core/debug: detect number of arguments

[kfessel]

Contribution description

this adds a number of arguments detection for the DEBUG_PRINT Macro to avoid the not very helpful "I don't print because the thread stack is to small" for cases that are cought by the printf to puts conversion (which is active starting on -O0 on gcc and llvm

Testing procedure

Debug print?

Issues/PRs references

[maribu]

That's not standard compliant, as the C standard requires at least on argument to be present for the ....

[kfessel]

the C23 working draft has it so its probably well supported on other compilers (than GCC an clang) too

https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3096.pdf p178:

If there is a ... in the identifier-list in the macro definition, then the trailing arguments (if any),
including any separating comma preprocessing tokens, are merged to form a single item: the variable
arguments.

[maribu]

#define THREAD_EXTRA_STACKSIZE_PRINTF 42
#define NULL ((void *)0)

typedef struct thread {
    /* bla blah doesn't matter */
    unsigned stack_size;
} thread_t;

extern int printf(const char *restrict format, ...);
extern int puts(const char *s);
extern thread_t * thread_get_active(void);

#define DEBUG(X, ...) \
    do { \
        if (sizeof((const char[]){"empty"#__VA_ARGS__}) == sizeof((const char[]){"empty"}))\
            printf(X, ##__VA_ARGS__);\
        else {\
            if ((thread_get_active() == NULL) || \
                (thread_get_active()->stack_size >= \
                THREAD_EXTRA_STACKSIZE_PRINTF)) { \
                    printf(X, ##__VA_ARGS__); \
                } \
            else { \
                puts("Cannot debug, stack too small. Consider using DEBUG_PUTS()."); \
            } }\
    } while (0)

extern int a, b, c, d;

void foo(void) {
    DEBUG("Hallo\n");
    DEBUG("a = %d\n", a);
    DEBUG("a = %d, b = %d\n", a, b);
    DEBUG("a = %d, b = %d, c = %d\n", a, b, c);
}

$ clang -c -Os -std=c2x -Weverything -o test.o test.c
test.c:16:21: warning: token pasting of ',' and __VA_ARGS__ is a GNU extension [-Wgnu-zero-variadic-macro-arguments]
   16 |             printf(X, ##__VA_ARGS__);\
      |                     ^
test.c:21:29: warning: token pasting of ',' and __VA_ARGS__ is a GNU extension [-Wgnu-zero-variadic-macro-arguments]
   21 |                     printf(X, ##__VA_ARGS__); \
      |                             ^
test.c:16:23: warning: token pasting of ',' and __VA_ARGS__ is a GNU extension [-Wgnu-zero-variadic-macro-arguments]
   16 |             printf(X, ##__VA_ARGS__);\
      |                       ^
test.c:21:31: warning: token pasting of ',' and __VA_ARGS__ is a GNU extension [-Wgnu-zero-variadic-macro-arguments]
   21 |                     printf(X, ##__VA_ARGS__); \
      |                               ^
test.c:16:23: warning: token pasting of ',' and __VA_ARGS__ is a GNU extension [-Wgnu-zero-variadic-macro-arguments]
   16 |             printf(X, ##__VA_ARGS__);\
      |                       ^
test.c:21:31: warning: token pasting of ',' and __VA_ARGS__ is a GNU extension [-Wgnu-zero-variadic-macro-arguments]
   21 |                     printf(X, ##__VA_ARGS__); \
      |                               ^
test.c:16:23: warning: token pasting of ',' and __VA_ARGS__ is a GNU extension [-Wgnu-zero-variadic-macro-arguments]
   16 |             printf(X, ##__VA_ARGS__);\
      |                       ^
test.c:21:31: warning: token pasting of ',' and __VA_ARGS__ is a GNU extension [-Wgnu-zero-variadic-macro-arguments]
   21 |                     printf(X, ##__VA_ARGS__); \
      |                               ^
test.c:30:6: warning: no previous prototype for function 'foo' [-Wmissing-prototypes]
   30 | void foo(void) {
      |      ^
test.c:30:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
   30 | void foo(void) {
      | ^
      | static 
9 warnings generated.

[kfessel]

<source>: .. warning: no previous prototype for function 'foo' [-Wmissing-prototypes] 

are you sure that is a applicable warning level ?

[kfessel]

#define DEBUG(X, ...) \
    do { \
        if (sizeof((const char[]){"empty"#__VA_ARGS__}) == sizeof((const char[]){"empty"}))\
            printf(X __VA_OPT__(,) __VA_ARGS__);\
        else {\
            if ((thread_get_active() == NULL) || \
                (thread_get_active()->stack_size >= \
                THREAD_EXTRA_STACKSIZE_PRINTF)) { \
                    printf(X __VA_OPT__(,) __VA_ARGS__); \
                } \
            else { \
                puts("Cannot debug, stack too small. Consider using DEBUG_PUTS()."); \
            } }\
    } while (0)

would be the solution following the c2x draft but clang doesn't like that either :

-Os -std=c2x -Weverything

    Output of x86-64 clang 17.0.1 (Compiler #1)

<source>:32:20: warning: must specify at least one argument for '...' parameter of variadic macro [-Wgnu-zero-variadic-macro-arguments]
  32 |     DEBUG("Hallo\n");

seems like clangs warnings are not up to date

[riot-ci]

Murdock results

✔️ PASSED

6dd4169 core/debug: detect nargs but not for everyone

Success	Failures	Total	Runtime
8082	0	8082	11m:27s

Artifacts

• Documentation preview

[kaspar030]

NACK.

• using GCC specifics
• making the macro larger instead of removing it
• really, "detect number of arguments" in the preprocessor? RIOT markets itself as "the friendly operating system", and this definitely isn't.

[maribu]

Btw: I don't think we would need the bail out mechanism anymore if we would switch to picolibc. Maybe this is something that we could push instead and get rid of the bail out entirely?