[PATCH] D84913: [libFuzzer] Enable for SystemZ

[Ilya Leoshkevich via Phabricator via llvm-commits]

iii 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);
----------------
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.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D84913/new/

https://reviews.llvm.org/D84913