[PATCH] arm64/debug: don't duplicate filenames.

[Dave Martin]

On Thu, Nov 09, 2017 at 01:08:51PM +0000, Jamie Iles wrote:
> Hi Dave,
> 
> On Thu, Nov 09, 2017 at 12:35:04PM +0000, Dave Martin wrote:
> > On Thu, Nov 09, 2017 at 12:14:40PM +0000, Jamie Iles wrote:
> > > Rather than explicitly pushing the filename into .rodata.str, use a
> > > compiler generated string literal and use the address of that as an
> > > input constraint to the inline assembly.  This allows the compiler to
> > > emit only one version of the string without relying on the linker to
> > > deduplicate.
> > 
> > But if the linker does deduplicate, why does it matter?
> 
> It's not broken, but at the moment we have multiple copies in the object 
> file then we're relying on the linker.  If we use the same pattern as 
> X86, we can let GCC assign sections+attributes for us and only get one 
> copy in the object file.
> 
> > Or is the linker not removing duplicates that some from the same source
> > file?
> 
> In my testing, yes, the linker is merging them.

So, playing devil's advocate here, what is this fixing?

It doesn't really matter where in the toolchain the duplicates get
removed, just that it happens somewhere...

It looks like ld -r doesn't do the deduplication, so there may be a fair
amount of duplicates before the final linux of vmlinux -- which I guess
could be an issue if BUG() is used in macros that get expanded all over
the place.

Cheers
---Dave