| Message ID | 20201028030701.14086-8-j@getutm.app (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | iOS and Apple Silicon host support | expand |
On Tue, Oct 27, 2020 at 08:07:01PM -0700, Joelle van Dyne wrote: > macOS 11/iOS 14 added preadv/pwritev APIs. Due to weak linking, configure > will succeed with CONFIG_PREADV even when targeting a lower OS version. We > therefore need to check at run time if we can actually use these APIs. > > Signed-off-by: Joelle van Dyne <j@getutm.app> > --- > block/file-posix.c | 12 ++++++++++++ > 1 file changed, 12 insertions(+) What happens when preadv() is called prior to macOS 11/iOS 14? If I understand correctly the runtime check is preferrable because otherwise a binary compiled on recent macOS/iOS would ship with preadv() support but fail when executed on an older macOS/iOS?
If built with Xcode 11 (or below), a compile time error will occur due to symbol not found. (QEMU's ./configure detects this and doesn't enable it) If built with Xcode 12 without the checks, a runtime error will occur. -j On Wed, Oct 28, 2020 at 5:23 AM Stefan Hajnoczi <stefanha@redhat.com> wrote: > > On Tue, Oct 27, 2020 at 08:07:01PM -0700, Joelle van Dyne wrote: > > macOS 11/iOS 14 added preadv/pwritev APIs. Due to weak linking, configure > > will succeed with CONFIG_PREADV even when targeting a lower OS version. We > > therefore need to check at run time if we can actually use these APIs. > > > > Signed-off-by: Joelle van Dyne <j@getutm.app> > > --- > > block/file-posix.c | 12 ++++++++++++ > > 1 file changed, 12 insertions(+) > > What happens when preadv() is called prior to macOS 11/iOS 14? > > If I understand correctly the runtime check is preferrable because > otherwise a binary compiled on recent macOS/iOS would ship with preadv() > support but fail when executed on an older macOS/iOS?
On Wed, Oct 28, 2020 at 06:07:16PM -0700, Joelle van Dyne wrote:
> If built with Xcode 12 without the checks, a runtime error will occur.
If that runtime error is ENOSYS then it's handled by existing code:
if (preadv_present) {
nbytes = handle_aiocb_rw_vector(aiocb);
if (nbytes == aiocb->aio_nbytes ||
(nbytes < 0 && nbytes != -ENOSYS)) {
goto out;
}
preadv_present = false;
}
Why is additional code needed for iOS?
Stefan
No it doesn't return ENOSYS. Dyld calls abort() when a weak link is not resolved at the time of call. -j On Thu, Oct 29, 2020 at 12:54 AM Stefan Hajnoczi <stefanha@gmail.com> wrote: > > On Wed, Oct 28, 2020 at 06:07:16PM -0700, Joelle van Dyne wrote: > > If built with Xcode 12 without the checks, a runtime error will occur. > > If that runtime error is ENOSYS then it's handled by existing code: > > if (preadv_present) { > nbytes = handle_aiocb_rw_vector(aiocb); > if (nbytes == aiocb->aio_nbytes || > (nbytes < 0 && nbytes != -ENOSYS)) { > goto out; > } > preadv_present = false; > } > > Why is additional code needed for iOS? > > Stefan
diff --git a/block/file-posix.c b/block/file-posix.c index 5560fd20ac..b5a7ce483d 100644 --- a/block/file-posix.c +++ b/block/file-posix.c @@ -1394,12 +1394,24 @@ static bool preadv_present = true; static ssize_t qemu_preadv(int fd, const struct iovec *iov, int nr_iov, off_t offset) { +#ifdef CONFIG_DARWIN /* preadv introduced in macOS 11 */ + if (!__builtin_available(macOS 11, iOS 14, watchOS 7, tvOS 14, *)) { + preadv_present = false; + return -ENOSYS; + } else +#endif return preadv(fd, iov, nr_iov, offset); } static ssize_t qemu_pwritev(int fd, const struct iovec *iov, int nr_iov, off_t offset) { +#ifdef CONFIG_DARWIN /* pwritev introduced in macOS 11 */ + if (!__builtin_available(macOS 11, iOS 14, watchOS 7, tvOS 14, *)) { + preadv_present = false; + return -ENOSYS; + } else +#endif return pwritev(fd, iov, nr_iov, offset); }
macOS 11/iOS 14 added preadv/pwritev APIs. Due to weak linking, configure will succeed with CONFIG_PREADV even when targeting a lower OS version. We therefore need to check at run time if we can actually use these APIs. Signed-off-by: Joelle van Dyne <j@getutm.app> --- block/file-posix.c | 12 ++++++++++++ 1 file changed, 12 insertions(+)