Re: [Crash-utility] [PATCH v5 3/4] arm64: correct a PC shown in bt

> On arm64, the link register (LR) holds a return address, which is the

> just after a branch instruction. So using a saved lr as PC for

> might cause some confusion. > For example, in kernel/entry.S, > work_resched: > ... > bl schedule > > ret_to_user: > ... > > The current code shows "ret_o_user", instead of "work_resched", > as a caller of schedule(). I see...

> > This patch corrects a PC by decrementing it by 4. > But please note that this change may also make people a bit confused > because a value of LR in the stack dump of "bt -f" doesn't match with > an address in one-line summary. > > #2 [ffffcc7511407eb0] schedule at ffff0000d628aee0 > ffffcc7511407eb0: ffffcc6d22f23080 ffff0000d5b44d6c <= LR > ffffcc7511407ec0: ffffcc7511407ed0 0000000000000000 > #3 [ffffcc7511407ed0] work_resched at ffff0000d5b44d68 <= correcrted

That's probably OK -- and at least "bt -F" would clarify it somewhat.

Thanks, Dave > > Signed-off-by: AKASHI Takahiro <takahiro.akashi(a)linaro.org&gt; > --- > arm64.c | 23 ++++++++++++++--------- > 1 file changed, 14 insertions(+), 9 deletions(-) > > diff --git a/arm64.c b/arm64.c > index b74d2c4..bad36aa 100644 > --- a/arm64.c > +++ b/arm64.c > @@ -1504,35 +1504,40 @@ static int > arm64_print_stackframe_entry(struct bt_info *bt, int level, struct > arm64_stackframe *frame, FILE *ofp) > { > char *name, *name_plus_offset; > - ulong symbol_offset; > + ulong pc, symbol_offset; > struct syment *sp; > struct load_module *lm; > char buf[BUFSIZE]; > > - name = closest_symbol(frame->pc); > + /* > + * if pc comes from a saved lr, it actually points to an

> + * after branch. To avoid any confusion, decrement pc by 4. > + * See, for example, "bl schedule" before ret_to_user(). > + */ > + pc = frame->pc - 0x4; > + name = closest_symbol(pc); > name_plus_offset = NULL; > > if (bt->flags & BT_SYMBOL_OFFSET) { > - sp = value_search(frame->pc, &symbol_offset); > + sp = value_search(pc, &symbol_offset); > if (sp && symbol_offset) > - name_plus_offset = > - value_to_symstr(frame->pc, buf,

> + name_plus_offset = value_to_symstr(pc, buf,

> } > > fprintf(ofp, "%s#%d [%8lx] %s at %lx", level < 10 ? " " : "",

> frame->fp ? frame->fp : bt->stacktop -

> - name_plus_offset ? name_plus_offset : name, frame->pc); > + name_plus_offset ? name_plus_offset : name, pc); > > if (BT_REFERENCE_CHECK(bt)) > - arm64_do_bt_reference_check(bt, frame->pc, name); > + arm64_do_bt_reference_check(bt, pc, name); > > - if (module_symbol(frame->pc, NULL, &lm, NULL, 0)) > + if (module_symbol(pc, NULL, &lm, NULL, 0)) > fprintf(ofp, " [%s]", lm->mod_name); > > fprintf(ofp, "\n"); > > if (bt->flags & BT_LINE_NUMBERS) { > - get_line_number(frame->pc, buf, FALSE); > + get_line_number(pc, buf, FALSE); > if (strlen(buf)) > fprintf(ofp, " %s\n", buf); > } > -- > 2.9.0 > > -- > Crash-utility mailing list > Crash-utility(a)redhat.com > https://www.redhat.com/mailman/listinfo/crash-utility > -- Crash-utility mailing list Crash-utility(a)redhat.com https://www.redhat.com/mailman/listinfo/crash-utility