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I've added Apple-only behavior that looks for libstdc++ in the same process and if found, checks the string stored in <stdexcept> exception objects to see if it is the gcc empty string singleton before manipulating the reference count. This is done so that if such an exception is created with a zero-length string in libstdc++, libc++abi won't try to delete the memory. This is part of a ongoing process to make libc++ exceptions ABI-compatible with libstdc++-4.2 exceptions, to the point that each library can catch exceptions thrown by the other. If other parties would also like this behavior, the #if __APPLE__ can be broadened.

Browse Source 
llvm-svn: 164170
This commit is contained in:
Howard Hinnant 2012-09-18 21:34:12 +00:00
parent 1de7ec8c7c
commit e115af2777
1 changed files with 44 additions and 6 deletions
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50
libcxxabi/src/stdexcept.cpp
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@ -14,6 +14,11 @@
#include <cstdint>
#include <cstddef>
#if __APPLE__
#include <dlfcn.h>
#include <mach-o/dyld.h>
#endif
// Note: optimize for size
#pragma GCC visibility push(hidden)
@ -33,6 +38,27 @@ private:
sizeof(count_t));
count_t& count() const _NOEXCEPT {return (count_t&)(*(str_ - sizeof(count_t)));}
#if __APPLE__
static
const void*
compute_gcc_empty_string_storage() _LIBCPP_CANTTHROW
{
void* handle = dlopen("libstdc++.dylib", RTLD_LAZY);
if (handle == 0)
return 0;
return (const char*)dlsym(handle, "_ZNSs4_Rep20_S_empty_rep_storageE") + offset;
}
static
const void*
get_gcc_empty_string_storage() _LIBCPP_CANTTHROW
{
static const void* p = compute_gcc_empty_string_storage();
return p;
}
#endif
public:
explicit __libcpp_nmstr(const char* msg);
__libcpp_nmstr(const __libcpp_nmstr& s) _LIBCPP_CANTTHROW;
@ -56,7 +82,10 @@ inline
__libcpp_nmstr::__libcpp_nmstr(const __libcpp_nmstr& s)
: str_(s.str_)
{
__sync_add_and_fetch(&count(), 1);
#if __APPLE__
if (str_ != get_gcc_empty_string_storage())
#endif
__sync_add_and_fetch(&count(), 1);
}
__libcpp_nmstr&
@ -64,17 +93,26 @@ __libcpp_nmstr::operator=(const __libcpp_nmstr& s)
{
const char* p = str_;
str_ = s.str_;
__sync_add_and_fetch(&count(), 1);
if (__sync_add_and_fetch((count_t*)(p-sizeof(count_t)), count_t(-1)) < 0)
delete [] (p-offset);
#if __APPLE__
if (str_ != get_gcc_empty_string_storage())
#endif
__sync_add_and_fetch(&count(), 1);
#if __APPLE__
if (p != get_gcc_empty_string_storage())
#endif
if (__sync_add_and_fetch((count_t*)(p-sizeof(count_t)), count_t(-1)) < 0)
delete [] (p-offset);
return *this;
}
inline
__libcpp_nmstr::~__libcpp_nmstr()
{
if (__sync_add_and_fetch(&count(), count_t(-1)) < 0)
delete [] (str_ - offset);
#if __APPLE__
if (str_ != get_gcc_empty_string_storage())
#endif
if (__sync_add_and_fetch(&count(), count_t(-1)) < 0)
delete [] (str_ - offset);
}
}