Changes between Version 7 and Version 8 of Developer/Tracing/Trace_Linker

Timestamp:

03/16/15 02:05:41 (9 years ago)

Author:

Chris Johns

Comment:

Update.

Developer/Tracing/Trace_Linker

@@ -39 +39 @@
 The trace linker requires you provide a configuration file using the `-C` or `--config`  option. This is an INI detailed in the Configuration section.
 
+If you are working with new configuration files and you want to view the files the trace linker generates add the `-k` option to keep the temporary files, and `-W` to specify an explicit wrapper C file name. 
+
 == Wrapping ==
 
@@ -46 +48 @@
 
 The trace linker generates C code with a wrapper for each function to be instrumented. The trace code generated is driven by the configuration INI files.
+
+== Function Signatures ==
+
+A function signature is the function's declaration. It is the name of the function, the return value and the arguments. Tracing using function wrappers requires we have accurate function signatures and ideally we would like to determine the function signature from the data held in ELF files. ELF files can contain DWARF data, the ELF debugging data format. In time the trace project would like to support `libdwarf` so the DWARF data can be accessed and use to determine a function's signature. This work is planned but not scheduled to be done and so in the meantime we explicitly define the function signatures in the configuration files.
 
 == Configuration ==
@@ -175 +181 @@
 A trace section can reference other trace sections of a specific type. This allows a trace sections to build on other trace sections.
 
-Function signatures are specified with the function being the key's name and they key's value is return value and a list of function arguments.
+Function signatures are specified with the function being the key's name and the key's value being the return value and a list of function arguments.
 
 === Generators ===
 
-Generators sections specify how to generate trace wrapping code.
+Generators sections specify how to generate trace wrapping code. The section's name specifies the generator and can be listed in a `generator` key in a `tracer` or `trace` section.
+
+A generator specifies the code generated when:
+
+* Entering a trace function (`entry-trace`)
+* Entry argument of a trace function (`arg-trace`), called once per argument
+* Return value of a trace function (`ret-trace`), called if not `void`.
+* Exit value of a trace function (`exit-trace`)
+
+The the generator is not interested in a specific phase it does not need to define and nothing will be generated. For example code to profile specific function may only provide the `entry-trace` and `exit-trace` code where a nano-second time stamp is taken.
+
+The section supports:
+
+ headers:: List of header sections.
+ header:: A header key. Typically the include code.
+ entry-trace: The code or call made on entry to a function.
+ arg-trace:: The code or call made for each argument to a function.
+ ret-trace:: The code or call made with the return value if not `void`.
+ exit-trace:: The code or call made after the trace function has exited.
+ code:: Code to be added into the trace file. The code is tagged between `<<<CODE` and `CODE` markers.
+
+An example generator section is:
+
+{{{
+#!c
+[printk-generator]
+headers = printk-generator-headers
+entry-trace = "rtld_pg_printk_entry(@FUNC_NAME@, (void*) &@FUNC_LABEL@);"
+arg-trace = "rtld_pg_printk_arg(@ARG_NUM@, @ARG_TYPE@, @ARG_SIZE@, (void*) &@ARG_LABEL@);"
+exit-trace = "rtld_pg_printk_exit(@FUNC_NAME@, (void*) &@FUNC_LABEL@);"
+ret-trace = "rtld_pg_printk_ret(@RET_TYPE@, @RET_SIZE@, (void*) &@RET_LABEL@);"
+code = <<<CODE
+static inline void rtld_pg_printk_entry(const char* func_name,
+                                        void*       func_addr)
+{
+  printk (">>> %s (0x%08x)\n", func_name, func_addr);
+}
+static inline void rtld_pg_printk_arg(int         arg_num,
+                                     const char* arg_type,
+                                     int         arg_size,
+                                     void*       arg)
+{
+  const unsigned char* p = arg;
+  int   i;
+  printk (" %2d] %s(%d) = ", arg_num, arg_type, arg_size);
+  for (i = 0; i < arg_size; ++i, ++p) printk ("%02x", (unsigned int) *p);
+  printk ("\n");
+}
+static inline void rtld_pg_printk_exit(const char* func_name,
+                                       void*       func_addr)
+{
+  printk ("<<< %s (0x%08x)\n", func_name, func_addr);
+}
+static inline void rtld_pg_printk_ret(const char* ret_type,
+                                      int         ret_size,
+                                      void*       ret)
+{
+  const unsigned char* p = ret;
+  int   i;
+  printk (" rt] %s(%d) = ", ret_type, ret_size);
+  for (i = 0; i < ret_size; ++i, ++p) printk ("%02x", (unsigned int) *p);
+  printk ("\n");
+}
+CODE
+
+[printk-generator-headers]
+header = "#include <stdio.h>"
+}}}
+
+The generator code can use a number of token's that are expanded when generating trace functions. They are:
+
+ @FUNC_NAME@:: The name of the function being wrapped.
+ @FUNC_LABEL@:: The C label of the function being wrapped. You can take the address of this label.
+ @ARG_NUM@:: The argument number bring processed.
+ @ARG_TYPE@:: The type of the argument.
+ @ARG_SIZE@::  The size of the argument in bytes.
+ @ARG_LABEL@:: The C label of the argument. You can take the address of this label.
+ @RET_TYPE@:: The type of the return value.
+ @RET_SIZE@:: The size of the return value in bytes.
+ @RET_LABEL@:: The C label of the return value as held in the wrapping code.
+
+== Limitation ==
+
+The trace linker and software tracing in this way currently has some limitations. The are:
+
+* Function signatures are held in configuration file and so a change in a signature will not be automatically handled.
+* Variable argument lists cannot be wrapped.
+* C++ is not supported. In time we would like to add C++ support via the demangler support in the RTEMS Toolkit, however there are C++ constructs that make wrapping difficult such as templates. C++ that results in explicit calls should be able to be wrapped.