Re: [Xen-devel] [PATCH 2/4] tools/fuzz: add AFL stub program for x86 insn emulator fuzzer

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Tue, Jan 24, 2017 at 05:22:37PM +0000, Ian Jackson wrote:
> Wei Liu writes ("Re: [PATCH 2/4] tools/fuzz: add AFL stub program for x86 
> insn emulator fuzzer"):
> > On Tue, Jan 24, 2017 at 05:05:16PM +0000, Ian Jackson wrote:
> > > If you use read you ought to put it in a loop to cope with potential
> > > partial reads.
> > 
> > Does fread have better properties than read?
> 
> Yes.  fread is not allowed to give a short read for no particular
> reason, nor to return with EINTR.
> 
> > I think to deal with short read we would need to stat the file to
> > get actual size for both fread and read, right?
> 
> No.  In both cases, it is possible to detect whether a short read is
> due to EOF.  With read, that would have to be in a loop.  With fread
> you can test feof.
> 
> You don't need to test with stat unless you want to support files
> bigger than your static buffer.
> 
> I recommend you:
>  * use fopen and fread
>  * complain if fread filled the whole buffer, on the grounds that
>    that means you may be ignoring a longer file than is supported
>  * check with feof or ferror that the short read was due to eof
> 

NP. This sounds sensible.

Wei.

> Ian.

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