[libcxx-commits] [libcxx] [libc++] Support file offsets larger than 2GB in basic_filebuf on 32-bit AIX and 32-bit glibc Linux (PR #215892)

[Hubert Tong via libcxx-commits]

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@@ -217,6 +217,20 @@ typedef basic_fstream<wchar_t> wfstream;
 #      pragma GCC system_header
 #    endif
 
+#    if defined(_AIX) || (defined(__linux__) && defined(__GLIBC__))
+#      define _LIBCPP_HAS_LARGEFILE_API 1
+#    else
+#      define _LIBCPP_HAS_LARGEFILE_API 0
+#    endif
+
+#    if _LIBCPP_HAS_LARGEFILE_API
+// On AIX and glibc on Linux, fopen64/fseeko64/ftello64 are not guaranteed to always be declared, so we declare them
+// here. They are not POSIX-reserved names, so we use __asm__ to guard them against a user #define.
+extern "C" FILE* __libcpp_fopen64(const char*, const char*) __asm__("fopen64");
+extern "C" long long __libcpp_ftello64(FILE*) __asm__("ftello64");
+extern "C" int __libcpp_fseeko64(FILE*, long long, int) __asm__("fseeko64");
+#    endif
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hubert-reinterpretcast wrote:

Adding declarations that we can use for the APIs is not really avoidable for AIX because the strategy of some porting efforts to AIX (including for C++ code that would be used with libc++) make use of "clean", non-namespace polluting configurations of the system headers (to avoid conflicts). Such header configurations do not declare these non-reserved names.

@philnik777, would you prefer if these were simply of the non-reserved names (opening the source to conflicts with user macros or declarations—say of something reasonable like a file-scope static variable that is a function pointer)? That way, at least the call sites between the glibc and the AIX cases can be common.

https://github.com/llvm/llvm-project/pull/215892