[flang] Handle missing LOGIN_NAME_MAX definition in runtime

[rorth]

18af032 broke the Solaris build:

/vol/llvm/src/llvm-project/dist/flang/runtime/extensions.cpp:60:24: error: use of undeclared identifier 'LOGIN_NAME_MAX'
   60 |   const int nameMaxLen{LOGIN_NAME_MAX + 1};
      |                        ^
/vol/llvm/src/llvm-project/dist/flang/runtime/extensions.cpp:61:12: warning: variable length arrays in C++ are a Clang extension [-Wvla-cxx-extension]
   61 |   char str[nameMaxLen];
      |            ^~~~~~~~~~
/vol/llvm/src/llvm-project/dist/flang/runtime/extensions.cpp:61:12: note: initializer of 'nameMaxLen' is unknown
/vol/llvm/src/llvm-project/dist/flang/runtime/extensions.cpp:60:13: note: declared here
   60 |   const int nameMaxLen{LOGIN_NAME_MAX + 1};
      |             ^

flang/unittests/Runtime/CommandTest.cpp has the same issue.

As documented in Solaris 11.4 limits.h(3HEAD), LOGIN_NAME_MAX can be undefined. To determine the value, sysconf(3C) needs to be used instead.

Beside that portable method, Solaris also provides a non-standard LOGNAME_MAX which could be used, but I've preferred the standard route instead which would support other targets with the same issue.

Tested on amd64-pc-solaris2.11 and x86_64-pc-linux-gnu.

[llvmbot]

@llvm/pr-subscribers-flang-runtime

Author: Rainer Orth (rorth)

Changes

18af032 broke the Solaris build:

/vol/llvm/src/llvm-project/dist/flang/runtime/extensions.cpp:60:24: error: use of undeclared identifier 'LOGIN_NAME_MAX'
   60 |   const int nameMaxLen{LOGIN_NAME_MAX + 1};
      |                        ^
/vol/llvm/src/llvm-project/dist/flang/runtime/extensions.cpp:61:12: warning: variable length arrays in C++ are a Clang extension [-Wvla-cxx-extension]
   61 |   char str[nameMaxLen];
      |            ^~~~~~~~~~
/vol/llvm/src/llvm-project/dist/flang/runtime/extensions.cpp:61:12: note: initializer of 'nameMaxLen' is unknown
/vol/llvm/src/llvm-project/dist/flang/runtime/extensions.cpp:60:13: note: declared here
   60 |   const int nameMaxLen{LOGIN_NAME_MAX + 1};
      |             ^

flang/unittests/Runtime/CommandTest.cpp has the same issue.

As documented in Solaris 11.4 limits.h(3HEAD), LOGIN_NAME_MAX can be undefined. To determine the value, sysconf(3C) needs to be used instead.

Beside that portable method, Solaris also provides a non-standard LOGNAME_MAX which could be used, but I've preferred the standard route instead which would support other targets with the same issue.

Tested on amd64-pc-solaris2.11 and x86_64-pc-linux-gnu.

---

Full diff: https://github.com/llvm/llvm-project/pull/77775.diff

2 Files Affected:

• (modified) flang/runtime/extensions.cpp (+8-1)
• (modified) flang/unittests/Runtime/CommandTest.cpp (+8-1)

diff --git a/flang/runtime/extensions.cpp b/flang/runtime/extensions.cpp
index 1c025d40b39524..d8fd2dff27742f 100644
--- a/flang/runtime/extensions.cpp
+++ b/flang/runtime/extensions.cpp
@@ -57,7 +57,14 @@ void FORTRAN_PROCEDURE_NAME(getarg)(
 // CALL GETLOG(USRNAME)
 void FORTRAN_PROCEDURE_NAME(getlog)(std::byte *arg, std::int64_t length) {
 #if _REENTRANT || _POSIX_C_SOURCE >= 199506L
-  const int nameMaxLen{LOGIN_NAME_MAX + 1};
+  int nameMaxLen;
+#ifdef LOGIN_NAME_MAX
+  nameMaxLen = LOGIN_NAME_MAX + 1;
+#else
+  nameMaxLen = sysconf(_SC_LOGIN_NAME_MAX) + 1;
+  if (nameMaxLen == -1)
+    nameMaxLen = _POSIX_LOGIN_NAME_MAX + 1;
+#endif
   char str[nameMaxLen];
 
   int error{getlogin_r(str, nameMaxLen)};
diff --git a/flang/unittests/Runtime/CommandTest.cpp b/flang/unittests/Runtime/CommandTest.cpp
index 50b11d7fe8a0d5..0085d42edd7076 100644
--- a/flang/unittests/Runtime/CommandTest.cpp
+++ b/flang/unittests/Runtime/CommandTest.cpp
@@ -635,7 +635,14 @@ TEST_F(EnvironmentVariables, GetlogGetName) {
 #if _REENTRANT || _POSIX_C_SOURCE >= 199506L
 TEST_F(EnvironmentVariables, GetlogPadSpace) {
   // guarantee 1 char longer than max, last char should be pad space
-  const int charLen{LOGIN_NAME_MAX + 2};
+  int charLen;
+#ifdef LOGIN_NAME_MAX
+  charLen = LOGIN_NAME_MAX + 2;
+#else
+  charLen = sysconf(_SC_LOGIN_NAME_MAX) + 2;
+  if (charLen == -1)
+    charLen = _POSIX_LOGIN_NAME_MAX + 2;
+#endif
   char input[charLen];
 
   FORTRAN_PROCEDURE_NAME(getlog)

[yiwu0b11]

LGTM, thanks for the fix!

[clementval]

This might have broke a buildbot https://lab.llvm.org/buildbot/#/builders/175

[rorth]

It seems so, yes. AFAICS that bot's use of -Werror is a non-standard configuration, so I missed this.

Unless I'm mistaken, this patch fixes the warnings.
flang-vla.txt

At least it made the warning vanish on amd64-pc-solaris2.11 and x86_64-pc-linux-gnu and passed testing on the latter.

[rorth]

I happened to notice that @kazutakahirata silently fixed the issue slightly differently in fb09447 and 18734f6.

[yiwu0b11]

I happened to notice that @kazutakahirata silently fixed the issue slightly differently in fb09447 and 18734f6.

@klausler notice a problem in this two fixes, https://flang-compiler.slack.com/archives/C5C58TT32/p1705019662369869
"also, i think that somebody must have introduced a dependency between the Fortran runtime library and the C++ runtime via use of operator new rather than calling runtime::AllocateMemory(). … probably via use of std::vector<> in the runtime (getlog in extensions.cpp)"