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Re: [PATCH] add -foverride-comp-dir

On Sat, Sep 30, 2006 at 09:38:19PM -0400, Daniel Jacobowitz wrote:
> On Wed, Sep 27, 2006 at 12:25:32AM -0700, Geoffrey Keating wrote:
> > Dan Aloni <> writes:
> > 
> > > Hello,
> > > 
> > > The following patch adds a new switch to gcc that allows to override
> > > the DW_AT_comp_dir DWARF2 attribute. The reason why I need this change
> > > is that one of our project's build system is using content-hashing in
> > > order to save build and compilation time among several developers that 
> > > are working on that project. 
> > > 
> > > When debug information is used, we need to make sure that that the
> > > result binaries are identical if compiled from the same source between 
> > > several developers working from different directories, and also to be 
> > > able to look at core files from gdb with proper (i.e. path-relative) 
> > > source code lookup. By simply passing -foverride-comp-dir=. to gcc
> > > after this feature is patched in, we are able to achieve our goals.
> > 
> > Would it be better to simply have a -fno-comp-dir flag, to omit this
> > information entirely from the DWARF output?

Could having no DW_AT_comp_dir confuse gdb? I'm not certain about it, but
we should check this. Anyway, it would require a longer patch.

> A related FYI: While it won't help with the content-hashing, the GDB
> side of this is addressed by the recently added substitution commands
> in CVS.

So, in that case we could run gdb from any directory and then run a command 
to substitute '.' with the `pwd` of compilation. Sounds useful.

BTW if I wasn't clear in my first mail, we are compiling all our C files 
from the same `pwd`, even if the files are in sub-directories.

  gcc -c dir/subdir/a.c  -o dir/subdir/a.o
  gcc -c other/b.c  -o other/b.o

I prefer to have this backward compatible - I already know that at least 
one older version of gdb perfectly handles the situation where '.' is the 

Dan Aloni, Linux specialist

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