To add to what Greg described you may also want to look at section 6.4.4 of the DWARF 5 specification that discusses these issues. In particular note the non-normative description in the fourth paragraph.
> 6.4.4 Call Frame Calling Address > > *When virtually unwinding frames, consumers frequently wish to obtain the > address of the instruction which called a subroutine. This information is not > always provided. Typically, however, one of the registers in the virtual > unwind table is the Return Address.* > > If a Return Address register is defined in the virtual unwind table, and its > rule is undefined (for example, by DW_CFA_undefined), then there is no > return address and no call address, and the virtual unwind of stack > activations is complete. > > *In most cases the return address is in the same context as the calling > address, but that need not be the case, especially if the producer knows in > some way the call never will return. The context of the ’return address’ > might be on a different line, in a different lexical block, or past the end > of the calling subroutine. If a consumer were to assume that it was in the > same context as the calling address, the virtual unwind might fail.* > > *For architectures with constant-length instructions where the return address > immediately follows the call instruction, a simple solution is to subtract > the length of an instruction from the return address to obtain the calling > instruction. For architectures with variable-length instructions (for > example, x86), this is not possible. However, subtracting 1 from the return > address, although not guaranteed to provide the exact calling address, > generally will produce an address within the same context as the calling > address, and that usually is sufficient.* Thanks, -Tony Tye _______________________________________________ Dwarf-Discuss mailing list Dwarf-Discuss@lists.dwarfstd.org http://lists.dwarfstd.org/listinfo.cgi/dwarf-discuss-dwarfstd.org
