[libc] Use Linux errno and signal strings for Fuchsia

[mcgrathr]

Summary

The exact set of supported values is determined by the <errno.h>
and <signal.h> headers, which don't (yet) come from llvm-libc on
Fuchsia. The mappings of SIG* and E* codes to psignal/strsignal
and perror/strerror text used in Fuchsia libc today is the same
as for Linux.

[sivachandra]

libc/src/__support/StringUtil/tables/error_table.h

32

If the else path is taken here, then LINUX_ERRORS will not be included and will lead to a build error. Do you have any suggestions on how to handle this? Following is an idea that comes to my mind.

I prefer to reduce the number of conditionals and use a more explicit structure like this.

1. The errors, as specified by the various [de facto] standards, can stay as they are today:

tables/
    stdc_errors.h
    posix_errors.h
    linux_extension_errors.h

2. We will add couple more tables (more can be added in future):

tables/
    ...
    linux_platform_errors.h
    minimal_platform_errors.h

3. linux_platform_errors.h will include stdc_errors.h,posix_errors.h and linux_extension_errors.h and define PLATFORM_ERRORS as

PLATFORM_ERRORS = STDC_ERRORS + POSIX_ERRORS + LINUX_ERRORS;

4. minimal_platform_errors.h will include only stdc_errors.h and define PLATFORM_ERRORS as:

PLATFORM_ERRORS = STDC_ERRORS;

5. In the parent directly, we will add a new file named platform_errors.h which will have the following structure:

#if defined(__linux__) || defined(__Fuchsia__)
#include "tables/linux_platform_errors.h"
#else
#include "tables/minimal_platform_errors.h"
#endif

In effect, there is only one condtional confined to platform_errors.h.

[mcgrathr]

libc/src/__support/StringUtil/tables/error_table.h

32

That sounds fine to me.

libc/src/__support/StringUtil/tables/error_table.h

 //===-- Map from error numbers to strings -----------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_LIBC_SRC_SUPPORT_STRING_UTIL_TABLES_ERROR_TABLE_H
 #define LLVM_LIBC_SRC_SUPPORT_STRING_UTIL_TABLES_ERROR_TABLE_H
 
 #include "src/__support/StringUtil/message_mapper.h"
 
 #include "posix_error_table.h"
 #include "stdc_error_table.h"
 
-#ifdef __linux__
+#if defined(__linux__) || defined(__Fuchsia__)
+#define USE_LINUX_PLATFORM_ERRORS 1
+#else
+#define USE_LINUX_PLATFORM_ERRORS 0
+#endif
+
+#if USE_LINUX_PLATFORM_ERRORS
 #include "linux/error_table.h"
 #endif
 
 namespace __llvm_libc::internal {
 
-#ifdef __linux__
-inline constexpr auto PLATFORM_ERRORS =
-    STDC_ERRORS + POSIX_ERRORS + LINUX_ERRORS;
-#else
-inline constexpr auto PLATFORM_ERRORS = STDC_ERRORS;
-#endif
+inline constexpr auto PLATFORM_ERRORS = []() {
+  if constexpr (USE_LINUX_PLATFORM_ERRORS) {
+    return STDC_ERRORS + POSIX_ERRORS + LINUX_ERRORS;
+  } else {
+    return STDC_ERRORS;
+  }
+}();
 
 } // namespace __llvm_libc::internal
 
 #endif // LLVM_LIBC_SRC_SUPPORT_STRING_UTIL_TABLES_ERROR_TABLE_H

libc/src/__support/StringUtil/tables/signal_table.h

 //===-- Map from signal numbers to strings ----------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_LIBC_SRC_SUPPORT_STRING_UTIL_TABLES_SIGNAL_TABLE_H
 #define LLVM_LIBC_SRC_SUPPORT_STRING_UTIL_TABLES_SIGNAL_TABLE_H
 
 #include "src/__support/StringUtil/message_mapper.h"
 
 #include "posix_signal_table.h"
 #include "stdc_signal_table.h"
 
-#ifdef __linux__
+#if defined(__linux__) || defined(__Fuchsia__)
+#define USE_LINUX_PLATFORM_SIGNALS 1
+#else
+#define USE_LINUX_PLATFORM_SIGNALS 0
+#endif
+
+#if USE_LINUX_PLATFORM_SIGNALS
 #include "linux/signal_table.h"
 #endif
 
 namespace __llvm_libc::internal {
 
-#ifdef __linux__
-inline constexpr auto PLATFORM_SIGNALS =
-    STDC_SIGNALS + POSIX_SIGNALS + LINUX_SIGNALS;
-#else
-inline constexpr auto PLATFORM_SIGNALS = STDC_SIGNALS;
-#endif
+inline constexpr auto PLATFORM_SIGNALS = []() {
+  if constexpr (USE_LINUX_PLATFORM_SIGNALS) {
+    return STDC_SIGNALS + POSIX_SIGNALS + LINUX_SIGNALS;
+  } else {
+    return STDC_SIGNALS;
+  }
+}();
 
 } // namespace __llvm_libc::internal
 
 #endif // LLVM_LIBC_SRC_SUPPORT_STRING_UTIL_TABLES_SIGNAL_TABLE_H