Re: [RFC PATCH 3/3] fuzz: Add callbacks for dma-access functions

[Stefan Hajnoczi]

On Thu, Jul 09, 2020 at 07:48:55PM -0400, Alexander Bulekov wrote:
> On 200623 1514, Stefan Hajnoczi wrote:
> > On Thu, Jun 11, 2020 at 01:56:51AM -0400, Alexander Bulekov wrote:
> > > Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
> > > ---
> > >  exec.c                                | 17 ++++++++++++++++-
> > >  include/exec/memory.h                 |  8 ++++++++
> > >  include/exec/memory_ldst_cached.inc.h |  9 +++++++++
> > >  include/sysemu/dma.h                  |  5 ++++-
> > >  memory_ldst.inc.c                     | 12 ++++++++++++
> > >  5 files changed, 49 insertions(+), 2 deletions(-)
> > 
> > Please rename dma_read_cb() to fuzz_dma_read_cb() so the purpose of the
> > function is clear.
> > 
> > The ifdefs can be avoided by defining an empty function when CONFIG_FUZZ
> > is undefined. In a header file:
> > 
> >   #ifdef CONFIG_FUZZ
> >   void fuzz_dma_read_cb(size_t addr, size_t len);
> >   #else
> >   static inline void fuzz_dma_read_cb(size_t addr, size_t len)
> >   {
> >       /* Do nothing */
> >   }
> >   #endif
> > 
> 
> If I understand correctly, this still has the problem that normal
> qemu-system builds under --enable-fuzzing are broken. I'm not sure if
> there is some nice solution for this. For example, a sort-of ugly
> solution could add this to softmmu/main.c (ie something that is linked
> for the qemu-system build, but not for qemu-fuzz).
> 
> #ifdef CONFIG_FUZZ
> #include "something.h"
> static void fuzz_dma_read_cb(size_t addr, size_t len)
> {
>     /* Do nothing */
> }
> #endif

Another ugly solution is using weak symbols in the main code and a
strong symbol in the fuzzer target:
https://en.wikipedia.org/wiki/Weak_symbol

Stefan

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