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Avoid z/OS function pointer comparison undefined behavior #23399

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Merged
khwilliamson merged 2 commits into from
Sep 1, 2025
Merged

Avoid z/OS function pointer comparison undefined behavior #23399

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99b33f7
Avoid z/OS function pointer comparison undefined behavior
khwilliamson Jun 8, 2025
efbf2c0
peep.c: Add some UNLIKELY()
khwilliamson Jul 3, 2025
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19 changes: 19 additions & 0 deletions opcode.h
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6 changes: 3 additions & 3 deletions peep.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2205,14 +2205,14 @@ S_maybe_multideref(pTHX_ OP *start, OP *orig_o, UV orig_action, U8 hints)
/* if a custom array/hash access checker is in scope,
* abandon optimisation attempt */
if ( (o->op_type == OP_AELEM || o->op_type == OP_HELEM)
&& PL_check[o->op_type] != Perl_ck_null)
&& UNLIKELY(PL_check[o->op_type] != PL_check[PERL_CK_NULL]))
return;
/* similarly for customised exists and delete */
if ( (o->op_type == OP_EXISTS)
&& PL_check[o->op_type] != Perl_ck_exists)
&& UNLIKELY(PL_check[o->op_type] != PL_check[PERL_CK_EXISTS]))
return;
if ( (o->op_type == OP_DELETE)
&& PL_check[o->op_type] != Perl_ck_delete)
&& UNLIKELY(PL_check[o->op_type] != PL_check[PERL_CK_DELETE]))
return;

if ( o->op_type != OP_AELEM
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27 changes: 27 additions & 0 deletions regen/opcode.pl
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Original file line number Diff line number Diff line change
Expand Up @@ -1114,13 +1114,40 @@ sub generate_opcode_h_pl_check {
INIT({
END


for (@ops) {
print "\t", tab(3, "Perl_$check{$_},"), "\t/* $_ */\n";
}

print <<~'END';

/* The final entries are function pointers not attached to an opcode.
* These are to be used to compare with function pointers in the earlier
* part of the array, since in some platforms (notably z/OS), it is
* undefined behavior to compare function pointers for equality, even
* though calling them will invoke the same function. IBM personnel say
* that the comparisons do work when the pointers are compiled in the same
* translation unit. Hence, ck_null in all positions in the array will
* have the same value. See GH #23399 */
END
my @perl_internal_extras = qw(ck_null ck_exists ck_delete);
for (@perl_internal_extras) {
print "\t", tab(3, "Perl_$_,"), "\n";
}

print <<~'END';
});

/* Indexes into PL_check for the comparison function pointers */
#ifdef PERL_IN_PEEP_C
END

for (my $i = 0; $i < @perl_internal_extras; $i++) {
my $index = @ops + $i;
my $define = uc $perl_internal_extras[$i];
print " #define PERL_$define $index\n";
}
print "#endif\n";
}

sub generate_opcode_h_pl_opargs {
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