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Re: [RFC PATCH 3/3] fuzz: Add callbacks for dma-access functions
From: |
Stefan Hajnoczi |
Subject: |
Re: [RFC PATCH 3/3] fuzz: Add callbacks for dma-access functions |
Date: |
Tue, 23 Jun 2020 15:14:56 +0100 |
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
Now the compiler should eliminate the deadcode:
#ifdef CONFIG_FUZZ
if (as->root == get_system_memory()) {
dma_read_cb(addr, len);
}
#endif
becomes:
if (as->root == get_system_memory()) {
fuzz_dma_read_cb(addr, len);
}
Hopefully gcc and clang will eliminate this and emit no instructions
when CONFIG_FUZZ is undefined. If not, you can simply pass in 'as' and
'is_write' too:
void fuzz_dma_read_cb(AddressSpace *as, bool is_write, size_t addr, size_t
len)
This way the conditional is moved inside fuzz_dma_read_cb() and deadcode
elimination becomes trivial for the compiler:
fuzz_read_cb(as, is_write, addr, len);
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