
+      sa_handler = reinterpret_cast<HandlerType *>(sa.sa_sigaction);
+    } else {
+      sa_handler = sa.sa_handler;
+    }
+    return *this;
+  }
+
+  operator struct sigaction() const {
+    struct sigaction sa;
+    sa.sa_flags = sa_flags;
+    sa.sa_mask = sa_mask;
+    sa.sa_restorer = sa_restorer;
+    if (sa_flags & SA_SIGINFO)
+      sa.sa_sigaction = reinterpret_cast<SiginfoHandlerType *>(sa_handler);
+    else
+      sa.sa_handler = sa_handler;
+    return sa;
+  }
+
+  HandlerType *sa_handler;
+  unsigned long sa_flags;
+  void (*sa_restorer)(void);
+  // Our public definition of sigset_t matches that of the kernel's definition.
+  // So, we can use the public sigset_t type here.
+  sigset_t sa_mask;
+};
+
+static constexpr size_t BITS_PER_SIGWORD = sizeof(unsigned long) * 8;
+
+constexpr sigset_t full_set() { return sigset_t{{-1UL}}; }
+
+constexpr sigset_t empty_set() { return sigset_t{{0}}; }
+
+// Set the bit corresponding to |signal| in |set|. Return true on success
+// and false on failure. The function will fail if |signal| is greater than
+// NSIG or negative.
+constexpr inline bool add_signal(sigset_t &set, int signal) {
+  if (signal > NSIG || signal <= 0)
+    return false;
+  size_t n = size_t(signal) - 1;
+  size_t word = n / BITS_PER_SIGWORD;
+  size_t bit = n % BITS_PER_SIGWORD;
+  set.__signals[word] |= (1UL << bit);
+  return true;
+}
+
+// Reset the bit corresponding to |signal| in |set|. Return true on success
+// and false on failure. The function will fail if |signal| is greater than
+// NSIG or negative.
+constexpr inline bool delete_signal(sigset_t &set, int signal) {
+  if (signal > NSIG || signal <= 0)
+    return false;
+  size_t n = size_t(signal) - 1;
+  size_t word = n / BITS_PER_SIGWORD;
+  size_t bit = n % BITS_PER_SIGWORD;
+  set.__signals[word] &= ~(1UL << bit);
+  return true;
+}
+
+static inline int block_all_signals(sigset_t &set) {
+  sigset_t full = full_set();
+  return __llvm_libc::syscall(SYS_rt_sigprocmask, SIG_BLOCK, &full, &set,
+                              sizeof(sigset_t));
+}
+
+static inline int restore_signals(const sigset_t &set) {
+  return __llvm_libc::syscall(SYS_rt_sigprocmask, SIG_SETMASK, &set, nullptr,
+                              sizeof(sigset_t));
+}
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_SIGNAL_LINUX_SIGNAL_UTILS_H

libc/src/signal/linux/sigprocmask.cpp

 //===-- Linux implementation of sigprocmask -------------------------------===//
 //
 // 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/sigprocmask.h"
-#include "src/errno/llvmlibc_errno.h"
-#include "src/signal/linux/signal.h"
+#include "include/sys/syscall.h"          // For syscall numbers.
+#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+#include "src/signal/linux/signal_utils.h"
 
 #include "src/__support/common.h"
 
+#include <errno.h>
+#include <signal.h>
+
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(int, sigprocmask,
                    (int how, const sigset_t *__restrict set,
                     sigset_t *__restrict oldset)) {
   int ret = __llvm_libc::syscall(SYS_rt_sigprocmask, how, set, oldset,
                                  sizeof(sigset_t));
   if (!ret)
     return 0;
 
-  llvmlibc_errno = -ret;
+  errno = -ret;
   return -1;
 }
 
 } // namespace __llvm_libc

libc/src/signal/sigaction.h

 //===-- Implementation header for sigaction ---------------------*- 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_SIGACTION_H
 #define LLVM_LIBC_SRC_SIGNAL_SIGACTION_H
 
-#define __LLVM_LIBC_INTERNAL_SIGACTION
-#include "include/signal.h"
+#include <signal.h>
 
 namespace __llvm_libc {
 
-int sigaction(int signal, const struct __sigaction *__restrict libc_new,
-              struct __sigaction *__restrict libc_old);
+int sigaction(int signal, const struct sigaction *__restrict libc_new,
+              struct sigaction *__restrict libc_old);
 
 } // namespace __llvm_libc
 
 #endif // LLVM_LIBC_SRC_SIGNAL_SIGACTION_H

libc/src/signal/sigaddset.h

 //===-- Implementation header for sigaddset ---------------------*- 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_SIGEADDSET_H
 #define LLVM_LIBC_SRC_SIGNAL_SIGEADDSET_H
 
-#include "include/signal.h"
+#include <signal.h>
 
 namespace __llvm_libc {
 
 int sigaddset(sigset_t *set, int signum);
 
 } // namespace __llvm_libc
 
 #endif // LLVM_LIBC_SRC_SIGNAL_SIGEADDSET_H

libc/src/stdlib/CMakeLists.txt

SRCS
     exit.cpp
   HDRS
     exit.h
   DEPENDS
     ._Exit
     .atexit
 )
 
-# add_entrypoint_object(
-#   abort
-#   ALIAS
-#   DEPENDS
-#     .${LIBC_TARGET_OS}.abort
-# )
+add_entrypoint_object(
+  abort
+  ALIAS
+  DEPENDS
+    .${LIBC_TARGET_OS}.abort
+)

libc/src/stdlib/linux/CMakeLists.txt

 add_entrypoint_object(
   _Exit
   SRCS
     _Exit.cpp
   HDRS
     ../_Exit.h
   DEPENDS
     libc.include.sys_syscall
     libc.include.stdlib
     libc.src.__support.OSUtil.osutil
 )
 
-# add_entrypoint_object(
-#   abort
-#   SRCS
-#     abort.cpp
-#   HDRS
-#     ../abort.h
-#   DEPENDS
-#     libc.include.stdlib
-#     libc.src.signal.raise
-#     ._Exit
-# )
+add_entrypoint_object(
+  abort
+  SRCS
+    abort.cpp
+  HDRS
+    ../abort.h
+  DEPENDS
+    libc.include.stdlib
+    libc.src.signal.raise
+    ._Exit
+)

libc/test/src/CMakeLists.txt

 if(NOT LLVM_LIBC_FULL_BUILD)
   return()
 endif()
 
 add_subdirectory(dirent)
 # The signal API is currently disabled as signal.h is incorrect.
 # since assert uses the signal API, we disable assert also.
 # add_subdirectory(assert)
-# add_subdirectory(signal)
+add_subdirectory(signal)
 add_subdirectory(time)
 
 if(${LIBC_TARGET_OS} STREQUAL "linux")
   add_subdirectory(pthread)
 endif()
 
 set(public_test ${CMAKE_CURRENT_BINARY_DIR}/public_api_test.cpp)
 

libc/test/src/signal/sigaction_test.cpp

 //===-- Unittests for sigaction -------------------------------------------===//
 //
 // 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/errno.h"
-#define __LLVM_LIBC_INTERNAL_SIGACTION
-#include "include/signal.h"
 #include "src/signal/raise.h"
 #include "src/signal/sigaction.h"
 
 #include "test/ErrnoSetterMatcher.h"
 #include "utils/UnitTest/Test.h"
 
+#include <errno.h>
+#include <signal.h>
+
 using __llvm_libc::testing::ErrnoSetterMatcher::Fails;
 using __llvm_libc::testing::ErrnoSetterMatcher::Succeeds;
 
 TEST(LlvmLibcSigaction, Invalid) {
   // -1 is a much larger signal that NSIG, so this should fail.
   EXPECT_THAT(__llvm_libc::sigaction(-1, nullptr, nullptr), Fails(EINVAL));
 }
 
 // SIGKILL cannot have its action changed, but it can be examined.
 TEST(LlvmLibcSigaction, Sigkill) {
-  struct __sigaction action;
+  struct sigaction action;
   EXPECT_THAT(__llvm_libc::sigaction(SIGKILL, nullptr, &action), Succeeds());
   EXPECT_THAT(__llvm_libc::sigaction(SIGKILL, &action, nullptr), Fails(EINVAL));
 }
 
 static int sigusr1Count;
 static bool correctSignal;
 
 TEST(LlvmLibcSigaction, CustomAction) {
   // Zero this incase tests get run multiple times in the future.
   sigusr1Count = 0;
 
-  struct __sigaction action;
+  struct sigaction action;
   EXPECT_THAT(__llvm_libc::sigaction(SIGUSR1, nullptr, &action), Succeeds());
 
   action.sa_handler = +[](int signal) {
     correctSignal = signal == SIGUSR1;
     sigusr1Count++;
   };
   EXPECT_THAT(__llvm_libc::sigaction(SIGUSR1, &action, nullptr), Succeeds());
 
   __llvm_libc::raise(SIGUSR1);
   EXPECT_EQ(sigusr1Count, 1);
   EXPECT_TRUE(correctSignal);
 
   action.sa_handler = SIG_DFL;
   EXPECT_THAT(__llvm_libc::sigaction(SIGUSR1, &action, nullptr), Succeeds());
 
   EXPECT_DEATH([] { __llvm_libc::raise(SIGUSR1); }, WITH_SIGNAL(SIGUSR1));
 }
 
 TEST(LlvmLibcSigaction, Ignore) {
-  struct __sigaction action;
+  struct sigaction action;
   EXPECT_THAT(__llvm_libc::sigaction(SIGUSR1, nullptr, &action), Succeeds());
   action.sa_handler = SIG_IGN;
   EXPECT_THAT(__llvm_libc::sigaction(SIGUSR1, &action, nullptr), Succeeds());
 
   EXPECT_EXITS([] { __llvm_libc::raise(SIGUSR1); }, 0);
 }

libc/test/src/stdlib/CMakeLists.txt

DEPENDS
       libc.include.stdlib
       libc.src.stdlib._Exit
       libc.src.stdlib.exit
       libc.src.stdlib.atexit
       libc.src.__support.CPP.array
       libc.src.__support.CPP.utility
   )
 
-  # add_libc_unittest(
-  #   abort_test
-  #   SUITE
-  #     libc_stdlib_unittests
-  #   SRCS
-  #     abort_test.cpp
-  #   DEPENDS
-  #     libc.include.stdlib
-  #     libc.include.signal
-  #     libc.src.stdlib.abort
-  #     libc.src.stdlib._Exit
-  #     libc.src.signal.raise
-  # )
+  add_libc_unittest(
+    abort_test
+    SUITE
+      libc_stdlib_unittests
+    SRCS
+      abort_test.cpp
+    DEPENDS
+      libc.include.stdlib
+      libc.include.signal
+      libc.src.stdlib.abort
+      libc.src.stdlib._Exit
+      libc.src.signal.raise
+  )
 
 endif()