[PATCH] D130877: [MCObjectFileInfo] Add getPCSection() helper

[Dmitry Vyukov via Phabricator via llvm-commits]

dvyukov added inline comments.


================
Comment at: llvm/lib/MC/MCObjectFileInfo.cpp:1189
+  // SHF_WRITE for relocations, and let user post-process data in-place.
+  unsigned Flags = ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_LINK_ORDER;
+
----------------
melver wrote:
> dvyukov wrote:
> > Do we actually plan to write to these sections? Does setting SHF_WRITE prevent sharing of pages across multiple processes? Of SHF_WRITE pages still mapped as shared/write-protected first and then subject to copy-on-write?
> This was needed for relocations (because linker needs section writable if it contains relocations).
> glibc seems to map sections as MAP_COPY (AFAIK), which is MAP_PRIVATE on Linux, so it'll COW.
> 
> Now that we have relative relocations, maybe we don't need it anymore, but I'd like to reserve the option to modify the data in-place (whether we do it, or someone else finds a use for it).
> Changing it again in future is too painful, and we're likely stuck with whatever we decide now. I don't see a huge downside to it being writable (there's no security concern here).
> 
> Cc @MaskRay 
If it's shared across processes and COW, then it should be fine.


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  https://reviews.llvm.org/D130877/new/

https://reviews.llvm.org/D130877