On Wed, Feb 05, 2025 at 02:56:36PM +0100, Jens Remus wrote: > On 29.01.2025 03:02, Josh Poimboeuf wrote: > > > Note FDEs aren't even needed here as the unwinder doesn't need to know > > when a function begins/ends. The only info needed by the unwinder is > > just the fre_data struct. So a simple binary search of fres[] is all > > that's really needed. > > In SFrame V2 FDEs specify ranges bound by function start address and > length. FREs in contrast specify open ranges bounded by start address. > Their effect ends either with the next FRE becoming into effect or when > their FDE range ends. > This concept enables holes in the .text section which do not have any > valid FDE/FRE information associated. > > Your proposal lacks some sort of mechanism to replicate those holes. > It could be FDEs with a flag (or no offsets?) that specifies their > range has no valid information.
In ORC, a hole is simply specified by an ORC entry (aka "FRE") of type UNDEFINED. That could be done here as well: the linker would replace a gap with an "undefined" FRE which could be identified either by setting a bit in the FRE header, or by using a special fre_data[] entry. For example, fre_data index 0 could just be a placeholder for the undefined FRE type. -- Josh
