[PATCH] D29751: [libFuzzer] Use dynamic loading for External Functions on Windows.

[Marcos Pividori via Phabricator via llvm-commits]

mpividori added inline comments.


================
Comment at: lib/Fuzzer/FuzzerExtFunctionsDlsymWin.cpp:46
+      this->NAME = (decltype(ExternalFunctions::NAME)) Fn;                     \
+    }
+#include "FuzzerExtFunctions.def"
----------------
zturner wrote:
> mpividori wrote:
> > zturner wrote:
> > > What if it still can't find it?  You don't set `this->NAME` to anything, so it's uninitialized memory, but you don't indicate any kind of error.
> > > 
> > > Also, what happens if it could be found in more than one module but we choose the wrong one?  
> > @zturner Yes, `this->NAME` is set to `NULL`  if `GetProcAddress` can't find the function. This is ok, because these functions are optional.
> > If the functions is not found after considering all the modules, a warning is printed depending on the flag `WARN`. Is the same than for other platforms. For example, for Darwin, when using `dlsym`, or for linux, when considering weak symbols, if the function is not present, we set a `null` pointer.
> > 
> > The functions that we look for are:
> >  * sanitizer's functions, like: `__sanitizer_*` , `__lsan__*`, etc. Which are very unlikely to be defined in another module.
> >  * fuzzer's functions, like: `LLVMFuzzerInitialize`, `LLVMFuzzerCustomMutator`, etc.
> > 
> > Anyway, I could update the code to fail if it finds more than one reference for the same function in different modules.
> No, because that would require searching a potentially huge module list even if you find it on the first one.  We should optimize for the normal case, not the exceptional case.  I don't know what the best solution is, just wanted to make sure you think about the possibility that the function exists in multiple modules.  
@zturner yes, exactly. Is the same than for  `dlsym(RTLD_DEFAULT, FnName)`,:
``
"... There are two special pseudo-handles, RTLD_DEFAULT and RTLD_NEXT. The former will find the first occurrence of the desired symbol using the default library search order. ..."
``
So, it finds the first occurrence.


https://reviews.llvm.org/D29751