Re: [Qemu-devel] [PATCH v3 17/22] fuzz: add support for fork-based fuzzing.

[Stefan Hajnoczi]

On Wed, Sep 18, 2019 at 11:19:44PM +0000, Oleinik, Alexander wrote:
> diff --git a/exec.c b/exec.c
> index 235d6bc883..d3838f4ea4 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -2295,7 +2295,9 @@ static void ram_block_add(RAMBlock *new_block, Error 
> **errp, bool shared)
>          qemu_ram_setup_dump(new_block->host, new_block->max_length);
>          qemu_madvise(new_block->host, new_block->max_length, 
> QEMU_MADV_HUGEPAGE);
>          /* MADV_DONTFORK is also needed by KVM in absence of synchronous MMU 
> */
> +#ifndef CONFIG_FUZZ /* This conflicts with fork-based fuzzing */
>          qemu_madvise(new_block->host, new_block->max_length, 
> QEMU_MADV_DONTFORK);
> +#endif
>          ram_block_notify_add(new_block->host, new_block->max_length);
>      }
>  }

I didn't check Makefile changes but regular softmmu binaries should
continue to work with --enable-fuzzing so we cannot use #ifdef here.

Perhaps this should be a runtime check similar to qtest_enabled():

  /* The fuzzer's fork child requires access to guest RAM */
  if (!fuzz_enabled()) {
      qemu_madvise(new_block->host, new_block->max_length, QEMU_MADV_DONTFORK);
  }

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