[libc] Add limits.h

[alfredfo]

Summary

This header contains implementation specific constants.

The compiler already provides its own limits.h with numerical limits
conforming to freestanding ISO C. But it is missing extensions like
POSIX, and does for example not include <linux/limits.h> which is
expected on a Linux system, therefore, an LLVM libc implementation of
limits.h is needed for hosted (STDC_HOSTED) environments.

[michaelrj]

The limits.h header is provided by the compiler, so us providing it will just cause problems

[alfredfo]

In D156961#4558158, @michaelrj wrote:

The limits.h header is provided by the compiler, so us providing it will just cause problems

Hmm, are you sure? I thought Clang headers and libc headers were both supposed to be used. Also, Clang headers only have standard C things, no POSIX/GNU extensions... etc.
I know SSIZE_MAX isn't there, also PATH_MAX is not available so it does not include <linux/limits.h> like musl and glibc.

[alfredfo]

Yeah prob should be provided by both :)

/* System headers include a number of constants from POSIX in <limits.h>.
   Include it if we're hosted. */
#if __STDC_HOSTED__ && __has_include_next(<limits.h>)
#include_next <limits.h>
#endif

https://github.com/llvm/llvm-project/blob/eac78fdf68f58e113b2cf18a14baccb8f5ebcf50/clang/lib/Headers/limits.h#L18

[michaelrj]

Ah! In that case, this looks good.

[michaelrj]

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

10

as an added thing, can we make it so that we only define these if they aren't already defined?

[sivachandra]

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

15

Considering LONG_MAX is already defined in the freestanding limits.h, may be all you need is:

#define SSIZE_MAX __LONG_MAX__

[alfredfo]

remove PATH_MAX definition

[alfredfo]

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

10

Sure, will fix tomorrow

15

Yes, done

[alfredfo]

only define SSIZE_MAX if not already defined

[alfredfo]

update msg

[alfredfo]

arc broken moment

[alfredfo]

update message

libc/config/linux/x86_64/headers.txt

 set(TARGET_PUBLIC_HEADERS
     libc.include.assert
     libc.include.ctype
     libc.include.dirent
     libc.include.errno
     libc.include.fcntl
     libc.include.fenv
     libc.include.inttypes
+    libc.include.limits
     libc.include.math
     libc.include.pthread
     libc.include.sched
     libc.include.signal
     libc.include.spawn
     libc.include.setjmp
     libc.include.stdio
     libc.include.stdlib

libc/include/CMakeLists.txt

add_gen_header(
   DEF_FILE inttypes.h.def
   GEN_HDR inttypes.h
   DEPENDS
     .llvm_libc_common_h
     .llvm-libc-types.imaxdiv_t
 )
 
 add_gen_header(
+  limits
+  DEF_FILE limits.h.def
+  GEN_HDR limits.h
+  DEPENDS
+    .llvm_libc_common_h
+    .llvm-libc-macros.limits_macros
+)
+
+add_gen_header(
   math
   DEF_FILE math.h.def
   GEN_HDR math.h
   DEPENDS
     .llvm_libc_common_h
     .llvm-libc-macros.math_macros
     .llvm-libc-types.double_t
     .llvm-libc-types.float_t

libc/include/limits.h.def

+//===-- C standard library header limits.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_LIMITS_H
+#define LLVM_LIBC_LIMITS_H
+
+#include <__llvm-libc-common.h>
+#include <llvm-libc-macros/limits-macros.h>
+
+%%public_api()
+
+#endif // LLVM_LIBC_LIMITS_H

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

DEPENDS
     .linux.unistd_macros
 )
 
 add_header(
   wchar_macros
   HDR
     wchar-macros.h
 )
+
+add_header(
+  limits_macros
+  HDR
+    limits-macros.h
+)

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

+#ifndef __LLVM_LIBC_MACROS_LIMITS_MACROS_H
+#define __LLVM_LIBC_MACROS_LIMITS_MACROS_H
+
+#ifdef __linux__
+#include <linux/limits.h>
+#endif
+
+#ifndef SSIZE_MAX
+#define SSIZE_MAX __LONG_MAX__
+#endif
+
+#endif // __LLVM_LIBC_MACROS_LIMITS_MACROS_H

libc/spec/posix.td

[
       FunctionSpec<
           "openat",
           RetValSpec<IntType>,
           [ArgSpec<IntType>, ArgSpec<ConstCharPtr>, ArgSpec<IntType>, ArgSpec<VarArgType>]
       >,
     ]
   >;
 
+  HeaderSpec Limits = HeaderSpec<
+    "limits.h",
+    [
+        Macro<"SSIZE_MAX">,
+    ],
+    [], // Types
+    [], // Enumerations
+    [] // Functions
+  >;
+
   HeaderSpec SysMMan = HeaderSpec<
       "sys/mman.h",
       [
         // TODO: Add a facility to bunch macros into bitwise-or-able groups.
         // POSIX requires it, so such thing should be captured in this spec.
         Macro<"PROT_EXEC">,
         Macro<"PROT_NONE">,
         Macro<"PROT_READ">,

   >;
 
   let Headers = [
     ArpaInet,
     CType,
     Dirent,
     Errno,
     FCntl,
+    Limits,
     PThread,
     Sched,
     Signal,
     Spawn,
     StdIO,
     StdLib,
     SysIOctl,
     SysMMan,

libc/spec/stdc.td

HeaderSpec IntTypes = HeaderSpec<
       [
           FunctionSpec<"imaxabs", RetValSpec<IntMaxTType>, [ArgSpec<IntMaxTType>]>,
           FunctionSpec<"imaxdiv", RetValSpec<IMaxDivTType>, [ArgSpec<IntMaxTType>, ArgSpec<IntMaxTType>]>,
           FunctionSpec<"strtoimax", RetValSpec<IntMaxTType>, [ArgSpec<ConstCharRestrictedPtr>, ArgSpec<CharRestrictedPtrPtr>, ArgSpec<IntType>]>,
           FunctionSpec<"strtoumax", RetValSpec<UIntMaxTType>, [ArgSpec<ConstCharRestrictedPtr>, ArgSpec<CharRestrictedPtrPtr>, ArgSpec<IntType>]>,
       ]
   >;
 
+  HeaderSpec Limits = HeaderSpec<
+      "limits.h",
+      [
+        Macro<"LONG_MAX">,
+      ],
+      [], // Types
+      [], // Enumerations
+      [] // Functions
+  >;
+
   HeaderSpec Errno = HeaderSpec<
       "errno.h",
       [
         Macro<"errno">,
         Macro<"EDOM">,
         Macro<"EILSEQ">,
         Macro<"ERANGE">,
       ]
let Headers = [
     CType,
     Errno,
     Fenv,
     Math,
     String,
     StdIO,
     StdLib,
     IntTypes,
+    Limits,
     SetJmp,
     Signal,
     Threads,
     Time,
     WChar,
   ];
 }