C exceptions with unwinding

#ifndef _CEXC_H_
#define _CEXC_H_

#include <assert.h>
#include <setjmp.h>
#include <unistd.h>
#include <unwind.h>


struct cexc_ctx {
    struct _Unwind_Exception uexc;
    void *exc;
};

typedef void * cexc_t;


#define CEXC_TRY {                                  \
    jmp_buf cexc_jmp_;                              \
    struct cexc_ctx cexc_ctx_ = {                           \
        .exc = NULL                             \
    };                                      \
                                            \
    if (cexc_ctx == NULL)                               \
        cexc_ctx = &cexc_ctx_;                          \
                                            \
    if (setjmp(cexc_jmp_) == 0) {                           \
        void cexc_landingpad_(int *unwind_)                 \
        {                                   \
            if (*unwind_ == 0)                      \
                return;                         \
                                            \
            longjmp(cexc_jmp_, 1);                      \
        }                                   \
        __attribute__((cleanup(cexc_landingpad_))) int cexc_unwind_ = 1;


#define CEXC_CATCH(exc_...)                             \
        cexc_unwind_ = 0;                           \
        if (cexc_ctx == &cexc_ctx_)                     \
            cexc_ctx = NULL;                        \
    } else {                                    \
        cexc_t unused_exc_ __attribute__((unused)), ##exc_ = cexc_ctx->exc; \
                                            \
        if (cexc_ctx == &cexc_ctx_)                     \
            cexc_ctx = NULL;

#define CEXC_END                                    \
    }                                       \
}

#define CEXC_THROW(e_...) ({                            \
    assert("uncaught throw" && cexc_ctx != NULL);               \
_Pragma("GCC diagnostic ignored \"-Wunused-value\"")                \
    cexc_ctx->exc = (cexc_ctx->exc, ##e_);                  \
_Pragma("GCC diagnostic pop")                           \
    _Unwind_ForcedUnwind(&cexc_ctx->uexc, cexc_unwind_stop, 0);     \
    assert("exception handling must be enabled (-fexceptions)" && 0);   \
    *(int *)0 = 0;                              \
})


static inline _Unwind_Reason_Code cexc_unwind_stop()
{
    return _URC_NO_REASON;
}


#ifndef CEXC_SOURCE
extern
#endif
struct cexc_ctx *cexc_ctx;

#endif // _CEXC_H_