perl/SOURCES/perl-5.30.0-Remove-undefined-behavior-from-IV-shifting.patch
2021-09-10 13:25:07 +00:00

76 lines
2.1 KiB
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From 7e5b390a008ccad094a39c350f385d58e8a5102a Mon Sep 17 00:00:00 2001
From: Karl Williamson <khw@cpan.org>
Date: Fri, 3 May 2019 13:57:47 -0600
Subject: [PATCH] Remove undefined behavior from IV shifting
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
It is undefined behavior to shift a negative integer to the left. This
commit avoids that by treating the value as unsigned, then casting back
to integer for return.
Petr Písař: Ported to 5.30.0 from
814735a391b874af8f00eaf89469e5ec7f38cd4aa.
Signed-off-by: Petr Písař <ppisar@redhat.com>
---
asan_ignore | 5 -----
pp.c | 21 ++++++++++++++++++++-
2 files changed, 20 insertions(+), 6 deletions(-)
diff --git a/asan_ignore b/asan_ignore
index e0f5685..f520546 100644
--- a/asan_ignore
+++ b/asan_ignore
@@ -18,11 +18,6 @@
fun:Perl_pp_i_*
-# Perl's << is defined as using the underlying C's << operator, with the
-# same undefined behaviour for shifts greater than the word size.
-# (UVs normally, IVs with 'use integer')
-
-fun:Perl_pp_left_shift
# this function numifies the field width in eg printf "%10f".
# It has its own overflow detection, so don't warn about it
diff --git a/pp.c b/pp.c
index 7afb090..3ca04e1 100644
--- a/pp.c
+++ b/pp.c
@@ -1991,10 +1991,29 @@ static IV S_iv_shift(IV iv, int shift, bool left)
shift = -shift;
left = !left;
}
+
if (UNLIKELY(shift >= IV_BITS)) {
return iv < 0 && !left ? -1 : 0;
}
- return left ? iv << shift : iv >> shift;
+ /* For left shifts, perl 5 has chosen to treat the value as unsigned for
+ * the * purposes of shifting, then cast back to signed. This is very
+ * different from perl 6:
+ *
+ * $ perl6 -e 'say -2 +< 5'
+ * -64
+ *
+ * $ ./perl -le 'print -2 << 5'
+ * 18446744073709551552
+ * */
+ if (left) {
+ if (iv == IV_MIN) { /* Casting this to a UV is undefined behavior */
+ return 0;
+ }
+ return (IV) (((UV) iv) << shift);
+ }
+
+ /* Here is right shift */
+ return iv >> shift;
}
#define UV_LEFT_SHIFT(uv, shift) S_uv_shift(uv, shift, TRUE)
--
2.20.1