Re: [Qemu-devel] [PATCH 2/2] tracetool: Forbid argument name 'next'

[Kevin Wolf <kwolf@redhat.com>]

Am 12.03.2012 12:01, schrieb Stefan Hajnoczi:
> On Mon, Mar 12, 2012 at 9:34 AM, Kevin Wolf <kwolf@redhat.com> wrote:
>> It has happened more than once that patches that look perfectly sane
>> and work with simpletrace broke systemtap because they use 'next' as an
>> argument name for a tracing function. However, 'next' is a keyword for
>> systemtap, so we shouldn't use it.
>>
>> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
>> ---
>>  scripts/tracetool |    4 ++++
>>  1 files changed, 4 insertions(+), 0 deletions(-)
>>
>> diff --git a/scripts/tracetool b/scripts/tracetool
>> index 4c9951d..f892af4 100755
>> --- a/scripts/tracetool
>> +++ b/scripts/tracetool
>> @@ -81,6 +81,10 @@ get_args()
>>     args=${1#*\(}
>>     args=${args%%\)*}
>>     echo "$args"
>> +
>> +    if (echo "$args" | grep "[ *]next\($\|[, ]\)" > /dev/null 2>&1); then
>> +        echo -e "\n#error 'next' is a bad argument name (clash with systemtap keyword)\n "
>> +    fi
> 
> Good idea, let's prevent it from being used.
> 
> I don't think this is the way to do it because callers will parse
> stdout and we're not guaranteed to be generating C code where #error
> works.  Instead, we can echo to stderr and do exit 1.

Yes, we may generate something else additionally. But trace.h is
generated in any case and it will cause a compile error before any non-C
file is used.

I tried the 'exit 1' approach first and it doesn't really work. This
function is called from a subshell, so you don't exit tracetool but just
the one subshell and end up with a broken trace.h that will fail
compilation in the same place, just with a less helpful error message.

Kevin