I have an almost identical question as How to add code at the entry of every function? but for C:
As I'm maintaining someone else's large undocumented project, I wish to have code similar to
static C0UNT_identifier_not_used_anywhere_else = 0;
printf("%s%s:%d#%d", __func__, strrchr(__FILE__,'/'), __LINE__, ++C0UNT_identifier_not_used_anywhere_else);
to run on entry of every function, so that I
have a log of what calls what, and
can tell, on which nth call to a function it breaks.
The existing code comprises hundreds of source files, so it is unfeasible to put a macro e.g.
#define ENTRY_CODE ...
...
int function() {
ENTRY_CODE
...
}
in every function. I am also not using DevStudio, Visual Studio or other compiler providing __cyg_profile_func_enter or such extensions.
Optionally, I'd like to printf the return value of each function on exit in a similar style. Can I do that too?
Since you have tagged with gcc it has the -finstrument-functions option:
Generate instrumentation calls for entry and exit to functions. ...
Related
I have a function whose behavior may need to be modified based on the file it is called from (e.g., to increase debugging trace output). This modification would need to be done without recompiling (e.g., by editing a configuration file or changing an environment variable).
Just as an example that would fill this need, I could write Function() as:
FunctionModifiable( const char* pszFile, int i );
Then make a macro thusly:
#define Function( i ) FunctionModifiable( __FILE__, (i) )
And FunctionModifiable() would have the duty to check pszFile in say an unordered_set<> that was populated during initialization to see if special functionality need be activated.
However, the overhead of that search is a minus (this is high-performance software and the function is called a huge number of times), and there is some per-file data that would need to be cached in this situation. We can eliminate the search, and have get storage for the cached info, by passing in not __FILE__ but a pointer to a helper object. This object needs the filename so that, when it undergoes one-off initialization, it can consult config or environment variables or what have you to know whether it needs special handling.
FunctionHelperObject fho( __FILE__ );
#define Function( i ) FunctionModifiable( &fho, (i) ) // C-style solution
#define Function( i ) fho.MethodModifiable( (i) ) // C++-style solution
OK, now say I want to avoid users having to define that fho in every file. (Inter alia, we can't re-write all existing files calling Function(), though say we're willing to recompile them).
The idea I had was the unusual step of putting a variable definition in the header file, so that any program including the header for Function() would get a FunctionHelperObject fho( __FILE__ ) for free. (Such definition would be #pragma once or guarded by a preprocessor variable.
The problem is that __FILE__ at that point would be the name of the header, not of the top-level compilation unit. If there was a __CFILE__ symbol, that would be the solution, but there's not.
Ultimately the best I can think of has shortcomings: 1) the "modifiable" aspect would only be available in source code explicitly written to use it, and 2) you'd have to do that explicit writing, and 3) starting to get a little complicated. In code you want to add the ability to modify behavior to you'd write USE_MODIFIABLE_FUNCTION somewhere after including the header in question. That'd be a macro that creates the FunctionHelperObject above, this time in the right "file" so __FILE__ would have the required value, and furthermore defines a macro as seen above that would mask the non-customizable function Function() with one of the two macros seen above. In short: the previous example, plus
#define USE_MODIFIABLE_FUNCTION FunctionHelperObject fho( __FILE__ );\n#define Function( i ) fho.MethodModifiable( (i) )
Code written without USE_MODIFIABLE_FUNCTION would simply call the uncustomizable Function() the normal way.
But surely this is some other accepted, portable way to provide this behavior? Although I've talked exclusively about the C preprocessor, is there perhaps any C++ template magic or any other approach that would work?
Cache the result.
// in the header with Function macro
static FunctionHelperObject functionhelper;
static inline void FunctionModifiableInterface(const char *file, int i) {
static initialized = 0;
if (initialized == 0) {
initialized = 1;
functionhelper = FunctionHelperObject(file);
}
FunctionModifiable(&functionhelper, i);
}
#define Function(i) FunctionModifiableInterface(__FILE__, (i))
You can't predict where the user would want to call you Function(i), so you can't predict the value of __FILE__. Just initialize it on the first call, which also is great, because you will not initialize it if Function is not called. You could do the same initialized check inside FunctionHelperObject constructor.
The really cool and hard to do trick is to modify your build system to allow you to pass a macro with the filename of compiled C file. Because build systems compile one C file at a time, it is possible (and it's a shame compilers doesn't do that by themselves). If you are using cmake with make backend (or really just make by itself), you could do something like this:
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -D__MY_FILE__='\"$(notdir $(abspath $<))\"'")
And then use FunctionHelperObject fho(__MY_FILE__) like you wanted to, because __MY_FILE__ depends only on the output filename from make.
One option is something like this (rough example, keeping the C++ syntax from the OP) :
#define Function(i) do { \
static FunctionHelperObject obj(__FILE__); \
FunctionModifiable(&obj, (i)); \
} while (0)
Note the above will have to be modified to accommodate for a return value if the function has one.
Also : an alternative to __FILE__ might be __func__ if that fits better with your needs.
In my project we are heavily using a C header which provides an API to comunicate to an external software. Long story short, in our project's bugs show up more often on the calling of the functions defined in those headers (it is an old and ugly legacy code).
I would like to implement an indirection on the calling of those functions, so I could include some profiling before calling the actual implementation.
Because I'm not the only person working on this project, I would like to make those wrappers in a such way that if someone uses the original implementations directly it should cause a compile error.
If those headers were C++ sources, I would be able to simply make a namespace, wrap the included files in it, and implement my functions using it (the other developers would be able to use the original implementation using the :: operator, but just not being able to call it directly is enough encapsulation to me). However the headers are C sources (which I have to include with extern "C" directive to include), so namespaces won't help me AFAIK.
I tried to play around with defines, but with no luck, like this:
#define my_func api_func
#define api_func NULL
What I wanted with the above code is to make my_func to be translated to api_func during the preprocessing, while making a direct call to api_func give a compile error, but that won't work because it will actually make my_func to be translated to NULL too.
So, basically, I would like to make a wrapper, and make sure the only way to access the API is through this wrapper (unless the other developers make some workaround, but this is inevitable).
Please note that I need to wrap hundreds of functions, which show up spread in the whole code several times.
My wrapper necessarily will have to include those C headers, but I would like to make them leave scope outside the file of my wrapper, and make them to be unavailable to every other file who includes my wrapper, but I guess this is not possible in C/C++.
You have several options, none of them wonderful.
if you have the sources of the legacy software, so that you can recompile it, you can just change the names of the API functions to make room for the wrapper functions. If you additionally make the original functions static and put the wrappers in the same source files, then you can ensure that the originals are called only via the wrappers. Example:
static int api_func_real(int arg);
int api_func(int arg) {
// ... instrumentation ...
int result = api_func_real(arg);
// ... instrumentation ...
return result;
}
static int api_func_real(int arg) {
// ...
}
The preprocessor can help you with that, but I hesitate to recommend specifics without any details to work with.
if you do not have sources for the legacy software, or if otherwise you are unwilling to modify it, then you need to make all the callers call your wrappers instead of the original functions. In this case you can modify the headers or include an additional header before that uses #define to change each of the original function names. That header must not be included in the source files containing the API function implementations, nor in those providing the wrapper function implementations. Each define would be of the form:
#define api_func api_func_wrapper
You would then implement the various api_func_wrapper() functions.
Among the ways those cases differ is that if you change the legacy function names, then internal calls among those functions will go through the wrappers bearing the original names (unless you change the calls, too), but if you implement wrappers with new names then they will be used only when called explicitly, which will not happen for internal calls within the legacy code (unless, again, you modify those calls).
You can do something like
[your wrapper's include file]
int origFunc1 (int x);
int origFunc2 (int x, int y);
#ifndef WRAPPER_IMPL
#define origFunc1 wrappedFunc1
#define origFunc2 wrappedFunc2
#else
int wrappedFunc1(int x);
int wrappedFunc2(int x, int y);
#endif
[your wrapper implementation]
#define WRAPPER_IMPL
#include "wrapper.h"
int wrapperFunc1 (...) {
printf("Wrapper1 called\n");
origFunc1(...);
}
Your wrapper's C file obviously needs to #define WRAPPER_IMPL before including the header.
That is neither nice nor clean (and if someone wants to cheat, he could simply define WRAPPER_IMPL), but at least some way to go.
There are two ways to wrap or override C functions in Linux:
Using LD_PRELOAD:
There is a shell environment variable in Linux called LD_PRELOAD,
which can be set to a path of a shared library,
and that library will be loaded before any other library (including glibc).
Using ‘ld --wrap=symbol‘:
This can be used to use a wrapper function for symbol.
Any further reference to symbol will be resolved to the wrapper function.
a complete writeup can be found at:
http://samanbarghi.com/blog/2014/09/05/how-to-wrap-a-system-call-libc-function-in-linux/
I'm developing some modules for an automation system written in C and I need to perform lots of work with hardware. And I see no simple way (like traditional) to debugging things instead of trace logs. So I'm looking for a good practice to log function calls. At least the sequence of calls and return values.
The way it is performed in application is quite straightforward and actually pollutes the code with irrelevant constructions like
int function (int param){
if(trace_level & LOG_FCALLS){
writelog("Entering function()");
}
/* something useful */
if(trace_level & LOG_FCALLS){
writelog("Exit from function()=%d", ret);
}
}
I decided to use a macro that will do all the dirty work. Now it looks like this
#define LOG_E(fn) const char *__fname=fn; printf("LOG: Entry to %s\n",__fname)
#define return(ret) printf("LOG: Exit from %s()=%d\n",__fname,ret)
int testFunc(){
LOG_E("testFunc");
/*do useful things */
return(ret);
}
I see the problems with this code
I'm overriding return statement, and it is requires to write return(ret) all the time instead of return ret. It is easy to forget this issue.
I'm defining string variable within my macro. I'm aware that __func__ macro exists in C99, but my compiler, unfortunately, doesn't support this macro or any other relevant macros.
How to log the values of function arguments?
I'm pretty sure that it is not a new problem and I'm not the first one who faced with it. I'm also aware about AOP thing, but the code instrumentation is not acceptable solution for my system and I haven't found any possibility to do it with my compiler.
So I'm looking for a good ideas how to implement tracing in the most elegant way.
My environment:
Legacy code, C, Watcom 10.x, real-time OS
The super-serious, professional way to do this is to make a separate debug/test project, which is separate from the production code entirely. It goes like this:
Make sure to have a backup/commit on the production code.
Make a hard-copy of the production code on the hard drive. This will become your test project.
Create a .txt log file where you write the full signature of each function you want to log, for example:
int function (int param)
float function2 (void)
...
Create a little PC program/script that takes the above .txt file as input, then searches through the source code for matching lines of function definitions. The PC program will then generate a new .c file based on the original code, where it inserts the debug logging code inside the desired functions, after { and before }. It will take a few hours of your time to make such a program.
Link your test project by using the modified source code created by your script.
The above method is how I do it myself on mission-critical software, where you have requirements from safety standards (MISRA, code coverage etc) saying that no code which is not executed in the final product is allowed.
This method ensures the integrity of the production code and guarantees that no accidental bugs are added to the program by the test/debug code. It also leaves the clutter of compile switches etc out of the production code. And you won't have any old debug code remains in your project that you forgot to delete (otherwise I always forget some snippet of debug code somewhere in my programs).
#if defined(DEBUG_BUILD)
# define START_FUNCTION if(trace_level & LOG_FCALLS){writelog("+++ %s()", __func__)
}
# define END_FUNCTION if(trace_level & LOG_FCALLS){writelog("--- %s()", __func__)
#elif defined (TIMING_BUILD)
# define START_FUNCTION WRITE_TIMED_LOG("+++")
# define END_FUNCTION WRITE_TIMED_LOG("---")
#else
# define START_FUNCTION
# define END_FUNCTION
#endif
int function (int param){
START_FUNCTION;
...
if(error_occurred) {
END_FUNCTION;
return errror_code;
}
...
END_FUNCTION;
return 42;
}
You might customize your compiler to handle that. You could use MELT (to customize your gcc compiler) if you are compiling with GCC.
Maybe you might customize openwatcom (or pay some OpenWatcom expert to do that)...
This works in MS Visual C. You will need different versions of the return macro for different data types (or none).
#include <stdio.h>
#define TRACING
#ifdef TRACING
#define LOG_E printf("Func: %s\n", __FUNCTION__);
#define LOG_R printf("Exit: %s\n", __FUNCTION__);
#define LOG_I(ival) printf("Exit: %s %d\n", __FUNCTION__, ival);
#else
#define LOG_E
#define LOG_R
#define LOG_I(ival)
#endif
int main(void){
int retval = 0;
LOG_E
printf("Hello world!\n");
LOG_I(retval)
return retval;
}
Output:
Func: main
Hello world!
Exit: main 0
I am trying to use a function-like macro to generate an object-like macro name (generically, a symbol). The following will not work because __func__ (C99 6.4.2.2-1) puts quotes around the function name.
#define MAKE_AN_IDENTIFIER(x) __func__##__##x
The desired result of calling MAKE_AN_IDENTIFIER(NULL_POINTER_PASSED) would be MyFunctionName__NULL_POINTER_PASSED. There may be other reasons this would not work (such as __func__ being taken literally and not interpreted, but I could fix that) but my question is what will provide a predefined macro like __func__ except without the quotes? I believe this is not possible within the C99 standard so valid answers could be references to other preprocessors.
Presently I have simply created my own object-like macro and redefined it manually before each function to be the function name. Obviously this is a poor and probably unacceptable practice. I am aware that I could take an existing cpp program or library and modify it to provide this functionality. I am hoping there is either a commonly used cpp replacement which provides this or a preprocessor library (prefer Python) which is designed for extensibility so as to allow me to 'configure' it to create the macro I need.
I wrote the above to try to provide a concise and well defined question but it is certainly the Y referred to by #Ruud. The X is...
I am trying to manage unique values for reporting errors in an embedded system. The values will be passed as a parameter to a(some) particular function(s). I have already written a Python program using pycparser to parse my code and identify all symbols being passed to the function(s) of interest. It generates a .h file of #defines maintaining the values of previously existing entries, commenting out removed entries (to avoid reusing the value and also allow for reintroduction with the same value), assigning new unique numbers for new identifiers, reporting malformed identifiers, and also reporting multiple use of any given identifier. This means that I can simply write:
void MyFunc(int * p)
{
if (p == NULL)
{
myErrorFunc(MYFUNC_NULL_POINTER_PASSED);
return;
}
// do something actually interesting here
}
and the Python program will create the #define MYFUNC_NULL_POINTER_PASSED 7 (or whatever next available number) for me with all the listed considerations. I have also written a set of macros that further simplify the above to:
#define FUNC MYFUNC
void MyFunc(int * p)
{
RETURN_ASSERT_NOT_NULL(p);
// do something actually interesting here
}
assuming I provide the #define FUNC. I want to use the function name since that will be constant throughout many changes (as opposed to LINE) and will be much easier for someone to transfer the value from the old generated #define to the new generated #define when the function itself is renamed. Honestly, I think the only reason I am trying to 'solve' this 'issue' is because I have to work in C rather than C++. At work we are writing fairly object oriented C and so there is a lot of NULL pointer checking and IsInitialized checking. I have two line functions that turn into 30 because of all these basic checks (these macros reduce those lines by a factor of five). While I do enjoy the challenge of crazy macro development, I much prefer to avoid them. That said, I dislike repeating myself and hiding the functional code in a pile of error checking even more than I dislike crazy macros.
If you prefer to take a stab at this issue, have at.
__FUNCTION__ used to compile to a string literal (I think in gcc 2.96), but it hasn't for many years. Now instead we have __func__, which compiles to a string array, and __FUNCTION__ is a deprecated alias for it. (The change was a bit painful.)
But in neither case was it possible to use this predefined macro to generate a valid C identifier (i.e. "remove the quotes").
But could you instead use the line number rather than function name as part of your identifier?
If so, the following would work. As an example, compiling the following 5-line source file:
#define CONCAT_TOKENS4(a,b,c,d) a##b##c##d
#define EXPAND_THEN_CONCAT4(a,b,c,d) CONCAT_TOKENS4(a,b,c,d)
#define MAKE_AN_IDENTIFIER(x) EXPAND_THEN_CONCAT4(line_,__LINE__,__,x)
static int MAKE_AN_IDENTIFIER(NULL_POINTER_PASSED);
will generate the warning:
foo.c:5: warning: 'line_5__NULL_POINTER_PASSED' defined but not used
As pointed out by others, there is no macro that returns the (unquoted) function name (mainly because the C preprocessor has insufficient syntactic knowledge to recognize functions). You would have to explicitly define such a macro yourself, as you already did yourself:
#define FUNC MYFUNC
To avoid having to do this manually, you could write your own preprocessor to add the macro definition automatically. A similar question is this: How to automatically insert pragmas in your program
If your source code has a consistent coding style (particularly indentation), then a simple line-based filter (sed, awk, perl) might do. In its most naive form: every function starts with a line that does not start with a hash or whitespace, and ends with a closing parenthesis or a comma. With awk:
{
print $0;
}
/^[^# \t].*[,\)][ \t]*$/ {
sub(/\(.*$/, "");
sub(/^.*[ \t]/, "");
print "#define FUNC " toupper($0);
}
For a more robust solution, you need a compiler framework like ROSE.
Gnu-C has a __FUNCTION__ macro, but sadly even that cannot be used in the way you are asking.
Is there any way to set a break point at the module level in Visual Studio so any calls to any functions defined in that particular DLL (3rd party, no source, no symbols) will trigger a break point before calling into the function?
I know you can break on a function name however I need all functions in a module (I could even make do with a wildcard as most of the API calls have a similar prefix)
Edit: If that's not possible can a callers graph be generated so I can find all the calls to the API used by my application?
I can't answer your original question, but this might help with what you ask in your edit.
Here's a trick I've used in the past to print all function calls and where they get called from. Since you don't have the 3rd party source, it won't be as clean, but you could move the logging statement to the macro and replace function calls with the macro using find/replace to get the same result.
#ifdef ENABLE_DEBUG
#define OriginalFunction(arg) OriginalFunctionDebug(arg, __FILE__, __LINE__)
void OriginalFunctionDebug(int originalArg, char* file, int line) {
[copy/paste variable declarations since they have to be at the top]
printf("%s called by %s:%d with arg %d", __FUNCTION__, file, line, arg); // use logging of your choice here
#else
void OriginalFunction(int originalArg) {
#endif
[rest of function]