[PATCH] D68101: [MC][ELF] Prevent globals with an explicit section from being mergeable

[Sjoerd Meijer via Phabricator via llvm-commits]

SjoerdMeijer added a comment.

I am getting up to speed with this... and created this reproducer:

  static int A[4] __attribute__ ((section ("HELLO"))) = {1,0,0,1} ;
  static long long B[9]  __attribute__ ((section ("HELLO"))) = {0,0,0,0,0,0,0,0,1};
  int foo (int i) {
    return A[i] + B[i];
  }

The corresponding ELF object contains this section:

  Name        : HELLO
  Type        : SHT_PROGBITS (0x00000001)
  Flags       : SHF_ALLOC + SHF_MERGE (0x00000012)
  Addr        : 0x00000000
  File Offset : 96 (0x60)
  Size        : 88 bytes (0x58)
  Link        : SHN_UNDEF
  Info        : 0
  Alignment   : 8
  Entry Size  : 16

You're unhappy about the `Entry Size  : 16`, as this sections contains entries of words and double-words. The ELF spec says this about this entry:

  The size of each element is specified in the section header's sh_entsize field. 

So yes, I guess that means the entry size needs to be uniform.

Now my question about this patch: why are we trying to patch things up when we can avoid putting incompatible symbols in the same section in the first place? In this case, the merging is achieved with a section attribute, but from the PR I understood the same can be achieved with a pragma, so from that point of view we perhaps got what we deserved? Would be nice though to warn about this, and/or the pass that does the merging should not do this?


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D68101/new/

https://reviews.llvm.org/D68101