From patchwork Tue Nov 1 12:07:49 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Richard Henderson X-Patchwork-Id: 689848 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from lists.gnu.org (lists.gnu.org [IPv6:2001:4830:134:3::11]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 3t7Vlr26cbz9sR9 for ; Tue, 1 Nov 2016 23:24:24 +1100 (AEDT) Authentication-Results: ozlabs.org; dkim=fail reason="signature verification failed" (2048-bit key; unprotected) header.d=gmail.com header.i=@gmail.com header.b=sNI+TU9x; dkim-atps=neutral Received: from localhost ([::1]:47505 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1c1Y73-0003SU-3m for incoming@patchwork.ozlabs.org; Tue, 01 Nov 2016 08:24:21 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:52616) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1c1XrM-0007qG-D2 for qemu-devel@nongnu.org; Tue, 01 Nov 2016 08:08:09 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1c1XrG-0007jS-Sv for qemu-devel@nongnu.org; Tue, 01 Nov 2016 08:08:08 -0400 Received: from mail-oi0-x242.google.com ([2607:f8b0:4003:c06::242]:34539) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1c1XrG-0007j8-Nn for qemu-devel@nongnu.org; Tue, 01 Nov 2016 08:08:02 -0400 Received: by mail-oi0-x242.google.com with SMTP id 62so13568344oif.1 for ; Tue, 01 Nov 2016 05:08:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=sender:from:to:cc:subject:date:message-id:in-reply-to:references; bh=yAdmCOEU9qWaA/d9AdgN99aLC1zzIbn0UQpmkK4cEEc=; b=sNI+TU9xFu6pYx1km6vJCnzq5c/ukTrz0mC+NoZ0uVm4rQG5QI75dyS6xLdlzLTyO4 7wXEp36tMabNQlHh2Bpq9PzbMcdBeSc7hvdKvl7FQeTK7LGBeBX1fNCB3iEinK9sdo95 npc5EDSi73qJN6KxkjLWhfrF41JEEqS9ioHlOl9+O6qzgHyA/Dvzevtw81woIQgVw/HI c+GHR3h42jsmOO3tNlK8keJK4uoV5Kizpfu4EBf+tLriczzvXjwCjg2ePFb7Qs2QAr1g 5u19uNr0GFn4TeOs6bgcI6KSst6sQiHzGOyQS7brrxz9cSlM0FuJxV/yMS36+2lpMKUi ZKYw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:sender:from:to:cc:subject:date:message-id :in-reply-to:references; bh=yAdmCOEU9qWaA/d9AdgN99aLC1zzIbn0UQpmkK4cEEc=; b=AHMVO/V2mY/QYoQHS+NoiJGdboKoW1BfAsH6aGN/cVYlFz0UKcwWlsVAYGkerhrMYx v9QvGQlz9d07arCBq0I1BIoKR1SmsioM5K+Z+lhd2eYFk6QNaiBzWqYv/EXS3E9PD6+Z NsGWHOA/NixRg+RGg4medYnw5fheyc73ndvv2hj9rQ/Fk7Kos1dwgFy1o/DMOJTPYxZA OETUD7XlutxVHEV41tvtZqgeSY8ytk1i+EZh225ZKh1N35GN+b2Dr36k4WY/PQ/l7hVm owcJQc6vROOlWCVj7HWgOaQSForxSF0lF4PJ+A4ifcbnKL59I95Um5e1/ZgRnH1a/bd9 thaA== X-Gm-Message-State: ABUngvelpJZs1pARKhIUi1xIaCAllbDtToH+El5z/qSt7X09Sql9tZV8U+dlgADcOxNjKQ== X-Received: by 10.202.61.2 with SMTP id k2mr20479487oia.44.1478002082193; Tue, 01 Nov 2016 05:08:02 -0700 (PDT) Received: from bigtime.twiddle.net.net ([64.134.26.173]) by smtp.gmail.com with ESMTPSA id d9sm9956164otb.0.2016.11.01.05.08.01 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 01 Nov 2016 05:08:01 -0700 (PDT) From: Richard Henderson To: qemu-devel@nongnu.org Date: Tue, 1 Nov 2016 06:07:49 -0600 Message-Id: <1478002070-26676-9-git-send-email-rth@twiddle.net> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1478002070-26676-1-git-send-email-rth@twiddle.net> References: <1478002070-26676-1-git-send-email-rth@twiddle.net> X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 2607:f8b0:4003:c06::242 Subject: [Qemu-devel] [PULL v2 for-2.8 8/9] tcg/tcg.h: Improve documentation of TCGv_i32 etc types X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: peter.maydell@linaro.org Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: "Qemu-devel" From: Peter Maydell The typedefs we use for the TCGv_i32, TCGv_i64 and TCGv_ptr types are somewhat confusing, because we define them as pointers to structs, but the structs themselves are never defined. Explain in the comments a bit more clearly why this is OK and what is going on under the hood. Signed-off-by: Peter Maydell Message-Id: <1477067922-26202-1-git-send-email-peter.maydell@linaro.org> Signed-off-by: Richard Henderson --- tcg/tcg.h | 38 ++++++++++++++++++++++++++++++-------- 1 file changed, 30 insertions(+), 8 deletions(-) diff --git a/tcg/tcg.h b/tcg/tcg.h index dc1281f..a35e4c4 100644 --- a/tcg/tcg.h +++ b/tcg/tcg.h @@ -376,14 +376,36 @@ static inline unsigned get_alignment_bits(TCGMemOp memop) typedef tcg_target_ulong TCGArg; -/* Define a type and accessor macros for variables. Using pointer types - is nice because it gives some level of type safely. Converting to and - from intptr_t rather than int reduces the number of sign-extension - instructions that get implied on 64-bit hosts. Users of tcg_gen_* don't - need to know about any of this, and should treat TCGv as an opaque type. - In addition we do typechecking for different types of variables. TCGv_i32 - and TCGv_i64 are 32/64-bit variables respectively. TCGv and TCGv_ptr - are aliases for target_ulong and host pointer sized values respectively. */ +/* Define type and accessor macros for TCG variables. + + TCG variables are the inputs and outputs of TCG ops, as described + in tcg/README. Target CPU front-end code uses these types to deal + with TCG variables as it emits TCG code via the tcg_gen_* functions. + They come in several flavours: + * TCGv_i32 : 32 bit integer type + * TCGv_i64 : 64 bit integer type + * TCGv_ptr : a host pointer type + * TCGv : an integer type the same size as target_ulong + (an alias for either TCGv_i32 or TCGv_i64) + The compiler's type checking will complain if you mix them + up and pass the wrong sized TCGv to a function. + + Users of tcg_gen_* don't need to know about any of the internal + details of these, and should treat them as opaque types. + You won't be able to look inside them in a debugger either. + + Internal implementation details follow: + + Note that there is no definition of the structs TCGv_i32_d etc anywhere. + This is deliberate, because the values we store in variables of type + TCGv_i32 are not really pointers-to-structures. They're just small + integers, but keeping them in pointer types like this means that the + compiler will complain if you accidentally pass a TCGv_i32 to a + function which takes a TCGv_i64, and so on. Only the internals of + TCG need to care about the actual contents of the types, and they always + box and unbox via the MAKE_TCGV_* and GET_TCGV_* functions. + Converting to and from intptr_t rather than int reduces the number + of sign-extension instructions that get implied on 64-bit hosts. */ typedef struct TCGv_i32_d *TCGv_i32; typedef struct TCGv_i64_d *TCGv_i64;