Weird behavior of string eval and true builtin on threaded perl

[bbrtj]

Description
This is a very weird bug that affects use v5.40 in a sandboxed string eval. I am evaling strings like these:

package Sandbox1;
use v5.40;
$code

where $code is usually just a perl hashref in a string, like a config file. I started using builtin booleans in these configs, since I am using 5.40 here. The problem is that on threaded perls, I get Bareword "true" not allowed while "strict subs" in use error, even though use 5.40 is clearly there. This does not happen on non-threaded perls.

Steps to Reproduce

Here is the most minimal example I could come up with:

repr.pl file:

use lib '.';
use eval_bug;
eval_bug::do_eval;

eval_bug.pm file:

package eval_bug;
$eval_bug::VERSION='0.001';

use v5.40;

sub do_eval
{
	eval 'use v5.40; true';
	die $@ if $@;
}

These files must be separate, putting the package in the same file does not cause the error. $VERSION declaration is necessary as well. I use 5.42 threaded, no error on 5.42 unthreaded.

Expected behavior

I'd expect true builtin to be imported. At the very least, behavior should be consistent on threaded and non-threaded perls.

Perl configuration

Summary of my perl5 (revision 5 version 42 subversion 0) configuration:

  Platform:
    osname=linux
    osvers=5.15.161
    archname=x86_64-linux-thread-multi
    uname='linux thinkpad.local 5.15.161 #1 smp preempt sun jun 16 15:55:06 cdt 2024 x86_64 intel(r) core(tm) i7-8650u cpu @ 1.90ghz genuineintel gnulinux '
    config_args='-de -Dprefix=/home/bartosz/perl5/perlbrew/perls/perl-5.42.0-thread -Duseshrplib -Dusethreads -Aeval:scriptdir=/home/bartosz/perl5/perlbrew/perls/perl-5.42.0-thread/bin'
    hint=recommended
    useposix=true
    d_sigaction=define
    useithreads=define
    usemultiplicity=define
    use64bitint=define
    use64bitall=define
    uselongdouble=undef
    usemymalloc=n
    default_inc_excludes_dot=define
  Compiler:
    cc='cc'
    ccflags ='-D_REENTRANT -D_GNU_SOURCE -fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -D_FORTIFY_SOURCE=2'
    optimize='-O2'
    cppflags='-D_REENTRANT -D_GNU_SOURCE -fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include'
    ccversion=''
    gccversion='11.2.0'
    gccosandvers=''
    intsize=4
    longsize=8
    ptrsize=8
    doublesize=8
    byteorder=12345678
    doublekind=3
    d_longlong=define
    longlongsize=8
    d_longdbl=define
    longdblsize=16
    longdblkind=3
    ivtype='long'
    ivsize=8
    nvtype='double'
    nvsize=8
    Off_t='off_t'
    lseeksize=8
    alignbytes=8
    prototype=define
  Linker and Libraries:
    ld='cc'
    ldflags =' -fstack-protector-strong -L/usr/local/lib'
    libpth=/usr/local/lib /usr/lib /lib64 /usr/lib64 /lib /usr/local/lib64
    libs=-lpthread -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc
    perllibs=-lpthread -ldl -lm -lcrypt -lutil -lc
    libc=libc-2.33.so
    so=so
    useshrplib=true
    libperl=libperl.so
    gnulibc_version='2.33'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs
    dlext=so
    d_dlsymun=undef
    ccdlflags='-Wl,-E -Wl,-rpath,/home/bartosz/perl5/perlbrew/perls/perl-5.42.0-thread/lib/5.42.0/x86_64-linux-thread-multi/CORE'
    cccdlflags='-fPIC'
    lddlflags='-shared -O2 -L/usr/local/lib -fstack-protector-strong'


Characteristics of this binary (from libperl):
  Compile-time options:
    HAS_LONG_DOUBLE
    HAS_STRTOLD
    HAS_TIMES
    MULTIPLICITY
    PERLIO_LAYERS
    PERL_COPY_ON_WRITE
    PERL_DONT_CREATE_GVSV
    PERL_HASH_FUNC_SIPHASH13
    PERL_HASH_USE_SBOX32
    PERL_MALLOC_WRAP
    PERL_OP_PARENT
    PERL_PRESERVE_IVUV
    PERL_USE_SAFE_PUTENV
    USE_64_BIT_ALL
    USE_64_BIT_INT
    USE_ITHREADS
    USE_LARGE_FILES
    USE_LOCALE
    USE_LOCALE_COLLATE
    USE_LOCALE_CTYPE
    USE_LOCALE_NUMERIC
    USE_LOCALE_TIME
    USE_PERLIO
    USE_PERL_ATOF
    USE_REENTRANT_API
    USE_THREAD_SAFE_LOCALE
  Built under linux
  Compiled at Jan  4 2026 15:22:53
  %ENV:
    PERLBREW_HOME="/home/bartosz/.perlbrew"
    PERLBREW_MANPATH="/home/bartosz/perl5/perlbrew/perls/perl-5.42.0-thread/man"
    PERLBREW_PATH="/home/bartosz/perl5/perlbrew/bin:/home/bartosz/perl5/perlbrew/perls/perl-5.42.0-thread/bin"
    PERLBREW_PERL="perl-5.42.0-thread"
    PERLBREW_ROOT="/home/bartosz/perl5/perlbrew"
    PERLBREW_SHELLRC_VERSION="1.01"
    PERLBREW_VERSION="1.01"
  @INC:
    /home/bartosz/perl5/perlbrew/perls/perl-5.42.0-thread/lib/site_perl/5.42.0/x86_64-linux-thread-multi
    /home/bartosz/perl5/perlbrew/perls/perl-5.42.0-thread/lib/site_perl/5.42.0
    /home/bartosz/perl5/perlbrew/perls/perl-5.42.0-thread/lib/5.42.0/x86_64-linux-thread-multi
    /home/bartosz/perl5/perlbrew/perls/perl-5.42.0-thread/lib/5.42.0

[bbrtj]

Perhaps more intrestingly, if our $VERSION = ... is used instead of $pkg::VERSION = ..., string eval causes Segmentation fault