-frecord-gcc-switches as default CFLAG?

[Jon Stanley]

I noticed on my Fedora 13 box that in the RPM macro %__global_cflags
that -frecord-gcc-switches is missing, which is a nifty compiler
feature that will record the flags passed to gcc in a section in the
object file, thus aiding in the "how in the world was this compiled?"
problem. An example:

[jstanley@hawtness ~]$ gcc -O2 -frecord-gcc-switches -g -o hello hello.c
[jstanley@hawtness ~]$ readelf -p .GCC.command.line hello

String dump of section '.GCC.command.line':
  [     0]  hello.c
  [     8]  -mtune=generic
  [    17]  -g
  [    1a]  -O2
  [    1e]  -frecord-gcc-switches

What do folks think about adding this as a default? Any reason not to
(other than possibly a few bytes extra in the object files)?

[Richard W.M. Jones]

On Sat, Oct 30, 2010 at 02:24:02AM -0400, Jon Stanley wrote:
>  I noticed on my Fedora 13 box that in the RPM macro %__global_cflags
>  that -frecord-gcc-switches is missing, which is a nifty compiler
>  feature that will record the flags passed to gcc in a section in the
>  object file, thus aiding in the "how in the world was this compiled?"
>  problem. An example:
>  
>  [jstanley@hawtness ~]$ gcc -O2 -frecord-gcc-switches -g -o hello hello.c
>  [jstanley@hawtness ~]$ readelf -p .GCC.command.line hello
>  
>  String dump of section '.GCC.command.line':
>    [     0]  hello.c
>    [     8]  -mtune=generic
>    [    17]  -g
>    [    1a]  -O2
>    [    1e]  -frecord-gcc-switches
>  
>  What do folks think about adding this as a default? Any reason not to
>  (other than possibly a few bytes extra in the object files)? 
+1

I think would also catch those cases where some gcc flag is found to
break code generation.  You reasonably see which binaries were
affected.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming blog: http://rwmj.wordpress.com
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[Tom Callaway]

On 10/30/2010 06:01 AM, Richard W.M. Jones wrote:
>  On Sat, Oct 30, 2010 at 02:24:02AM -0400, Jon Stanley wrote:
> > I noticed on my Fedora 13 box that in the RPM macro %__global_cflags
> > that -frecord-gcc-switches is missing, which is a nifty compiler
> > feature that will record the flags passed to gcc in a section in the
> > object file, thus aiding in the "how in the world was this compiled?"
> > problem. An example:
> >
> > [jstanley@hawtness ~]$ gcc -O2 -frecord-gcc-switches -g -o hello hello.c
> > [jstanley@hawtness ~]$ readelf -p .GCC.command.line hello
> >
> > String dump of section '.GCC.command.line':
> >   [     0]  hello.c
> >   [     8]  -mtune=generic
> >   [    17]  -g
> >   [    1a]  -O2
> >   [    1e]  -frecord-gcc-switches
> >
> > What do folks think about adding this as a default? Any reason not to
> > (other than possibly a few bytes extra in the object files)?
>  
>  +1
>  
>  I think would also catch those cases where some gcc flag is found to
>  break code generation.  You reasonably see which binaries were
>  affected. 
I agree. Unless there is a notable performance cost in this, I say we
should go for it.

~spot

[Josh Boyer]

On Mon, Nov 1, 2010 at 9:04 AM, Tom "spot" Callaway <tcallawa(a)redhat.com&gt;
wrote:
>  On 10/30/2010 06:01 AM, Richard W.M. Jones wrote:
> > On Sat, Oct 30, 2010 at 02:24:02AM -0400, Jon Stanley wrote:
> >> I noticed on my Fedora 13 box that in the RPM macro %__global_cflags
> >> that -frecord-gcc-switches is missing, which is a nifty compiler
> >> feature that will record the flags passed to gcc in a section in the
> >> object file, thus aiding in the "how in the world was this compiled?"
> >> problem. An example:
> >>
> >> [jstanley@hawtness ~]$ gcc -O2 -frecord-gcc-switches -g -o hello hello.c
> >> [jstanley@hawtness ~]$ readelf -p .GCC.command.line hello
> >>
> >> String dump of section '.GCC.command.line':
> >>   [     0]  hello.c
> >>   [     8]  -mtune=generic
> >>   [    17]  -g
> >>   [    1a]  -O2
> >>   [    1e]  -frecord-gcc-switches
> >>
> >> What do folks think about adding this as a default? Any reason not to
> >> (other than possibly a few bytes extra in the object files)?
> >
> > +1
> >
> > I think would also catch those cases where some gcc flag is found to
> > break code generation.  You reasonably see which binaries were
> > affected.
>
>  I agree. Unless there is a notable performance cost in this, I say we
>  should go for it. 
How do you envision this working with debuginfo?  Does this section
get stripped out from normal install and collected into the -debuginfo
subpackage, or does debuginfo need to be taught to leave this section
intact in the actual installed binary?

josh

[Jakub Jelinek]

On Mon, Nov 01, 2010 at 09:04:12AM -0400, Tom "spot" Callaway wrote:
>  On 10/30/2010 06:01 AM, Richard W.M. Jones wrote:
>  > On Sat, Oct 30, 2010 at 02:24:02AM -0400, Jon Stanley wrote:
>  >> I noticed on my Fedora 13 box that in the RPM macro %__global_cflags
>  >> that -frecord-gcc-switches is missing, which is a nifty compiler
>  >> feature that will record the flags passed to gcc in a section in the
>  >> object file, thus aiding in the "how in the world was this compiled?"
>  >> problem. An example:
>  >>
>  >> [jstanley@hawtness ~]$ gcc -O2 -frecord-gcc-switches -g -o hello hello.c
>  >> [jstanley@hawtness ~]$ readelf -p .GCC.command.line hello
>  >>
>  >> String dump of section '.GCC.command.line':
>  >>   [     0]  hello.c
>  >>   [     8]  -mtune=generic
>  >>   [    17]  -g
>  >>   [    1a]  -O2
>  >>   [    1e]  -frecord-gcc-switches
>  >>
>  >> What do folks think about adding this as a default? Any reason not to
>  >> (other than possibly a few bytes extra in the object files)?
>  > 
>  > +1
>  > 
>  > I think would also catch those cases where some gcc flag is found to
>  > break code generation.  You reasonably see which binaries were
>  > affected.
>  
>  I agree. Unless there is a notable performance cost in this, I say we
>  should go for it. 
-frecord-gcc-switches is unfortunately pretty much useless, see
http://gcc.gnu.org/PR32998.  Please don't add it, we want something actually
usable, not this option.

	Jakub

[Jon Stanley]

On Mon, Nov 1, 2010 at 9:12 AM, Jakub Jelinek <jakub(a)redhat.com&gt; wrote:

>  -frecord-gcc-switches is unfortunately pretty much useless, see
>  http://gcc.gnu.org/PR32998.  Please don't add it, we want something actually
>  usable, not this option. 
Isn't it more useful in this state than not having the data at all? It
seems that the bug that you refer to is about appending things to
DW_AT_producer at this point, which is also useful, but I'm not
convinced about that use of DW_AT_producer either, but that's another
thread.