Re: [Qemu-devel] [PATCH] trace: fix group name generation

[Eric Blake]

On 10/14/2016 04:26 PM, Greg Kurz wrote:
> Since commit "80dd5c4918ab trace: introduce a formal group name for trace
> events", tracetool generates C variable names and macro definitions out
> of the path to the trace-events-all file.
> 
> The current code takes care of turning '/' and '-' characters into
> underscores so that the resulting names are valid C tokens. This is
> enough because these are the only illegal characters that appear in
> a relative path within the QEMU source tree.
> 
> Things are different for out of tree builds where the path may contain
> arbitrary character combinations, causing tracetool to generate invalid
> names.
> 

> This patch ensures that only letters [A-Za-z], digits [0-9] and underscores
> are kept. All other characters are turned into underscores. Also, since the
> first character of C symbol names cannot be a digit, an underscore is
> prepended to the group name.
> 
> Signed-off-by: Greg Kurz <address@hidden>
> ---
>  scripts/tracetool.py |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/scripts/tracetool.py b/scripts/tracetool.py
> index 629b2593c846..b81b834db924 100755
> --- a/scripts/tracetool.py
> +++ b/scripts/tracetool.py
> @@ -70,7 +70,7 @@ def make_group_name(filename):
>  
>      if dirname == "":
>          return "common"
> -    return re.sub(r"/|-", "_", dirname)
> +    return "_" + re.sub(r"[^\w]", "_", dirname)

This STILL doesn't solve the complaint that the build is now dependent
on the location.  Why can't we STRIP off any prefix prior to the in-tree
portion of the naming that we know is sane, instead of munging the
prefix but in the process creating source code that generates with
different lengths?

Ideally, compiling twice, once in directory 'a', and the second time in
directory 'aaaaaaaaaaaaaaaaaaaaaaaaaaaa', should not make a noticeable
difference in the final size of the executable due to the difference in
lengths of the debugging symbols used to record the longer name of the
second directory being encoded into lots of macro names.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

signature.asc
Description: OpenPGP digital signature