Prepare PrettyStackTrace for LLDB adoption

[spyffe]

Summary

This patch fixes the linkage for __crashtracer_info__ making it have the proper mangling (extern "C") and linkage (private extern).
It also adds a new PrettyStackTrace type, allowing LLDB to adopt this instead of Host::SetCrashDescriptionWithFormat().

Without this patch, CrashTracer on macOS won't pick up pretty stack traces from any LLVM client. Also, this patch needs to be synced with an LLDB patch that adopts it.

[spyffe]

The LLDB side of this is https://reviews.llvm.org/D27735

[beanz]

LGTM other than a few style comments. Please clang-format before committing. Some of the formatting looks off (although that might just be my phone).

lib/Support/PrettyStackTrace.cpp

152 ↗

(On Diff #81304)

Your variable names are very LLDB-esque. Please follow the LLVM style guide, which is CamelCase.

[thakis]

llvm/trunk/lib/Support/PrettyStackTrace.cpp

93

As far as I can tell, making this a hidden symbol makes the .desc ___crashreporter_info__, 0x10 (ie REFERENCED_DYNAMICALLY) not have any effect:

% cat crashref.cc
extern "C" const char *__crashreporter_info__  __attribute__((visibility("hidden"))) = 0;
asm(".desc ___crashreporter_info__, 0x10");
int main() {}
% clang crashref.cc
% nm -m a.out
0000000100004000 (__DATA,__common) non-external (was a private external) ___crashreporter_info__
0000000100000000 (__TEXT,__text) [referenced dynamically] external __mh_execute_header
0000000100003fb0 (__TEXT,__text) external _main
                 (undefined) external dyld_stub_binder (from libSystem)
% strip -r a.out
% nm -m a.out
0000000100000000 (__TEXT,__text) [referenced dynamically] external __mh_execute_header

It does have an effect without it:

% cat crashref.cc
extern "C" const char *__crashreporter_info__ = 0;
asm(".desc ___crashreporter_info__, 0x10");
int main() {}
% clang crashref.cc
% nm -m a.out
0000000100004000 (__DATA,__common) [referenced dynamically] external ___crashreporter_info__
0000000100000000 (__TEXT,__text) [referenced dynamically] external __mh_execute_header
0000000100003fb0 (__TEXT,__text) external _main
                 (undefined) external dyld_stub_binder (from libSystem)
% strip -r a.out
% nm -m a.out
0000000100004000 (__DATA,__common) [referenced dynamically] external ___crashreporter_info__
0000000100000000 (__TEXT,__text) [referenced dynamically] external __mh_execute_header

Is that intentional? Should we just remove the .desc line?

[clayborg]

llvm/trunk/lib/Support/PrettyStackTrace.cpp

92–93

lol, if we still need the ___crashreporter_info__ symbol to be around, then it should be visible so that ReportCrash can find it...

llvm/trunk/include/llvm/Support/PrettyStackTrace.h

 // crashes give more contextual information about what the program was doing
 // when it crashed.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_SUPPORT_PRETTYSTACKTRACE_H
 #define LLVM_SUPPORT_PRETTYSTACKTRACE_H
 
+#include "llvm/ADT/SmallVector.h"
 #include "llvm/Support/Compiler.h"
 
 namespace llvm {
   class raw_ostream;
 
   void EnablePrettyStackTrace();
 
   /// PrettyStackTraceEntry - This class is used to represent a frame of the
namespace llvm {
   /// occurs.
   class PrettyStackTraceString : public PrettyStackTraceEntry {
     const char *Str;
   public:
     PrettyStackTraceString(const char *str) : Str(str) {}
     void print(raw_ostream &OS) const override;
   };
 
+  /// PrettyStackTraceFormat - This object prints a string (which may use
+  /// printf-style formatting but should not contain newlines) to the stream
+  /// as the stack trace when a crash occurs.
+  class PrettyStackTraceFormat : public PrettyStackTraceEntry {
+    llvm::SmallVector<char, 32> Str;
+  public:
+    PrettyStackTraceFormat(const char *Format, ...);
+    void print(raw_ostream &OS) const override;
+  };
+
   /// PrettyStackTraceProgram - This object prints a specified program arguments
   /// to the stream as the stack trace when a crash occurs.
   class PrettyStackTraceProgram : public PrettyStackTraceEntry {
     int ArgC;
     const char *const *ArgV;
   public:
     PrettyStackTraceProgram(int argc, const char * const*argv)
       : ArgC(argc), ArgV(argv) {

llvm/trunk/lib/Support/PrettyStackTrace.cpp

 //  If any clients of llvm try to link to libCrashReporterClient.a themselves,
 //  only one crash info struct will be used.
 extern "C" {
 CRASH_REPORTER_CLIENT_HIDDEN 
 struct crashreporter_annotations_t gCRAnnotations 
         __attribute__((section("__DATA," CRASHREPORTER_ANNOTATIONS_SECTION))) 
         = { CRASHREPORTER_ANNOTATIONS_VERSION, 0, 0, 0, 0, 0, 0 };
 }
-#elif defined (__APPLE__) && HAVE_CRASHREPORTER_INFO
-static const char *__crashreporter_info__ = 0;
+#elif defined(__APPLE__) && HAVE_CRASHREPORTER_INFO
+extern "C" const char *__crashreporter_info__
+    __attribute__((visibility("hidden"))) = 0;
 asm(".desc ___crashreporter_info__, 0x10");
 #endif
 
-
 /// CrashHandler - This callback is run if a fatal signal is delivered to the
 /// process, it prints the pretty stack trace.
 static void CrashHandler(void *) {
 #ifndef __APPLE__
   // On non-apple systems, just emit the crash stack trace to stderr.
   PrintCurStackTrace(errs());
 #else
   // Otherwise, emit to a smallvector of chars, send *that* to stderr, but also

 PrettyStackTraceEntry::~PrettyStackTraceEntry() {
 #if defined(HAVE_BACKTRACE) && ENABLE_BACKTRACES
   assert(PrettyStackTraceHead == this &&
          "Pretty stack trace entry destruction is out of order");
   PrettyStackTraceHead = NextEntry;
 #endif
 }
 
-void PrettyStackTraceString::print(raw_ostream &OS) const {
-  OS << Str << "\n";
+void PrettyStackTraceString::print(raw_ostream &OS) const { OS << Str << "\n"; }
+
+PrettyStackTraceFormat::PrettyStackTraceFormat(const char *Format, ...) {
+  va_list AP;
+  va_start(AP, Format);
+  const int SizeOrError = vsnprintf(nullptr, 0, Format, AP);
+  va_end(AP);
+  if (SizeOrError < 0) {
+    return;
   }
 
+  const int Size = SizeOrError + 1; // '\0'
+  Str.resize(Size);
+  va_start(AP, Format);
+  vsnprintf(Str.data(), Size, Format, AP);
+  va_end(AP);
+}
+
+void PrettyStackTraceFormat::print(raw_ostream &OS) const { OS << Str << "\n"; }
+
 void PrettyStackTraceProgram::print(raw_ostream &OS) const {
   OS << "Program arguments: ";
   // Print the argument list.
   for (unsigned i = 0, e = ArgC; i != e; ++i)
     OS << ArgV[i] << ' ';
   OS << '\n';
 }