[Git][ghc/ghc][master] rts/linker: Align bssSize to page size when mapping symbol extras

[Marge Bot]

 Marge Bot pushed to branch master at Glasgow Haskell Compiler / GHC


Commits:
9f40cf6c by Ben Gamari at 2020-11-20T02:11:07-05:00
rts/linker: Align bssSize to page size when mapping symbol extras

We place symbol_extras right after bss. We also need
to ensure that symbol_extras can be mprotect'd independently from the
rest of the image. To ensure this we round up the size of bss to a page
boundary, thus ensuring that symbol_extras is also page-aligned.

- - - - -


1 changed file:

- rts/linker/SymbolExtras.c


Changes:

=====================================
rts/linker/SymbolExtras.c
=====================================
@@ -77,7 +77,9 @@ int ocAllocateExtras(ObjectCode* oc, int count, int first, int bssSize)
       /* N.B. We currently can't mark symbol extras as non-executable in this
        * case. */
       size_t n = roundUpToPage(oc->fileSize);
-      bssSize = roundUpToAlign(bssSize, 8);
+      // round bssSize up to the nearest page size since we need to ensure that
+      // symbol_extras is aligned to a page boundary so it can be mprotect'd.
+      bssSize = roundUpToPage(bssSize);
       size_t allocated_size = n + bssSize + extras_size;
       void *new = mmapForLinker(allocated_size, PROT_READ | PROT_WRITE, MAP_ANONYMOUS, -1, 0);
       if (new) {



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/9f40cf6ca9fb24dbc55f7eae43e2b89aa12bf251

-- 
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/9f40cf6ca9fb24dbc55f7eae43e2b89aa12bf251
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