[Qemu-devel] [PATCH v2 3/4] trace: forbid use of %m in trace event format strings

["Daniel P. Berrangé" <berrange@redhat.com>]

The '%m' format specifier instructs glibc's printf() implementation to
insert the contents of strerror(errno). This is not something that
should ever be used in trace-events files because several of the
backends do not use the format string and so this error information is
invisible to them. The errno value should be given as an explicit
trace argument instead. Use of '%m' should also be avoided as it is not
portable to all QEMU build targets.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
 hw/vfio/pci.c                 | 2 +-
 hw/vfio/trace-events          | 2 +-
 scripts/tracetool/__init__.py | 4 ++++
 3 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
index c0cb1ec289..85f1908cfe 100644
--- a/hw/vfio/pci.c
+++ b/hw/vfio/pci.c
@@ -2581,7 +2581,7 @@ static void vfio_populate_device(VFIOPCIDevice *vdev, Error **errp)
     ret = ioctl(vdev->vbasedev.fd, VFIO_DEVICE_GET_IRQ_INFO, &irq_info);
     if (ret) {
         /* This can fail for an old kernel or legacy PCI dev */
-        trace_vfio_populate_device_get_irq_info_failure();
+        trace_vfio_populate_device_get_irq_info_failure(errno);
     } else if (irq_info.count == 1) {
         vdev->pci_aer = true;
     } else {
diff --git a/hw/vfio/trace-events b/hw/vfio/trace-events
index a85e8662ea..6d412afc83 100644
--- a/hw/vfio/trace-events
+++ b/hw/vfio/trace-events
@@ -37,7 +37,7 @@ vfio_pci_hot_reset_has_dep_devices(const char *name) "%s: hot reset dependent de
 vfio_pci_hot_reset_dep_devices(int domain, int bus, int slot, int function, int group_id) "\t%04x:%02x:%02x.%x group %d"
 vfio_pci_hot_reset_result(const char *name, const char *result) "%s hot reset: %s"
 vfio_populate_device_config(const char *name, unsigned long size, unsigned long offset, unsigned long flags) "Device %s config:\n  size: 0x%lx, offset: 0x%lx, flags: 0x%lx"
-vfio_populate_device_get_irq_info_failure(void) "VFIO_DEVICE_GET_IRQ_INFO failure: %m"
+vfio_populate_device_get_irq_info_failure(int err) "VFIO_DEVICE_GET_IRQ_INFO failure: %d"
 vfio_realize(const char *name, int group_id) " (%s) group %d"
 vfio_mdev(const char *name, bool is_mdev) " (%s) is_mdev %d"
 vfio_add_ext_cap_dropped(const char *name, uint16_t cap, uint16_t offset) "%s 0x%x@0x%x"
diff --git a/scripts/tracetool/__init__.py b/scripts/tracetool/__init__.py
index 3478ac93ab..6fca674936 100644
--- a/scripts/tracetool/__init__.py
+++ b/scripts/tracetool/__init__.py
@@ -274,6 +274,10 @@ class Event(object):
         props = groups["props"].split()
         fmt = groups["fmt"]
         fmt_trans = groups["fmt_trans"]
+        if fmt.find("%m") != -1 or fmt_trans.find("%m") != -1:
+            raise ValueError("Event format '%m' is forbidden, pass the error "
+                             "as an explicit trace argument")
+
         if len(fmt_trans) > 0:
             fmt = [fmt_trans, fmt]
         args = Arguments.build(groups["args"])
-- 
2.20.1