d51aa1a build-time failure with clang++ and g++

[jkeenan]

In this smoke-testing report filed by @cjg-cguevara, we observe a build-time (make) failure when compiling with clang++ version 19 on FreeBSD-14.3.

I have reproduced this failure on the FreeBSD machine from which I customarily generate smoke-test reports. I rarely smoke-test clang++, so the point when this build failure started to occur was not immediately evident to me.

On this machine, the default clang++ (/usr/bin/clang++) is version 18. Configuring and building as follows:

sh ./Configure -des -Dusedevel -Dusethreads -Dcc=clang++ && make test_prep 2>&1

... I got plenty of this kind of warning in both ./Configure and make test_prep ...

clang++: warning: treating 'c' input as 'c++' when in C++ mode, this behavior is deprecated [-Wdeprecated]

... but, then again, I've come to expect that with c++-equivalent compilers. What I did not expect was for the build to fail here:

clang++ -c -DPERL_CORE -DHAS_FPSETMASK -DHAS_FLOATINGPOINT_H -DNO_POSIX_2008_LOCALE -I/usr/local/include -O2 -Wall -Werror=pointer-arith -Werror=vla -Wextra -Wno-long-long -Wno-declaration-after-statement -Wc++-compat -Wwrite-strings pp.c
clang++: warning: treating 'c' input as 'c++' when in C++ mode, this behavior is deprecated [-Wdeprecated]
pp.c:1343:18: error: use of undeclared identifier '_Bool'
 1343 |             if (!S_iv_mul_may_overflow(il, ir, &result)) {
      |                  ^
./inline.h:3540:51: note: expanded from macro 'S_iv_mul_may_overflow'
 3540 | #    define S_iv_mul_may_overflow(il, ir, result) ckd_mul(result, il, ir)
      |                                                   ^
/usr/include/stdckdint.h:32:3: note: expanded from macro 'ckd_mul'
   32 |         (_Bool)__builtin_mul_overflow((a), (b), (result))
      |          ^
pp.c:1409:18: error: use of undeclared identifier '_Bool'
 1409 |             if (!S_uv_mul_overflow(alow, blow, &product)) {
      |                  ^
./inline.h:3567:49: note: expanded from macro 'S_uv_mul_overflow'
 3567 | #    define S_uv_mul_overflow(auv, buv, result) ckd_mul(result, auv, buv)
      |                                                 ^
/usr/include/stdckdint.h:32:3: note: expanded from macro 'ckd_mul'
   32 |         (_Bool)__builtin_mul_overflow((a), (b), (result))
      |          ^
pp.c:1874:18: error: use of undeclared identifier '_Bool'
 1874 |             if (!S_iv_sub_may_overflow(il, ir, &result)) {
      |                  ^
./inline.h:3507:51: note: expanded from macro 'S_iv_sub_may_overflow'
 3507 | #    define S_iv_sub_may_overflow(il, ir, result) ckd_sub(result, il, ir)
      |                                                   ^
/usr/include/stdckdint.h:24:3: note: expanded from macro 'ckd_sub'
   24 |         (_Bool)__builtin_sub_overflow((a), (b), (result))
      |          ^
3 errors generated.
*** Error code 1

Stop.
make: stopped in /usr/home/jkeenan/gitwork/perl

I got the same build-time failure when using clang++19 on the same box. (I have not yet tried clang++20.)

I also got a build-time failure when targeting miniperl:

sh ./Configure -des -Dusedevel -Dusethreads -Dcc=clang++ && make miniperl
...
clang++ -c -DPERL_CORE -DHAS_FPSETMASK -DHAS_FLOATINGPOINT_H -DNO_POSIX_2008_LOCALE -I/usr/local/include -O2 -Wall -Werror=pointer-arith -Werror=vla -Wextra -Wno-long-long -Wno-declaration-after-statement -Wc++-compat -Wwrite-strings pp.c
clang++: warning: treating 'c' input as 'c++' when in C++ mode, this behavior is deprecated [-Wdeprecated]
pp.c:1343:18: error: use of undeclared identifier '_Bool'
 1343 |             if (!S_iv_mul_may_overflow(il, ir, &result)) {
      |                  ^
./inline.h:3540:51: note: expanded from macro 'S_iv_mul_may_overflow'
 3540 | #    define S_iv_mul_may_overflow(il, ir, result) ckd_mul(result, il, ir)
      |                                                   ^
/usr/include/stdckdint.h:32:3: note: expanded from macro 'ckd_mul'
   32 |         (_Bool)__builtin_mul_overflow((a), (b), (result))
      |          ^
pp.c:1409:18: error: use of undeclared identifier '_Bool'
 1409 |             if (!S_uv_mul_overflow(alow, blow, &product)) {
      |                  ^
./inline.h:3567:49: note: expanded from macro 'S_uv_mul_overflow'
 3567 | #    define S_uv_mul_overflow(auv, buv, result) ckd_mul(result, auv, buv)
      |                                                 ^
/usr/include/stdckdint.h:32:3: note: expanded from macro 'ckd_mul'
   32 |         (_Bool)__builtin_mul_overflow((a), (b), (result))
      |          ^
pp.c:1874:18: error: use of undeclared identifier '_Bool'
 1874 |             if (!S_iv_sub_may_overflow(il, ir, &result)) {
      |                  ^
./inline.h:3507:51: note: expanded from macro 'S_iv_sub_may_overflow'
 3507 | #    define S_iv_sub_may_overflow(il, ir, result) ckd_sub(result, il, ir)
      |                                                   ^
/usr/include/stdckdint.h:24:3: note: expanded from macro 'ckd_sub'
   24 |         (_Bool)__builtin_sub_overflow((a), (b), (result))
      |          ^
3 errors generated.
*** Error code 1

Stop.

I next tried using g++. The latest version available on this machine was 14. Here I configured with:

$ sh ./Configure -des -Dusedevel -Dcc=g++14 && make miniperl

make miniperl died here:

g++14 -c -DPERL_CORE -DHAS_FPSETMASK -DHAS_FLOATINGPOINT_H -DNO_POSIX_2008_LOCALE -fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include -D_FORTIFY_SOURCE=2 -O2 -Wall -Werror=pointer-arith -Werror=vla -Wextra -Wno-long-long -Wwrite-strings pp.c
In file included from inline.h:3460,
                 from perl.h:8080,
                 from pp.c:28:
pp.c: In function 'OP* Perl_pp_multiply()':
inline.h:3540:51: error: '_Bool' was not declared in this scope
 3540 | #    define S_iv_mul_may_overflow(il, ir, result) ckd_mul(result, il, ir)
      |                                                   ^~~~~~~
pp.c:1343:18: note: in expansion of macro 'S_iv_mul_may_overflow'
 1343 |             if (!S_iv_mul_may_overflow(il, ir, &result)) {
      |                  ^~~~~~~~~~~~~~~~~~~~~
inline.h:3540:51: error: expected ')' before '__builtin_mul_overflow'
 3540 | #    define S_iv_mul_may_overflow(il, ir, result) ckd_mul(result, il, ir)
      |                                                   ^~~~~~~
pp.c:1343:18: note: in expansion of macro 'S_iv_mul_may_overflow'
 1343 |             if (!S_iv_mul_may_overflow(il, ir, &result)) {
      |                  ^~~~~~~~~~~~~~~~~~~~~
pp.c:1346:14: error: expected ')' before 'goto'
 1346 |             }
      |              ^
      |              )
 1347 |             goto generic;
      |             ~~~~
pp.c:1343:16: note: to match this '('
 1343 |             if (!S_iv_mul_may_overflow(il, ir, &result)) {
      |                ^
pp.c:1347:25: warning: suggest braces around empty body in an 'if' statement [-Wempty-body]
 1347 |             goto generic;
      |                         ^
pp.c:1339:16: warning: unused variable 'result' [-Wunused-variable]
 1339 |             IV result;
      |                ^~~~~~
inline.h:3567:49: error: '_Bool' was not declared in this scope
 3567 | #    define S_uv_mul_overflow(auv, buv, result) ckd_mul(result, auv, buv)
      |                                                 ^~~~~~~
pp.c:1409:18: note: in expansion of macro 'S_uv_mul_overflow'
 1409 |             if (!S_uv_mul_overflow(alow, blow, &product)) {
      |                  ^~~~~~~~~~~~~~~~~
inline.h:3567:49: error: expected ')' before '__builtin_mul_overflow'
 3567 | #    define S_uv_mul_overflow(auv, buv, result) ckd_mul(result, auv, buv)
      |                                                 ^~~~~~~
pp.c:1409:18: note: in expansion of macro 'S_uv_mul_overflow'
 1409 |             if (!S_uv_mul_overflow(alow, blow, &product)) {
      |                  ^~~~~~~~~~~~~~~~~
pp.c:1419:14: error: expected ')' before '}' token
 1419 |             } /* ahigh && bhigh */
      |              ^
      |              )
 1420 |         } /* SvIOK(svl) */
      |         ~     
pp.c:1409:16: note: to match this '('
 1409 |             if (!S_uv_mul_overflow(alow, blow, &product)) {
      |                ^
pp.c:1420:9: error: expected primary-expression before '}' token
 1420 |         } /* SvIOK(svl) */
      |         ^
pp.c:1382:16: warning: unused variable 'product' [-Wunused-variable]
 1382 |             UV product;
      |                ^~~~~~~
pp.c:1370:3: warning: label 'generic' defined but not used [-Wunused-label]
 1370 |   generic:
      |   ^~~~~~~
pp.c: In function 'OP* Perl_pp_subtract()':
inline.h:3507:51: error: '_Bool' was not declared in this scope
 3507 | #    define S_iv_sub_may_overflow(il, ir, result) ckd_sub(result, il, ir)
      |                                                   ^~~~~~~
pp.c:1874:18: note: in expansion of macro 'S_iv_sub_may_overflow'
 1874 |             if (!S_iv_sub_may_overflow(il, ir, &result)) {
      |                  ^~~~~~~~~~~~~~~~~~~~~
inline.h:3507:51: error: expected ')' before '__builtin_sub_overflow'
 3507 | #    define S_iv_sub_may_overflow(il, ir, result) ckd_sub(result, il, ir)
      |                                                   ^~~~~~~
pp.c:1874:18: note: in expansion of macro 'S_iv_sub_may_overflow'
 1874 |             if (!S_iv_sub_may_overflow(il, ir, &result)) {
      |                  ^~~~~~~~~~~~~~~~~~~~~
pp.c:1877:14: error: expected ')' before 'goto'
 1877 |             }
      |              ^
      |              )
 1878 |             goto generic;
      |             ~~~~
pp.c:1874:16: note: to match this '('
 1874 |             if (!S_iv_sub_may_overflow(il, ir, &result)) {
      |                ^
pp.c:1878:25: warning: suggest braces around empty body in an 'if' statement [-Wempty-body]
 1878 |             goto generic;
      |                         ^
pp.c:1870:16: warning: unused variable 'result' [-Wunused-variable]
 1870 |             IV result;
      |                ^~~~~~
pp.c:1894:3: warning: label 'generic' defined but not used [-Wunused-label]
 1894 |   generic:
      |   ^~~~~~~
*** Error code 1

Stop.

Finally, I bisected using the following invocation:

$ perl Porting/bisect.pl \
--test-build -Dcc=clang++ \
--start c4da28b08d \
--end e96b7226ea

Behavior changed at d51aa1a, committed to blead on Sept 16.

d51aa1a511cb145eb6487dbc3bef0397bd6ea156 is the first bad commit
commit d51aa1a511cb145eb6487dbc3bef0397bd6ea156
Author: TAKAI Kousuke <62541129+t-a-k@users.noreply.github.com>
Date:   Fri Aug 29 01:48:30 2025 +0900
Commit:     Karl Williamson <khw@cpan.org>
CommitDate: Tue Sep 16 13:55:31 2025 -0600


    Introduce I_STDCKDINT config macro

    This macro is defined in config.h if <stdckdint.h> is available,
    and used in previously commited code
    (0f2b1e648156555a96ed54170e1b385a60010910, GH #23503).

@t-a-k, @khwilliamson, can you take a look? Thanks.

[jkeenan]

Behavior changed at d51aa1a, committed to blead on Sept 16.

d51aa1a511cb145eb6487dbc3bef0397bd6ea156 is the first bad commit
commit d51aa1a511cb145eb6487dbc3bef0397bd6ea156
Author: TAKAI Kousuke <62541129+t-a-k@users.noreply.github.com>
Date:   Fri Aug 29 01:48:30 2025 +0900
Commit:     Karl Williamson <khw@cpan.org>
CommitDate: Tue Sep 16 13:55:31 2025 -0600


    Introduce I_STDCKDINT config macro

    This macro is defined in config.h if <stdckdint.h> is available,
    and used in previously commited code
    (0f2b1e648156555a96ed54170e1b385a60010910, GH #23503).

@t-a-k, @khwilliamson, can you take a look? Thanks.

The code committed in the breaking commit was developed in this pull request:
#23703

[Leont]

It seems like your stdckdint.h assumes the C99 type _Bool is defined, but it isn't on C++. On my computer (gcc 15.2.1) there's a C++ override header that fixes this, but I guess that wasn't there from the start. This is all most unfortunate.

[t-a-k]

@jkeenan Could you please run the same test with -Ui_stdckdint added to ./Configure ?

If that works, I'll submit a PR to tweak Configure to avoid defining I_STDCKDINT when ckd_* macros fail to compile.

[jkeenan]

@jkeenan Could you please run the same test with -Ui_stdckdint added to ./Configure ?

If that works, I'll submit a PR to tweak Configure to avoid defining I_STDCKDINT when ckd_* macros fail to compile.

g++14

$ sh ./Configure -des -Dusedevel -Dcc=g++14 -Ui_stdckdint && make miniperl
$ make minitest
$ make test_harness

The above commands completed successfully.

clang++18 (default clang on this machine)

$ sh ./Configure -des -Dusedevel -Dusethreads -Dcc=clang++ -Ui_stdckdint && make test_prep 2>&1 | tee $P5P_DIR/make-output/`extract-sha`.freebsd.threaded.clang++18.modified.maketp.output.txt

makefailed, ending like this:

...
clang++ -c -DPERL_CORE -DHAS_FPSETMASK -DHAS_FLOATINGPOINT_H -DNO_POSIX_2008_LOCALE -I/usr/local/include -O2 -Wall -Werror=pointer-arith -Werror=vla -Wextra -Wno-long-long -Wno-declaration-after-statement -Wc++-compat -Wwrite-strings pp.c
clang++: warning: treating 'c' input as 'c++' when in C++ mode, this behavior is deprecated [-Wdeprecated]
pp.c:1343:18: error: use of undeclared identifier '_Bool'
 1343 |             if (!S_iv_mul_may_overflow(il, ir, &result)) {
      |                  ^
./inline.h:3542:51: note: expanded from macro 'S_iv_mul_may_overflow'
 3542 | #    define S_iv_mul_may_overflow(il, ir, result) ckd_mul(result, il, ir)
      |                                                   ^
/usr/include/stdckdint.h:32:3: note: expanded from macro 'ckd_mul'
   32 |         (_Bool)__builtin_mul_overflow((a), (b), (result))
      |          ^
pp.c:1409:18: error: use of undeclared identifier '_Bool'
 1409 |             if (!S_uv_mul_overflow(alow, blow, &product)) {
      |                  ^
./inline.h:3569:49: note: expanded from macro 'S_uv_mul_overflow'
 3569 | #    define S_uv_mul_overflow(auv, buv, result) ckd_mul(result, auv, buv)
      |                                                 ^
/usr/include/stdckdint.h:32:3: note: expanded from macro 'ckd_mul'
   32 |         (_Bool)__builtin_mul_overflow((a), (b), (result))
      |          ^
pp.c:1874:18: error: use of undeclared identifier '_Bool'
 1874 |             if (!S_iv_sub_may_overflow(il, ir, &result)) {
      |                  ^
./inline.h:3509:51: note: expanded from macro 'S_iv_sub_may_overflow'
 3509 | #    define S_iv_sub_may_overflow(il, ir, result) ckd_sub(result, il, ir)
      |                                                   ^
/usr/include/stdckdint.h:24:3: note: expanded from macro 'ckd_sub'
   24 |         (_Bool)__builtin_sub_overflow((a), (b), (result))
      |          ^
3 errors generated.
*** Error code 1

Stop.

The error output was, with the exception of a few line numbers in inline.h, identical to that reported previously for this version of clang++.

clang++19

$ sh ./Configure -des -Dusedevel -Dusethreads -Dcc=clang++19 -Ui_stdckdint && make test_prep 2>&1 | \
  tee $P5P_DIR/make-output/`extract-sha`.freebsd.threaded.clang++19.modified.maketp.output.txt

make test_prep completed successfully (albeit with build-time warnings I've come to expect; won't complain about those here). make test_harness PASS

clang++20

(First time attempting this version of clang++.)

$ sh ./Configure -des -Dusedevel -Dusethreads -Dcc=clang++20 -Ui_stdckdint && make test_prep 2>&1 | \
  tee $P5P_DIR/make-output/`extract-sha`.freebsd.threaded.clang++20.modified.maketp.output.txt

Same (good) results as from using clang++19.

I was not at first surprised by the results with clang++ version 18. But when versions 19 and 20 PASSed, I decided to re-run with what on this version of FreeBSD is the default C compiler. This time, make completed (with the expected build-time warnings) and make test_harness PASSed.

$ sh ./Configure -des -Dusedevel -Dusethreads -Dcc=clang++ -Ui_stdckdint && make test_prep 2>&1 | \
  tee $P5P_DIR/make-output/`extract-sha`.freebsd.threaded.clang++18.modified.maketp.2.output.txt

So, @t-a-k I think you should proceed to submit a pull request. However, I don't know what code changes should go into ./Configure and what into, say, hints/freebsd.sh.

[t-a-k]

My apologies, -Ui_stdckdint doesn't work as expected.
I've mixed up with other Configure variables that can be overridden with -U (such as -Ud_builtin_add_overflow)

I've also submit PR #23739 to fix this. I would appreciate it if you could check.

[jkeenan]

My apologies, -Ui_stdckdint doesn't work as expected. I've mixed up with other Configure variables that can be overridden with -U (such as -Ud_builtin_add_overflow)

I've also submit PR #23739 to fix this. I would appreciate it if you could check.

#23739, a possible solution to this Issue, awaits further code review.

[tonycoz]

#23739, a possible solution to this Issue, awaits further code review.

which has been approved and merged.

[jkeenan]

#23739, a possible solution to this Issue, awaits further code review.

which has been approved and merged.

I'll build myself and watch smoke-test reports and close this in a couple of days.