From 96c9925be98578480be79d2385ab4dc005f8218d Mon Sep 17 00:00:00 2001
Message-Id: <address@hidden>
From: Blue Swirl <address@hidden>
Date: Tue, 23 Aug 2011 21:08:53 +0000
Subject: [PATCH] Introduce tracing system from QEMU

Instead of traditional debugging printf statements, which
have the bad habit of suffering from bit rot, introduce
tracepoints based on similar system in QEMU.

Only stderr (printk) and simpletrace (output via fw_cfg
device to QEMU) back ends are supported.

Signed-off-by: Blue Swirl <address@hidden>
---
 config/examples/amd64_config.xml   |    3 +-
 config/examples/ppc64_config.xml   |    3 +-
 config/examples/ppc_config.xml     |    3 +-
 config/examples/sparc32_config.xml |    3 +-
 config/examples/sparc64_config.xml |    3 +-
 config/scripts/tracetool           |  692 ++++++++++++++++++++++++++++++++++++
 drivers/esp.c                      |    3 +-
 drivers/fw_cfg.c                   |   22 ++
 drivers/ide.c                      |    6 +-
 include/arch/common/fw_cfg.h       |    9 +-
 include/libopenbios/simpletrace.h  |   31 ++
 libopenbios/build.xml              |   33 ++
 libopenbios/simpletrace.c          |   76 ++++
 trace-events                       |    3 +
 14 files changed, 879 insertions(+), 11 deletions(-)
 create mode 100644 config/scripts/tracetool
 create mode 100644 include/libopenbios/simpletrace.h
 create mode 100644 libopenbios/simpletrace.c
 create mode 100644 trace-events

diff --git a/config/examples/amd64_config.xml b/config/examples/amd64_config.xml
index 33d4267..ba3838b 100644
--- a/config/examples/amd64_config.xml
+++ b/config/examples/amd64_config.xml
@@ -14,7 +14,8 @@
   <option name="CONFIG_SERIAL_PORT" type="boolean" value="true"/>
   <option name="CONFIG_SERIAL_SPEED" type="integer" value="115200"/>
   <option name="CONFIG_DEBUG_CONSOLE_VGA" type="boolean" value="true"/>
-
+  <option name="CONFIG_TRACE_SIMPLETRACE" type="boolean" value="false"/>
+  <option name="CONFIG_TRACE_STDERR" type="boolean" value="true"/>
 
   <!-- Module Configuration -->
   <option name="CONFIG_CMDLINE" type="boolean" value="true"/>
diff --git a/config/examples/ppc64_config.xml b/config/examples/ppc64_config.xml
index 5f79c21..bca5cc5 100644
--- a/config/examples/ppc64_config.xml
+++ b/config/examples/ppc64_config.xml
@@ -12,7 +12,8 @@
   <option name="CONFIG_SERIAL_SPEED" type="integer" value="115200"/>
   <option name="CONFIG_DEBUG_CONSOLE_VGA" type="boolean" value="true"/>
   <option name="CONFIG_DEBUG_OFMEM" type="boolean" value="false"/>
-
+  <option name="CONFIG_TRACE_SIMPLETRACE" type="boolean" value="false"/>
+  <option name="CONFIG_TRACE_STDERR" type="boolean" value="true"/>
 
   <!-- Module Configuration -->
   <option name="CONFIG_CMDLINE" type="boolean" value="true"/>
diff --git a/config/examples/ppc_config.xml b/config/examples/ppc_config.xml
index 352cb57..a338d56 100644
--- a/config/examples/ppc_config.xml
+++ b/config/examples/ppc_config.xml
@@ -12,7 +12,8 @@
   <option name="CONFIG_SERIAL_SPEED" type="integer" value="115200"/>
   <option name="CONFIG_DEBUG_CONSOLE_VGA" type="boolean" value="true"/>
   <option name="CONFIG_DEBUG_OFMEM" type="boolean" value="false"/>
-
+  <option name="CONFIG_TRACE_SIMPLETRACE" type="boolean" value="false"/>
+  <option name="CONFIG_TRACE_STDERR" type="boolean" value="true"/>
 
   <!-- Module Configuration -->
   <option name="CONFIG_CMDLINE" type="boolean" value="true"/>
diff --git a/config/examples/sparc32_config.xml b/config/examples/sparc32_config.xml
index f2d6afc..2b449cc 100644
--- a/config/examples/sparc32_config.xml
+++ b/config/examples/sparc32_config.xml
@@ -19,7 +19,8 @@
   <option name="CONFIG_SERIAL_PORT" type="integer" value="0"/>
   <option name="CONFIG_SERIAL_SPEED" type="integer" value="9600"/>
   <option name="CONFIG_DEBUG_OFMEM" type="boolean" value="false"/>
-
+  <option name="CONFIG_TRACE_SIMPLETRACE" type="boolean" value="true"/>
+  <option name="CONFIG_TRACE_STDERR" type="boolean" value="false"/>
 
   <!-- Module Configuration -->
   <option name="CONFIG_CMDLINE" type="boolean" value="true"/>
diff --git a/config/examples/sparc64_config.xml b/config/examples/sparc64_config.xml
index a4e1336..40fb7a6 100644
--- a/config/examples/sparc64_config.xml
+++ b/config/examples/sparc64_config.xml
@@ -16,7 +16,8 @@
   <option name="CONFIG_SERIAL_SPEED" type="integer" value="115200"/>
   <option name="CONFIG_DEBUG_CONSOLE_VGA" type="boolean" value="true"/>
   <option name="CONFIG_DEBUG_OFMEM" type="boolean" value="false"/>
-
+  <option name="CONFIG_TRACE_SIMPLETRACE" type="boolean" value="true"/>
+  <option name="CONFIG_TRACE_STDERR" type="boolean" value="false"/>
 
   <!-- Module Configuration -->
   <option name="CONFIG_CMDLINE" type="boolean" value="true"/>
diff --git a/config/scripts/tracetool b/config/scripts/tracetool
new file mode 100644
index 0000000..5c0534f
--- /dev/null
+++ b/config/scripts/tracetool
@@ -0,0 +1,692 @@
+#!/bin/sh
+#
+# Code generator for trace events
+#
+# Copyright IBM, Corp. 2010
+#
+# This work is licensed under the terms of the GNU GPL, version 2.  See
+# the COPYING file in the top-level directory.
+
+# Disable pathname expansion, makes processing text with '*' characters simpler
+set -f
+
+usage()
+{
+    cat >&2 <<EOF
+usage: $0 [--nop | --simple | --stderr | --ust | --dtrace] [-h | -c | -d | -g]
+Generate tracing code for a file on stdin.
+
+Backends:
+  --nop     Tracing disabled
+  --simple  Simple built-in backend
+  --stderr  Stderr built-in backend
+  --ust     LTTng User Space Tracing backend
+  --dtrace  DTrace/SystemTAP backend
+
+Output formats:
+  -h     Generate .h file
+  -c     Generate .c file
+  -d     Generate .d file (DTrace only)
+  -g     Generate guest trace .c file
+  --stap Generate .stp file (DTrace with SystemTAP only)
+
+Options:
+  --binary       [path]    Full path to QEMU binary
+  --target-arch  [arch]    QEMU emulator target arch
+  --target-type  [type]    QEMU emulator target type ('system' or 'user')
+  --probe-prefix [prefix]  Prefix for dtrace probe names
+                           (default: qemu-\$targettype-\$targetarch)
+  --guest-trace            Generate guest trace function
+
+EOF
+    exit 1
+}
+
+# Get the name of a trace event
+get_name()
+{
+    echo ${1%%\(*}
+}
+
+# Get the argument list of a trace event, including types and names
+get_args()
+{
+    local args
+    args=${1#*\(}
+    args=${args%%\)*}
+    echo "$args"
+}
+
+# Get the argument name list of a trace event
+get_argnames()
+{
+    local nfields field name sep
+    nfields=0
+    sep="$2"
+    for field in $(get_args "$1"); do
+        nfields=$((nfields + 1))
+
+        # Drop pointer star
+        field=${field#\*}
+
+        # Only argument names have commas at the end
+        name=${field%,}
+        test "$field" = "$name" && continue
+
+        printf "%s%s " $name $sep
+    done
+
+    # Last argument name
+    if [ "$nfields" -gt 1 ]
+    then
+        printf "%s" "$name"
+    fi
+}
+
+# Get the number of arguments to a trace event
+get_argc()
+{
+    local name argc
+    argc=0
+    for name in $(get_argnames "$1", ","); do
+        argc=$((argc + 1))
+    done
+    echo $argc
+}
+
+# Get the format string for a trace event
+get_fmt()
+{
+    local fmt
+    fmt=${1#*\"}
+    fmt=${fmt%\"*}
+    echo "$fmt"
+}
+
+# Get the state of a trace event
+get_state()
+{
+    local str disable state
+    str=$(get_name "$1")
+    disable=${str##disable }
+    if [ "$disable" = "$str" ] ; then
+        state=1
+    else
+        state=0
+    fi
+    echo "$state"
+}
+
+linetoh_begin_nop()
+{
+    return
+}
+
+linetoh_nop()
+{
+    local name args
+    name=$(get_name "$1")
+    args=$(get_args "$1")
+
+    # Define an empty function for the trace event
+    cat <<EOF
+static inline void trace_$name($args)
+{
+}
+EOF
+}
+
+linetoh_end_nop()
+{
+    return
+}
+
+linetoc_begin_nop()
+{
+    return
+}
+
+linetoc_nop()
+{
+    # No need for function definitions in nop backend
+    return
+}
+
+linetoc_end_nop()
+{
+    return
+}
+
+linetoh_begin_simple()
+{
+    cat <<EOF
+#include "libopenbios/simpletrace.h"
+EOF
+
+    simple_event_num=0
+}
+
+cast_args_to_uint64_t()
+{
+    local arg
+    for arg in $(get_argnames "$1", ","); do
+        printf "%s" "(uint64_t)(uintptr_t)$arg"
+    done
+}
+
+linetoh_simple()
+{
+    local name args argc trace_args state
+    name=$(get_name "$1")
+    args=$(get_args "$1")
+    argc=$(get_argc "$1")
+    state=$(get_state "$1")
+    if [ "$state" = "0" ]; then
+        name=${name##disable }
+    fi
+
+    trace_args="$simple_event_num"
+    if [ "$argc" -gt 0 ]
+    then
+        trace_args="$trace_args, $(cast_args_to_uint64_t "$1")"
+    fi
+
+    cat <<EOF
+static inline void trace_$name($args)
+{
+    trace$argc($trace_args);
+}
+EOF
+
+    simple_event_num=$((simple_event_num + 1))
+}
+
+linetoh_end_simple()
+{
+    cat <<EOF
+#define NR_TRACE_EVENTS $simple_event_num
+extern TraceEvent trace_list[NR_TRACE_EVENTS];
+EOF
+}
+
+linetoc_begin_simple()
+{
+    cat <<EOF
+#include "trace.h"
+
+TraceEvent trace_list[] = {
+EOF
+    simple_event_num=0
+
+}
+
+linetoc_simple()
+{
+    local name state
+    name=$(get_name "$1")
+    state=$(get_state "$1")
+    if [ "$state" = "0" ] ; then
+        name=${name##disable }
+    fi
+    cat <<EOF
+{.tp_name = "$name", .state=$state},
+EOF
+    simple_event_num=$((simple_event_num + 1))
+}
+
+linetoc_end_simple()
+{
+    cat <<EOF
+};
+EOF
+}
+
+#STDERR
+linetoh_begin_stderr()
+{
+    cat <<EOF
+#include "libc/vsprintf.h"
+EOF
+}
+
+linetoh_stderr()
+{
+    local name args argnames argc fmt
+    name=$(get_name "$1")
+    args=$(get_args "$1")
+    argnames=$(get_argnames "$1" ",")
+    argc=$(get_argc "$1")
+    fmt=$(get_fmt "$1")
+
+    if [ "$argc" -gt 0 ]; then
+        argnames=", $argnames"
+    fi
+
+    cat <<EOF
+static inline void trace_$name($args)
+{
+    printk("$name $fmt\n" $argnames);
+}
+EOF
+}
+
+linetoh_end_stderr()
+{
+return
+}
+
+linetoc_begin_stderr()
+{
+return
+}
+
+linetoc_stderr()
+{
+return
+}
+
+linetoc_end_stderr()
+{
+return
+}
+#END OF STDERR
+
+# Clean up after UST headers which pollute the namespace
+ust_clean_namespace() {
+    cat <<EOF
+#undef mutex_lock
+#undef mutex_unlock
+#undef inline
+#undef wmb
+EOF
+}
+
+linetoh_begin_ust()
+{
+    echo "#include <ust/tracepoint.h>"
+    ust_clean_namespace
+}
+
+linetoh_ust()
+{
+    local name args argnames
+    name=$(get_name "$1")
+    args=$(get_args "$1")
+    argnames=$(get_argnames "$1", ",")
+
+    cat <<EOF
+DECLARE_TRACE(ust_$name, TP_PROTO($args), TP_ARGS($argnames));
+#define trace_$name trace_ust_$name
+EOF
+}
+
+linetoh_end_ust()
+{
+    return
+}
+
+linetoc_begin_ust()
+{
+    cat <<EOF
+#include <ust/marker.h>
+$(ust_clean_namespace)
+#include "trace.h"
+EOF
+}
+
+linetoc_ust()
+{
+    local name args argnames fmt
+    name=$(get_name "$1")
+    args=$(get_args "$1")
+    argnames=$(get_argnames "$1", ",")
+    [ -z "$argnames" ] || argnames=", $argnames"
+    fmt=$(get_fmt "$1")
+
+    cat <<EOF
+DEFINE_TRACE(ust_$name);
+
+static void ust_${name}_probe($args)
+{
+    trace_mark(ust, $name, "$fmt"$argnames);
+}
+EOF
+
+    # Collect names for later
+    names="$names $name"
+}
+
+linetoc_end_ust()
+{
+    cat <<EOF
+static void __attribute__((constructor)) trace_init(void)
+{
+EOF
+
+    for name in $names; do
+        cat <<EOF
+    register_trace_ust_$name(ust_${name}_probe);
+EOF
+    done
+
+    echo "}"
+}
+
+linetoh_begin_dtrace()
+{
+    cat <<EOF
+#include "trace-dtrace.h"
+EOF
+}
+
+linetoh_dtrace()
+{
+    local name args argnames state nameupper
+    name=$(get_name "$1")
+    args=$(get_args "$1")
+    argnames=$(get_argnames "$1", ",")
+    state=$(get_state "$1")
+    if [ "$state" = "0" ] ; then
+        name=${name##disable }
+    fi
+
+    nameupper=`echo $name | tr '[:lower:]' '[:upper:]'`
+
+    # Define an empty function for the trace event
+    cat <<EOF
+static inline void trace_$name($args) {
+    if (QEMU_${nameupper}_ENABLED()) {
+        QEMU_${nameupper}($argnames);
+    }
+}
+EOF
+}
+
+linetoh_end_dtrace()
+{
+    return
+}
+
+linetoc_begin_dtrace()
+{
+    return
+}
+
+linetoc_dtrace()
+{
+    # No need for function definitions in dtrace backend
+    return
+}
+
+linetoc_end_dtrace()
+{
+    return
+}
+
+linetod_begin_dtrace()
+{
+    cat <<EOF
+provider qemu {
+EOF
+}
+
+linetod_dtrace()
+{
+    local name args state
+    name=$(get_name "$1")
+    args=$(get_args "$1")
+    state=$(get_state "$1")
+    if [ "$state" = "0" ] ; then
+        name=${name##disable }
+    fi
+
+    # DTrace provider syntax expects foo() for empty
+    # params, not foo(void)
+    if [ "$args" = "void" ]; then
+       args=""
+    fi
+
+    # Define prototype for probe arguments
+    cat <<EOF
+        probe $name($args);
+EOF
+}
+
+linetod_end_dtrace()
+{
+    cat <<EOF
+};
+EOF
+}
+
+linetostap_begin_dtrace()
+{
+    return
+}
+
+linetostap_dtrace()
+{
+    local i arg name args arglist state
+    name=$(get_name "$1")
+    args=$(get_args "$1")
+    arglist=$(get_argnames "$1", "")
+    state=$(get_state "$1")
+    if [ "$state" = "0" ] ; then
+        name=${name##disable }
+    fi
+
+    # Define prototype for probe arguments
+    cat <<EOF
+probe $probeprefix.$name = process("$binary").mark("$name")
+{
+EOF
+
+    i=1
+    for arg in $arglist
+    do
+        # 'limit' is a reserved keyword
+        if [ "$arg" = "limit" ]; then
+          arg="_limit"
+        fi
+        cat <<EOF
+  $arg = \$arg$i;
+EOF
+        i="$((i+1))"
+    done
+
+    cat <<EOF
+}
+EOF
+}
+
+linetostap_end_dtrace()
+{
+    return
+}
+
+linetog_begin_all()
+{
+    id=0
+    cat <<EOF
+#include "trace.h"
+#include "guest-trace.h"
+
+void guest_trace(uint64_t event_id, uint64_t arg1, uint64_t arg2,
+                 uint64_t arg3, uint64_t arg4, uint64_t arg5, uint64_t arg6)
+
+{
+    switch (event_id) {
+EOF
+}
+
+linetog_all()
+{
+    local name args argc arg
+    name=$(get_name "$1")
+    argc=$(get_argc "$1")
+    fieldno=1
+    args=
+    for arg in $(get_argnames "$1", ","); do
+        args="${args}arg$fieldno"
+        [ "$fieldno" = "$argc" ] || args="$args, "
+        fieldno="$((fieldno + 1))"
+    done
+    cat <<EOF
+    case $id:
+        trace_$name($args);
+        break;
+EOF
+    id="$((id + 1))"
+}
+
+linetog_end_all()
+{
+    cat <<EOF
+    default:
+        break;
+   }
+}
+EOF
+}
+
+# Process stdin by calling begin, line, and end functions for the backend
+convert()
+{
+    local begin process_line end str disable
+    begin="lineto$1_begin_$backend"
+    process_line="lineto$1_$backend"
+    end="lineto$1_end_$backend"
+
+    "$begin"
+
+    while read -r str; do
+        # Skip comments and empty lines
+        test -z "${str%%#*}" && continue
+
+        # Process the line.  The nop backend handles disabled lines.
+        disable=${str%%disable *}
+        echo
+        if test -z "$disable"; then
+            # Pass the disabled state as an arg for the simple
+            # or DTrace backends which handle it dynamically.
+            # For all other backends, call lineto$1_nop()
+            if [ $backend = "simple" -o "$backend" = "dtrace" ]; then
+                "$process_line" "$str"
+            else
+                "lineto$1_nop" "${str##disable }"
+            fi
+        else
+            "$process_line" "$str"
+        fi
+    done
+
+    echo
+    "$end"
+}
+
+tracetoh()
+{
+    cat <<EOF
+#ifndef TRACE_H
+#define TRACE_H
+
+/* This file is autogenerated by tracetool, do not edit. */
+
+EOF
+    convert h
+    echo "#endif /* TRACE_H */"
+}
+
+tracetoc()
+{
+    echo "/* This file is autogenerated by tracetool, do not edit. */"
+    convert c
+}
+
+tracetog()
+{
+    echo "/* This file is autogenerated by tracetool, do not edit. */"
+    backend=all
+    convert g
+}
+
+tracetod()
+{
+    if [ $backend != "dtrace" ]; then
+       echo "DTrace probe generator not applicable to $backend backend"
+       exit 1
+    fi
+    echo "/* This file is autogenerated by tracetool, do not edit. */"
+    convert d
+}
+
+tracetostap()
+{
+    if [ $backend != "dtrace" ]; then
+       echo "SystemTAP tapset generator not applicable to $backend backend"
+       exit 1
+    fi
+    if [ -z "$binary" ]; then
+       echo "--binary is required for SystemTAP tapset generator"
+       exit 1
+    fi
+    if [ -z "$probeprefix" -a -z "$targettype" ]; then
+       echo "--target-type is required for SystemTAP tapset generator"
+       exit 1
+    fi
+    if [ -z "$probeprefix" -a -z "$targetarch" ]; then
+       echo "--target-arch is required for SystemTAP tapset generator"
+       exit 1
+    fi
+    if [ -z "$probeprefix" ]; then
+        probeprefix="qemu.$targettype.$targetarch";
+    fi
+    echo "/* This file is autogenerated by tracetool, do not edit. */"
+    convert stap
+}
+
+
+backend=
+output=
+binary=
+targettype=
+targetarch=
+probeprefix=
+guesttrace=
+
+
+until [ -z "$1" ]
+do
+  case "$1" in
+    "--nop" | "--simple" | "--stderr" | "--ust" | "--dtrace") backend="${1#--}" ;;
+
+    "--binary") shift ; binary="$1" ;;
+    "--target-arch") shift ; targetarch="$1" ;;
+    "--target-type") shift ; targettype="$1" ;;
+    "--probe-prefix") shift ; probeprefix="$1" ;;
+    "--guest-trace") guesttrace="yes" ;;
+
+    "-h" | "-c" | "-d" | "-g") output="${1#-}" ;;
+    "--stap") output="${1#--}" ;;
+
+    "--check-backend") exit 0 ;; # used by ./configure to test for backend
+
+    "--list-backends") # used by ./configure to list available backends
+          echo "nop simple stderr ust dtrace"
+          exit 0
+          ;;
+
+    *)
+      usage;;
+  esac
+  shift
+done
+
+if [ "$backend" = "" -o "$output" = "" ]; then
+  usage
+fi
+
+gen="traceto$output"
+"$gen"
+
+exit 0
diff --git a/drivers/esp.c b/drivers/esp.c
index 41e0394..0ab1893 100644
--- a/drivers/esp.c
+++ b/drivers/esp.c
@@ -25,6 +25,7 @@
 #include "asm/dma.h"
 #include "esp.h"
 #include "libopenbios/ofmem.h"
+#include "trace.h"
 
 #define BUFSIZE         4096
 
@@ -106,7 +107,7 @@ do_command(esp_private_t *esp, sd_private_t *sd, int cmdlen, int replylen)
     // Clear interrupts to avoid guests seeing spurious interrupts
     (void)esp->ll->regs[ESP_INTRPT];
 
-    DPRINTF("do_command: id %d, cmd[0] 0x%x, status 0x%x\n", sd->id, esp->buffer[0], status);
+    trace_esp_do_command(sd->id, esp->buffer[0], status);
 
     /* Target didn't want all command data? */
     if ((status & ESP_STAT_TCNT) != ESP_STAT_TCNT) {
diff --git a/drivers/fw_cfg.c b/drivers/fw_cfg.c
index 4027570..caaab3b 100644
--- a/drivers/fw_cfg.c
+++ b/drivers/fw_cfg.c
@@ -18,6 +18,17 @@ fw_cfg_read(uint16_t cmd, char *buf, unsigned int nbytes)
     for (i = 0; i < nbytes; i++)
         buf[i] = *fw_cfg_data;
 }
+
+void
+fw_cfg_write(uint16_t cmd, char *buf, unsigned int nbytes)
+{
+    unsigned int i;
+
+    *fw_cfg_cmd = cmd;
+    for (i = 0; i < nbytes; i++) {
+        *fw_cfg_data = buf[i];
+    }
+}
 #else
 // XXX depends on PCI bus location, should be removed
 void
@@ -29,6 +40,17 @@ fw_cfg_read(uint16_t cmd, char *buf, unsigned int nbytes)
     for (i = 0; i < nbytes; i++)
         buf[i] = inb(CONFIG_FW_CFG_ADDR + 1);
 }
+
+void
+fw_cfg_write(uint16_t cmd, char *buf, unsigned int nbytes)
+{
+    unsigned int i;
+
+    outw(cmd, CONFIG_FW_CFG_ADDR);
+    for (i = 0; i < nbytes; i++) {
+        outb(buf[i], CONFIG_FW_CFG_ADDR + 1);
+    }
+}
 #endif
 
 uint64_t
diff --git a/drivers/ide.c b/drivers/ide.c
index 0d09bcd..e4f68f4 100644
--- a/drivers/ide.c
+++ b/drivers/ide.c
@@ -23,6 +23,7 @@
 #include "ide.h"
 #include "hdreg.h"
 #include "timer.h"
+#include "trace.h"
 
 #ifdef CONFIG_DEBUG_IDE
 #define IDE_DPRINTF(fmt, args...) \
@@ -161,7 +162,7 @@ ob_ide_pio_insw(struct ide_drive *drive, unsigned int offset,
 	struct ide_channel *chan = drive->channel;
 
 	if (len & 1) {
-		IDE_DPRINTF("%d: command not word aligned\n", drive->nr);
+                trace_ob_ide_pio_insw(drive->nr);
 		return;
 	}
 
@@ -1193,8 +1194,7 @@ ob_ide_read_blocks(int *idx)
 	unsigned char *dest = (unsigned char *)cell2pointer(POP());
 	struct ide_drive *drive = *(struct ide_drive **)idx;
 
-        IDE_DPRINTF("ob_ide_read_blocks %lx block=%ld n=%ld\n",
-                    (unsigned long)dest, (unsigned long)blk, (long)n);
+        trace_ob_ide_read_blocks((unsigned long)dest, (unsigned long)blk, (long)n);
 
 	while (n) {
 		int len = n;
diff --git a/include/arch/common/fw_cfg.h b/include/arch/common/fw_cfg.h
index b0a23cd..1448961 100644
--- a/include/arch/common/fw_cfg.h
+++ b/include/arch/common/fw_cfg.h
@@ -1,6 +1,9 @@
 #ifndef FW_CFG_H
 #define FW_CFG_H
 
+#define FW_CFG_WRITE_CHANNEL    0x4000
+#define FW_CFG_ARCH_LOCAL       0x8000
+
 #define FW_CFG_SIGNATURE        0x00
 #define FW_CFG_ID               0x01
 #define FW_CFG_UUID             0x02
@@ -30,10 +33,11 @@
 
 #define FW_CFG_FILE_FIRST       0x20
 #define FW_CFG_FILE_SLOTS       0x10
+
+#define FW_CFG_GUEST_TRACE      (FW_CFG_WRITE_CHANNEL | (FW_CFG_FILE_FIRST+FW_CFG_FILE_SLOTS))
+
 #define FW_CFG_MAX_ENTRY        (FW_CFG_FILE_FIRST+FW_CFG_FILE_SLOTS)
 
-#define FW_CFG_WRITE_CHANNEL    0x4000
-#define FW_CFG_ARCH_LOCAL       0x8000
 #define FW_CFG_ENTRY_MASK       ~(FW_CFG_WRITE_CHANNEL | FW_CFG_ARCH_LOCAL)
 
 #define FW_CFG_PPC_WIDTH        (FW_CFG_ARCH_LOCAL + 0x00)
@@ -78,6 +82,7 @@ FWCfgState *fw_cfg_init(uint32_t ctl_port, uint32_t data_port,
 
 #ifndef NO_OPENBIOS_PROTOS
 void fw_cfg_read(uint16_t cmd, char *buf, unsigned int nbytes);
+void fw_cfg_write(uint16_t cmd, char *buf, unsigned int nbytes);
 uint64_t fw_cfg_read_i64(uint16_t cmd);
 uint32_t fw_cfg_read_i32(uint16_t cmd);
 uint16_t fw_cfg_read_i16(uint16_t cmd);
diff --git a/include/libopenbios/simpletrace.h b/include/libopenbios/simpletrace.h
new file mode 100644
index 0000000..aa98ee3
--- /dev/null
+++ b/include/libopenbios/simpletrace.h
@@ -0,0 +1,31 @@
+/*
+ * Simple trace backend
+ *
+ * Copyright IBM, Corp. 2010
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ *
+ */
+
+#ifndef SIMPLETRACE_H
+#define SIMPLETRACE_H
+
+#include "asm/types.h"
+
+typedef uint64_t TraceEventID;
+
+typedef struct {
+    const char *tp_name;
+    int state;
+} TraceEvent;
+
+void trace0(TraceEventID event);
+void trace1(TraceEventID event, uint64_t x1);
+void trace2(TraceEventID event, uint64_t x1, uint64_t x2);
+void trace3(TraceEventID event, uint64_t x1, uint64_t x2, uint64_t x3);
+void trace4(TraceEventID event, uint64_t x1, uint64_t x2, uint64_t x3, uint64_t x4);
+void trace5(TraceEventID event, uint64_t x1, uint64_t x2, uint64_t x3, uint64_t x4, uint64_t x5);
+void trace6(TraceEventID event, uint64_t x1, uint64_t x2, uint64_t x3, uint64_t x4, uint64_t x5, uint64_t x6);
+
+#endif /* SIMPLETRACE_H */
diff --git a/libopenbios/build.xml b/libopenbios/build.xml
index 04e3800..b16cd35 100644
--- a/libopenbios/build.xml
+++ b/libopenbios/build.xml
@@ -19,6 +19,39 @@
   <object source="linuxbios_info.c" condition="LINUXBIOS"/>
   <object source="ofmem_common.c" condition="OFMEM"/>
   <object source="xcoff_load.c" condition="LOADER_XCOFF"/>
+  <object source="simpletrace.c" condition="TRACE_SIMPLETRACE"/>
+ <executable name="target/include/trace.h" condition="TRACE_SIMPLETRACE">
+  <rule><![CDATA[ $(ODIR)/target/include/trace.h-timestamp
+
+$(ODIR)/target/include/trace.h-timestamp: $(SRCDIR)/trace-events
+	$(call quiet-command,sh $(SRCDIR)/config/scripts/tracetool --simple -h < $< > $@,"  GEN   trace.h")
+	@cmp -s $@ $(ODIR)/target/include/trace.h || cp $@ $(ODIR)/target/include/trace.h]]></rule>
+  </executable>
+ <executable name="target/libopenbios/trace.c" condition="TRACE_SIMPLETRACE">
+  <rule><![CDATA[ $(ODIR)/target/libopenbios/trace.c-timestamp
+
+$(ODIR)/target/libopenbios/trace.c-timestamp: $(SRCDIR)/trace-events
+	$(call quiet-command,sh $(SRCDIR)/config/scripts/tracetool --simple -c < $< > $@,"  GEN   trace.c")
+	@cmp -s $@ $(ODIR)/target/libopenbios/trace.c || cp $@ $(ODIR)/target/libopenbios/trace.c]]></rule>
+  </executable>
+ <executable name="target/include/trace.h" condition="TRACE_STDERR">
+  <rule><![CDATA[ $(ODIR)/target/include/trace.h-timestamp
+
+$(ODIR)/target/include/trace.h-timestamp: $(SRCDIR)/trace-events
+	$(call quiet-command,sh $(SRCDIR)/config/scripts/tracetool --stderr -h < $< > $@,"  GEN   trace.h")
+	@cmp -s $@ $(ODIR)/target/include/trace.h || cp $@ $(ODIR)/target/include/trace.h]]></rule>
+  </executable>
+ <executable name="target/libopenbios/trace.c" condition="TRACE_STDERR">
+  <rule><![CDATA[ $(ODIR)/target/libopenbios/trace.c-timestamp
+
+$(ODIR)/target/libopenbios/trace.c-timestamp: $(SRCDIR)/trace-events
+	$(call quiet-command,sh $(SRCDIR)/config/scripts/tracetool --stderr -c < $< > $@,"  GEN   trace.c")
+	@cmp -s $@ $(ODIR)/target/libopenbios/trace.c || cp $@ $(ODIR)/target/libopenbios/trace.c]]></rule>
+  </executable>
+  <executable name="target/libopenbios/trace.o">
+   <rule><![CDATA[ $(ODIR)/target/libopenbios/trace.c $(ODIR)/target/include/trace.h
+	$(call quiet-command,$(CC) $$EXTRACFLAGS $(CFLAGS) $(INCLUDES) -c -o $@ $<, "  CC    $(TARGET_DIR)$@")]]></rule>
+  </executable>
  </library>
 
  <dictionary name="openbios" target="forth">
diff --git a/libopenbios/simpletrace.c b/libopenbios/simpletrace.c
new file mode 100644
index 0000000..8795b81
--- /dev/null
+++ b/libopenbios/simpletrace.c
@@ -0,0 +1,76 @@
+/*
+ * Simple trace backend
+ *
+ * Copyright IBM, Corp. 2010
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ *
+ */
+
+#include "libopenbios/simpletrace.h"
+#include "trace.h"
+#include "libc/byteorder.h"
+#define NO_QEMU_PROTOS
+#include "arch/common/fw_cfg.h"
+
+/** Trace buffer entry, without timestamp */
+typedef struct {
+    uint64_t event;
+    uint64_t x1;
+    uint64_t x2;
+    uint64_t x3;
+    uint64_t x4;
+    uint64_t x5;
+    uint64_t x6;
+} TraceRecord;
+
+static void trace(TraceEventID event, uint64_t x1, uint64_t x2, uint64_t x3,
+                  uint64_t x4, uint64_t x5, uint64_t x6)
+{
+    TraceRecord tmp = (TraceRecord){
+        .event = __cpu_to_le64(event),
+        .x1 = __cpu_to_le64(x1),
+        .x2 = __cpu_to_le64(x2),
+        .x3 = __cpu_to_le64(x3),
+        .x4 = __cpu_to_le64(x4),
+        .x5 = __cpu_to_le64(x5),
+        .x6 = __cpu_to_le64(x6),
+    };
+    fw_cfg_write(FW_CFG_GUEST_TRACE, (char *)&tmp, sizeof(tmp));
+}
+
+void trace0(TraceEventID event)
+{
+    trace(event, 0, 0, 0, 0, 0, 0);
+}
+
+void trace1(TraceEventID event, uint64_t x1)
+{
+    trace(event, x1, 0, 0, 0, 0, 0);
+}
+
+void trace2(TraceEventID event, uint64_t x1, uint64_t x2)
+{
+    trace(event, x1, x2, 0, 0, 0, 0);
+}
+
+void trace3(TraceEventID event, uint64_t x1, uint64_t x2, uint64_t x3)
+{
+    trace(event, x1, x2, x3, 0, 0, 0);
+}
+
+void trace4(TraceEventID event, uint64_t x1, uint64_t x2, uint64_t x3, uint64_t x4)
+{
+    trace(event, x1, x2, x3, x4, 0, 0);
+}
+
+void trace5(TraceEventID event, uint64_t x1, uint64_t x2, uint64_t x3, uint64_t x4, uint64_t x5)
+{
+    trace(event, x1, x2, x3, x4, x5, 0);
+}
+
+void trace6(TraceEventID event, uint64_t x1, uint64_t x2, uint64_t x3, uint64_t x4, uint64_t x5, uint64_t x6)
+{
+    trace(event, x1, x2, x3, x4, x5, x6);
+}
diff --git a/trace-events b/trace-events
new file mode 100644
index 0000000..0fbb853
--- /dev/null
+++ b/trace-events
@@ -0,0 +1,3 @@
+esp_do_command(int id, int cmd, int status) "id %d, cmd[0] 0x%x, status 0x%x"
+ob_ide_pio_insw(int drive) "%d: command not word aligned"
+ob_ide_read_blocks(unsigned long dest, unsigned long blk, long n) "%lx block=%ld n=%ld"
-- 
1.7.2.5