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tracing_macro_constexpr_for_gcc.cc
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| context: crbug.com/708990 | |
| #include <stdint.h> | |
| #include <stdio.h> | |
| #include <string.h> | |
| struct Category { | |
| const char *name; | |
| uint8_t is_enabled; | |
| }; | |
| constexpr uint32_t N = 100; | |
| constexpr Category kKnownCategories[N] = { | |
| {"foo", false}, | |
| {"bar", false}, | |
| {"toplevel", false}, | |
| {"cc", false}, | |
| // The remaining slots are zero-initialized and available for the dynamic categories. | |
| }; | |
| Category g_categories[N] = { | |
| // Having to do these assignments is really awkward. But I don't know | |
| // enough constexpr magic to be able to just assign the array to the | |
| // constexpr one. | |
| kKnownCategories[0], | |
| kKnownCategories[1], | |
| kKnownCategories[2], | |
| kKnownCategories[3], | |
| }; | |
| constexpr bool ConstexprStrcmp(const char* a, const char* b, int n = 0) { | |
| return (!a[n] && !b[n]) ? true : ((a[n] == b[n]) ? ConstexprStrcmp(a, b, n + 1) : false); | |
| } | |
| constexpr uint8_t *GetEnabledPtrAtCompileTime(const char *cat, uint32_t i = 0) { | |
| // Apologies for the nested ternary operators, but any other more readable | |
| // option (if statements, variables) was a C++14 extension. | |
| return (kKnownCategories[i].name == nullptr) | |
| ? nullptr | |
| : (ConstexprStrcmp(cat, kKnownCategories[i].name) | |
| ? &g_categories[i].is_enabled | |
| : (GetEnabledPtrAtCompileTime(cat, i + 1))); | |
| } | |
| uint8_t *__attribute__((noinline)) GetEnabledPtrAtRunTime(const char *cat) { | |
| // Assume this has the proper locks for thread-safety. | |
| for (uint32_t i = 0; i < N; i++) { | |
| // Reached empty slot, just append the new cat. | |
| if (g_categories[i].name == nullptr) | |
| g_categories[i].name = cat; | |
| if (strcmp(g_categories[i].name, cat) == 0) | |
| return &g_categories[i].is_enabled; | |
| } | |
| // more than 100 categories. the real implementation has a fallback for this. | |
| return nullptr; | |
| } | |
| void __attribute__((noinline)) AddEvent(const char *cat, const char *evt_name) { | |
| // LOL, assume this does TraceLog::GetInstance()->AddTraceEvent(...). | |
| printf("EVT: %s %s (ptr: %p)\n", cat, evt_name, GetEnabledPtrAtRunTime(cat)); | |
| } | |
| #define TOKENPASTE(x, y) x##y | |
| #define TOKENPASTE2(x, y) TOKENPASTE(x, y) | |
| #define UNIQUE_VAR TOKENPASTE2(var, __LINE__) | |
| #define TRACE_EVENT0(cat, event_name) \ | |
| static uint8_t *UNIQUE_VAR = nullptr; \ | |
| constexpr uint8_t *k_##UNIQUE_VAR = GetEnabledPtrAtCompileTime(cat); \ | |
| if (k_##UNIQUE_VAR) { \ | |
| UNIQUE_VAR = k_##UNIQUE_VAR; \ | |
| } else if (UNIQUE_VAR == nullptr) { \ | |
| UNIQUE_VAR = GetEnabledPtrAtRunTime(cat); \ | |
| printf("Dynamically getting pointer '%s' : %p\n", cat, UNIQUE_VAR); \ | |
| } \ | |
| do { \ | |
| if (*((volatile uint8_t *)UNIQUE_VAR)) \ | |
| AddEvent(cat, event_name); \ | |
| } while (0) | |
| extern "C" void __attribute__((visibility("default"))) __attribute__((noinline)) | |
| foo() { | |
| TRACE_EVENT0("foo", "foo::something"); | |
| } | |
| extern "C" void __attribute__((visibility("default"))) __attribute__((noinline)) | |
| baz() { | |
| TRACE_EVENT0("baz", "baz::something"); | |
| } | |
| int main() { | |
| foo(); | |
| baz(); | |
| for (uint32_t i = 0; i < N && g_categories[i].name; i++) | |
| g_categories[i].is_enabled = true; | |
| foo(); | |
| baz(); | |
| return 0; | |
| } |
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