Re: [PATCH] fix bug with command `printf "%s\n", $_as_string($pc)`

[Simon Marchi <simon.marchi@polymtl.ca>]

Hi Matthew,

I noted mostly some minor formatting issues, in general it looks good to 
me.  One comment about malloc.

On 2017-02-25 06:45, Matthew Malcomson wrote:
> CHANGELOG:
> 
> 2017-02-19  Matthew Malcomson <hardenedapple@gmail.com>
> 
>     * python/py-value.c (convert_value_from_python): Include NULL
> terminator in result.
>     testsuite/gdb.python/py-as-string.c,
> testsuite/gdb.python/py-as-string.exp: Update tests
>     to account for NULL terminator from python string values.
>     doc/gdb.texinfo ($trace_func): Mention this value can't be used 
> with printf.

There is a ChangeLog in the doc and testsuite directories, so you should 
place these entries in the relevant ChangeLogs.  Also, look at this 
section of the GDB wiki for more info on the proper format.

https://sourceware.org/gdb/wiki/ContributionChecklist#Properly_Formatted_GNU_ChangeLog

> +static char arena[51] = 
> "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";
> +
> +/* Override malloc() so value_coerce_to_target() gets a known pointer, 
> and we
> +   know we'll see an error if $_as_string() returns a string that 
> isn't NULL
> +   terminated. */

IIUC, the goal of overriding malloc is to ensure that the memory return 
by malloc is not all zeroes, which would potentially hide the bug?  If 
that's right, you could instead write a wrapper for malloc instead of a 
replacement.  The wrapper would memset the allocated buffer to 'x'es, 
for example.  This way, it will be safer in case there are many calls to 
malloc or calls with size > 51.

See option #2 of this answer: http://stackoverflow.com/a/262481

> +void *malloc(size_t size)

We try to respect the GNU/GDB coding style even in tests, so please put 
the return type on its own line and put a space after the function name:

void *
malloc (size_t size)
{
   ...
}

> +{
> +    if (size > sizeof(arena))

Space after sizeof.

> +        return NULL;
> +
> +    return arena;
> +}

The indentation in C/C++ code sould be two spaces per indent, until you 
have 8 spaces, it then becomes a tab.

> +
>  static enum EnumType enum_valid = ENUM_VALUE_B;
>  static enum EnumType enum_invalid = 20;
> 
> diff --git a/gdb/testsuite/gdb.python/py-as-string.exp
> b/gdb/testsuite/gdb.python/py-as-string.exp
> index 0c44d5f174..819442834c 100644
> --- a/gdb/testsuite/gdb.python/py-as-string.exp
> +++ b/gdb/testsuite/gdb.python/py-as-string.exp
> @@ -35,6 +35,12 @@ proc test_as_string { } {
>      gdb_test "p \$_as_string(2)" "\"2\""
>      gdb_test "p \$_as_string(enum_valid)" "\"ENUM_VALUE_B\""
>      gdb_test "p \$_as_string(enum_invalid)" "\"20\""
> +    # Test that the NULL character is included in the returned value.
> +    gdb_test "printf \"%s\\n\", \$_as_string(\"hi\")" "\"hi\""
> +    # Quote once to define the string, and once for the regexp.
> +    gdb_test "interpreter-exec mi '-var-create test *
> \$_as_string(\"Hello\")'" \
> + "\\^done,name=\"test\",numchild=\"8\",value=\"\\\[8]\",type=\"char
> \\\[8]\",has_more=\"0\""

Indent this with a leading tab.

If you want to avoid massive escaping, you can use {} strings instead of 
"" strings.  {} strings are treated literally, so there's no $variable 
substitution, no [proc invocation], no need to escape a literal 
backslash, etc.  You still need to escape characters that have a special 
meaning in regex though.

   "\\^done,name=\"test\",numchild=\"8\",value=\"\\\[8]\",type=\"char 
\\\[8]\",has_more=\"0\""

would become (I think, I have not tested)

   {\^done,name="test",numchild="8",value="\[8]",type="char 
\[8]",has_more="0"}

Finally, feel free to add newlines between logical groups of lines to 
make the code more readable.

Thanks,

Simon