zunstack

Unwind the stack on fatal signals!

Currently in demo stage, don't use it in production.

Try it!

An example is included in test.c, compile it together with zunstack, e.g.

$ clang test.c zunstack.c -o test \
	-fno-omit-frame-pointer		\
	-Wl,--export-dynamic		\
	-Wl,--hash-style=both
$ ./test
Frame #0 (0x0x7fffd3a453b0): PC = 0x5596779e3adc
	symbol foo in ./test
Frame #1 (0x0x7fffd3a453e0): PC = 0x5596779e3b0d
        symbol main in ./test
Aborted

How does it work

Stack Unwind

Most compilers will generate code in a fixed pattern if -fno-omit-frame-pointer is specified:

• Stackframe is always hold by a register, called FP (frame pointer). On x86_64 it is %rbp.
• Address of caller's frame and PC could be indexed by FP

If all DSO are compiled with -fno-omit-frame-pointer, we could simply walk through the stack like iterating a linked list.

Symbol Resolve

zunstack does not depend on debuginfo to resolve symbol information. Instead, it iterates all loaded DSO and check whether a dynamic symbols' address region covers PC.

Limitations

• -fno-omit-frame-pointer must be applied for all DSOs. CFI-based unwinding could be added later to avoid this.
• Only exported dynamic symbols could be resolved. (force symbols in exexcutable to be exported by -Wl,--export-dynamic)
• Currently, symbol resolving supports only traditional ELF hashtable. (-Wl,--hash-style=both ensures traditional ELF hashtable is generated)

Compatiblity

Tested on x86_64 eweOS (musl-based Linux distro). Only musl and x86_64 is supported for now.

Copyright

Copyright (c) 2024 Yao Zi. All rights reserved.
zunstack is distributed under Mozilla Public License Version 2.0.