iii added inline comments.

================
Comment at: compiler-rt/lib/tsan/rtl/tsan_platform_posix.cpp:123
+#if defined(__s390x__)
+  ProtectRange(HiAppMemEnd(), 0xfffffffffffff000ull);
+#endif
----------------
uweigand wrote:
> iii wrote:
> > uweigand wrote:
> > > Did you test this on older kernels without 5-level page table support?   
> > > I believe the allocation / mprotect may fail on those ...
> > No, not really. Would it make sense to probe here? E.g. first try 
> > 0xfffffffffffff000, then 0x20000000000000. Or is there a way to query 
> > user_addr_max() / TASK_SIZE_MAX / TASK_SIZE?
> I don't know of any way to query this.  You can simply do the allocation in 
> stages (first to the top of the three-pagetable range, then four, then five), 
> and ignore failures.   As an unfortunate side effect this will force the 
> kernel to allocate five levels of page tables even when unnecessary, but I 
> don't think there's anything we can do about that.
3-level page table limit is quite below the application range defined in this 
series (0x40000000000 < 0xc00000000000). Are there any relevant kernels that do 
not support 4-level page tables? I tried to search the git history, and it 
looks as if even 2.6 ones have it.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D105629/new/

https://reviews.llvm.org/D105629

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