Configure: check usability of <stdckdint.h>, not only its existence

[t-a-k]

Some FreeBSD systems have <stdckdint.h>, but it cannot be compiled with C++ compilers. This patch modifies Configure to check whether ckd_* functions can be compiled, and leave I_STDCKDINT undefined (so that <stdckdint.h> won't be used in build time) if the compilation failed.

Will fix GH #23725.

---

• This set of changes does not require a perldelta entry.

[jkeenan]

IIUC, the differences which your patch would effect could be detected simply by running ./Configure, i.e., even before running make.

I decided to use the same FreeBSD machine on which I explored #23725 to test this out. I took my regular configuration command (which by default uses clang in whatever is its current default version), substitute in clang++ (in its current default version, 18):

sh ./Configure -des -Dusedevel \
  -Dcc=clang++ \
  -Duseithreads \
  -Doptimize="-O2 -pipe -fstack-protector-strong -fno-strict-aliasing"

... and use that first on blead, then on the branch in your pull request. I then compared their respective config.sh files. This is what I got:

diff --ignore-matching-lines 'Configuration time:' \
     --ignore-matching-lines 'cf_time=' \
     blead.clang++.config.sh \
     branch.clang++.config.sh

814c814
< i_stdckdint='define'
---
> i_stdckdint='undef'

@t-a-k, is this what you would have expected?

On each of these two builds I then ran make test_prep. In blead, the build failed in the same way as reported in #23725 (comment). In branch, the build succeeded, as did make test_harness.

$ ./perl -Ilib -v | head -2 | tail -1
This is perl 5, version 43, subversion 3 (v5.43.3 (v5.43.2-339-g9f09ee5689)) built for amd64-freebsd-thread-multi

$ ./perl -Ilib -V:config_args
config_args='-des -Dusedevel -Dcc=clang++ -Duseithreads -Doptimize=-O2 -pipe -fstack-protector-strong -fno-strict-aliasing';

This pull request DWIMs for me, but it should also be reviewed by people more familiar with ./Configure than me. @khwilliamson, @Tux, can you take a look?

[t-a-k]

Thank you for testing!

... and use that first on blead, then on the branch in your pull request. I then compared their respective config.sh files. This is what I got:

diff --ignore-matching-lines 'Configuration time:' \
     --ignore-matching-lines 'cf_time=' \
     blead.clang++.config.sh \
     branch.clang++.config.sh

814c814
< i_stdckdint='define'
---
> i_stdckdint='undef'

@t-a-k, is this what you would have expected?

Yes. In this case <stdckdint.h> is present but fails to compile with specified compiler (probably because it is not compatible with C++), therefore Configure in this branch will set i_stdckdint to undef to indicate <stdckdint.h> is not usable.

[khwilliamson]

My question is, is there a C++ compatible hdr that would serve instead of this

[khwilliamson]

And the answer to my question is no

[t-a-k]

Thank you for merging.

My question is, is there a C++ compatible hdr that would serve instead of this

As far as I can see, Clang 19's own stdckdint.h seems to be C++ compatible, and GCC 15's libstdc++ seems to have its own stdckdint.h for C++ programs.

I verified the former on Debian 13 (whose default Clang is v19, and which does not have /usr/include/stdckdint.h) as ./Configure ... -Dcc=clang++ leaves i_stdckdint='define' and perl builds successfully.

[jkeenan]

Thank you for merging.

My question is, is there a C++ compatible hdr that would serve instead of this

As far as I can see, Clang 19's own stdckdint.h seems to be C++ compatible, and GCC 15's libstdc++ seems to have its own stdckdint.h for C++ programs.

I verified the former on Debian 13 (whose default Clang is v19, and which does not have /usr/include/stdckdint.h) as ./Configure ... -Dcc=clang++ leaves i_stdckdint='define' and perl builds successfully.

FWIW, here are the different flavors of stdckdint.h I was able to locate on the FreeBSD-14 machine from which I have been reporting:

$ find /usr -type f -name '*stdckdint.h' 2>/dev/null | sort | xargs ls -l
-r--r--r--  1 root wheel 1050 Apr 14 20:28 /usr/include/stdckdint.h
-r--r--r--  1 root wheel 1666 Apr 14 20:28 /usr/lib/clang/18/include/stdckdint.h
-rw-r--r--  1 root wheel 1509 Jul 24 10:51 /usr/local/lib/gcc14/gcc/x86_64-portbld-freebsd14.2/14.3.1/include/stdckdint.h
-rw-r--r--  1 root wheel 1666 Jan 14  2025 /usr/local/llvm19/lib/clang/19/include/stdckdint.h
-rw-r--r--  1 root wheel 1666 Jul  8 23:06 /usr/local/llvm20/lib/clang/20/include/stdckdint.h
-rw-r--r--  1 root wheel 1666 Apr 14 20:47 /usr/src/contrib/llvm-project/clang/lib/Headers/stdckdint.h
-rw-r--r--  1 root wheel 1050 Apr 14 20:47 /usr/src/include/stdckdint.h

Let's see what's different.

$ diff -w /usr/include/stdckdint.h /usr/src/include/stdckdint.h
[ no diffs ]

$ diff -w /usr/lib/clang/18/include/stdckdint.h /usr/local/llvm19/lib/clang/19/include/stdckdint.h
[ no diffs ]

$ diff -w /usr/lib/clang/18/include/stdckdint.h /usr/local/llvm20/lib/clang/20/include/stdckdint.h
[ no diffs ]

$ diff -w /usr/lib/clang/18/include/stdckdint.h /usr/src/contrib/llvm-project/clang/lib/Headers/stdckdint.h
[ no diffs ]

But ...

$ diff -w /usr/include/stdckdint.h /usr/lib/clang/18/include/stdckdint.h
1,2c1
< /*-
<  * Copyright (c) 2023 Dag-Erling Smørgrav
---
> /*===---- stdckdint.h - Standard header for checking integer----------------===
4c3,7
<  * SPDX-License-Identifier: BSD-2-Clause
---
>  * 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
>  *
>  *===-----------------------------------------------------------------------===
7,8c10,11
< #ifndef __STDC_VERSION_STDCKDINT_H__
< #define __STDC_VERSION_STDCKDINT_H__ 202311L
---
> #ifndef __STDCKDINT_H
> #define __STDCKDINT_H
10c13,20
< #include <sys/cdefs.h>
---
> /* If we're hosted, fall back to the system's stdckdint.h. FreeBSD, for
>  * example, already has a Clang-compatible stdckdint.h header.
>  *
>  * The `stdckdint.h` header requires C 23 or newer.
>  */
> #if __STDC_HOSTED__ && __has_include_next(<stdckdint.h>)
> #include_next <stdckdint.h>
> #else
12c22
< #if __BSD_VISIBLE || __ISO_C_VISIBLE >= 2023
---
> /* C23 7.20.1 Defines several macros for performing checked integer arithmetic*/
14,20c24
< #if __GNUC_PREREQ__(5, 1) || __has_builtin(__builtin_add_overflow)
< #define ckd_add(result, a, b)						\
< 	(_Bool)__builtin_add_overflow((a), (b), (result))
< #else
< #define ckd_add(result, a, b)						\
< 	_Static_assert(0, "checked addition not supported")
< #endif
---
> #define __STDC_VERSION_STDCKDINT_H__ 202311L
22,28c26,27
< #if __GNUC_PREREQ__(5, 1) || __has_builtin(__builtin_sub_overflow)
< #define ckd_sub(result, a, b)						\
< 	(_Bool)__builtin_sub_overflow((a), (b), (result))
< #else
< #define ckd_sub(result, a, b)						\
< 	_Static_assert(0, "checked subtraction not supported")
< #endif
---
> // Both A and B shall be any integer type other than "plain" char, bool, a bit-
> // precise integer type, or an enumerated type, and they need not be the same.
30,36c29,32
< #if __GNUC_PREREQ__(5, 1) || __has_builtin(__builtin_mul_overflow)
< #define ckd_mul(result, a, b)						\
< 	(_Bool)__builtin_mul_overflow((a), (b), (result))
< #else
< #define ckd_mul(result, a, b)						\
< 	_Static_assert(0, "checked multiplication not supported")
< #endif
---
> // R shall be a modifiable lvalue of any integer type other than "plain" char,
> // bool, a bit-precise integer type, or an enumerated type. It shouldn't be
> // short type, either. Otherwise, it may be unable to hold two the result of
> // operating two 'int's.
38c34,39
< #endif
---
> // A diagnostic message will be produced if A or B are not suitable integer
> // types, or if R is not a modifiable lvalue of a suitable integer type or R
> // is short type.
> #define ckd_add(R, A, B) __builtin_add_overflow((A), (B), (R))
> #define ckd_sub(R, A, B) __builtin_sub_overflow((A), (B), (R))
> #define ckd_mul(R, A, B) __builtin_mul_overflow((A), (B), (R))
40c41,42
< #endif
---
> #endif /* __STDC_HOSTED__ */
> #endif /* __STDCKDINT_H */