[binutils-gdb] Avoid undefined behavior in ada_operator_length

[Tom Tromey <tromey at sourceware dot org>]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=5e70ee0905a848701bb929a66f84ff2e212cfa81

commit 5e70ee0905a848701bb929a66f84ff2e212cfa81
Author: Tom Tromey <tom@tromey.com>
Date:   Sat Aug 18 14:51:46 2018 -0600

    Avoid undefined behavior in ada_operator_length
    
    -fsanitize=undefined pointed out this error:
    
        runtime error: load of value 2887952, which is not a valid value for type 'exp_opcode'
    
    This happens in gdb.ada/complete.exp when processing "complete p
    my_glob".  This does not parse, so the Ada parser throws an exception;
    but then the code in parse_exp_in_context_1 accepts the expression
    anyway.  However, as no elements have been written to the expression,
    undefined behavior results.
    
    The fix is to notice this case in parse_exp_in_context_1.  This patch
    also adds an assertion to prefixify_expression to enforce this
    pre-existing constraint.
    
    gdb/ChangeLog
    2018-10-03  Tom Tromey  <tom@tromey.com>
    
    	* parse.c (prefixify_expression): Add assert.
    	(parse_exp_in_context_1): Throw exception if the expression is
    	empty.

Diff:
---
 gdb/ChangeLog | 8 +++++++-
 gdb/parse.c   | 6 +++++-
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 9731c99..1a3cc6c 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,11 @@
 2018-10-03  Tom Tromey  <tom@tromey.com>
 
+	* parse.c (prefixify_expression): Add assert.
+	(parse_exp_in_context_1): Throw exception if the expression is
+	empty.
+
+2018-10-03  Tom Tromey  <tom@tromey.com>
+
 	* dwarf2read.c (read_signed_leb128): Work in ULONGEST.
 
 2018-10-03  Tom Tromey  <tom@tromey.com>
@@ -14219,7 +14225,7 @@
 
 	Update copyright year range in all GDB files.
 
-2018-01-01  Joel Brobecker  <brobecker@adacore.com>
+2018-01-01, 18  Joel Brobecker  <brobecker@adacore.com>
 
 	* copyright.py (BY_HAND): Remove gdb/testsuite/gdb.base/step-line.inp
 	and gdb/testsuite/gdb.base/step-line.c.
diff --git a/gdb/parse.c b/gdb/parse.c
index 163852c..8a128a7 100644
--- a/gdb/parse.c
+++ b/gdb/parse.c
@@ -792,6 +792,7 @@ copy_name (struct stoken token)
 int
 prefixify_expression (struct expression *expr)
 {
+  gdb_assert (expr->nelts > 0);
   int len = sizeof (struct expression) + EXP_ELEM_TO_BYTES (expr->nelts);
   struct expression *temp;
   int inpos = expr->nelts, outpos = 0;
@@ -1205,7 +1206,10 @@ parse_exp_in_context_1 (const char **stringptr, CORE_ADDR pc,
     }
   CATCH (except, RETURN_MASK_ALL)
     {
-      if (! parse_completion)
+      /* If parsing for completion, allow this to succeed; but if no
+	 expression elements have been written, then there's nothing
+	 to do, so fail.  */
+      if (! parse_completion || ps.expout_ptr == 0)
 	throw_exception (except);
     }
   END_CATCH