HomePhabricator

[PPC64] Sort .toc sections accessed with small code model relocs close to .got.

Description

[PPC64] Sort .toc sections accessed with small code model relocs close to .got.

Small code model global variable access on PPC64 has a very limited range of
addressing. The instructions the relocations are used on add an offset in the
range [-0x8000, 0x7FFC] to the toc pointer which points to .got +0x8000, giving
an addressable range of [.got, .got + 0xFFFC]. While user code can be recompiled
with medium and large code models when the binary grows too large for small code
model, there are small code model relocations in the crt files and libgcc.a
which are typically shipped with the distros, and the ABI dictates that linkers
must allow linking of relocatable object files using different code models.

To minimze the chance of relocation overflow, any file that contains a small
code model relocation should have its .toc section placed closer to the .got
then any .toc from a file without small code model relocations.

Differential Revision: https://reviews.llvm.org/D56920

Details

Committed
sfertileJan 23 2019, 1:04 PM
Differential Revision
D56920: [PPC64] Sort .toc sections accessed with small code model relocs close to the .got
Branches
Unknown
Tags
Unknown