cppify (#3)

* c++ify bunch of files
* fix tracer env issue (std::string was not available in fork due to
`init()` not being called in fork)
* some refactoring
* making parts optional
* add a bit of debug

.github/workflows/build.yml

@@ -9,7 +9,7 @@ on:
 
 jobs:
   build:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
 
     steps:
       - uses: actions/checkout@v4
@@ -30,7 +30,7 @@ jobs:
           export LIBSEGFAULT_TRACER="$PWD/build/tracer"
           export LIBSEGFAULT_DEBUG=1
           export LD_PRELOAD="$PWD/build/libSegFault.so"
-          build/faulty-example 2>&1
+          build/faulty-example 2>&1 | grep "faulty-example.cpp"
 
       - name: Release
         uses: softprops/action-gh-release@v2

CMakeLists.txt

@@ -20,8 +20,9 @@ FetchContent_MakeAvailable(cpptrace)
 add_library(
   SegFault
   SHARED
-  libSegFault/segfault.c
-  libSegFault/_itoa.c
+  libSegFault/config.cpp
+  libSegFault/segfault.cpp
+  libSegFault/_itoa.cpp
   libSegFault/signal-safe-trace.cpp
 )
 target_include_directories(SegFault PRIVATE libSegFault/${ARCH} libSegFault/) # Note: Order is important

README.md

@@ -1,18 +1,46 @@
 This is a compiler-explorer fork of the glibc-tools repository, which contains tools and library provided by glibc that
 either have been deprectated of moved out from the project. At the time of this fork, it contained only libSegFault.
 
-Changes to libSegFault:
+## Changes to libSegFault
 - CMake for building
 - Improved stack tracing with [cpptrace](https://github.com/jeremy-rifkin/cpptrace)
 
-Dependencies:
+## Dependencies
 
+- GCC 11 or higher (or equivalent)
 - Cpptrace depends on libdwarf, zlib, zstd, and is configured to use libunwind.
 
-Contributing:
+## Contributing
 
 To build locally run `make build`. Example usage:
 
 ```
 LD_PRELOAD=$LD_PRELOAD:build/libSegFault.so LIBSEGFAULT_TRACER=build/tracer ./some_program
 ```
+
+## Environment variables
+
+### Required
+
+* LIBSEGFAULT_TRACER
+  - Full path to the `tracer` program
+
+### Optional
+
+* SEGFAULT_SIGNALS="..."
+  - Space separated list of signals to listen to
+  - Supported values are: segv, ill, abrt, fpe, bus, stkflt, all
+
+* LIBSEGFAULT_REGISTERS=1
+  - Include the state of all the registers
+
+* LIBSEGFAULT_MEMORY=1
+  - Include a memory map
+
+* LIBSEGFAULT_DEBUG=1
+  - For situations when libSegFault doesn't work as expected
+
+### Deprecated / Should not use
+
+* SEGFAULT_USE_ALTSTACK
+* SEGFAULT_OUTPUT_NAME

libSegFault/_itoa.c → libSegFault/_itoa.cpp

@@ -17,9 +17,9 @@
 #include <_itoa.h>
 
 /* Upper-case digits.  */
-static const char _itoa_upper_digits[36] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+static const char _itoa_upper_digits[37] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
 /* Lower-case digits.  */
-static const char _itoa_lower_digits[36] = "0123456789abcdefghijklmnopqrstuvwxyz";
+static const char _itoa_lower_digits[37] = "0123456789abcdefghijklmnopqrstuvwxyz";
 
 char *_itoa_word(_ITOA_WORD_TYPE value, char *buflim, unsigned int base, int upper_case)
 {

libSegFault/config.cpp

@@ -0,0 +1,51 @@
+#include <cstdlib>
+#include <cstring>
+
+const char *getTracerProgram()
+{
+    static const char *emptystr = "";
+    if (const char *value = getenv("LIBSEGFAULT_TRACER"))
+    {
+        return value;
+    }
+
+    return emptystr;
+}
+
+bool isDebugMode()
+{
+    if (const char *value = getenv("LIBSEGFAULT_DEBUG"))
+    {
+        if (strcmp(value, "1") == 0)
+            return true;
+    }
+
+    return false;
+}
+
+bool useAlternativeStack()
+{
+    return getenv("SEGFAULT_USE_ALTSTACK") != 0;
+}
+
+bool dumpRegisters()
+{
+    if (const char *value = getenv("LIBSEGFAULT_REGISTERS"))
+    {
+        if (strcmp(value, "1") == 0)
+            return true;
+    }
+
+    return false;
+}
+
+bool dumpMemory()
+{
+    if (const char *value = getenv("LIBSEGFAULT_MEMORY"))
+    {
+        if (strcmp(value, "1") == 0)
+            return true;
+    }
+
+    return false;
+}

libSegFault/config.hpp

@@ -0,0 +1,7 @@
+#pragma once
+
+bool isDebugMode();
+const char *getTracerProgram();
+bool useAlternativeStack();
+bool dumpRegisters();
+bool dumpMemory();

libSegFault/segfault.c → libSegFault/segfault.cpp

@@ -33,6 +33,7 @@
 #include <sigcontextinfo.h>
 
 #include "signal-safe-trace.hpp"
+#include "config.hpp"
 
 #ifdef SA_SIGINFO
 #define SIGCONTEXT siginfo_t *info, void *
@@ -84,27 +85,33 @@ static void catch_segfault(int signal, SIGCONTEXT ctx)
     WRITE_STRING("\n");
 
 #ifdef REGISTER_DUMP
-    REGISTER_DUMP;
+    if (dumpRegisters())
+    {
+        REGISTER_DUMP;
+    }
 #endif
 
     WRITE_STRING("\n");
 
     do_signal_safe_trace();
 
 #ifdef HAVE_PROC_SELF
-    /* Now the link map.  */
-    int mapfd = open("/proc/self/maps", O_RDONLY);
-    if (mapfd != -1)
+    if (dumpMemory())
     {
-        WRITE_STRING("\nMemory map:\n\n");
+        /* Now the link map.  */
+        int mapfd = open("/proc/self/maps", O_RDONLY);
+        if (mapfd != -1)
+        {
+            WRITE_STRING("\nMemory map:\n\n");
 
-        char buf[256];
-        ssize_t n;
+            char buf[256];
+            ssize_t n;
 
-        while ((n = TEMP_FAILURE_RETRY(read(mapfd, buf, sizeof(buf)))) > 0)
-            TEMP_FAILURE_RETRY(write(fd, buf, n));
+            while ((n = TEMP_FAILURE_RETRY(read(mapfd, buf, sizeof(buf)))) > 0)
+                TEMP_FAILURE_RETRY(write(fd, buf, n));
 
-        close(mapfd);
+            close(mapfd);
+        }
     }
 #endif
 
@@ -133,8 +140,7 @@ static void __attribute__((constructor)) install_handler(void)
     sigemptyset(&sa.sa_mask);
     sa.sa_flags |= SA_RESTART;
 
-    /* Maybe we are expected to use an alternative stack.  */
-    if (getenv("SEGFAULT_USE_ALTSTACK") != 0)
+    if (useAlternativeStack())
     {
         void *stack_mem = malloc(2 * SIGSTKSZ);
         stack_t ss;

libSegFault/signal-safe-trace.cpp

@@ -1,4 +1,5 @@
 #include "signal-safe-trace.hpp"
+#include "config.hpp"
 
 #include <cpptrace/cpptrace.hpp>
 
@@ -14,6 +15,8 @@
 #include <sys/wait.h>
 #include <unistd.h>
 
+#include <errno.h>
+
 using namespace std::literals;
 
 struct pipe_t
@@ -30,8 +33,6 @@ struct pipe_t
 };
 static_assert(sizeof(pipe_t) == 2 * sizeof(int), "Unexpected struct packing");
 
-std::string tracer_program = "tracer";
-
 void warmup_cpptrace()
 {
     cpptrace::frame_ptr buffer[10];
@@ -40,19 +41,17 @@ void warmup_cpptrace()
     cpptrace::get_safe_object_frame(buffer[0], &frame);
 }
 
+
 [[gnu::constructor]] void init()
 {
     warmup_cpptrace();
-    if (const char *value = getenv("LIBSEGFAULT_TRACER"))
-    {
-        tracer_program = value;
-    }
 }
 
-constexpr auto fork_failure_message = "fork() failed, unable to collect trace\n"sv;
-auto no_tracer_message = "exec(signal_tracer) failed: Please supply the environment variable LIBSEGFAULT_TRACER.\n"sv;
+const auto fork_failure_message = "fork() failed, unable to collect trace\n"sv;
+const auto no_tracer_message = "exec(signal_tracer) failed: Please supply the environment variable LIBSEGFAULT_TRACER.\n"sv;
 
-auto exec_failure_message = "exec(signal_tracer) failed: Make sure the signal_tracer exists and the executable permissions are correct.\n"sv;
+const auto exec_failure_message =
+"exec(signal_tracer) failed: Make sure the signal_tracer exists and the executable permissions are correct.\n"sv;
 
 void do_signal_safe_trace()
 {
@@ -74,10 +73,23 @@ void do_signal_safe_trace()
         dup2(input_pipe.read_end, STDIN_FILENO);
         close(input_pipe.read_end);
         close(input_pipe.write_end);
-        if (tracer_program.length() == 0) {
+
+        bool is_debug = isDebugMode();
+        const char *tracer_program = getTracerProgram();
+        if (strlen(tracer_program) == 0)
+        {
             std::ignore = write(STDERR_FILENO, no_tracer_message.data(), no_tracer_message.size());
-        } else {
-            execl(tracer_program.c_str(), tracer_program.c_str(), nullptr);
+        }
+        else
+        {
+            execl(tracer_program, tracer_program, nullptr);
+
+            if (is_debug)
+            {
+                auto errcode = errno;
+                fprintf(stderr, "errno: %d\n", errcode);
+                fprintf(stderr, "tried to execute: %s\n", tracer_program);
+            }
 
             // https://linux.die.net/man/3/execl - execl() only returns when an error has occured
             //  otherwise this basically exits out of this code

libSegFault/x86_64/register-dump.h

@@ -319,4 +319,4 @@ static void register_dump(int fd, ucontext_t *ctx)
 }
 
 
-#define REGISTER_DUMP register_dump(fd, ctx)
+#define REGISTER_DUMP register_dump(fd, static_cast<ucontext_t *>(ctx))