options/glibc: implement backtrace

Author: no92

meson.build

@@ -452,6 +452,7 @@ rtlib_deps = []
 
 if not headers_only
 	if libgcc_dependency
+		libgcc_s = meson.get_compiler('c').find_library('gcc_s', required: false)
 		libgcc = meson.get_compiler('c').find_library('gcc', required: false)
 
 		compiler_rt_name = 'libclang_rt.builtins-' + host_machine.cpu_family()
@@ -462,6 +463,10 @@ if not headers_only
 			compiler_rt = meson.get_compiler('c').find_library(compiler_rt_name, required: false)
 		endif
 
+		if libgcc_s.found()
+			rtlib_deps += libgcc_s
+		endif
+
 		if libgcc.found()
 			rtlib_deps += libgcc
 		elif compiler_rt.found()

options/glibc/generic/execinfo.cpp

@@ -1,11 +1,47 @@
 #include <execinfo.h>
+#include <unwind.h>
 
 #include <bits/ensure.h>
 #include <mlibc/debug.hpp>
 
-int backtrace(void **, int) {
-	mlibc::infoLogger() << "mlibc: backtrace() is a stub!" << frg::endlog;
-	return 0;
+namespace {
+
+struct UnwindState {
+	void **frames;
+	int count;
+	int current_frame = 0;
+};
+
+_Unwind_Reason_Code trace(_Unwind_Context *context, void *arg) {
+	uintptr_t ip = _Unwind_GetIP(context);
+
+	if (ip) {
+#if defined(__x86_64__) || defined(__i386__)
+		ip--;
+#elif defined(__aarch64__) || defined(__loongarch64)
+		ip -= 4;
+#elif defined(__riscv) || defined(__m68k__)
+		ip -= 2;
+#else
+#warning "Missing support for architecture"
+		ip--;
+#endif
+	}
+
+	UnwindState *state = static_cast<UnwindState *>(arg);
+	state->frames[state->current_frame++] = reinterpret_cast<void *>(ip);
+	return (state->current_frame >= state->count) ? _URC_END_OF_STACK : _URC_NO_REASON;
+}
+
+} // namespace
+
+int backtrace(void **buffer, int size) {
+	if (size <= 0)
+		return 0;
+
+	UnwindState state{buffer, size};
+	_Unwind_Backtrace(trace, &state);
+	return state.current_frame;
 }
 
 char **backtrace_symbols(void *const *, int) {