Symbols - TinyCC

This page covers additional symbol management functions and advanced features of the libtcc API.

Symbol lookup and enumeration

After relocating your compiled code, you can retrieve and enumerate symbols.

tcc_get_symbol

Retrieves a pointer to a compiled symbol. See Execution for detailed documentation.

void *tcc_get_symbol(TCCState *s, const char *name);

tcc_list_symbols

Enumerates all global symbols. See Execution for detailed documentation.

void tcc_list_symbols(TCCState *s, void *ctx,
    void (*symbol_cb)(void *ctx, const char *name, const void *val));

Symbol introspection

Finding all functions

#include <string.h>

typedef struct {
    char **names;
    void **pointers;
    int count;
    int capacity;
} SymbolList;

void add_symbol(SymbolList *list, const char *name, const void *ptr) {
    if (list->count >= list->capacity) {
        list->capacity = list->capacity ? list->capacity * 2 : 10;
        list->names = realloc(list->names, list->capacity * sizeof(char*));
        list->pointers = realloc(list->pointers, list->capacity * sizeof(void*));
    }
    list->names[list->count] = strdup(name);
    list->pointers[list->count] = (void*)ptr;
    list->count++;
}

void collect_symbol(void *ctx, const char *name, const void *val) {
    SymbolList *list = (SymbolList*)ctx;
    add_symbol(list, name, val);
}

SymbolList get_all_symbols(TCCState *s) {
    SymbolList list = {NULL, NULL, 0, 0};
    tcc_list_symbols(s, &list, collect_symbol);
    return list;
}

// Usage
SymbolList symbols = get_all_symbols(s);
printf("Found %d symbols:\n", symbols.count);
for (int i = 0; i < symbols.count; i++) {
    printf("  %s -> %p\n", symbols.names[i], symbols.pointers[i]);
}

Symbol filtering

typedef struct {
    const char *prefix;
    SymbolList *list;
} FilterContext;

void filter_by_prefix(void *ctx, const char *name, const void *val) {
    FilterContext *fc = (FilterContext*)ctx;
    if (strncmp(name, fc->prefix, strlen(fc->prefix)) == 0) {
        add_symbol(fc->list, name, val);
    }
}

SymbolList get_symbols_with_prefix(TCCState *s, const char *prefix) {
    SymbolList list = {NULL, NULL, 0, 0};
    FilterContext fc = {prefix, &list};
    tcc_list_symbols(s, &fc, filter_by_prefix);
    return list;
}

// Find all functions starting with "test_"
SymbolList tests = get_symbols_with_prefix(s, "test_");
for (int i = 0; i < tests.count; i++) {
    void (*test_func)(void) = tests.pointers[i];
    printf("Running %s...\n", tests.names[i]);
    test_func();
}

Debugging support

elf_output_obj

Outputs an object file after relocation for debugging purposes. The file is only generated if debugging is enabled.

int elf_output_obj(TCCState *s, const char *filename);

TCCState*

required

The compilation context (must be after tcc_relocate()).

const char*

required

Output filename for the object file.

int

Returns 0 on success, -1 on error.

Example:

TCCState *s = tcc_new();
tcc_set_output_type(s, TCC_OUTPUT_MEMORY);

// Enable debugging
tcc_set_options(s, "-g");

tcc_compile_string(s, 
    "int add(int a, int b) { return a + b; }");

tcc_relocate(s);

// Output object file for debugging
elf_output_obj(s, "debug.o");

// Can now use: gdb -ex "add-symbol-file debug.o 0x..." your_program

tcc_set_backtrace_func

Sets a custom backtrace function for runtime exceptions when using -bt option.

typedef int TCCBtFunc(void *udata, void *pc, const char *file, 
                       int line, const char *func, const char *msg);
void tcc_set_backtrace_func(TCCState *s, void *userdata, TCCBtFunc *func);

TCCState*

required

The compilation context.

void*

User data pointer passed to the backtrace callback.

TCCBtFunc*

required

Callback function for backtrace entries. Return 0 to stop backtrace.

Example:

int custom_backtrace(void *udata, void *pc, const char *file,
                     int line, const char *func, const char *msg) {
    FILE *log = (FILE*)udata;
    fprintf(log, "  at %s:%d in %s() [pc=%p]\n", 
            file, line, func, pc);
    if (msg) {
        fprintf(log, "    %s\n", msg);
    }
    return 1; // Continue backtrace
}

TCCState *s = tcc_new();
tcc_set_output_type(s, TCC_OUTPUT_MEMORY);
tcc_set_options(s, "-bt");  // Enable backtrace support

FILE *log = fopen("backtrace.log", "w");
tcc_set_backtrace_func(s, log, custom_backtrace);

// Compile and run code with backtrace support

Advanced symbol patterns

Function registry

typedef void (*CommandFunc)(int argc, char **argv);

typedef struct {
    const char *name;
    CommandFunc func;
} Command;

Command *commands = NULL;
int num_commands = 0;

void register_command_callback(void *ctx, const char *name, const void *val) {
    // Only register functions starting with "cmd_"
    if (strncmp(name, "cmd_", 4) == 0) {
        commands = realloc(commands, (num_commands + 1) * sizeof(Command));
        commands[num_commands].name = strdup(name + 4); // Remove "cmd_" prefix
        commands[num_commands].func = (CommandFunc)val;
        num_commands++;
    }
}

void register_commands(TCCState *s) {
    tcc_list_symbols(s, NULL, register_command_callback);
}

CommandFunc find_command(const char *name) {
    for (int i = 0; i < num_commands; i++) {
        if (strcmp(commands[i].name, name) == 0) {
            return commands[i].func;
        }
    }
    return NULL;
}

// Usage:
const char *plugin_code = 
    "#include <stdio.h>\n"
    "void cmd_hello(int argc, char **argv) {\n"
    "    printf(\"Hello command!\\n\");\n"
    "}\n"
    "void cmd_echo(int argc, char **argv) {\n"
    "    for (int i = 1; i < argc; i++)\n"
    "        printf(\"%s \", argv[i]);\n"
    "    printf(\"\\n\");\n"
    "}\n";

tcc_compile_string(s, plugin_code);
tcc_relocate(s);
register_commands(s);

// Execute commands
CommandFunc cmd = find_command("hello");
if (cmd) cmd(0, NULL);

Type-safe symbol access

#define GET_FUNC(s, name, ret, ...) \
    ((ret (*)(__VA_ARGS__))tcc_get_symbol(s, name))

#define GET_VAR(s, name, type) \
    ((type*)tcc_get_symbol(s, name))

// Usage:
int (*add)(int, int) = GET_FUNC(s, "add", int, int, int);
void (*print)(const char*) = GET_FUNC(s, "print", void, const char*);
int *counter = GET_VAR(s, "counter", int);

if (add && print && counter) {
    *counter = add(5, 3);
    print("Success");
}

Symbol validation

typedef struct {
    const char *name;
    int found;
} RequiredSymbol;

void check_symbol(void *ctx, const char *name, const void *val) {
    RequiredSymbol *required = (RequiredSymbol*)ctx;
    for (int i = 0; required[i].name != NULL; i++) {
        if (strcmp(required[i].name, name) == 0) {
            required[i].found = 1;
        }
    }
}

int validate_symbols(TCCState *s, const char **required_names) {
    // Count required symbols
    int count = 0;
    while (required_names[count]) count++;
    
    // Build validation list
    RequiredSymbol *required = calloc(count + 1, sizeof(RequiredSymbol));
    for (int i = 0; i < count; i++) {
        required[i].name = required_names[i];
        required[i].found = 0;
    }
    required[count].name = NULL;
    
    // Check symbols
    tcc_list_symbols(s, required, check_symbol);
    
    // Report missing symbols
    int all_found = 1;
    for (int i = 0; i < count; i++) {
        if (!required[i].found) {
            fprintf(stderr, "Missing required symbol: %s\n", required[i].name);
            all_found = 0;
        }
    }
    
    free(required);
    return all_found;
}

// Usage:
const char *required[] = {"init", "update", "cleanup", NULL};
if (!validate_symbols(s, required)) {
    fprintf(stderr, "Plugin missing required functions\n");
    return 1;
}

Runtime exception handling

_tcc_setjmp (experimental)

Catches runtime exceptions when using backtrace support. This is an experimental/advanced feature.

void *_tcc_setjmp(TCCState *s, void *jmp_buf, void *top_func, void *longjmp);

#define tcc_setjmp(s, jb, f) setjmp(_tcc_setjmp(s, jb, f, longjmp))

This is an experimental feature. See libtcc_test_mt.c in the TCC source for usage examples.

Example:

#include <setjmp.h>

jmp_buf jbuf;

TCCState *s = tcc_new();
tcc_set_output_type(s, TCC_OUTPUT_MEMORY);
tcc_set_options(s, "-bt");  // Enable backtrace

const char *code = 
    "void crash() {\n"
    "    int *p = 0;\n"
    "    *p = 42;  // Segfault\n"
    "}\n";

tcc_compile_string(s, code);
tcc_relocate(s);

void (*crash)(void) = tcc_get_symbol(s, "crash");

if (tcc_setjmp(s, jbuf, crash) == 0) {
    crash();  // This will crash
} else {
    printf("Caught exception!\n");
}

Complete example: Dynamic module system

#include "libtcc.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct {
    int version;
    const char *name;
    void (*init)(void);
    void (*shutdown)(void);
} ModuleInterface;

typedef struct {
    TCCState *state;
    ModuleInterface *interface;
    char *source;
} Module;

Module *load_module(const char *source) {
    Module *mod = calloc(1, sizeof(Module));
    mod->source = strdup(source);
    mod->state = tcc_new();
    
    tcc_set_output_type(mod->state, TCC_OUTPUT_MEMORY);
    tcc_set_options(mod->state, "-g -bt");
    
    if (tcc_compile_string(mod->state, source) < 0) {
        fprintf(stderr, "Failed to compile module\n");
        tcc_delete(mod->state);
        free(mod->source);
        free(mod);
        return NULL;
    }
    
    if (tcc_relocate(mod->state) < 0) {
        fprintf(stderr, "Failed to relocate module\n");
        tcc_delete(mod->state);
        free(mod->source);
        free(mod);
        return NULL;
    }
    
    mod->interface = tcc_get_symbol(mod->state, "module_interface");
    if (!mod->interface) {
        fprintf(stderr, "Module missing interface\n");
        tcc_delete(mod->state);
        free(mod->source);
        free(mod);
        return NULL;
    }
    
    printf("Loaded module: %s (version %d)\n", 
           mod->interface->name, mod->interface->version);
    
    if (mod->interface->init) {
        mod->interface->init();
    }
    
    return mod;
}

void unload_module(Module *mod) {
    if (mod->interface && mod->interface->shutdown) {
        mod->interface->shutdown();
    }
    tcc_delete(mod->state);
    free(mod->source);
    free(mod);
}

int main() {
    const char *module_source = 
        "#include <stdio.h>\n"
        "\n"
        "void my_init(void) {\n"
        "    printf(\"Module initializing...\\n\");\n"
        "}\n"
        "\n"
        "void my_shutdown(void) {\n"
        "    printf(\"Module shutting down...\\n\");\n"
        "}\n"
        "\n"
        "typedef struct {\n"
        "    int version;\n"
        "    const char *name;\n"
        "    void (*init)(void);\n"
        "    void (*shutdown)(void);\n"
        "} ModuleInterface;\n"
        "\n"
        "ModuleInterface module_interface = {\n"
        "    .version = 1,\n"
        "    .name = \"TestModule\",\n"
        "    .init = my_init,\n"
        "    .shutdown = my_shutdown\n"
        "};\n";
    
    Module *mod = load_module(module_source);
    if (!mod) {
        return 1;
    }
    
    // Use module...
    
    unload_module(mod);
    return 0;
}

​Symbol lookup and enumeration

​tcc_get_symbol

​tcc_list_symbols

​Symbol introspection

​Finding all functions

​Symbol filtering

​Debugging support

​elf_output_obj

​tcc_set_backtrace_func

​Advanced symbol patterns

​Function registry

​Type-safe symbol access

​Symbol validation

​Runtime exception handling

​_tcc_setjmp (experimental)

​Complete example: Dynamic module system

Symbol lookup and enumeration

tcc_get_symbol

tcc_list_symbols

Symbol introspection

Finding all functions

Symbol filtering

Debugging support

elf_output_obj

tcc_set_backtrace_func

Advanced symbol patterns

Function registry

Type-safe symbol access

Symbol validation

Runtime exception handling

_tcc_setjmp (experimental)

Complete example: Dynamic module system