From patchwork Mon Aug 29 03:05:09 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Tiezhu Yang X-Patchwork-Id: 12957407 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8E3AEECAAA2 for ; Mon, 29 Aug 2022 03:05:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229673AbiH2DFc (ORCPT ); Sun, 28 Aug 2022 23:05:32 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38136 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229675AbiH2DF2 (ORCPT ); Sun, 28 Aug 2022 23:05:28 -0400 Received: from loongson.cn (mail.loongson.cn [114.242.206.163]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 9957913EB2; Sun, 28 Aug 2022 20:05:26 -0700 (PDT) Received: from linux.localdomain (unknown [113.200.148.30]) by localhost.localdomain (Coremail) with SMTP id AQAAf8Bx5OHlLAxjCJ4LAA--.51514S2; Mon, 29 Aug 2022 11:05:10 +0800 (CST) From: Tiezhu Yang To: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Johan Almbladh , Paul Burton , Thomas Bogendoerfer Cc: bpf@vger.kernel.org, linux-mips@vger.kernel.org Subject: [PATCH bpf-next v2] bpf, mips: No need to use min() to get MAX_TAIL_CALL_CNT Date: Mon, 29 Aug 2022 11:05:09 +0800 Message-Id: <1661742309-2320-1-git-send-email-yangtiezhu@loongson.cn> X-Mailer: git-send-email 2.1.0 X-CM-TRANSID: AQAAf8Bx5OHlLAxjCJ4LAA--.51514S2 X-Coremail-Antispam: 1UD129KBjvJXoWxWw4UZr1xGF47CFy7CryrCrg_yoW5Gw18pr 4rJwnxKr4qgr4fX3Z3Aa18Xw1rWFsY9rW7AFWjgFyIyan8WFn7WF13Kr15uFyYvrW8J3Wf XrWqkwn8u34kAw7anT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUk2b7Iv0xC_Kw4lb4IE77IF4wAFF20E14v26r4j6ryUM7CY07I2 0VC2zVCF04k26cxKx2IYs7xG6rWj6s0DM7CIcVAFz4kK6r1j6r18M28lY4IEw2IIxxk0rw A2F7IY1VAKz4vEj48ve4kI8wA2z4x0Y4vE2Ix0cI8IcVAFwI0_Xr0_Ar1l84ACjcxK6xII jxv20xvEc7CjxVAFwI0_Cr0_Gr1UM28EF7xvwVC2z280aVAFwI0_Gr1j6F4UJwA2z4x0Y4 vEx4A2jsIEc7CjxVAFwI0_Cr1j6rxdM2AIxVAIcxkEcVAq07x20xvEncxIr21l5I8CrVAC Y4xI64kE6c02F40Ex7xfMcIj6xIIjxv20xvE14v26r106r15McIj6I8E87Iv67AKxVWUJV W8JwAm72CE4IkC6x0Yz7v_Jr0_Gr1lF7xvr2IYc2Ij64vIr41lc2xSY4AK67AK6r48MxAI w28IcxkI7VAKI48JMxC20s026xCaFVCjc4AY6r1j6r4UMI8I3I0E5I8CrVAFwI0_Jr0_Jr 4lx2IqxVCjr7xvwVAFwI0_JrI_JrWlx4CE17CEb7AF67AKxVWUtVW8ZwCIc40Y0x0EwIxG rwCI42IY6xIIjxv20xvE14v26r1j6r1xMIIF0xvE2Ix0cI8IcVCY1x0267AKxVWUJVW8Jw CI42IY6xAIw20EY4v20xvaj40_Jr0_JF4lIxAIcVC2z280aVAFwI0_Jr0_Gr1lIxAIcVC2 z280aVCY1x0267AKxVWUJVW8JbIYCTnIWIevJa73UjIFyTuYvjxUghIDDUUUU X-CM-SenderInfo: p1dqw3xlh2x3gn0dqz5rrqw2lrqou0/ Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org MAX_TAIL_CALL_CNT is 33, so min(MAX_TAIL_CALL_CNT, 0xffff) is always MAX_TAIL_CALL_CNT, it is better to use MAX_TAIL_CALL_CNT directly. At the same time, add BUILD_BUG_ON(MAX_TAIL_CALL_CNT > 0xffff) with a comment on why the assertion is there. Suggested-by: Daniel Borkmann Suggested-by: Johan Almbladh Signed-off-by: Tiezhu Yang --- v2: Add BUILD_BUG_ON(MAX_TAIL_CALL_CNT > 0xffff) with a comment suggested by Daniel and Johan, thank you. arch/mips/net/bpf_jit_comp32.c | 10 +++++++++- arch/mips/net/bpf_jit_comp64.c | 10 +++++++++- 2 files changed, 18 insertions(+), 2 deletions(-) diff --git a/arch/mips/net/bpf_jit_comp32.c b/arch/mips/net/bpf_jit_comp32.c index 83c975d..ace5db3 100644 --- a/arch/mips/net/bpf_jit_comp32.c +++ b/arch/mips/net/bpf_jit_comp32.c @@ -1377,11 +1377,19 @@ void build_prologue(struct jit_context *ctx) int stack, saved, locals, reserved; /* + * In the unlikely event that the TCC limit is raised to more + * than 16 bits, it is clamped to the maximum value allowed for + * the generated code (0xffff). It is better fail to compile + * instead of degrading gracefully. + */ + BUILD_BUG_ON(MAX_TAIL_CALL_CNT > 0xffff); + + /* * The first two instructions initialize TCC in the reserved (for us) * 16-byte area in the parent's stack frame. On a tail call, the * calling function jumps into the prologue after these instructions. */ - emit(ctx, ori, MIPS_R_T9, MIPS_R_ZERO, min(MAX_TAIL_CALL_CNT, 0xffff)); + emit(ctx, ori, MIPS_R_T9, MIPS_R_ZERO, MAX_TAIL_CALL_CNT); emit(ctx, sw, MIPS_R_T9, 0, MIPS_R_SP); /* diff --git a/arch/mips/net/bpf_jit_comp64.c b/arch/mips/net/bpf_jit_comp64.c index 6475828..0e7c1bd 100644 --- a/arch/mips/net/bpf_jit_comp64.c +++ b/arch/mips/net/bpf_jit_comp64.c @@ -548,11 +548,19 @@ void build_prologue(struct jit_context *ctx) int stack, saved, locals, reserved; /* + * In the unlikely event that the TCC limit is raised to more + * than 16 bits, it is clamped to the maximum value allowed for + * the generated code (0xffff). It is better fail to compile + * instead of degrading gracefully. + */ + BUILD_BUG_ON(MAX_TAIL_CALL_CNT > 0xffff); + + /* * The first instruction initializes the tail call count register. * On a tail call, the calling function jumps into the prologue * after this instruction. */ - emit(ctx, ori, tc, MIPS_R_ZERO, min(MAX_TAIL_CALL_CNT, 0xffff)); + emit(ctx, ori, tc, MIPS_R_ZERO, MAX_TAIL_CALL_CNT); /* === Entry-point for tail calls === */