[binutils-gdb] Avoid crash from coerce_unspec_val_to_type

[Tom Tromey]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=f73e424f7bb51d4a5164320107f386b8fec34f4b

commit f73e424f7bb51d4a5164320107f386b8fec34f4b
Author: Tom Tromey <tromey@adacore.com>
Date:   Tue Feb 9 12:15:39 2021 -0700

    Avoid crash from coerce_unspec_val_to_type
    
    With a certain Ada program, ada-lang.c:coerce_unspec_val_to_type can
    cause a crash.  This function may copy a value, and in the particular
    case in the crash, the new value's type is smaller than the original
    type.  This causes coerce_unspec_val_to_type to create a lazy value --
    but the original value is also not_lval, so later, when the value is
    un-lazied, gdb asserts.
    
    As with the previous patch, we believe there is a compiler bug here,
    but it is difficult to reproduce, so we're not completely certain.
    
    In the particular case we saw, the original value has record type, and
    the record holds some variable-length arrays.  This leads to the
    type's length being 0.  At the same time, the value is optimized out.
    
    This patch changes coerce_unspec_val_to_type to handle an
    optimized-out value correctly.
    
    It also slightly restructures this code to avoid a crash should a
    not_lval value wind up here.  This is a purely defensive change.
    
    This change also made it clear that value_contents_copy_raw can now be
    made static, so that is also done.
    
    gdb/ChangeLog
    2021-02-09  Tom Tromey  <tromey@adacore.com>
    
            * ada-lang.c (coerce_unspec_val_to_type): Avoid making lazy
            not_lval value.
            * value.c (value_contents_copy_raw): Now static.
            * value.h (value_contents_copy_raw): Don't declare.

Diff:
---
 gdb/ChangeLog  |  7 +++++++
 gdb/ada-lang.c | 10 +++++++---
 gdb/value.c    |  2 +-
 gdb/value.h    |  3 ---
 4 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 6470c996a30..5c66f99e817 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,10 @@
+2021-02-09  Tom Tromey  <tromey@adacore.com>
+
+	* ada-lang.c (coerce_unspec_val_to_type): Avoid making lazy
+	not_lval value.
+	* value.c (value_contents_copy_raw): Now static.
+	* value.h (value_contents_copy_raw): Don't declare.
+
 2021-02-09  Tom Tromey  <tromey@adacore.com>
 
 	* gdbtypes.c (resolve_dynamic_struct): Handle structure with no
diff --git a/gdb/ada-lang.c b/gdb/ada-lang.c
index 70296f97797..416a45be58e 100644
--- a/gdb/ada-lang.c
+++ b/gdb/ada-lang.c
@@ -601,13 +601,17 @@ coerce_unspec_val_to_type (struct value *val, struct type *type)
 	 trying to allocate some memory for it.  */
       ada_ensure_varsize_limit (type);
 
-      if (value_lazy (val)
-	  || TYPE_LENGTH (type) > TYPE_LENGTH (value_type (val)))
+      if (value_optimized_out (val))
+	result = allocate_optimized_out_value (type);
+      else if (value_lazy (val)
+	       /* Be careful not to make a lazy not_lval value.  */
+	       || (VALUE_LVAL (val) != not_lval
+		   && TYPE_LENGTH (type) > TYPE_LENGTH (value_type (val))))
 	result = allocate_value_lazy (type);
       else
 	{
 	  result = allocate_value (type);
-	  value_contents_copy_raw (result, 0, val, 0, TYPE_LENGTH (type));
+	  value_contents_copy (result, 0, val, 0, TYPE_LENGTH (type));
 	}
       set_value_component_location (result, val);
       set_value_bitsize (result, value_bitsize (val));
diff --git a/gdb/value.c b/gdb/value.c
index 4135d5ec339..bddf9a47923 100644
--- a/gdb/value.c
+++ b/gdb/value.c
@@ -1304,7 +1304,7 @@ value_ranges_copy_adjusted (struct value *dst, int dst_bit_offset,
    It is assumed the contents of DST in the [DST_OFFSET,
    DST_OFFSET+LENGTH) range are wholly available.  */
 
-void
+static void
 value_contents_copy_raw (struct value *dst, LONGEST dst_offset,
 			 struct value *src, LONGEST src_offset, LONGEST length)
 {
diff --git a/gdb/value.h b/gdb/value.h
index 39e94f45ea6..60a831c38c4 100644
--- a/gdb/value.h
+++ b/gdb/value.h
@@ -739,9 +739,6 @@ extern struct value *allocate_value_lazy (struct type *type);
 extern void value_contents_copy (struct value *dst, LONGEST dst_offset,
 				 struct value *src, LONGEST src_offset,
 				 LONGEST length);
-extern void value_contents_copy_raw (struct value *dst, LONGEST dst_offset,
-				     struct value *src, LONGEST src_offset,
-				     LONGEST length);
 
 extern struct value *allocate_repeat_value (struct type *type, int count);