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 CDA9E201017; Wed, 12 Feb 2025 20:01:32 +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=1739390492; cv=none; b=aZ3F+CU/vH28peLkzniN0ogBoge6DMSNG/jhTQdOeXpTjOmSUeU0DSGrPdfhlV4LG88JV0UEYUXsfZE72HNuoZR21Ae77f3cl11lVzd8GyrK88RXq8GPKaNsnQhWM1N/cI/KEPREw32Gq2gyKEo4P3qUuY2oYCIWBpdPDf2HiUk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739390492; c=relaxed/simple; bh=ih7UwWQTGH9m1+e48DnI4Kmn77m9E1quXg8pFdtmvwE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Na/O+DlcVoNz6zuJywiDuyBGPmXWFajH3gCXWrEYZfDsl32x2v3R378GBqnPPbX9aG5YiTQSl7QwxnHr4fOfzyNunS52X4qtGSj6AX4nCgcaXN2O+MDtw5wRPzXNkNEMqgrSv+k1aozEk3V0ungOyZdivu4btmyFz4rZEehMBCk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=u/SYAqBl; 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="u/SYAqBl" Received: by smtp.kernel.org (Postfix) with ESMTPSA id ECF7BC4CEDF; Wed, 12 Feb 2025 20:01:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1739390492; bh=ih7UwWQTGH9m1+e48DnI4Kmn77m9E1quXg8pFdtmvwE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=u/SYAqBlCpPfF1iq+4ICv36S0WZyNqpyqeX0b1enYwZlNh5j2DPR8Opx8VV7fzkX4 3a0UmILl6EVPNFxAerkdjEk1xBH3Az1b8tEjoLNLcsUXFQ2q9mnnK9f5hSM4NoivI8 VK83HinlUaR1JvKM4QXOmocK/H9riF648gVnrJx90CVsSupWQrM20TXYfbfi4soNyC iofcBj2lqigFLl4YqTHcEt8kzHL2cyc9LgfOXFtCOjTqcW8U5+d/IQZygN0lFMy7dC Lh91Z9CHzPW0d5m6xoDI/2nuUa3GX0wvyGPDxhFlrXzjOznYXifgMaB2nMASjxEmFJ Li17Bkvb2AwfQ== Date: Wed, 12 Feb 2025 21:01:26 +0100 From: Danilo Krummrich To: Tamir Duberstein Cc: Gary Guo , 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=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Wed, Feb 12, 2025 at 01:44:45PM -0500, Tamir Duberstein wrote: > On Wed, Feb 12, 2025 at 12:01 PM Danilo Krummrich wrote: > > > > 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? > > Formally, I agree. I tried testing (in allocator_test.rs): > > #[cfg(test)] > mod tests { > use super::*; > > #[test] > fn test_allocate() { > #[inline(never)] > fn non_const_usize() -> usize { > let x = 0; > &x as *const _ as usize > } > > let layout = Layout::array::(non_const_usize()).unwrap(); > let ptr = Cmalloc::alloc(layout, GFP_KERNEL).unwrap(); > let ptr = ptr.cast(); > // SAFETY: > // - `ptr` was previously allocated with `Cmalloc`. > // - `layout` is equal to the `Layout´ `ptr` was allocated with. > unsafe { Cmalloc::free(ptr, layout) }; > } > } > > and it compiled (and passed). I suggest to try the following. Move non_const_usize() into allocator_test.rs and within realloc(), try [1]; then try [2]. Besides that, I still think build_error!() can't be used here correctly, since layout.size() might not be known at compile time. Please change things to what I did suggest previously. -- [1] ``` if non_const_usize() < 0x42 { crate::build_error!(); } ``` [2] ``` if non_const_usize() >= 0x42 { crate::build_error!(); } ```