From: Sean Christopherson <seanjc@google.com>
To: Jacob Xu <jacobhxu@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Jim Mattson <jmattson@google.com>, kvm list <kvm@vger.kernel.org>
Subject: Re: [kvm-unit-tests PATCH v2] x86: Do not assign values to unaligned pointer to 128 bits
Date: Thu, 6 May 2021 19:25:26 +0000 [thread overview]
Message-ID: <YJRCpv9O/Q24DKmZ@google.com> (raw)
In-Reply-To: <CAJ5mJ6gYmwXEQZASk8A_Ozt6asW6ZDTnDs83nCfLNTa62x7n+g@mail.gmail.com>
On Thu, May 06, 2021, Jacob Xu wrote:
> > memset() takes a void *, which it casts to an char, i.e. it works on one byte at
> a time.
> Huh, TIL. Based on this I'd thought that I don't need a cast at all,
> but doing so actually results in a movaps instruction.
Ewwww. That's likely because emulator.c does:
#define memset __builtin_memset
and the compiler is clever enough to know that __attribute__((vector_size(16)))
means the variable is (supposed to be) aligned.
> I've changed the cast back to (uint8_t *).
I assume removing the above #define and grabbing memset() from string.c fixes
the movaps generation? If so, that has my vote, as opposed to fudging around
the compiler by casting to uint8_t *.
As evidenced by this issue, using the compiler's memset() in kvm-unit-tests seems
inherently dangerous since the tests are often doing intentionally stupid things.
next prev parent reply other threads:[~2021-05-06 19:25 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-06 18:49 [kvm-unit-tests PATCH v2] x86: Do not assign values to unaligned pointer to 128 bits Jacob Xu
2021-05-06 18:57 ` Sean Christopherson
2021-05-06 19:13 ` Jacob Xu
2021-05-06 19:25 ` Sean Christopherson [this message]
2021-05-06 20:11 ` Jim Mattson
2021-05-11 1:47 ` Jacob Xu
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=YJRCpv9O/Q24DKmZ@google.com \
--to=seanjc@google.com \
--cc=jacobhxu@google.com \
--cc=jmattson@google.com \
--cc=kvm@vger.kernel.org \
--cc=pbonzini@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.