forked from OSchip/llvm-project
e6892c8149
This reapplies r235060 and 235070, which were reverted because of test failures in LLDB. The failure was caused because at moment RuntimeDyld is processing relocations for all sections, irrespective of whether we actually load them into memory or not, but RuntimeDyld was not actually remembering where in memory the unrelocated section is. This commit includes a fix for that issue by remembering that pointer, though the longer term fix should be to stop processing unneeded sections. Original Summary: This allows us to get rid of the original unrelocated object file after we're done processing relocations (but before applying them). MachO and COFF already do not require this (currently we have temporary hacks to prevent ownership from being released, but those are brittle and should be removed soon). The placeholder mechanism allowed the relocation resolver to look at original object file to obtain more information that are required to apply the relocations. This is usually necessary in two cases: - For relocations targetting sub-word memory locations, there may be pieces of the instruction at the target address which we should not override. - Some relocations on some platforms allow an extra addend to be encoded in their immediate fields. The problem is that in the second case the information cannot be recovered after the relocations have been applied once because they will have been overridden. In the first case we also need to be careful to not use any bits that aren't fixed and may have been overriden by applying a first relocation. In the past both have been fixed by just looking at original object file. This patch attempts to recover the information from the first by looking at the relocated object file, while the extra addend in the second case is read upon relocation processing and addend to the regular addend. I have tested this on X86. Other platforms represent my best understanding of how those relocations should work, but I may have missed something because I do not have access to those platforms. We will keep the ugly workarounds in place for a couple of days, so this commit can be reverted if it breaks the bots. Differential Revision: http://reviews.llvm.org/D9028 llvm-svn: 236341 |
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README.txt
Low Level Virtual Machine (LLVM) ================================ This directory and its subdirectories contain source code for LLVM, a toolkit for the construction of highly optimized compilers, optimizers, and runtime environments. LLVM is open source software. You may freely distribute it under the terms of the license agreement found in LICENSE.txt. Please see the documentation provided in docs/ for further assistance with LLVM, and in particular docs/GettingStarted.rst for getting started with LLVM and docs/README.txt for an overview of LLVM's documentation setup. If you're writing a package for LLVM, see docs/Packaging.rst for our suggestions.