On Tue, 2017-04-25 at 14:49 +0200, Mark Wielaard wrote:
> +bool
> +EBLHOOK(unwind) (Ebl *ebl __attribute__ ((unused)), Dwarf_Addr pc
> __attribute__ ((unused)),
> + ebl_tid_registers_t *setfunc, ebl_tid_registers_get_t
> *getfunc,
> + ebl_pid_memory_read_t *readfunc, void *arg,
> + bool *signal_framep __attribute__ ((unused)))
> +{
> + Dwarf_Word fp, lr, sp;
> +
> + if (!getfunc(LR_REG, 1, &lr, arg))
> + return false;
> +
> + if (!getfunc(FP_REG, 1, &fp, arg))
> + fp = 0;
> +
> + if (!getfunc(SP_REG, 1, &sp, arg))
> + sp = 0;
> +
> + Dwarf_Word newPc, newLr, newFp, newSp;
> +
> + // The initial frame is special. We are expected to return lr directly in
> this case, and we'll
> + // come back to the same frame again in the next round.
> + if ((pc & 0x1) == 0)
> + {
> + newLr = lr;
> + newFp = fp;
> + newSp = sp;
> + }
> + else
> + {
> + if (!readfunc(fp + LR_OFFSET, &newLr, arg))
> + newLr = 0;
> +
> + if (!readfunc(fp + FP_OFFSET, &newFp, arg))
> + newFp = 0;
> +
> + newSp = fp + SP_OFFSET;
> + }
> +
> + newPc = newLr & (~0x1);
> + if (!setfunc(-1, 1, &newPc, arg))
> + return false;
My question is about this "initial frame". In our testcase we don't have
this case since the backtrace starts in a function that has some CFI.
But I assume you have some tests that rely on this behavior.
The first question is how/why the (pc & 0x1) == 0 check works?
Why is that the correct check?
Secondly, if it really is the initial (or signal frame) we are after,
should we pass in into bool *signal_framep argument. Currently we don't
Lastly could you instead of returning the frame itself with just the pc
adjusted do that directly?
if ((pc & 0x1) == 0)
lr = lr & (~0x1);
And then use the code in the else clause always?
All the above might simply be me not understanding the significance of
the initial frame.
Cheers,
Mark
