Linkers, Loaders and Shared Libraries in Windows, Linux, and C++ - Ofek Shilon - CppCon 2023

Explore the intricacies of linkers, loaders, and shared libraries in Windows, Linux, and C++ with this talk, delving into symbol resolution, interposition, and more.

Key takeaways

The Linux binary loader uses separate techniques for resolving symbol addresses compared to Windows.
Lazy binding, which postpones symbol resolution until first use, is not the default behavior in Windows, but can be enabled with the delay load switch.
In Linux, a symbol can be overridden from another binary using interposition, but this is not supported by default.
The ELF (Executable and Linkable Format) linker assists shared libraries by resolving symbols and adjusting permissions.
Linkers, particularly in Linux, have specific design goals that affect performance and symbol resolution.
By default, most binaries are linked with f_visibility=hidden, making it easy to override symbols.
To use interposition, mark symbols as dll_export or dll_import to modify visibility.
On Windows, f_visibility=hidden is not the default, but can be achieved with specific linker switches.
shared libraries are outside the scope of C++, but impact its implementation.
In Linux, the linker resolves symbols at runtime and uses the global offset table to facilitate interposition.
The performance cost of interposition can be substantial.
Interposition can be used to override symbols in shared libraries.
Linux uses multiple sections to encode information about shared libraries, while Windows uses a single edata section.
Linkers and shared libraries have a direct impact on C++ development.
The procedure lookup table (PLT) enables lazy binding and is specific to each binary.
The C++ standard does not provide a direct mechanism for interposition, but dll_export and dll_import attributes can achieve similar results.
The bsymbolic linker switch can be used to resolve symbol clashes and optimize code.
The ELF linker defaults to lazy binding, but can be configured to use direct binding instead.
Developing code that works across different platforms and linkers is crucial for software development.

Linkers, Loaders and Shared Libraries in Windows, Linux, and C++ - Ofek Shilon - CppCon 2023

More talks