From: John David Anglin <dave.anglin@bell.net>
To: Helge Deller <deller@gmx.de>,
linux-parisc@vger.kernel.org,
James Bottomley <James.Bottomley@hansenpartnership.com>
Subject: Re: [PATCH] parisc: Add static branch and JUMP_LABEL feature (v2)
Date: Fri, 3 May 2019 18:31:33 -0400 [thread overview]
Message-ID: <ce170758-ec9a-7f30-64ea-e153ed27242b@bell.net> (raw)
In-Reply-To: <20190503214006.GA25013@ls3530.dellerweb.de>
On 2019-05-03 5:40 p.m., Helge Deller wrote:
> + void *target = (void *)jump_entry_target(entry);
> + int distance = target - addr;
> + /*
> + * Encode the PA1.1 "b,n" instruction with a 17-bit
> + * displacement. In case we hit the BUG(), we could use
> + * another branch instruction with a 22-bit displacement on
> + * 64-bit CPUs instead. But this seems sufficient for now.
> + */
Just a note on the comment. The branch instruction with 22-bit displacement uses
the return pointer register %rp. It is available on 32 and 64-bit PA 2.0 machines but
one would have to clobber %rp, or save and restore it on stack. The former would cause
%rp to be saved and restored in the function's prologue and epilogue, respectively.
Dave
--
John David Anglin dave.anglin@bell.net
prev parent reply other threads:[~2019-05-03 22:31 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-01 20:02 [PATCH] parisc: Add static branch / JUMP_LABEL feature Helge Deller
2019-05-02 5:05 ` Sven Schnelle
2019-05-03 21:40 ` [PATCH] parisc: Add static branch and JUMP_LABEL feature (v2) Helge Deller
2019-05-03 22:31 ` John David Anglin [this message]
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