2020-11-08

Stack unwinding

Update in 2025-11.

The main usage of stack unwinding is:

To obtain a stack trace for debuggers, crash reporters, profilers, garbage collectors, etc.
To implement C++ exceptions (Itanium C++ ABI) using personality routines and language-specific data area. See C++ exception handling ABI

Some people use "stack walking" to refer to obtaining a stack trace, while "stack unwinding" refers to an enhanced operation that also recovers callee-saved registers. In this post, we don't make the distinction.

2020-10-15

模块内函数调用和libc符号重命名

Translation unit外的函数调用

2020-10-03

Command line processing in LLVM

中文版

Updated in 2023-05.

There are two libraries for processing command line options in LLVM.

`llvm/Support/ComandLine.h`

See https://llvm.org/docs/CommandLine.html for documentation.

Global variables (mostly llvm::cl::opt<type>, some llvm::cl::list<type>) are most common to represent command-line options. The llvm::cl::opt constructor registers this command line option in a global registry. The program calls llvm::cl::ParseCommandLineOptions(argc, argv, ...) in main to parse the command line options. opt supports various integer types, bool, std::string, etc. Defining some specialization can support support custom class/enum types.

2020-09-27

gcov与LLVM中的实现

打算以后不定期写一点LLVM的学习(开发)笔记。写作上不想过多花时间(加语文水平所限...)，所以字句不作过多斟酌。

gcov

https://gcc.gnu.org/onlinedocs/gcc/Gcov.html

_Optimally Profiling and Tracing Programs_描述了一个edge-frequency/edge-placement problem。选择control-flow graph的一些边，加上监控代码，推导所有边的执行次数。 gcov是一种实现。

在gcov的模型中，一个源文件包含若干函数，一个函数包含若干基本块，一个基本块占据若干行，这些信息保存在.gcno文件中。 Instrument程序，在基本块间转移时记录边的执行次数，程序退出时为每个translation unit输出一个.gcda文件。 .gcda文件可以累计多次程序执行的计数。

2020-02-01