| /* |
| * Copyright (C) 2006 The Android Open Source Project |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| #include<endian.h> |
| #include<limits.h> |
| #include<stdatomic.h> |
| #include<stddef.h> |
| |
| #include"private/bionic_futex.h" |
| |
| // This file contains C++ ABI support functions for one time |
| // constructors as defined in the "Run-time ABI for the ARM Architecture" |
| // section 4.4.2 |
| // |
| // ARM C++ ABI and Itanium/x86 C++ ABI has different definition for |
| // one time construction: |
| // |
| // ARM C++ ABI defines the LSB of guard variable should be tested |
| // by compiler-generated code before calling __cxa_guard_acquire et al. |
| // |
| // The Itanium/x86 C++ ABI defines the low-order _byte_ should be |
| // tested instead. |
| // |
| // Meanwhile, guard variable are 32bit aligned for ARM, and 64bit |
| // aligned for x86. |
| // |
| // Reference documentation: |
| // |
| // section 3.2.3 of ARM IHI 0041C (for ARM) |
| // section 3.3.2 of the Itanium C++ ABI specification v1.83 (for x86). |
| // |
| // There is no C++ ABI available for other ARCH. But the gcc source |
| // shows all other ARCH follow the definition of Itanium/x86 C++ ABI. |
| |
| #if defined(__arm__) |
| // The ARM C++ ABI mandates that guard variables are 32-bit aligned, 32-bit |
| // values. The LSB is tested by the compiler-generated code before calling |
| // __cxa_guard_acquire. |
| union_guard_t{ |
| atomic_int state; |
| int32_t aligner; |
| }; |
| |
| #else |
| // The Itanium/x86 C++ ABI (used by all other architectures) mandates that |
| // guard variables are 64-bit aligned, 64-bit values. The LSB is tested by |
| // the compiler-generated code before calling __cxa_guard_acquire. |
| union_guard_t{ |
| atomic_int state; |
| int64_t aligner; |
| }; |
| |
| #endif |
| |
| // Set construction state values according to reference documentation. |
| // 0 is the initialization value. |
| // Arm requires ((*gv & 1) == 1) after __cxa_guard_release, ((*gv & 3) == 0) after __cxa_guard_abort. |
| // X86 requires first byte not modified by __cxa_guard_acquire, first byte is non-zero after |
| // __cxa_guard_release. |
| |
| #define CONSTRUCTION_NOT_YET_STARTED0 |
| #define CONSTRUCTION_COMPLETE1 |
| #define CONSTRUCTION_UNDERWAY_WITHOUT_WAITER0x100 |
| #define CONSTRUCTION_UNDERWAY_WITH_WAITER0x200 |
| |
| extern"C"int __cxa_guard_acquire(_guard_t* gv){ |
| int old_value= atomic_load_explicit(&gv->state, memory_order_acquire); |
| // In the common CONSTRUCTION_COMPLETE case we have to ensure that all the stores performed by |
| // the construction function are observable on this CPU after we exit. A similar constraint may |
| // apply in the CONSTRUCTION_NOT_YET_STARTED case with a prior abort. |
| |
| while(true){ |
| if(old_value== CONSTRUCTION_COMPLETE){ |
| return0; |
| }elseif(old_value== CONSTRUCTION_NOT_YET_STARTED){ |
| if(!atomic_compare_exchange_weak_explicit(&gv->state,&old_value, |
| CONSTRUCTION_UNDERWAY_WITHOUT_WAITER, |
| memory_order_acquire/* or relaxed in C++17 */, |
| memory_order_acquire)){ |
| continue; |
| } |
| return1; |
| }elseif(old_value== CONSTRUCTION_UNDERWAY_WITHOUT_WAITER){ |
| if(!atomic_compare_exchange_weak_explicit(&gv->state,&old_value, |
| CONSTRUCTION_UNDERWAY_WITH_WAITER, |
| memory_order_acquire/* or relaxed in C++17 */, |
| memory_order_acquire)){ |
| continue; |
| } |
| } |
| |
| __futex_wait_ex(&gv->state,false, CONSTRUCTION_UNDERWAY_WITH_WAITER); |
| old_value= atomic_load_explicit(&gv->state, memory_order_acquire); |
| } |
| } |
| |
| extern"C"void __cxa_guard_release(_guard_t* gv){ |
| // Release fence is used to make all stores performed by the construction function |
| // visible in other threads. |
| int old_value= atomic_exchange_explicit(&gv->state, CONSTRUCTION_COMPLETE, memory_order_release); |
| if(old_value== CONSTRUCTION_UNDERWAY_WITH_WAITER){ |
| __futex_wake_ex(&gv->state,false, INT_MAX); |
| } |
| } |
| |
| extern"C"void __cxa_guard_abort(_guard_t* gv){ |
| // Release fence is used to make all stores performed by the construction function |
| // visible in other threads. |
| int old_value= atomic_exchange_explicit(&gv->state, CONSTRUCTION_NOT_YET_STARTED, memory_order_release); |
| if(old_value== CONSTRUCTION_UNDERWAY_WITH_WAITER){ |
| __futex_wake_ex(&gv->state,false, INT_MAX); |
| } |
| } |
