From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 91482271838; Wed, 12 Feb 2025 17:01:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739379697; cv=none; b=Rz4sW1aHD/8J2xs948/1qUi3i+7QmHBf2HPDp3vXvABCZR00dDSOywoQWWPi4GtlBZSr+T623R4kT+W9hxie1N6FDO+roq96itWAeoUSwE/3DJBAXL2LsKmW3R/E+cWT8RLeFKo6Ue6BlD54vVWjNgpLChVbV929gYZd4pO/V+c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739379697; c=relaxed/simple; bh=jRMoKpDWtWnYgacxLrf0ZiTJcjhUjLEbiD4mNMIMBNs=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=XBlXNX0kcf1R9KMfuxqTwdaayhWr9HAVwLCczER5sUKqYwWdyiQvJgFMrjOCKzzQ5SKNs7jVmpMBl4Bs+AY42L51CiuHlUezUehQ6i4gzKOloJ90UxS+f26HKJerduAvEyhmGDIORpi/fLPc2jL2VuZsKOM3jBm2gfXB/z5+pI4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=M9m6FvDL; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="M9m6FvDL" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D04A4C4CEDF; Wed, 12 Feb 2025 17:01:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1739379697; bh=jRMoKpDWtWnYgacxLrf0ZiTJcjhUjLEbiD4mNMIMBNs=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=M9m6FvDLhCR/khET7YRAqdzGD6HkViGAQzefjUtC5JopCmnY1FjCXfbO6GgBQzlXA eKwSrVzaRVTc83WTn19YyfG/xrsALN5Su6ikDMl8eeKZ7olTuHObHybxreTVsHZb/5 CWUdgaisehmGjtZ/wiZumhaEtAK9GuCRWeV6dpGZF10wU8FhAko3n7AmAA8qfShnhi J23U+2UP5uo7WxUd7DBz2c3HS+XcWzoXR2kMXJP7MDLzuJPlVwa8W3VCo2v6PuRa10 nUX/Ng0V7/QGVEo8qkNY8GBzhABaGyYAONjWgYDrWQUOoVkUEc37Mk3tqy2RVpo8SJ s4lmnzPxdeLkA== Date: Wed, 12 Feb 2025 18:01:30 +0100 From: Danilo Krummrich To: Gary Guo Cc: Tamir Duberstein , Miguel Ojeda , DJ Delorie , Eric Blake , Paul Eggert , Alex Gaynor , Boqun Feng , =?iso-8859-1?Q?Bj=F6rn?= Roy Baron , Benno Lossin , Andreas Hindborg , Alice Ryhl , Trevor Gross , rust-for-linux@vger.kernel.org, linux-man@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5] rust: alloc: satisfy POSIX alignment requirement Message-ID: References: <20250212-aligned-alloc-v5-1-c51e0b17dee9@gmail.com> <20250212163848.22e8dcff@eugeo> Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250212163848.22e8dcff@eugeo> On Wed, Feb 12, 2025 at 04:38:48PM +0000, Gary Guo wrote: > On Wed, 12 Feb 2025 16:40:37 +0100 > Danilo Krummrich wrote: > > > On Wed, Feb 12, 2025 at 09:43:02AM -0500, Tamir Duberstein wrote: > > > diff --git a/rust/kernel/alloc/allocator_test.rs b/rust/kernel/alloc/allocator_test.rs > > > index e3240d16040b..17a475380253 100644 > > > --- a/rust/kernel/alloc/allocator_test.rs > > > +++ b/rust/kernel/alloc/allocator_test.rs > > > @@ -62,6 +62,26 @@ unsafe fn realloc( > > > )); > > > } > > > > > > + // ISO C (ISO/IEC 9899:2011) defines `aligned_alloc`: > > > + // > > > + // > The value of alignment shall be a valid alignment supported by the implementation > > > + // [...]. > > > + // > > > + // As an example of the "supported by the implementation" requirement, POSIX.1-2001 (IEEE > > > + // 1003.1-2001) defines `posix_memalign`: > > > + // > > > + // > The value of alignment shall be a power of two multiple of sizeof (void *). > > > + // > > > + // and POSIX-based implementations of `aligned_alloc` inherit this requirement. At the time > > > + // of writing, this is known to be the case on macOS (but not in glibc). > > > + // > > > + // Satisfy the stricter requirement to avoid spurious test failures on some platforms. > > > + let min_align = core::mem::size_of::<*const crate::ffi::c_void>(); > > > + let layout = layout.align_to(min_align).unwrap_or_else(|_err| { > > > + crate::build_error!("invalid alignment") > > > > That's not what I thought this patch will look like. I thought you'll directly > > follow Gary's proposal, which is why I said you can keep the ACK. > > > > build_error!() doesn't work here, there is no guarantee that this can be > > evaluated at compile time. > > `align_to` will only fail if `min_align` is not a valid alignment (i.e. > not power of two), which the compiler should be easy to notice that the > size of pointer is indeed power of 2. >From the documentation of align_to(): "Returns an error if the combination of self.size() and the given align violates the conditions listed in Layout::from_size_align." Formally self.size() may still be unknown at compile time. Do I miss anything? > > I think both `build_error!` and `map_err` version below is fine to me. > > Best, > Gary > > > > > I think this should just be: > > > > let layout = layout.align_to(min_align).map_err(|_| AllocError)?.pad_to_align(); > > > > - Danilo > > > > > + }); > > > + let layout = layout.pad_to_align(); > > > + > > > // SAFETY: Returns either NULL or a pointer to a memory allocation that satisfies or > > > // exceeds the given size and alignment requirements. > > > let dst = unsafe { libc_aligned_alloc(layout.align(), layout.size()) } as *mut u8; >