[libc-commits] [libc] [libc] Support configurable errno modes (PR #98287)

[Petr Hosek via libc-commits]

================
@@ -9,44 +9,91 @@
 #include "libc_errno.h"
 #include "src/__support/CPP/atomic.h"
 
-#ifdef LIBC_TARGET_ARCH_IS_GPU
-// LIBC_THREAD_LOCAL on GPU currently does nothing. So essentially this is just
-// a global errno for gpu to use for now.
+#define LIBC_ERRNO_MODE_UNDEFINED 0x01
+#define LIBC_ERRNO_MODE_THREAD_LOCAL 0x02
+#define LIBC_ERRNO_MODE_GLOBAL 0x04
+#define LIBC_ERRNO_MODE_EXTERNAL 0x08
+#define LIBC_ERRNO_MODE_SYSTEM 0x10
+
+#ifndef LIBC_ERRNO_MODE
+#ifndef LIBC_COPT_PUBLIC_PACKAGING
+// This mode is for unit testing. We just use our internal errno.
+#define LIBC_ERRNO_MODE LIBC_ERRNO_MODE_INTERNAL
+#elif defined(LIBC_FULL_BUILD)
+// In full build mode, we provide the errno storage ourselves.
+#define LIBC_ERRNO_MODE LIBC_ERRNO_MODE_THREAD_LOCAL
+#else
+#define LIBC_ERRNO_MODE LIBC_ERRNO_MODE_SYSTEM
+#endif
+#endif // LIBC_ERRNO_MODE
+
+#if LIBC_ERRNO_MODE != LIBC_ERRNO_MODE_UNDEFINED &&                            \
+    LIBC_ERRNO_MODE != LIBC_ERRNO_MODE_THREAD_LOCAL &&                         \
+    LIBC_ERRNO_MODE != LIBC_ERRNO_MODE_GLOBAL &&                               \
+    LIBC_ERRNO_MODE != LIBC_ERRNO_MODE_EXTERNAL &&                             \
+    LIBC_ERRNO_MODE != LIBC_ERRNO_MODE_SYSTEM
+#error LIBC_ERRNO_MODE must be one of the following values: \
+LIBC_ERRNO_MODE_NONE, \
+LIBC_ERRNO_MODE_THREAD_LOCAL, \
+LIBC_ERRNO_MODE_GLOBAL, \
+LIBC_ERRNO_MODE_EXTERNAL, \
+LIBC_ERRNO_MODE_SYSTEM
+#endif
+
+namespace LIBC_NAMESPACE {
+
+// Define the global `libc_errno` instance.
+Errno libc_errno;
+
+#if LIBC_ERRNO_MODE == LIBC_ERRNO_MODE_UNDEFINED
+
+void Errno::operator=(int) {}
+Errno::operator int() { return 0; }
+
+#elif LIBC_ERRNO_MODE == LIBC_ERRNO_MODE_THREAD_LOCAL
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petrhosek wrote:

Ack.

https://github.com/llvm/llvm-project/pull/98287