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[libc++][hardening] Allow setting the assertion semantic via CMake. #167636

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Merged
merged 11 commits into from
Nov 14, 2025
Merged

[libc++][hardening] Allow setting the assertion semantic via CMake. #167636

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4a3a6fc
[libc++][hardening] Allow setting the assertion semantic via CMake.
var-const Nov 12, 2025
827c6ab
Fix the check for empty string in `CMakeLists.txt`.
var-const Nov 12, 2025
2a2469b
Fix formatting.
var-const Nov 12, 2025
5208926
- Add new tests to check that the choice of the assertion semantic is
var-const Nov 13, 2025
b0f8174
Make `hardening_dependent` a special value for choosing the assertion
var-const Nov 13, 2025
096249d
CI fixes (formatting, disable semantic-related tests in the C++03 mode)
var-const Nov 13, 2025
9b0daf4
Fix CI (formatting, make semantics tests require experimental)
var-const Nov 13, 2025
f613fde
- Reflect the assertion semantic in the library ABI tag (with a test);
var-const Nov 13, 2025
ae0a272
Address feedback: update documentation, marka test unsupported in C++03.
var-const Nov 14, 2025
76119b1
Fix the check for C++03 in a test
var-const Nov 14, 2025
a6c5e9f
Mark a test as unsupported, take 3
var-const Nov 14, 2025
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22 changes: 22 additions & 0 deletions libcxx/CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -66,6 +66,19 @@ if (NOT "${LIBCXX_HARDENING_MODE}" IN_LIST LIBCXX_SUPPORTED_HARDENING_MODES)
message(FATAL_ERROR
"Unsupported hardening mode: '${LIBCXX_HARDENING_MODE}'. Supported values are ${LIBCXX_SUPPORTED_HARDENING_MODES}.")
endif()
set(LIBCXX_SUPPORTED_ASSERTION_SEMANTICS ignore observe quick_enforce enforce)
set(LIBCXX_ASSERTION_SEMANTIC "" CACHE STRING
"Specify the default assertion semantic to use. This semantic will be used
inside the compiled library and will be the default when compiling user code.
If not defined, the library will select the assertion semantic based on the hardening
mode in effect. Note that users can override this setting in their own code.
This does not affect the ABI. Supported values are
${LIBCXX_SUPPORTED_ASSERTION_SEMANTICS}.")

if (NOT "${LIBCXX_ASSERTION_SEMANTIC}" STREQUAL "" AND NOT "${LIBCXX_ASSERTION_SEMANTIC}" IN_LIST LIBCXX_SUPPORTED_ASSERTION_SEMANTICS)
message(FATAL_ERROR
"Unsupported assertion semantic: '${LIBCXX_ASSERTION_SEMANTIC}'. Supported values are ${LIBCXX_SUPPORTED_ASSERTION_SEMANTICS}.")
endif()
set(LIBCXX_ASSERTION_HANDLER_FILE
"vendor/llvm/default_assertion_handler.in"
CACHE STRING
Expand Down Expand Up @@ -763,6 +776,15 @@ elseif (LIBCXX_HARDENING_MODE STREQUAL "extensive")
elseif (LIBCXX_HARDENING_MODE STREQUAL "debug")
config_define(8 _LIBCPP_HARDENING_MODE_DEFAULT)
endif()
if (LIBCXX_ASSERTION_SEMANTIC STREQUAL "ignore")
config_define(2 _LIBCPP_ASSERTION_SEMANTIC_DEFAULT)
elseif (LIBCXX_ASSERTION_SEMANTIC STREQUAL "observe")
config_define(4 _LIBCPP_ASSERTION_SEMANTIC_DEFAULT)
elseif (LIBCXX_ASSERTION_SEMANTIC STREQUAL "quick_enforce")
config_define(8 _LIBCPP_ASSERTION_SEMANTIC_DEFAULT)
elseif (LIBCXX_ASSERTION_SEMANTIC STREQUAL "enforce")
config_define(16 _LIBCPP_ASSERTION_SEMANTIC_DEFAULT)
endif()

if (LIBCXX_PSTL_BACKEND STREQUAL "serial")
config_define(1 _LIBCPP_PSTL_BACKEND_SERIAL)
Expand Down
1 change: 1 addition & 0 deletions libcxx/include/__config_site.in
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Expand Up @@ -40,6 +40,7 @@

// Hardening.
#cmakedefine _LIBCPP_HARDENING_MODE_DEFAULT @_LIBCPP_HARDENING_MODE_DEFAULT@
#cmakedefine _LIBCPP_ASSERTION_SEMANTIC_DEFAULT @_LIBCPP_ASSERTION_SEMANTIC_DEFAULT@

// __USE_MINGW_ANSI_STDIO gets redefined on MinGW
#ifdef __clang__
Expand Down
128 changes: 75 additions & 53 deletions libcxx/include/__configuration/hardening.h
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Expand Up @@ -7,32 +7,32 @@
//===----------------------------------------------------------------------===//

#ifndef _LIBCPP___CONFIGURATION_HARDENING_H
#define _LIBCPP___CONFIGURATION_HARDENING_H
# define _LIBCPP___CONFIGURATION_HARDENING_H

#include <__config_site>
#include <__configuration/experimental.h>
#include <__configuration/language.h>
# include <__config_site>
# include <__configuration/experimental.h>
# include <__configuration/language.h>

#ifndef _LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER
# pragma GCC system_header
#endif
# ifndef _LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER
# pragma GCC system_header
# endif

// TODO(LLVM 23): Remove this. We're making these an error to catch folks who might not have migrated.
// Since hardening went through several changes (many of which impacted user-facing macros),
// we're keeping these checks around for a bit longer than usual. Failure to properly configure
// hardening results in checks being dropped silently, which is a pretty big deal.
#if defined(_LIBCPP_ENABLE_ASSERTIONS)
# error "_LIBCPP_ENABLE_ASSERTIONS has been removed, please use _LIBCPP_HARDENING_MODE=<mode> instead (see docs)"
#endif
#if defined(_LIBCPP_ENABLE_HARDENED_MODE)
# error "_LIBCPP_ENABLE_HARDENED_MODE has been removed, please use _LIBCPP_HARDENING_MODE=<mode> instead (see docs)"
#endif
#if defined(_LIBCPP_ENABLE_SAFE_MODE)
# error "_LIBCPP_ENABLE_SAFE_MODE has been removed, please use _LIBCPP_HARDENING_MODE=<mode> instead (see docs)"
#endif
#if defined(_LIBCPP_ENABLE_DEBUG_MODE)
# error "_LIBCPP_ENABLE_DEBUG_MODE has been removed, please use _LIBCPP_HARDENING_MODE=<mode> instead (see docs)"
#endif
# if defined(_LIBCPP_ENABLE_ASSERTIONS)
# error "_LIBCPP_ENABLE_ASSERTIONS has been removed, please use _LIBCPP_HARDENING_MODE=<mode> instead (see docs)"
# endif
# if defined(_LIBCPP_ENABLE_HARDENED_MODE)
# error "_LIBCPP_ENABLE_HARDENED_MODE has been removed, please use _LIBCPP_HARDENING_MODE=<mode> instead (see docs)"
# endif
# if defined(_LIBCPP_ENABLE_SAFE_MODE)
# error "_LIBCPP_ENABLE_SAFE_MODE has been removed, please use _LIBCPP_HARDENING_MODE=<mode> instead (see docs)"
# endif
# if defined(_LIBCPP_ENABLE_DEBUG_MODE)
# error "_LIBCPP_ENABLE_DEBUG_MODE has been removed, please use _LIBCPP_HARDENING_MODE=<mode> instead (see docs)"
# endif

// The library provides the macro `_LIBCPP_HARDENING_MODE` which can be set to one of the following values:
//
Expand Down Expand Up @@ -115,25 +115,26 @@
# define _LIBCPP_HARDENING_MODE_DEBUG (1 << 3)
// clang-format on

#ifndef _LIBCPP_HARDENING_MODE
# ifndef _LIBCPP_HARDENING_MODE

# ifndef _LIBCPP_HARDENING_MODE_DEFAULT
# error _LIBCPP_HARDENING_MODE_DEFAULT is not defined. This definition should be set at configuration time in the \
# ifndef _LIBCPP_HARDENING_MODE_DEFAULT
# error _LIBCPP_HARDENING_MODE_DEFAULT is not defined. This definition should be set at configuration time in the \
`__config_site` header, please make sure your installation of libc++ is not broken.
# endif
# endif

# define _LIBCPP_HARDENING_MODE _LIBCPP_HARDENING_MODE_DEFAULT
#endif
# define _LIBCPP_HARDENING_MODE _LIBCPP_HARDENING_MODE_DEFAULT
# endif

#if _LIBCPP_HARDENING_MODE != _LIBCPP_HARDENING_MODE_NONE && _LIBCPP_HARDENING_MODE != _LIBCPP_HARDENING_MODE_FAST && \
_LIBCPP_HARDENING_MODE != _LIBCPP_HARDENING_MODE_EXTENSIVE && \
_LIBCPP_HARDENING_MODE != _LIBCPP_HARDENING_MODE_DEBUG
# error _LIBCPP_HARDENING_MODE must be set to one of the following values: \
# if _LIBCPP_HARDENING_MODE != _LIBCPP_HARDENING_MODE_NONE && \
_LIBCPP_HARDENING_MODE != _LIBCPP_HARDENING_MODE_FAST && \
_LIBCPP_HARDENING_MODE != _LIBCPP_HARDENING_MODE_EXTENSIVE && \
_LIBCPP_HARDENING_MODE != _LIBCPP_HARDENING_MODE_DEBUG
# error _LIBCPP_HARDENING_MODE must be set to one of the following values: \
_LIBCPP_HARDENING_MODE_NONE, \
_LIBCPP_HARDENING_MODE_FAST, \
_LIBCPP_HARDENING_MODE_EXTENSIVE, \
_LIBCPP_HARDENING_MODE_DEBUG
#endif
# endif

// Hardening assertion semantics generally mirror the evaluation semantics of C++26 Contracts:
// - `ignore` evaluates the assertion but doesn't do anything if it fails (note that it differs from the Contracts
Expand All @@ -156,26 +157,47 @@ _LIBCPP_HARDENING_MODE_DEBUG
# define _LIBCPP_ASSERTION_SEMANTIC_ENFORCE (1 << 4)
// clang-format on

// Allow users to define an arbitrary assertion semantic; otherwise, use the default mapping from modes to semantics.
// The default is for production-capable modes to use `quick-enforce` (i.e., trap) and for the `debug` mode to use
// `enforce` (i.e., log and abort).
#ifndef _LIBCPP_ASSERTION_SEMANTIC

# if _LIBCPP_HARDENING_MODE == _LIBCPP_HARDENING_MODE_DEBUG
# define _LIBCPP_ASSERTION_SEMANTIC _LIBCPP_ASSERTION_SEMANTIC_ENFORCE
# else
# define _LIBCPP_ASSERTION_SEMANTIC _LIBCPP_ASSERTION_SEMANTIC_QUICK_ENFORCE
# endif

#else

# if !_LIBCPP_HAS_EXPERIMENTAL_LIBRARY
# error "Assertion semantics are an experimental feature."
# endif
# if defined(_LIBCPP_CXX03_LANG)
# error "Assertion semantics are not available in the C++03 mode."
# endif

#endif // _LIBCPP_ASSERTION_SEMANTIC

#endif // _LIBCPP___CONFIGURATION_HARDENING_H
// If the user or the vendor attempt to configure the assertion semantic, check that it is allowed in the current
// environment.
# if defined(_LIBCPP_ASSERTION_SEMANTIC) || defined(_LIBCPP_ASSERTION_SEMANTIC_DEFAULT)
# if !_LIBCPP_HAS_EXPERIMENTAL_LIBRARY
# error "Assertion semantics are an experimental feature."
# endif
# if defined(_LIBCPP_CXX03_LANG)
# error "Assertion semantics are not available in the C++03 mode."
# endif
# endif // defined(_LIBCPP_ASSERTION_SEMANTIC) || defined(_LIBCPP_ASSERTION_SEMANTIC_DEFAULT)

// There are 2 ways to configure the assertion semantic, listed in order of precedence:
// 1. The `_LIBCPP_ASSERTION_SEMANTIC` macro, defined directly by the user.
// 2. The `LIBCXX_ASSERTION_SEMANTIC` CMake variable, set by the vendor.
// If neither `_LIBCPP_ASSERTION_SEMANTIC` nor `LIBCXX_ASSERTION_SEMANTIC` are defined, the default mapping is used
// which determines the semantic based on the hardening mode in effect: production-capable modes map to `quick-enforce`
// (i.e., trap) and the `debug` mode maps to `enforce` (i.e., log and abort).
# ifndef _LIBCPP_ASSERTION_SEMANTIC // User-provided semantic takes top priority -- don't override if set.

# ifdef _LIBCPP_ASSERTION_SEMANTIC_DEFAULT // Vendor-provided semantic takes second priority.
# define _LIBCPP_ASSERTION_SEMANTIC _LIBCPP_ASSERTION_SEMANTIC_DEFAULT
# else // Fallback: use the default mapping.
# if _LIBCPP_HARDENING_MODE == _LIBCPP_HARDENING_MODE_DEBUG
# define _LIBCPP_ASSERTION_SEMANTIC _LIBCPP_ASSERTION_SEMANTIC_ENFORCE
# else
# define _LIBCPP_ASSERTION_SEMANTIC _LIBCPP_ASSERTION_SEMANTIC_QUICK_ENFORCE
# endif
#endif // ifdef _LIBCPP_ASSERTION_SEMANTIC_DEFAULT

# endif // _LIBCPP_ASSERTION_SEMANTIC

// Finally, validate the selected semantic (in case the user tries setting it to an incorrect value):
# if _LIBCPP_ASSERTION_SEMANTIC != _LIBCPP_ASSERTION_SEMANTIC_IGNORE && \
_LIBCPP_ASSERTION_SEMANTIC != _LIBCPP_ASSERTION_SEMANTIC_OBSERVE && \
_LIBCPP_ASSERTION_SEMANTIC != _LIBCPP_ASSERTION_SEMANTIC_QUICK_ENFORCE && \
_LIBCPP_ASSERTION_SEMANTIC != _LIBCPP_ASSERTION_SEMANTIC_ENFORCE
# error _LIBCPP_ASSERTION_SEMANTIC must be set to one of the following values: \
_LIBCPP_ASSERTION_SEMANTIC_IGNORE, \
_LIBCPP_ASSERTION_SEMANTIC_OBSERVE, \
_LIBCPP_ASSERTION_SEMANTIC_QUICK_ENFORCE, \
_LIBCPP_ASSERTION_SEMANTIC_ENFORCE
# endif

# endif // _LIBCPP___CONFIGURATION_HARDENING_H
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