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Prepare libcxx and libcxxabi for pointer field protection. #151651

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Prepare libcxx and libcxxabi for pointer field protection. #151651

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[𝘀𝗽𝗿] initial version
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21 changes: 20 additions & 1 deletion libcxx/include/__config
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Original file line number Diff line number Diff line change
Expand Up @@ -484,8 +484,21 @@ typedef __char32_t char32_t;
# define _LIBCPP_EXCEPTIONS_SIG e
# endif

# if !_LIBCPP_HAS_EXCEPTIONS
# define _LIBCPP_EXCEPTIONS_SIG n
# else
# define _LIBCPP_EXCEPTIONS_SIG e
# endif

# if defined(__POINTER_FIELD_PROTECTION__)
# define _LIBCPP_PFP_SIG p
# else
# define _LIBCPP_PFP_SIG
# endif
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My understanding is that pfp changes the layout of certain types? Why should there be an ABI tag for it?

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Yes, the in-memory pointer format changes so it's effectively a layout (ABI) change. Therefore we need an ABI tag change to detect/prevent linking against mismatching ABIs. This was requested by @mordante in #133538.

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That's only for ceses where we want different TUs to link together. Since PFP changes the layout of types that's not something we want users to do, which in turn means that we don't want to make it visible in the ABI tag. We should instead change the whole inline namespace.

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Okay, I removed this logic and added CMake logic to modify the namespace name if PFP is enabled.


# define _LIBCPP_ODR_SIGNATURE \
_LIBCPP_CONCAT(_LIBCPP_CONCAT(_LIBCPP_HARDENING_SIG, _LIBCPP_EXCEPTIONS_SIG), _LIBCPP_VERSION)
_LIBCPP_CONCAT(_LIBCPP_CONCAT(_LIBCPP_CONCAT(_LIBCPP_HARDENING_SIG, _LIBCPP_EXCEPTIONS_SIG), _LIBCPP_PFP_SIG), \
_LIBCPP_VERSION)

// This macro marks a symbol as being hidden from libc++'s ABI. This is achieved
// on two levels:
Expand Down Expand Up @@ -1263,6 +1276,12 @@ typedef __char32_t char32_t;
# define _LIBCPP_HAS_EXPLICIT_THIS_PARAMETER 0
# endif

# if __has_cpp_attribute(_Clang::__no_field_protection__)
# define _LIBCPP_NO_PFP [[_Clang::__no_field_protection__]]
# else
# define _LIBCPP_NO_PFP
# endif

#endif // __cplusplus

#endif // _LIBCPP___CONFIG
3 changes: 3 additions & 0 deletions libcxx/include/__type_traits/is_trivially_relocatable.h
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Expand Up @@ -34,10 +34,13 @@ template <class _Tp, class = void>
struct __libcpp_is_trivially_relocatable : is_trivially_copyable<_Tp> {};
#endif

// __trivially_relocatable on libc++'s builtin types does not currently return the right answer with PFP.
#if !defined(__POINTER_FIELD_PROTECTION__)
template <class _Tp>
struct __libcpp_is_trivially_relocatable<_Tp,
__enable_if_t<is_same<_Tp, typename _Tp::__trivially_relocatable>::value> >
: true_type {};
#endif

_LIBCPP_END_NAMESPACE_STD

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2 changes: 1 addition & 1 deletion libcxx/include/typeinfo
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Expand Up @@ -300,7 +300,7 @@ class _LIBCPP_EXPORTED_FROM_ABI _LIBCPP_TYPE_INFO_VTABLE_POINTER_AUTH type_info
protected:
typedef __type_info_implementations::__impl __impl;

__impl::__type_name_t __type_name;
_LIBCPP_NO_PFP __impl::__type_name_t __type_name;

_LIBCPP_HIDE_FROM_ABI explicit type_info(const char* __n) : __type_name(__impl::__string_to_type_name(__n)) {}

Expand Down
6 changes: 6 additions & 0 deletions libcxxabi/include/__cxxabi_config.h
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Expand Up @@ -109,4 +109,10 @@
# define _LIBCXXABI_NOEXCEPT noexcept
#endif

#if defined(__POINTER_FIELD_PROTECTION__)
# define _LIBCXXABI_NO_PFP [[_Clang::__no_field_protection__]]
#else
# define _LIBCXXABI_NO_PFP
#endif

#endif // ____CXXABI_CONFIG_H
6 changes: 3 additions & 3 deletions libcxxabi/src/private_typeinfo.h
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Expand Up @@ -145,7 +145,7 @@ class _LIBCXXABI_TYPE_VIS __class_type_info : public __shim_type_info {
// Has one non-virtual public base class at offset zero
class _LIBCXXABI_TYPE_VIS __si_class_type_info : public __class_type_info {
public:
const __class_type_info *__base_type;
_LIBCXXABI_NO_PFP const __class_type_info *__base_type;

_LIBCXXABI_HIDDEN virtual ~__si_class_type_info();

Expand Down Expand Up @@ -204,7 +204,7 @@ class _LIBCXXABI_TYPE_VIS __vmi_class_type_info : public __class_type_info {
class _LIBCXXABI_TYPE_VIS __pbase_type_info : public __shim_type_info {
public:
unsigned int __flags;
const __shim_type_info *__pointee;
_LIBCXXABI_NO_PFP const __shim_type_info *__pointee;

enum __masks {
__const_mask = 0x1,
Expand Down Expand Up @@ -245,7 +245,7 @@ class _LIBCXXABI_TYPE_VIS __pointer_type_info : public __pbase_type_info {
class _LIBCXXABI_TYPE_VIS __pointer_to_member_type_info
: public __pbase_type_info {
public:
const __class_type_info *__context;
_LIBCXXABI_NO_PFP const __class_type_info *__context;

_LIBCXXABI_HIDDEN virtual ~__pointer_to_member_type_info();
_LIBCXXABI_HIDDEN virtual bool can_catch(const __shim_type_info *,
Expand Down
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