[PATCH] D84913: [libFuzzer] Enable for SystemZ
Kostya Serebryany via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Thu Jul 30 09:43:15 PDT 2020
kcc added inline comments.
================
Comment at: compiler-rt/lib/fuzzer/FuzzerTracePC.h:198
+ if (LargeType Bundle = *reinterpret_cast<const LargeType *>(P)) {
+#if __BYTE_ORDER == __BIG_ENDIAN
+ Bundle = Bswap(Bundle);
----------------
iii wrote:
> kcc wrote:
> > iii wrote:
> > > kcc wrote:
> > > > please avoid #ifdefs inside functions.
> > > > If there is some logic that needs to depend on the platform, it needs to reside in a separate dedicated function.
> > > >
> > > > FuzzerBuiltins.h is probably the place for such a function.
> > > >
> > > > Also, what about
> > > > #include <endian.h>
> > > > uint64_t htole64(uint64_t host_64bits);
> > > > is that portable?
> > > >
> > > I think this might not work as expected on 32-bit systems. I'll add a separate function.
> > No strong preference.
> > I've just checked, on Linux x86_64: it inlines and works great.
> > Dunno if it will have portability issues.
> >
> > ```
> > % cat x.cc
> > #include <endian.h>
> > #include <stdint.h>
> >
> > uint64_t foo(uint64_t x) {
> > return htole64(x);
> > }
> > % clang -O2 -S -o - x.cc -m32
> > movl 4(%esp), %eax
> > movl 8(%esp), %edx
> > retl
> >
> > % clang -O2 -S -o - x.cc
> >
> > movq %rdi, %rax
> > retq
> > ```
> >
> > `htobe64` also looks nice, it translates into one `bswapq` on 64-bit and two `bswapl` on 32-bit,
> > i.e. in your case this is what `htole64` will do.
> My thinking is that LargeType is uintptr_t, so it will be uint32_t on a 32-bit system.
> So if we have something like
>
> uint32_t Bundle = 0xAABBCCDD;
>
> htole64(Bundle) would give us (uint64_t)0xDDCCBBAA00000000, and then when we cast it back to uint32_t, we'll get just 0. Isn't that right?
>
> So the idea I'm currently regtesting is:
>
> ```
> --- a/compiler-rt/lib/fuzzer/FuzzerUtil.h
> +++ b/compiler-rt/lib/fuzzer/FuzzerUtil.h
> @@ -106,6 +106,12 @@ inline uint8_t *RoundDownByPage(uint8_t *P) {
> return reinterpret_cast<uint8_t *>(X);
> }
>
> +#if __BYTE_ORDER == __LITTLE_ENDIAN
> +template <typename T> T HToLE(T X) { return X; }
> +#else
> +template <typename T> T HToLE(T X) { return Bswap(X); }
> +#endif
> +
> } // namespace fuzzer
>
> #endif // LLVM_FUZZER_UTIL_H
> ```
>
> ... it's in FuzzerUtil.h and not in FuzzerBuiltins.h, because it uses Bswap, which is defined in a separate header for MSVC.
Sounds good, thanks!
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https://reviews.llvm.org/D84913/new/
https://reviews.llvm.org/D84913
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