Re: [PATCH] tracetool: strip %l and %ll from systemtap format strings

[Laurent Vivier <lvivier@redhat.com>]

On 06/01/2021 13:19, Daniel P. Berrangé wrote:
> All variables are 64-bit and so %l / %ll are not required, and the
> latter is actually invalid:
> 
>   $ sudo stap -e 'probe begin{printf ("BEGIN")}'  -I .
>   parse error: invalid or missing conversion specifier
>           saw: operator ',' at ./qemu-system-x86_64-log.stp:15118:101
>        source:     printf("%d@%d vhost_vdpa_set_log_base dev: %p base: 0x%x size: %llu
> refcnt: %d fd: %d log: %p\n", pid(), gettimeofday_ns(), dev, base, size, refcnt, fd, log)
> 
>                        ^
> 
> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
> ---
>  scripts/tracetool/format/log_stap.py | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> This is an alternative approach to
> 
>   https://lists.gnu.org/archive/html/qemu-devel/2021-01/msg00550.html

Your patch is indeed a better solution.

> 
> diff --git a/scripts/tracetool/format/log_stap.py b/scripts/tracetool/format/log_stap.py
> index b486beb672..7bac10784b 100644
> --- a/scripts/tracetool/format/log_stap.py
> +++ b/scripts/tracetool/format/log_stap.py
> @@ -49,6 +49,12 @@ def c_fmt_to_stap(fmt):
>          elif fmt[i] == '"' and not escape:
>              if state == STATE_LITERAL:
>                  state = STATE_SKIP
> +                # All variables in systemtap are 64-bit in size
> +                # The "%l" integer size qualifiers is thus redundant
> +                # and "%ll" is not valid at all. Simply strip all
> +                # size qualifiers for sanity
> +                literal = literal.replace("%ll", "%")
> +                literal = literal.replace("%l", "%")
>                  bits.append(literal)
>                  literal = ""
>              else:
> 

There is a 'sub("%(\d*)z(x|u|d)", "%\\1\\2",..)' later in the code,
can we have here the '\d*" case or the 'z' case?

I'm wondering if it can be handled in a more generic way by something like:

--- a/scripts/tracetool/format/log_stap.py
+++ b/scripts/tracetool/format/log_stap.py
@@ -78,6 +78,7 @@ def c_fmt_to_stap(fmt):
         bits.append(literal)

     fmt = re.sub("%(\d*)z(x|u|d)", "%\\1\\2", "".join(bits))
+    fmt = re.sub("%(\d*)l*(x|u|d)", "%\\1\\2", fmt)
     return fmt

 def generate(events, backend, group):

Thanks,
Laurent