folly::symbolizer::UnsafeSelfAllocateStackTracePrinter Class Reference

#include <Symbolizer.h>

Inheritance diagram for folly::symbolizer::UnsafeSelfAllocateStackTracePrinter:

Protected Member Functions
void	printSymbolizedStackTrace () override

Protected Attributes
const long	pageSizeUnchecked_ = sysconf(_SC_PAGESIZE)

Additional Inherited Members
Public Member Functions inherited from folly::symbolizer::SafeStackTracePrinter
	SafeStackTracePrinter (size_t minSignalSafeElfCacheSize=kDefaultMinSignalSafeElfCacheSize, int fd=STDERR_FILENO)
virtual	~SafeStackTracePrinter ()
FOLLY_NOINLINE void	printStackTrace (bool symbolize)
void	print (StringPiece sp)
void	flush ()
Static Public Attributes inherited from folly::symbolizer::SafeStackTracePrinter
static constexpr size_t	kDefaultMinSignalSafeElfCacheSize = 500

Detailed Description

Use this class in rare situations where signal handlers are running in a tiny stack specified by sigaltstack.

This is neither thread-safe nor signal-safe. However, it can usually print something useful while SafeStackTracePrinter would stack overflow.

Signal handlers would need to block other signals to make this safer. Note it's still unsafe even with that.

Definition at line 434 of file Symbolizer.h.

Member Function Documentation

void folly::symbolizer::UnsafeSelfAllocateStackTracePrinter::printSymbolizedStackTrace ( )

overrideprotectedvirtual

Reimplemented from folly::symbolizer::SafeStackTracePrinter.

Definition at line 563 of file Symbolizer.cpp.

                                                                    {
  if (pageSizeUnchecked_ <= 0) {
    return;
  }

  ucontext_t cur;
  memset(&cur, 0, sizeof(cur));
  ucontext_t alt;
  memset(&alt, 0, sizeof(alt));

  if (getcontext(&alt) != 0) {
    return;
  }
  alt.uc_link = &cur;

  MmapPtr p = allocateStack(&alt, (size_t)pageSizeUnchecked_);
  if (!p) {
    return;
  }

  auto contextStart = [](UnsafeSelfAllocateStackTracePrinter* that) {
    that->SafeStackTracePrinter::printSymbolizedStackTrace();
  };

  makecontext(
      &alt,
      (void (*)())(void (*)(UnsafeSelfAllocateStackTracePrinter*))(
          contextStart),
      /* argc */ 1,
      /* arg */ this);
  // NOTE: swapcontext is not async-signal-safe
  if (swapcontext(&cur, &alt) != 0) {
    return;
  }
}

Member Data Documentation

const long folly::symbolizer::UnsafeSelfAllocateStackTracePrinter::pageSizeUnchecked_ = sysconf(_SC_PAGESIZE)

protected

Definition at line 437 of file Symbolizer.h.

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The documentation for this class was generated from the following files:

• proxygen/folly/folly/experimental/symbolizer/Symbolizer.h
• proxygen/folly/folly/experimental/symbolizer/Symbolizer.cpp