stacktrace.cpp: hardened parsing of backtrace output [skip ci]

Author: firewave

cli/stacktrace.cpp

@@ -31,9 +31,17 @@
 void print_stacktrace(FILE* output, int start_idx, bool demangling, int maxdepth, bool omit_above_own)
 {
     // 32 vs. 64bit
-#define ADDRESSDISPLAYLENGTH ((sizeof(long)==8)?12:8)
+    static constexpr auto ADDRESSDISPLAYLENGTH = (sizeof(long) == 8) ? 12 : 8;
+
     void *callstackArray[32]= {nullptr}; // the less resources the better...
     const int currentdepth = backtrace(callstackArray, static_cast<int>(getArrayLength(callstackArray)));
+    if (currentdepth == 0) {
+        fputs("Callstack could not be obtained (backtrace)\n", output);
+        return;
+    }
+    if (currentdepth == getArrayLength(callstackArray)) {
+        fputs("Callstack might be truncated\n", output);
+    }
     // set offset to 1 to omit the printing function itself
     int offset=start_idx+1; // some entries on top are within our own exception handling code or libc
     if (maxdepth<0)
@@ -43,61 +51,78 @@ void print_stacktrace(FILE* output, int start_idx, bool demangling, int maxdepth
 
     char **symbolStringList = backtrace_symbols(callstackArray, currentdepth);
     if (!symbolStringList) {
-        fputs("Callstack could not be obtained\n", output);
+        fputs("Callstack could not be obtained (backtrace_symbols)\n", output);
         return;
     }
 
     fputs("Callstack:\n", output);
     bool own_code = false;
     char demangle_buffer[2048]= {0};
-    for (int i = offset; i < maxdepth; ++i) {
+    for (int i = 0; i < maxdepth; ++i) {
         const char * const symbolString = symbolStringList[i];
         // TODO: implement parsing for __APPLE__
+        // 0   test-signalhandler                  0x0000000100dbf42c _Z16print_stacktraceP7__sFILEibib + 124
+
+        /*
+         * examples:
+         * ./test-signalhandler(_Z16print_stacktraceP8_IO_FILEibib+0xa1) [0x55cb65e41464]
+         * ./test-signalhandler(+0xf9d9) [0x55cb65e3c9d9]
+         */
+
         // skip all leading libc symbols so the first symbol is our code
         if (omit_above_own && !own_code) {
             if (strstr(symbolString, "/libc.so.6") != nullptr)
                 continue;
             own_code = true;
-            offset = i; // make sure the numbering is continous if we omit frames
+            offset = i; // make sure the numbering is continuous if we omit frames
         }
         const char * realnameString = nullptr;
-        const char * const firstBracketName     = strchr(symbolString, '(');
-        const char * const firstBracketAddress  = strchr(symbolString, '[');
-        const char * const secondBracketAddress = strchr(firstBracketAddress, ']');
-        const char * const beginAddress         = firstBracketAddress+3;
-        const int addressLen = int(secondBracketAddress-beginAddress);
-        const int padLen     = (ADDRESSDISPLAYLENGTH-addressLen);
-        if (demangling && firstBracketName) {
-            const char * const plus = strchr(firstBracketName, '+');
-            if (plus && (plus>(firstBracketName+1))) {
-                char input_buffer[1024]= {0};
-                strncpy(input_buffer, firstBracketName+1, plus-firstBracketName-1);
-                size_t length = getArrayLength(demangle_buffer);
-                int status=0;
-                // We're violating the specification - passing stack address instead of malloc'ed heap.
-                // Benefit is that no further heap is required, while there is sufficient stack...
-                realnameString = abi::__cxa_demangle(input_buffer, demangle_buffer, &length, &status); // non-NULL on success
+        if (demangling) {
+            const char * const firstBracketName = strchr(symbolString, '(');
+            if (firstBracketName) {
+                const char * const plus = strchr(firstBracketName, '+');
+                if (plus && (plus>(firstBracketName+1))) {
+                    char input_buffer[1024]= {0};
+                    strncpy(input_buffer, firstBracketName+1, plus-firstBracketName-1);
+                    size_t length = getArrayLength(demangle_buffer);
+                    int status=0;
+                    // We're violating the specification - passing stack address instead of malloc'ed heap.
+                    // Benefit is that no further heap is required, while there is sufficient stack...
+                    realnameString = abi::__cxa_demangle(input_buffer, demangle_buffer, &length, &status); // non-NULL on success
+                }
             }
         }
         const int ordinal=i-offset;
         fprintf(output, "#%-2d 0x",
                 ordinal);
+
+        const char * const firstBracketAddress = strchr(symbolString, '[');// TODO: check
+        const char * const secondBracketAddress = strchr(firstBracketAddress, ']'); // TODO: check
+        const int padLen = [&]() {
+            // TODO: handle firstBracketAddress being NULL
+            const char * const beginAddress = firstBracketAddress+3;
+            const int addressLen = int(secondBracketAddress-beginAddress);
+            return (ADDRESSDISPLAYLENGTH-addressLen);
+        }();
         if (padLen>0)
             fprintf(output, "%0*d",
-                    padLen, 0);
+                    padLen,
+                    0);
         if (realnameString) {
             fprintf(output, "%.*s in %s\n",
-                    static_cast<int>(secondBracketAddress - firstBracketAddress - 3), firstBracketAddress+3,
+                    static_cast<int>(secondBracketAddress - firstBracketAddress - 3),
+                    firstBracketAddress+3,
                     realnameString);
         } else {
             fprintf(output, "%.*s in %.*s\n",
-                    static_cast<int>(secondBracketAddress - firstBracketAddress - 3), firstBracketAddress+3,
-                    static_cast<int>(firstBracketAddress - symbolString), symbolString);
+                    static_cast<int>(secondBracketAddress - firstBracketAddress - 3),
+                    firstBracketAddress+3,
+                    static_cast<int>(firstBracketAddress - symbolString),
+                    symbolString);
         }
     }
     // NOLINTNEXTLINE(bugprone-multi-level-implicit-pointer-conversion) - code matches the documented usage
     free(symbolStringList);
-#undef ADDRESSDISPLAYLENGTH
 }
 
 #endif // USE_UNIX_BACKTRACE_SUPPORT