[PATCH] D63121: [ELF] Make the rule to create relative relocations in a writable section stricter

[Peter Smith via Phabricator via llvm-commits]

peter.smith added a comment.

A look at the differences between libclang.so with and without the patch is that what used to be a R_ARM_RELATIVE relocation is now a R_ARM_ABS32 relocation to an undefined symbol. The latter will likely resolve to 0. All of the difference is concentrated in the .init_array section which uses the R_ARM_TARGET1 relocation, which is treated as R_ARM_ABS32 by default but with an option be treated as R_ARM_REL32 (some embedded systems use offsets rather than addresses).
For example:
Good

  Contents of section .init_array:
   2d21008 c980c300 c46fb301 f89ab301 acfbb601  .....o..........
   2d21018 8067b801 8040b901 403fbf01 00bec101  .g... at ..@?......
   2d21028 c0bdc201 c873c301 8c52c501 7810c601  .....s...R..x...
  ...
  02d21008  00000017 R_ARM_RELATIVE   
  02d2100c  00000017 R_ARM_RELATIVE   
  02d21010  00000017 R_ARM_RELATIVE   
  02d21014  00000017 R_ARM_RELATIVE   
  02d21018  00000017 R_ARM_RELATIVE   
  02d2101c  00000017 R_ARM_RELATIVE   
  02d21020  00000017 R_ARM_RELATIVE   
  02d21024  00000017 R_ARM_RELATIVE   
  02d21028  00000017 R_ARM_RELATIVE   

Bad:

  Contents of section .init_array:
   2d21008 c980c300 00000000 00000000 00000000  ................
   2d21018 00000000 00000000 00000000 00000000  ................
   2d21028 00000000 00000000 00000000 00000000  ................
  ...
  02d21008  00000017 R_ARM_RELATIVE
  02d2100c  00000002 R_ARM_ABS32      
  02d21010  00000002 R_ARM_ABS32      
  02d21014  00000002 R_ARM_ABS32      
  02d21018  00000002 R_ARM_ABS32      
  02d2101c  00000002 R_ARM_ABS32      
  02d21020  00000002 R_ARM_ABS32      
  02d21024  00000002 R_ARM_ABS32      
  02d21028  00000002 R_ARM_ABS32      

So far I've not been able to make a simpler reproducer, as can be seen from the first entry in the .init_array there must be some special case.


Repository:
  rL LLVM

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D63121/new/

https://reviews.llvm.org/D63121