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

[Ian Jackson <ian.jackson@xxxxxxxxxxxxx>]

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

Ian.

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