Dear all,
I had thought that we had fixed this in the past (see PR31001),
but it did fail for me with all gcc versions I have tried (7-12)
for a slightly more elaborate case as in the old testcase.
The loop in pack_internal did try to access the first element of
the array argument to PACK even if one (or more) extents were zero.
This is not good.
Solution: check the extents and return early. (We already do a
related check for the vector argument if present).
Regtested on x86_64-pc-linux-gnu. OK for mainline?
As this segfaults on valid code at runtime: I am considering
backporting this, if there are no objections.
Thanks,
Harald
From dfa1e1ac5d8e43f1ca8f13b64330825581174f36 Mon Sep 17 00:00:00 2001
From: Harald Anlauf <anl...@gmx.de>
Date: Thu, 9 Dec 2021 20:55:08 +0100
Subject: [PATCH] Fortran: PACK intrinsic should not try to read from
zero-sized array
libgfortran/ChangeLog:
PR libfortran/103634
* intrinsics/pack_generic.c (pack_internal): Handle case when the
array argument of PACK has one extent of size zero to avoid
invalid reads.
gcc/testsuite/ChangeLog:
PR libfortran/103634
* gfortran.dg/zero_sized_13.f90: New test.
---
gcc/testsuite/gfortran.dg/zero_sized_13.f90 | 20 ++++++++++++++++++++
libgfortran/intrinsics/pack_generic.c | 4 ++++
2 files changed, 24 insertions(+)
create mode 100644 gcc/testsuite/gfortran.dg/zero_sized_13.f90
diff --git a/gcc/testsuite/gfortran.dg/zero_sized_13.f90 b/gcc/testsuite/gfortran.dg/zero_sized_13.f90
new file mode 100644
index 00000000000..5620514334c
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/zero_sized_13.f90
@@ -0,0 +1,20 @@
+! { dg-do run }
+! PR libfortran/103634 - Runtime crash with PACK on zero-sized arrays
+
+program p
+ implicit none
+ type t
+ real :: r(24) = -99.
+ end type
+ type(t), allocatable :: new(:), old(:)
+ logical, allocatable :: mask(:)
+ integer :: n, m
+! m = 1 ! works
+ m = 0 ! failed with SIGSEGV in pack_internal
+ allocate (old(m), mask(m))
+ mask(:) = .false.
+ n = count (mask)
+ allocate (new(n))
+ new(:) = pack (old, mask)
+ print *, size (new)
+end
diff --git a/libgfortran/intrinsics/pack_generic.c b/libgfortran/intrinsics/pack_generic.c
index cad2fbbfbcd..f629e0e8469 100644
--- a/libgfortran/intrinsics/pack_generic.c
+++ b/libgfortran/intrinsics/pack_generic.c
@@ -126,6 +126,10 @@ pack_internal (gfc_array_char *ret, const gfc_array_char *array,
if (mstride[0] == 0)
mstride[0] = mask_kind;
+ for (n = 0; n < dim; n++)
+ if (extent[n] == 0)
+ return;
+
if (ret->base_addr == NULL || unlikely (compile_options.bounds_check))
{
/* Count the elements, either for allocating memory or
--
2.26.2
