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Set hidden visibility on global symbols accessed from AArch64

Closed Thomas Guillem requested to merge tguillem/x264:relocation-aarch64 into master
  1. Jul 27, 2022
    • Thomas Guillem's avatar
      Set hidden visibility on global symbols accessed from AArch64 · fe8f0c92
      Thomas Guillem authored
      From Martin Storsjö:
      https://patchwork.ffmpeg.org/project/ffmpeg/patch/20220714195325.297691-1-martin@martin.st/
      
      "The AArch64 assembly accesses those symbols directly, without
      indirection via e.g. the GOT on ELF. In order for this not to
      require text relocations, those symbols need to be resolved fully
      at link time, i.e. those symbols can't be interposable.
      
      Normally, so far, this is achieved when linking shared libraries
      in two ways; we have a version script (libavcodec/libavcodec.v) which
      marks all symbols that don't start with av* as local. Additionally,
      we try to add -Wl,-Bsymbolic to the linker options if supported,
      making sure that such symbol references are resolved fully at link
      time, instead of making them interposable.
      
      When the libavcodec static library is linked into another shared
      library, there's no guarantee that it uses similar options (even though
      that would be favourable), which would end up requiring text relocations
      in the AArch64 assembly.
      
      Explicitly mark the symbols that are accessed from AArch64 assembly
      as hidden, so that they are resolved fully at link time even without
      the version script and -Wl,-Bsymbolic."
      fe8f0c92
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