[binutils-gdb] Avoid undefined behavior in read_subrange_type

[Tom Tromey]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=d359392f976d48b04a27e6a09b5b61846b0727f9

commit d359392f976d48b04a27e6a09b5b61846b0727f9
Author: Tom Tromey <tom@tromey.com>
Date:   Sun Jul 29 17:29:24 2018 -0600

    Avoid undefined behavior in read_subrange_type
    
    -fsanitize=undefined pointed out an undefined shift of a negative
    value in read_subrange_type.  The fix is to do the work in an unsigned
    type, where this is defined.
    
    gdb/ChangeLog
    2018-10-03  Tom Tromey  <tom@tromey.com>
    
    	* dwarf2read.c (read_subrange_type): Make "negative_mask"
    	unsigned.

Diff:
---
 gdb/ChangeLog    | 5 +++++
 gdb/dwarf2read.c | 4 ++--
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 5787d44..4be3033 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,10 @@
 2018-10-03  Tom Tromey  <tom@tromey.com>
 
+	* dwarf2read.c (read_subrange_type): Make "negative_mask"
+	unsigned.
+
+2018-10-03  Tom Tromey  <tom@tromey.com>
+
 	* findvar.c (extract_integer): Do work in an unsigned type.
 
 2018-10-03  Tom Tromey  <tom@tromey.com>
diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
index 4a35e38..4013c19 100644
--- a/gdb/dwarf2read.c
+++ b/gdb/dwarf2read.c
@@ -17709,7 +17709,7 @@ read_subrange_type (struct die_info *die, struct dwarf2_cu *cu)
   int low_default_is_valid;
   int high_bound_is_count = 0;
   const char *name;
-  LONGEST negative_mask;
+  ULONGEST negative_mask;
 
   orig_base_type = die_type (die, cu);
   /* If ORIG_BASE_TYPE is a typedef, it will not be TYPE_UNSIGNED,
@@ -17842,7 +17842,7 @@ read_subrange_type (struct die_info *die, struct dwarf2_cu *cu)
      the bounds as signed, and thus sign-extend their values, when
      the base type is signed.  */
   negative_mask =
-    -((LONGEST) 1 << (TYPE_LENGTH (base_type) * TARGET_CHAR_BIT - 1));
+    -((ULONGEST) 1 << (TYPE_LENGTH (base_type) * TARGET_CHAR_BIT - 1));
   if (low.kind == PROP_CONST
       && !TYPE_UNSIGNED (base_type) && (low.data.const_val & negative_mask))
     low.data.const_val |= negative_mask;