1- the frame state consists of the following: 2 3 - ip current instruction pointer 4 - sp current stack pointer value 5 - bsp current backing store pointer 6 - cfm current frame mask 7 8 these are derived from the next younger (more deeply nested) frame 9 as follows: 10 11 - ip == saved return-link (may be b0 or an alternate branch-reg) 12 - sp == if younger frame has a fixed-sized frame, sp + size-of-frame, 13 else saved sp 14 - cfm == saved ar.pfs 15 - bsp == if ar.bsp has been saved, saved ar.bsp, otherwise, 16 ar.bsp \ominus saved ar.pfs.pfm.sol 17 18The unwind cursor should represent the machine state as it existed at 19the address contained in register ip. This state consists of the 20*current* frame state and the save locations in the next younger 21frame. 22 23An unwind script current takes the old save locations and updates them 24for the next older frame. With the new setup, we need to update the 25frame state first, without updating the other save locations. For this 26to work, we need the following info: 27 28 - save location of return-link 29 - save location of ar.pfs 30 - save location of bsp (if it has been saved) 31 - size of stack frame (fixed case) or save location of sp 32 33 34setup: 35 36 func: ... 37 ... 38 ... 39 br.call foo <-- call site 40 ... <-- ip 41 ... 42 43initial state: 44 45 The unwind cursor represents the (preserved) machine state 46 as it existed at "ip". 47 48 Evaluating the unwind descriptors for "ip" yields the following 49 info: 50 51 - frame size at call site (or previous sp) 52 - what registers where saved where by func before 53 the call site was reached 54 55 56 Note that there is some procedure info that needs to be obtained 57 for the new "ip" which is contained in the unwind descriptors. 58 Specifically, the following is needed: 59 60 - procedure's start address 61 - personality address 62 - pointer to language-specific data area 63 64 This info is stored in a separate proc_info structure and needs 65 to be obtained right after running the unwind script for func. 66