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

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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