From: Simon Marchi <simon.marchi@polymtl.ca>
To: Tom Tromey <tom@tromey.com>
Cc: gdb-patches@sourceware.org, Simon Marchi <simon.marchi@ericsson.com>
Subject: Re: [RFC PATCH] Read pseudo registers from frame instead of regcache
Date: Mon, 28 May 2018 16:10:00 -0000 [thread overview]
Message-ID: <255f6a7ccf53928bc0fb2ac5a94fa234@polymtl.ca> (raw)
In-Reply-To: <87r2lxzrvx.fsf@tromey.com>
On 2018-05-26 23:42, Tom Tromey wrote:
>>>>>> "Simon" == Simon Marchi <simon.marchi@polymtl.ca> writes:
>
> Simon> The problem: Reading pseudo registers from an upper stack frame
> does not
> Simon> work. The raw registers needed to compose the pseudo registers
> are
> Simon> always read from the current thread's regcache, which is
> effectively
> Simon> frame #0's registers.
> [...]
> Simon> The gdbarch hooks
>
> Simon> - pseudo_register_read
> Simon> - pseudo_register_read_value
> Simon> - pseudo_register_write
>
> Simon> receive a regcache as a parameter, as a way to get the values of
> the raw
> Simon> registers required to compute the pseudo register value.
> However, the
> Simon> regcache object always contains the current register values, not
> the
> Simon> values unwound to the frame we're interested in.
>
> I don't know this area very well, so apologies if this is really off
> target; but I am wondering why not just make a regcache for the desired
> frame and pass that to the gdbarch hooks?
That sounds like a good idea, at least to avoid changing the gdbarch
interface. The current regcache always fetches raw registers using
target_fetch_registers (which gets the current values of the thread's
registers), but we could have another kind of regcache that instead gets
raw register values by unwinding from the previous frame.
> Another thing I am curious about is how far back this bug goes. Like,
> if it were introduced in one of the last few releases, then it might be
> worth bisecting to find out what happened.
The oldest version of GDB with which I could print $ebx is 7.2 (did
pseudo registers not exist before?), and it exhibits the same problem.
So I would think that the problem exists since "forever".
Simon
next prev parent reply other threads:[~2018-05-28 13:18 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-26 1:14 Simon Marchi
2018-05-27 5:14 ` Tom Tromey
2018-05-28 16:10 ` Simon Marchi [this message]
2018-05-28 19:13 ` Ulrich Weigand
2018-05-28 22:06 ` Simon Marchi
2018-05-29 2:52 ` Simon Marchi
2018-05-29 14:53 ` Ulrich Weigand
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