| There's essentially three separate moving pieces here. At the bottom layer you have the unwind API. This is actually generally defined by the platform-specific ABI, although the definition here on most Unixes is "we have a .eh_frame section that's basically the same as .debug_frame in DWARF." The API is provided by some platform library (libunwind), and it's language-agnostic. Part of the generic unwind structure is that each stack frame has a personality function and a Language-Specific Data Area, and the unwind semantics will call the personality function to figure out whether to drop off into the stack frame, and where in the function to drop off, or continue unwinding the stack. The personality function itself uses the LSDA to figure out what to do. The personality function lives in the language standard library (e.g., libstdc++), and the LSDA format is of course entirely undocumented (i.e., read Ian Lance Taylor's blog posts as the best documentation that exists). The final level of the ABI is how you actually represent the exceptions themselves. This is provided by the Itanium ABI and describes the names of the functions needed to effect exception handling (e.g., __cxa_begin_catch), the structure layouts involved, and even some nominal data on how to handle foreign exceptions which don't really exist. And that's not entirely true for all systems. ARM notably uses a different ABI exception handling, which is rather close to the standard Itanium exception handling except the details are different. Some operating systems choose to forgo unwinding-based exceptions in lieu of setjmp/longjmp as the standard ABI, which of course requires different versions of everything. And Windows has an entirely different form of exception handling which isn't centered around unwinding but actually calling exception handlers as new functions on the stack, requiring frame links to the original-would-be-unwound-to function. |