diff options
Diffstat (limited to 'docs/tracing.txt')
| -rw-r--r-- | docs/tracing.txt | 23 |
1 files changed, 14 insertions, 9 deletions
diff --git a/docs/tracing.txt b/docs/tracing.txt index f15069c96..c99a0f27c 100644 --- a/docs/tracing.txt +++ b/docs/tracing.txt @@ -26,14 +26,14 @@ for debugging, profiling, and observing execution. == Trace events == -There is a set of static trace events declared in the trace-events source +There is a set of static trace events declared in the "trace-events" source file. Each trace event declaration names the event, its arguments, and the format string which can be used for pretty-printing: qemu_malloc(size_t size, void *ptr) "size %zu ptr %p" qemu_free(void *ptr) "ptr %p" -The trace-events file is processed by the tracetool script during build to +The "trace-events" file is processed by the "tracetool" script during build to generate code for the trace events. Trace events are invoked directly from source code like this: @@ -52,10 +52,10 @@ source code like this: === Declaring trace events === -The tracetool script produces the trace.h header file which is included by +The "tracetool" script produces the trace.h header file which is included by every source file that uses trace events. Since many source files include -trace.h, it uses a minimum of types and other header files included to keep -the namespace clean and compile times and dependencies down. +trace.h, it uses a minimum of types and other header files included to keep the +namespace clean and compile times and dependencies down. Trace events should use types as follows: @@ -69,6 +69,11 @@ Trace events should use types as follows: cannot include all user-defined struct declarations and it is therefore necessary to use void * for pointers to structs. + Pointers (including char *) cannot be dereferenced easily (or at all) in + some trace backends. If pointers are used, ensure they are meaningful by + themselves and do not assume the data they point to will be traced. Do + not pass in string arguments. + * For everything else, use primitive scalar types (char, int, long) with the appropriate signedness. @@ -105,10 +110,10 @@ portability macros, ensure they are preceded and followed by double quotes: == Trace backends == -The tracetool script automates tedious trace event code generation and also +The "tracetool" script automates tedious trace event code generation and also keeps the trace event declarations independent of the trace backend. The trace events are not tightly coupled to a specific trace backend, such as LTTng or -SystemTap. Support for trace backends can be added by extending the tracetool +SystemTap. Support for trace backends can be added by extending the "tracetool" script. The trace backend is chosen at configure time and only one trace backend can @@ -176,12 +181,12 @@ events at runtime inside QEMU: ==== Analyzing trace files ==== The "simple" backend produces binary trace files that can be formatted with the -simpletrace.py script. The script takes the trace-events file and the binary +simpletrace.py script. The script takes the "trace-events" file and the binary trace: ./simpletrace.py trace-events trace-12345 -You must ensure that the same trace-events file was used to build QEMU, +You must ensure that the same "trace-events" file was used to build QEMU, otherwise trace event declarations may have changed and output will not be consistent. |