329008fdf1
Summary: Lldb support base address selection entries in location lists was broken for a long time. This wasn't noticed until llvm started producing these kinds of entries more frequently with r374600. In r374769, I made a quick patch which added sufficient support for them to get the test suite to pass. However, I did not fully understand how this code operates, and so the fix was not complete. Specifically, what was lacking was the ability to handle modules which were not loaded at their preferred load address (for instance, due to ASLR). Now that I better understand how this code works, I've come to the conclusion that the current setup does not provide enough information to correctly process these entries. In the current setup the location lists were parameterized by two addresses: - the distance of the function start from the start of the compile unit. The purpose of this was to make the location ranges relative to the start of the function. - the actual address where the function was loaded at. With this the function-start-relative ranges can be translated to actual memory locations. The reason for the two values, instead of just one (the load bias) is (I think) MachO, where the debug info in the object files will appear to be relative to the address zero, but the actual code it refers to can be moved and reordered by the linker. This means that the location lists need to be "linked" to reflect the locations in the actual linked file. These two bits of information were enough to correctly process location lists which do not contain base address selection entries (and so all entries are relative to the CU base). However, they don't work with them because, in theory two base address can be completely unrelated (as can happen for instace with hot/cold function splitting, where the linker can reorder the two pars arbitrarily). To fix that, I split the first parameter into two: - the compile unit base address - the function start address, as is known in the object file The new algorithm becomes: - the location lists are processed as they were meant to be processed. The CU base address is used as the initial base address value. Base address selection entries can set a new base. - the difference between the "file" and "load" function start addresses is used to compute the load bias. This value is added to the final ranges to get the actual memory location. This algorithm is correct for non-MachO debug info, as there the location lists correctly describe the code in the final executable, and the dynamic linker can just move the entire module, not pieces of it. It will also be correct for MachO if the static linker preserves relative positions of the various parts of the location lists -- I don't know whether it actually does that, but judging by the lack of base address selection support in dsymutil and lldb, this isn't something that has come up in the past. I add a test case which simulates the ASLR scenario and demonstrates that base address selection entries now work correctly here. Reviewers: JDevlieghere, aprantl, clayborg Subscribers: dblaikie, lldb-commits Tags: #lldb Differential Revision: https://reviews.llvm.org/D70532 |
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| clang | ||
| clang-tools-extra | ||
| compiler-rt | ||
| debuginfo-tests | ||
| libc | ||
| libclc | ||
| libcxx | ||
| libcxxabi | ||
| libunwind | ||
| lld | ||
| lldb | ||
| llgo | ||
| llvm | ||
| openmp | ||
| parallel-libs | ||
| polly | ||
| pstl | ||
| .arcconfig | ||
| .clang-format | ||
| .clang-tidy | ||
| .git-blame-ignore-revs | ||
| .gitignore | ||
| CONTRIBUTING.md | ||
| README.md | ||
README.md
The LLVM Compiler Infrastructure
This directory and its subdirectories contain source code for LLVM, a toolkit for the construction of highly optimized compilers, optimizers, and runtime environments.
The README briefly describes how to get started with building LLVM. For more information on how to contribute to the LLVM project, please take a look at the Contributing to LLVM guide.
Getting Started with the LLVM System
Taken from https://llvm.org/docs/GettingStarted.html.
Overview
Welcome to the LLVM project!
The LLVM project has multiple components. The core of the project is itself called "LLVM". This contains all of the tools, libraries, and header files needed to process intermediate representations and converts it into object files. Tools include an assembler, disassembler, bitcode analyzer, and bitcode optimizer. It also contains basic regression tests.
C-like languages use the Clang front end. This component compiles C, C++, Objective C, and Objective C++ code into LLVM bitcode -- and from there into object files, using LLVM.
Other components include: the libc++ C++ standard library, the LLD linker, and more.
Getting the Source Code and Building LLVM
The LLVM Getting Started documentation may be out of date. The Clang Getting Started page might have more accurate information.
This is an example workflow and configuration to get and build the LLVM source:
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Checkout LLVM (including related subprojects like Clang):
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git clone https://github.com/llvm/llvm-project.git -
Or, on windows,
git clone --config core.autocrlf=false https://github.com/llvm/llvm-project.git
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Configure and build LLVM and Clang:
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cd llvm-project -
mkdir build -
cd build -
cmake -G <generator> [options] ../llvmSome common generators are:
Ninja--- for generating Ninja build files. Most llvm developers use Ninja.Unix Makefiles--- for generating make-compatible parallel makefiles.Visual Studio--- for generating Visual Studio projects and solutions.Xcode--- for generating Xcode projects.
Some Common options:
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-DLLVM_ENABLE_PROJECTS='...'--- semicolon-separated list of the LLVM subprojects you'd like to additionally build. Can include any of: clang, clang-tools-extra, libcxx, libcxxabi, libunwind, lldb, compiler-rt, lld, polly, or debuginfo-tests.For example, to build LLVM, Clang, libcxx, and libcxxabi, use
-DLLVM_ENABLE_PROJECTS="clang;libcxx;libcxxabi". -
-DCMAKE_INSTALL_PREFIX=directory--- Specify for directory the full pathname of where you want the LLVM tools and libraries to be installed (default/usr/local). -
-DCMAKE_BUILD_TYPE=type--- Valid options for type are Debug, Release, RelWithDebInfo, and MinSizeRel. Default is Debug. -
-DLLVM_ENABLE_ASSERTIONS=On--- Compile with assertion checks enabled (default is Yes for Debug builds, No for all other build types).
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Run your build tool of choice!
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The default target (i.e.
ninjaormake) will build all of LLVM. -
The
check-alltarget (i.e.ninja check-all) will run the regression tests to ensure everything is in working order. -
CMake will generate build targets for each tool and library, and most LLVM sub-projects generate their own
check-<project>target. -
Running a serial build will be slow. To improve speed, try running a parallel build. That's done by default in Ninja; for
make, usemake -j NNN(NNN is the number of parallel jobs, use e.g. number of CPUs you have.)
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For more information see CMake
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Consult the Getting Started with LLVM page for detailed information on configuring and compiling LLVM. You can visit Directory Layout to learn about the layout of the source code tree.