Major reliability improvement for logging stack traces (#287)

Author: borrrden

Fleece/Support/Backtrace+capture-darwin.cc

@@ -0,0 +1,56 @@
+#ifndef __APPLE__
+#    error This file is only for Darwin (macOS/iOS) platforms
+#endif
+
+#include "Backtrace.hh"
+#include <execinfo.h>
+#include <dlfcn.h>
+#include "betterassert.hh"
+
+namespace fleece {
+    Backtrace::frameInfo Backtrace::getFrame(const void* addr, bool stack_top) {
+        Backtrace::frameInfo frame = {};
+        frame.pc                   = addr;
+
+        Dl_info info = {};
+        if ( !dladdr(addr, &info) ) { return frame; }
+
+        if ( info.dli_fname ) {
+            frame.library = info.dli_fname;
+            if ( const char* slash = strrchr(frame.library, '/') ) frame.library = slash + 1;
+        }
+
+        frame.function = info.dli_sname;
+        if ( info.dli_saddr )
+            frame.offset = reinterpret_cast<size_t>(frame.pc) - reinterpret_cast<size_t>(info.dli_saddr);
+
+        if ( info.dli_fbase ) {
+            auto pc = reinterpret_cast<uintptr_t>(frame.pc);
+            if ( !stack_top ) pc -= 1;
+            frame.imageOffset = pc - reinterpret_cast<uintptr_t>(info.dli_fbase);
+        }
+
+        return frame;
+    }
+
+    int Backtrace::raw_capture(void** buffer, int max, void* context) {
+        if ( max == 0 ) return 0;
+        return backtrace(buffer, max);
+    }
+
+    const char* Backtrace::getSymbol(unsigned i) const {
+        precondition(i < _addrs.size());
+        if ( !_symbols ) _symbols = backtrace_symbols(_addrs.data(), int(_addrs.size()));
+
+        if ( _symbols ) {
+            const char* s = _symbols[i];
+
+            // Skip line number and whitespace:
+            while ( *s && isdigit(*s) ) ++s;
+            while ( *s && isspace(*s) ) ++s;
+
+            return s;
+        }
+        return nullptr;
+    }
+}  // namespace fleece

Fleece/Support/Backtrace+capture-linux.cc

@@ -0,0 +1,143 @@
+#if !defined(__linux__) && !defined(__ANDROID__)
+#    error "This implementation is meant for Linux and Android only"
+#endif
+
+#include "Backtrace.hh"
+#include <dlfcn.h>   // dladdr()
+#include <unwind.h>  // part of compiler runtime, no extra link needed
+#include <backtrace.h>
+#include <mutex>
+#include <cstring>
+
+namespace fleece {
+    using namespace std;
+
+    struct BacktraceState {
+        void** current;
+        void** end;
+    };
+
+    static _Unwind_Reason_Code unwindCallback(struct _Unwind_Context* context, void* arg) {
+        BacktraceState* state = static_cast<BacktraceState*>(arg);
+        uintptr_t       pc    = _Unwind_GetIP(context);
+        if ( pc ) {
+            if ( state->current == state->end ) return _URC_END_OF_STACK;
+            *state->current++ = reinterpret_cast<void*>(pc);
+        }
+        return _URC_NO_REASON;
+    }
+
+    int Backtrace::raw_capture(void** buffer, int max, void* context) {
+        BacktraceState state = {buffer, buffer + max};
+        _Unwind_Backtrace(unwindCallback, &state);
+        return int(state.current - buffer);
+    }
+
+    static backtrace_state* getBacktraceState() {
+        static std::once_flag   once;
+        static backtrace_state* state;
+        std::call_once(once, [] { state = backtrace_create_state(nullptr, /*threaded=*/1, nullptr, nullptr); });
+        return state;
+    }
+
+    struct ResolvedInfo {
+        const char* function = nullptr;
+        const char* file     = nullptr;
+        int         line     = 0;
+        uintptr_t   symval   = 0;  // function start address, for offset calculation
+    };
+
+    static ResolvedInfo backtraceResolve(uintptr_t pc) {
+        ResolvedInfo info;
+        backtrace_pcinfo(
+                getBacktraceState(), pc,
+                [](void* data, uintptr_t, const char* file, int line, const char* fn) -> int {
+                    auto* r = static_cast<ResolvedInfo*>(data);
+                    if ( fn && !r->function ) r->function = fn;
+                    if ( file && !r->file ) {
+                        r->file = file;
+                        r->line = line;
+                    }
+                    return 0;
+                },
+                nullptr, &info);
+
+        // Always call syminfo: provides symval (function start) for offset, and function name fallback
+        backtrace_syminfo(
+                getBacktraceState(), pc,
+                [](void* data, uintptr_t, const char* sym, uintptr_t symval, uintptr_t) {
+                    auto* r = static_cast<ResolvedInfo*>(data);
+                    if ( !r->function && sym ) r->function = sym;
+                    if ( symval ) r->symval = symval;
+                },
+                nullptr, &info);
+        return info;
+    }
+
+    Backtrace::frameInfo Backtrace::getFrame(const void* addr, bool stack_top) {
+        Backtrace::frameInfo frame = {};
+        frame.pc                   = addr;
+
+        // dladdr gives us the library name regardless of symbol visibility,
+        // and a fallback saddr/sname for exported symbols.
+        Dl_info dlInfo = {};
+        if ( !dladdr(frame.pc, &dlInfo) ) { return frame; }
+
+        if ( dlInfo.dli_fname ) {
+            frame.library = dlInfo.dli_fname;
+            if ( const char* slash = strrchr(frame.library, '/') ) frame.library = slash + 1;
+        }
+
+#ifdef __ANDROID__
+        frame.function = info.dli_sname;
+        if ( info.dli_saddr )
+            frame.offset = reinterpret_cast<size_t>(frame.pc) - reinterpret_cast<size_t>(info.dli_saddr);
+
+        if ( info.dli_fbase ) {
+            auto pc = reinterpret_cast<uintptr_t>(frame.pc);
+            if ( !stack_top ) pc -= 1;
+            frame.imageOffset = pc - reinterpret_cast<uintptr_t>(info.dli_fbase);
+        }
+#else
+        uintptr_t pc = reinterpret_cast<uintptr_t>(frame.pc);
+        if ( !stack_top ) pc -= 1;  // return address → call site
+        if ( dlInfo.dli_fbase ) frame.imageOffset = pc - reinterpret_cast<uintptr_t>(dlInfo.dli_fbase);
+        auto resolved  = backtraceResolve(pc);
+        frame.function = resolved.function;
+        frame.file     = resolved.file;
+        frame.line     = resolved.line;
+        // Prefer symval from libbacktrace (works for hidden-visibility symbols);
+        // fall back to dladdr's saddr for exported symbols.
+        if ( resolved.symval ) frame.offset = reinterpret_cast<uintptr_t>(frame.pc) - resolved.symval;
+        else if ( dlInfo.dli_saddr )
+            frame.offset = (size_t)frame.pc - (size_t)dlInfo.dli_saddr;
+#endif
+
+        return frame;
+    }
+
+    const char* Backtrace::getSymbol(unsigned i) const {
+        // delegate to getFrame which already uses libbacktrace
+        static thread_local string tName;
+        auto                       frame = getFrame(i);
+        if ( frame.function ) {
+            tName = frame.function;
+            return tName.c_str();
+        }
+
+        return nullptr;
+    }
+
+    string FunctionName(const void* pc) {
+#if !defined(__ANDROID__)
+        uintptr_t addr = reinterpret_cast<uintptr_t>(pc) - 1;
+        if ( const char* name = backtraceResolve(addr).function ) return Unmangle(name);
+        return {};
+#else
+        Dl_info info = {};
+        dladdr(pc, &info);
+        if ( info.dli_sname ) return Unmangle(info.dli_sname);
+        return {};
+#endif
+    }
+}  // namespace fleece