From patchwork Fri Jan 25 15:43:37 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Markus Armbruster X-Patchwork-Id: 215801 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id 462EC2C008C for ; Sat, 26 Jan 2013 03:23:45 +1100 (EST) Received: from localhost ([::1]:42914 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TylS3-0007y6-RW for incoming@patchwork.ozlabs.org; Fri, 25 Jan 2013 10:44:23 -0500 Received: from eggs.gnu.org ([208.118.235.92]:53709) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TylRX-0006T8-Ad for qemu-devel@nongnu.org; Fri, 25 Jan 2013 10:43:52 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1TylRP-0007wQ-NH for qemu-devel@nongnu.org; Fri, 25 Jan 2013 10:43:51 -0500 Received: from oxygen.pond.sub.org ([2a01:4f8:121:10e4::3]:51460) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TylRP-0007vc-Ds for qemu-devel@nongnu.org; Fri, 25 Jan 2013 10:43:43 -0500 Received: from blackfin.pond.sub.org (p5B32AD3C.dip.t-dialin.net [91.50.173.60]) by oxygen.pond.sub.org (Postfix) with ESMTPA id 4F5059FF74; Fri, 25 Jan 2013 16:43:41 +0100 (CET) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 6F09E200A9; Fri, 25 Jan 2013 16:43:40 +0100 (CET) From: Markus Armbruster To: qemu-devel@nongnu.org Date: Fri, 25 Jan 2013 16:43:37 +0100 Message-Id: <1359128620-14226-2-git-send-email-armbru@redhat.com> X-Mailer: git-send-email 1.7.11.7 In-Reply-To: <1359128620-14226-1-git-send-email-armbru@redhat.com> References: <1359128620-14226-1-git-send-email-armbru@redhat.com> X-detected-operating-system: by eggs.gnu.org: Error: Malformed IPv6 address (bad octet value). X-Received-From: 2a01:4f8:121:10e4::3 Cc: harsh@linux.vnet.ibm.com, stefanha@redhat.com Subject: [Qemu-devel] [PATCH 1/4] trace: Fix simple trace dropped event record for big endian X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org We use atomic operations to keep track of dropped events. Inconveniently, GLib supports only int and void * atomics, but the counter dropped_events is uint64_t. Can't stop commit 62bab732: a quick (gint *)&dropped_events bludgeons the compiler into submission. That cast is okay only when int is exactly 64 bits wide, which it commonly isn't. If int is even wider, we clobber whatever follows dropped_events. Not worth worrying about, as none of the machines that interest us have such morbidly obese ints. That leaves the common case: int narrower than 64 bits. Harmless on little endian hosts: we just don't access the most significant bits of dropped_events. They remain zero. On big endian hosts, we use only the most significant bits of dropped_events as counter. The least significant bits remain zero. However, we write out the full value, which is the correct counter shifted left a bunch of places. Fix by changing the variables involved to int. There's another, equally suspicious-looking (gint *)&trace_idx argument to g_atomic_int_compare_and_exchange(), but that one casts unsigned *, so it's okay. But it's also superfluous, because GLib's atomic int operations work just fine for unsigned. Drop it. Signed-off-by: Markus Armbruster Reviewed-by: Laszlo Ersek --- trace/simple.c | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-) diff --git a/trace/simple.c b/trace/simple.c index ce17d64..ccbdb6a 100644 --- a/trace/simple.c +++ b/trace/simple.c @@ -53,7 +53,7 @@ enum { uint8_t trace_buf[TRACE_BUF_LEN]; static unsigned int trace_idx; static unsigned int writeout_idx; -static uint64_t dropped_events; +static int dropped_events; static FILE *trace_fp; static char *trace_file_name; @@ -63,7 +63,7 @@ typedef struct { uint64_t timestamp_ns; uint32_t length; /* in bytes */ uint32_t reserved; /* unused */ - uint8_t arguments[]; + uint64_t arguments[]; } TraceRecord; typedef struct { @@ -160,7 +160,7 @@ static gpointer writeout_thread(gpointer opaque) uint8_t bytes[sizeof(TraceRecord) + sizeof(uint64_t)]; } dropped; unsigned int idx = 0; - uint64_t dropped_count; + int dropped_count; size_t unused __attribute__ ((unused)); for (;;) { @@ -169,16 +169,16 @@ static gpointer writeout_thread(gpointer opaque) if (dropped_events) { dropped.rec.event = DROPPED_EVENT_ID, dropped.rec.timestamp_ns = get_clock(); - dropped.rec.length = sizeof(TraceRecord) + sizeof(dropped_events), + dropped.rec.length = sizeof(TraceRecord) + sizeof(uint64_t), dropped.rec.reserved = 0; while (1) { dropped_count = dropped_events; - if (g_atomic_int_compare_and_exchange((gint *)&dropped_events, + if (g_atomic_int_compare_and_exchange(&dropped_events, dropped_count, 0)) { break; } } - memcpy(dropped.rec.arguments, &dropped_count, sizeof(uint64_t)); + dropped.rec.arguments[0] = dropped_count; unused = fwrite(&dropped.rec, dropped.rec.length, 1, trace_fp); } @@ -220,11 +220,11 @@ int trace_record_start(TraceBufferRecord *rec, TraceEventID event, size_t datasi if (new_idx - writeout_idx > TRACE_BUF_LEN) { /* Trace Buffer Full, Event dropped ! */ - g_atomic_int_inc((gint *)&dropped_events); + g_atomic_int_inc(&dropped_events); return -ENOSPC; } - if (g_atomic_int_compare_and_exchange((gint *)&trace_idx, + if (g_atomic_int_compare_and_exchange(&trace_idx, old_idx, new_idx)) { break; }