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[libc] Support configurable errno modes (#98287)
Rather than selecting the errno implementation based on the platform which doesn't provide the necessary flexibility, make it configurable. The errno value location is returned by `int *__llvm_libc_errno()` which is a common design used by other C libraries.
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9 files changed

+117
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lines changed

‎libc/config/baremetal/config.json

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{
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"errno": {
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"LIBC_CONF_ERRNO_MODE": {
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"value": "LIBC_ERRNO_MODE_EXTERNAL"
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}
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},
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"printf": {
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"LIBC_CONF_PRINTF_DISABLE_FLOAT": {
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"value": true

‎libc/config/config.json

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{
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"errno": {
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"LIBC_CONF_ERRNO_MODE": {
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"value": "",
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"doc": "The implementation used for errno, acceptable values are LIBC_ERRNO_MODE_UNDEFINED, LIBC_ERRNO_MODE_THREAD_LOCAL, LIBC_ERRNO_MODE_SHARED, LIBC_ERRNO_MODE_EXTERNAL, and LIBC_ERRNO_MODE_SYSTEM."
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}
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},
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"printf": {
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"LIBC_CONF_PRINTF_DISABLE_FLOAT": {
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"value": false,

‎libc/config/gpu/config.json

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{
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"errno": {
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"LIBC_CONF_ERRNO_MODE": {
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"value": "LIBC_ERRNO_MODE_SHARED"
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}
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},
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"printf": {
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"LIBC_CONF_PRINTF_DISABLE_FLOAT": {
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"value": true

‎libc/docs/configure.rst

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@@ -28,6 +28,8 @@ to learn about the defaults for your platform and target.
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* **"codegen" options**
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- ``LIBC_CONF_ENABLE_STRONG_STACK_PROTECTOR``: Enable -fstack-protector-strong to defend against stack smashing attack.
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- ``LIBC_CONF_KEEP_FRAME_POINTER``: Keep frame pointer in functions for better debugging experience.
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* **"errno" options**
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- ``LIBC_CONF_ERRNO_MODE``: The implementation used for errno, acceptable values are LIBC_ERRNO_MODE_UNDEFINED, LIBC_ERRNO_MODE_THREAD_LOCAL, LIBC_ERRNO_MODE_SHARED, LIBC_ERRNO_MODE_EXTERNAL, and LIBC_ERRNO_MODE_SYSTEM.
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* **"malloc" options**
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- ``LIBC_CONF_FREELIST_MALLOC_BUFFER_SIZE``: Default size for the constinit freelist buffer used for the freelist malloc implementation (default 1o 1GB).
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* **"math" options**

‎libc/include/errno.h.def

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@@ -25,18 +25,12 @@
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#include "llvm-libc-macros/generic-error-number-macros.h"
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#endif
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#if defined(__AMDGPU__) || defined(__NVPTX__)
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extern int __llvmlibc_errno; // Not thread_local!
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#else
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#ifdef __cplusplus
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extern "C" {
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extern thread_local int __llvmlibc_errno;
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}
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#else
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extern _Thread_local int __llvmlibc_errno;
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#endif // __cplusplus
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#endif
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__BEGIN_C_DECLS
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int *__llvm_libc_errno(void) __NOEXCEPT;
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__END_C_DECLS
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#define errno __llvmlibc_errno
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#define errno (*__llvm_libc_errno())
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#endif // LLVM_LIBC_ERRNO_H

‎libc/src/errno/CMakeLists.txt

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@@ -9,14 +9,20 @@ if(LLVM_LIBC_FULL_BUILD)
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set(full_build_flag "-DLIBC_FULL_BUILD")
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endif()
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if(LIBC_CONF_ERRNO_MODE)
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set(errno_config_copts "-DLIBC_ERRNO_MODE=${LIBC_CONF_ERRNO_MODE}")
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endif()
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add_entrypoint_object(
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errno
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SRCS
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libc_errno.cpp
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HDRS
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errno.h
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libc_errno.h # Include this
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COMPILE_OPTIONS
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${full_build_flag}
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${errno_config_copts}
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DEPENDS
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libc.hdr.errno_macros
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libc.src.__support.common

‎libc/src/errno/errno.h

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@@ -0,0 +1,14 @@
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//===-- Implementation header for errno -------------------------*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_LIBC_SRC_ERRNO_ERRNO_H
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#define LLVM_LIBC_SRC_ERRNO_ERRNO_H
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extern "C" int *__llvm_libc_errno();
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#endif // LLVM_LIBC_SRC_ERRNO_ERRNO_H

‎libc/src/errno/libc_errno.cpp

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@@ -7,47 +7,90 @@
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//===----------------------------------------------------------------------===//
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#include "libc_errno.h"
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#include "src/__support/CPP/atomic.h"
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#include "src/errno/errno.h"
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#include "src/__support/macros/config.h"
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#ifdef LIBC_TARGET_ARCH_IS_GPU
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// LIBC_THREAD_LOCAL on GPU currently does nothing. So essentially this is just
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// a global errno for gpu to use for now.
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extern "C" {
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LIBC_THREAD_LOCAL LIBC_NAMESPACE::cpp::Atomic<int> __llvmlibc_errno;
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}
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// libc never stores a value; `errno` macro uses get link-time failure.
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#define LIBC_ERRNO_MODE_UNDEFINED 1
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// libc maintains per-thread state (requires C++ `thread_local` support).
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#define LIBC_ERRNO_MODE_THREAD_LOCAL 2
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// libc maintains shared state used by all threads, contrary to standard C
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// semantics unless always single-threaded; nothing prevents data races.
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#define LIBC_ERRNO_MODE_SHARED 3
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// libc doesn't maintain any internal state, instead the embedder must define
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// `int *__llvm_libc_errno(void);` C function.
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#define LIBC_ERRNO_MODE_EXTERNAL 4
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// libc uses system `<errno.h>` `errno` macro directly in the overlay mode; in
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// fullbuild mode, effectively the same as `LIBC_ERRNO_MODE_EXTERNAL`.
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#define LIBC_ERRNO_MODE_SYSTEM 5
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#ifndef LIBC_ERRNO_MODE
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#if defined(LIBC_FULL_BUILD) || !defined(LIBC_COPT_PUBLIC_PACKAGING)
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#define LIBC_ERRNO_MODE LIBC_ERRNO_MODE_THREAD_LOCAL
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#else
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#define LIBC_ERRNO_MODE LIBC_ERRNO_MODE_SYSTEM
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#endif
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#endif // LIBC_ERRNO_MODE
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#if LIBC_ERRNO_MODE != LIBC_ERRNO_MODE_UNDEFINED && \
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LIBC_ERRNO_MODE != LIBC_ERRNO_MODE_THREAD_LOCAL && \
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LIBC_ERRNO_MODE != LIBC_ERRNO_MODE_SHARED && \
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LIBC_ERRNO_MODE != LIBC_ERRNO_MODE_EXTERNAL && \
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LIBC_ERRNO_MODE != LIBC_ERRNO_MODE_SYSTEM
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#error LIBC_ERRNO_MODE must be one of the following values: \
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LIBC_ERRNO_MODE_UNDEFINED, \
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LIBC_ERRNO_MODE_THREAD_LOCAL, \
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LIBC_ERRNO_MODE_SHARED, \
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LIBC_ERRNO_MODE_EXTERNAL, \
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LIBC_ERRNO_MODE_SYSTEM
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#endif
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namespace LIBC_NAMESPACE_DECL {
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// Define the global `libc_errno` instance.
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Errno libc_errno;
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#if LIBC_ERRNO_MODE == LIBC_ERRNO_MODE_UNDEFINED
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void Errno::operator=(int) {}
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Errno::operator int() { return 0; }
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void LIBC_NAMESPACE::Errno::operator=(int a) {
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__llvmlibc_errno.store(a, cpp::MemoryOrder::RELAXED);
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#elif LIBC_ERRNO_MODE == LIBC_ERRNO_MODE_THREAD_LOCAL
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60+
namespace {
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LIBC_THREAD_LOCAL int thread_errno;
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}
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LIBC_NAMESPACE::Errno::operator int() {
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return __llvmlibc_errno.load(cpp::MemoryOrder::RELAXED);
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64+
extern "C" {
65+
int *__llvm_libc_errno() { return &thread_errno; }
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}
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27-
#elif !defined(LIBC_COPT_PUBLIC_PACKAGING)
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// This mode is for unit testing. We just use our internal errno.
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LIBC_THREAD_LOCAL int __llvmlibc_internal_errno;
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void Errno::operator=(int a) { thread_errno = a; }
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Errno::operator int() { return thread_errno; }
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void LIBC_NAMESPACE::Errno::operator=(int a) { __llvmlibc_internal_errno = a; }
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LIBC_NAMESPACE::Errno::operator int() { return __llvmlibc_internal_errno; }
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#elif LIBC_ERRNO_MODE == LIBC_ERRNO_MODE_SHARED
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namespace {
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int shared_errno;
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}
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#elif defined(LIBC_FULL_BUILD)
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// This mode is for public libc archive, hermetic, and integration tests.
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// In full build mode, we provide the errno storage ourselves.
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extern "C" {
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LIBC_THREAD_LOCAL int __llvmlibc_errno;
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int *__llvm_libc_errno() { return &shared_errno; }
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}
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void LIBC_NAMESPACE::Errno::operator=(int a) { __llvmlibc_errno = a; }
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LIBC_NAMESPACE::Errno::operator int() { return __llvmlibc_errno; }
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void Errno::operator=(int a) { shared_errno = a; }
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Errno::operator int() { return shared_errno; }
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#else
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void LIBC_NAMESPACE::Errno::operator=(int a) { errno = a; }
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LIBC_NAMESPACE::Errno::operator int() { return errno; }
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#elif LIBC_ERRNO_MODE == LIBC_ERRNO_MODE_EXTERNAL
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#endif // LIBC_FULL_BUILD
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void Errno::operator=(int a) { *__llvm_libc_errno() = a; }
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Errno::operator int() { return *__llvm_libc_errno(); }
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#elif LIBC_ERRNO_MODE == LIBC_ERRNO_MODE_SYSTEM
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void Errno::operator=(int a) { errno = a; }
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Errno::operator int() { return errno; }
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#endif
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namespace LIBC_NAMESPACE_DECL {
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// Define the global `libc_errno` instance.
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Errno libc_errno;
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} // namespace LIBC_NAMESPACE_DECL

‎libc/src/errno/libc_errno.h

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// - Still depend on libc.src.errno.errno
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namespace LIBC_NAMESPACE_DECL {
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struct Errno {
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void operator=(int);
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operator int();

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