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65 lines
1.9 KiB
Text
65 lines
1.9 KiB
Text
- the frame state consists of the following:
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- ip current instruction pointer
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- sp current stack pointer value
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- bsp current backing store pointer
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- cfm current frame mask
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these are derived from the next younger (more deeply nested) frame
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as follows:
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- ip == saved return-link (may be b0 or an alternate branch-reg)
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- sp == if younger frame has a fixed-sized frame, sp + size-of-frame,
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else saved sp
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- cfm == saved ar.pfs
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- bsp == if ar.bsp has been saved, saved ar.bsp, otherwise,
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ar.bsp \ominus saved ar.pfs.pfm.sol
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The unwind cursor should represent the machine state as it existed at
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the address contained in register ip. This state consists of the
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*current* frame state and the save locations in the next younger
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frame.
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An unwind script current takes the old save locations and updates them
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for the next older frame. With the new setup, we need to update the
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frame state first, without updating the other save locations. For this
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to work, we need the following info:
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- save location of return-link
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- save location of ar.pfs
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- save location of bsp (if it has been saved)
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- size of stack frame (fixed case) or save location of sp
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setup:
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func: ...
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...
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...
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br.call foo <-- call site
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... <-- ip
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...
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initial state:
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The unwind cursor represents the (preserved) machine state
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as it existed at "ip".
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Evaluating the unwind descriptors for "ip" yields the following
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info:
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- frame size at call site (or previous sp)
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- what registers where saved where by func before
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the call site was reached
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Note that there is some procedure info that needs to be obtained
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for the new "ip" which is contained in the unwind descriptors.
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Specifically, the following is needed:
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- procedure's start address
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- personality address
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- pointer to language-specific data area
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This info is stored in a separate proc_info structure and needs
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to be obtained right after running the unwind script for func.
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