On Thu, Jul 17, 2025 at 01:28:25PM +0200, Jens Remus wrote:
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}
/* Get the Frame Pointer (FP) */
- if (frame->fp_off && unwind_get_user_long(fp, cfa + frame->fp_off, state))
+ switch (frame->fp.loc) {
+ case UNWIND_USER_LOC_NONE:
+ break;
The UNWIND_USER_LOC_NONE behavior is different here compared to above.
See my comments below.
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Do we also need UNWIND_USER_LOC_PT_REGS?
Sorry, I cannot follow. Do you suggest to rename UNWIND_USER_LOC_REG to
UNWIND_USER_LOC_PT_REGS?
I think I completely misunderstood the meaning of UNWIND_USER_LOC_NONE.
Never mind :-)
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+ case UNWIND_USER_LOC_STACK:
+ if (!frame->fp.frame_off)
+ goto done;
+ if (unwind_get_user_long(fp, cfa + frame->fp.frame_off, state))
+ goto done;
+ break;
+ case UNWIND_USER_LOC_REG:
+ if (!IS_ENABLED(CONFIG_HAVE_UNWIND_USER_LOC_REG) || !topmost)
+ goto done;
The topmost checking is *really* getting cumbersome, I do hope we can
get rid of that.
Restoring from arbitrary registers is only valid in the topmost frame,
as their values (i.e. task_pt_regs(current)) are only available there.
For other frames only SP, FP, and RA register values are available.
I think this test makes sense. Is this test really that expensive?
ra_off=0 (UNWIND_USER_LOC_NONE) on a !topmost frame should never happen
unless the sframe entry is bad. But 0 is *far* from the only potential
bad RA offset value. In the absolute worst case of a 4 byte offset,
there are 4+ billion other possible bad values that can still go
undetected.
So I question the usefulness of those !topmost tests. And they do add
complexity to the code.
--
Josh