https://gcc.gnu.org/bugzilla/show_bug.cgi?id=38534
--- Comment #23 from H.J. Lu <hjl.tools at gmail dot com> --- (In reply to Andrew Burgess from comment #21) > Setting to DW_CFA_undefined is the right thing to do. DWARF says: > > The DW_CFA_undefined instruction takes a single unsigned LEB128 operand > that represents a register number. The required action is to set the rule > for the > specified register to “undefined.” > > which is exactly what you'd want here. > > GDB has a distinction between "unspecified" (not really a DWARF thing) and > "undefined" (the DWARF thing). Registers that aren't given an initial state > in the CIE start as "unspecified", the idea being (I believe) that we then > apply some kind of ABI based rules on top. So an "unspecified" > call-clobbered register would be treated as "undefined", while a > callee-saved register would be treated as "same-value" to begin with. > > Setting a register to "undefined" in the DWARF should, I think, do what you > want. A patch is posted at https://patchwork.sourceware.org/project/gcc/list/?series=30283
