Hi!
On Wed, Nov 10, 2021 at 06:59:23PM -0300, Raphael Moreira Zinsly wrote:
> At the end of the backtrace stream _Unwind_Find_FDE() may not be able
> to find the frame unwind info and will later call the backtrace fallback
> instead of finishing. This occurs when using an old libc on ppc64 due to
> dl_iterate_phdr() not being able to set the fde in the last trace.
> When this occurs the cfa of the trace will be behind of context's cfa.
> Also, libgo’s probestackmaps() calls the backtrace with a null pointer
> and can get to the backchain fallback with the same problem, in this case
> we are only interested in find a stack map, we don't need nor can do a
> backchain.
> _Unwind_ForcedUnwind_Phase2() can hit the same issue as it uses
> uw_frame_state_for(), so we need to treat _URC_NORMAL_STOP.
>
> libgcc/ChangeLog:
>
> * config/rs6000/linux-unwind.h (ppc_backchain_fallback): turn into
> static to fix -Wmissing-prototypes. Check if it's called with a null
> argument or at the end of the backtrace and return.
> * unwind.inc (_Unwind_ForcedUnwind_Phase2): treat _URC_NORMAL_STOP.
Formatting is messed up. Lines start with a capital. Two spaces after
full stop, while you're at it.
> -void ppc_backchain_fallback (struct _Unwind_Context *context, void *a)
> +static void
> +ppc_backchain_fallback (struct _Unwind_Context *context, void *a)
This was already fixed in 75ef0353a2d3.
> {
> struct frame_layout *current;
> struct trace_arg *arg = a;
> int count;
>
> - /* Get the last address computed and start with the next. */
> + /* Get the last address computed. */
> current = context->cfa;
Empty line after here please. Most of the time if you have a full-line
comment it means a new paragraph is starting.
> + /* If the trace CFA is not the context CFA the backtrace is done. */
> + if (arg == NULL || arg->cfa != current)
> + return;
> +
> + /* Start with next address. */
> current = current->backchain;
Like you did here :-)
Do you have a testcase (that failed without this, but now doesn't)?
Looks okay, but please update and resend.
Segher
