Re: [RFA] PR python/20190 - compute TLS symbol without a frame

[Yao Qi <qiyaoltc at gmail dot com>]

Hi Tom,

On Fri, Jun 3, 2016 at 10:16 PM, Tom Tromey <tom@tromey.com> wrote:
> PR python/20190 arose from an exception I noticed when trying to use
> the Python unwinder for Spider Monkey in Firefox.
>
> The problem is that the unwinder wants to examine the value of a
> thread-local variable.  However, sympy_value rejects this because
> symbol_read_needs_frame returns true for a TLS variable.
>
> This problem arose once before, though in a different context:
>
> https://sourceware.org/bugzilla/show_bug.cgi?id=11803
>
> At the time Pedro and Daniel pointed out a simpler way to fix that bug
> (see links in 20190 if you are interested); but for this new bug I
> couldn't think of a similar fix and ended up implementing Daniel's
> other suggestion:
>
> https://sourceware.org/ml/gdb-patches/2010-07/msg00393.html
>
> That is, this patch makes it possible to detect whether a symbol needs
> a specific frame, or whether it just needs the inferior to have
> registers.
>

I don't understand why your original attempt fixing PR11803
(https://sourceware.org/ml/gdb-patches/2010-07/msg00374.html) doesn't work
here.  IMO, it doesn't require frame when resolving tls.  In the process of
getting address of tls variable, the offset is available in the debug info, gdb
gets the module address first, then delegate target (linux-thread-db or remote)
to get the address.  Frame is not involved in this process.