Export of internal Abseil changes

--
0b01bad05b4cdea647ad274d64af0d6732787a1d by Gennadiy Rozental <rogeeff@google.com>:

Internal change

PiperOrigin-RevId: 433124996
Change-Id: I0a081fb5cbb628901e4913a9c587468ca3b3aaa4
GitOrigin-RevId: 0b01bad05b4cdea647ad274d64af0d6732787a1d

absl/debugging/internal/examine_stack.cc

diff --git a/absl/debugging/internal/examine_stack.cc b/absl/debugging/internal/examine_stack.cc
index 2fbfea8..81d216f 100644
--- a/absl/debugging/internal/examine_stack.cc
+++ b/absl/debugging/internal/examine_stack.cc
@@ -37,6 +37,16 @@
 ABSL_NAMESPACE_BEGIN
 namespace debugging_internal {
 
+namespace {
+ABSL_CONST_INIT SymbolizeUrlEmitter debug_stack_trace_hook = nullptr;
+}  // namespace
+
+void RegisterDebugStackTraceHook(SymbolizeUrlEmitter hook) {
+  debug_stack_trace_hook = hook;
+}
+
+SymbolizeUrlEmitter GetDebugStackTraceHook() { return debug_stack_trace_hook; }
+
 // Returns the program counter from signal context, nullptr if
 // unknown. vuc is a ucontext_t*. We use void* to avoid the use of
 // ucontext_t on non-POSIX systems.

absl/debugging/internal/examine_stack.h

diff --git a/absl/debugging/internal/examine_stack.h b/absl/debugging/internal/examine_stack.h
index 3933691..61f0056 100644
--- a/absl/debugging/internal/examine_stack.h
+++ b/absl/debugging/internal/examine_stack.h
@@ -23,6 +23,21 @@
 ABSL_NAMESPACE_BEGIN
 namespace debugging_internal {
 
+// Type of function used for printing in stack trace dumping, etc.
+// We avoid closures to keep things simple.
+typedef void OutputWriter(const char*, void*);
+
+// RegisterDebugStackTraceHook() allows to register a single routine
+// `hook` that is called each time DumpStackTrace() is called.
+// `hook` may be called from a signal handler.
+typedef void (*SymbolizeUrlEmitter)(void* const stack[], int depth,
+                                    OutputWriter writer, void* writer_arg);
+
+// Registration of SymbolizeUrlEmitter for use inside of a signal handler.
+// This is inherently unsafe and must be signal safe code.
+void RegisterDebugStackTraceHook(SymbolizeUrlEmitter hook);
+SymbolizeUrlEmitter GetDebugStackTraceHook();
+
 // Returns the program counter from signal context, or nullptr if
 // unknown. `vuc` is a ucontext_t*. We use void* to avoid the use of
 // ucontext_t on non-POSIX systems.