[PATCH] D67206: [ELF][MC] Fix IFunc alias resolving issue

[Sr.Zhang via Phabricator via llvm-commits]

zsrkmyn added a comment.

Suppose we have foo.s as follows:

  .text
  .p2align 3
  
  .globl foo_impl
  .type foo_impl, at function
  foo_impl:
    ret
  
  .globl foo_resolver
  .type foo_resolver, at function
  foo_resolver:
    mov $foo_impl, %rax
    ret
  
  .globl foo
  .type foo, at gnu_indirect_function
  .set foo,foo_resolver
  
  .globl foo2
  .set foo2,foo

and assemble foo.s with GNU as, and check foo.o with nm:

  $ as foo.s -o foo.o
  $ nm foo.o | grep foo2
  0000000000000006 i foo
  0000000000000006 i foo2   <- foo2 is an ifunc identical to foo
  0000000000000000 T foo_impl
  0000000000000006 T foo_resolver

and the 'foo2' is also an ifunc whose resolver is foo_resolver.

However, when assemble with llvm-mc, the 'foo2' becomes normal a
function identical to 'foo_resolver':

  $ llvm-mc foo.s -filetype obj -o foo.o
  $ nm foo.o
  0000000000000006 i foo
  0000000000000006 T foo2   <- foo2 is a strong symbol identical to foo_resolver
  0000000000000000 T foo_impl
  0000000000000006 T foo_resolver

The reason is as follows:

When we 'getBaseSymbol' from 'ELFwriter::writeSymbol' in lib/MC/ELFObjectWriter.cpp, it recursively evaluates the 'Value' of the 'Symbol', and the two direcives -- '.set foo,foo_resolver' and '.set foo2,foo' -- make foo2 is evaluated as 'foo_resolver', and the 'Type' we get below becomes function, while it should be ifunc.


Repository:
  rL LLVM

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  https://reviews.llvm.org/D67206/new/

https://reviews.llvm.org/D67206