Fix cross-compilation for musl C library

This adds a PHP_C_STANDARD_LIBRARY Autoconf macro to detect glibc/musl
more accurately and fixes "cross-compilation" with musl-libc on glibc
systems.

Co-authored-by: Peter Kokot <[email protected]>

Closes GH-19352

Author: henderkes

NEWS

@@ -15,6 +15,8 @@ PHP                                                                        NEWS
   . Fixed bug GH-19480 (error_log php.ini cannot be unset when open_basedir is
     configured). (nielsdos)
   . Fixed bug GH-20002 (Broken build on *BSD with MSAN). (outtersg)
+  . Fixed bug GH-19352 (Cross-compilation with musl C library).
+    (henderkes, Peter Kokot)
 
 - Curl:
   . Fix cloning of CURLOPT_POSTFIELDS when using the clone operator instead

build/php.m4

@@ -2502,3 +2502,43 @@ AC_DEFUN([PHP_REMOVE_OPTIMIZATION_FLAGS], [
   CFLAGS=$(echo "$CFLAGS" | $SED -e "$sed_script")
   CXXFLAGS=$(echo "$CXXFLAGS" | $SED -e "$sed_script")
 ])
+
+dnl
+dnl PHP_C_STANDARD_LIBRARY
+dnl
+dnl Determine the C standard library used for the build. The uclibc is checked
+dnl first because it also defines the __GLIBC__ and could otherwise be detected
+dnl as glibc. Musl C library is determined heuristically.
+dnl
+AC_DEFUN([PHP_C_STANDARD_LIBRARY],
+[AC_CACHE_CHECK([C standard library implementation],
+[php_cv_c_standard_library],
+[php_cv_c_standard_library=unknown
+dnl Check if C standard library is uclibc.
+AS_VAR_IF([php_cv_c_standard_library], [unknown],
+[AC_COMPILE_IFELSE([AC_LANG_PROGRAM([#include <features.h>],
+[#ifndef __UCLIBC__
+  (void) __UCLIBC__;
+#endif])],
+[php_cv_c_standard_library=uclibc],
+[php_cv_c_standard_library=unknown])])
+dnl Check if C standard library is GNU C.
+AS_VAR_IF([php_cv_c_standard_library], [unknown],
+[AC_COMPILE_IFELSE([AC_LANG_PROGRAM([#include <features.h>],
+[#ifndef __GLIBC__
+  (void) __GLIBC__;
+#endif])],
+[php_cv_c_standard_library=glibc],
+[php_cv_c_standard_library=unknown])])
+dnl Check if C standard library is musl libc.
+AS_VAR_IF([php_cv_c_standard_library], [unknown],
+[AC_COMPILE_IFELSE([AC_LANG_PROGRAM([#include <stdarg.h>],
+[#ifndef __DEFINED_va_list
+  (void) __DEFINED_va_list;
+#endif])],
+[php_cv_c_standard_library=musl],
+[AS_IF([command -v ldd >/dev/null && ldd --version 2>&1 | grep ^musl >/dev/null 2>&1],
+[php_cv_c_standard_library=musl],
+[php_cv_c_standard_library=unknown])])])
+])
+])

configure.ac

@@ -250,15 +250,10 @@ case $host_alias in
     ;;
 esac
 
-dnl Detect musl libc
-AC_MSG_CHECKING([whether we are using musl libc])
-if command -v ldd >/dev/null && ldd --version 2>&1 | grep ^musl >/dev/null 2>&1
-then
-  AC_MSG_RESULT([yes])
-  AC_DEFINE([__MUSL__], [1], [Define to 1 when using musl libc.])
-else
-  AC_MSG_RESULT([no])
-fi
+dnl Detect C library.
+PHP_C_STANDARD_LIBRARY
+AS_VAR_IF([php_cv_c_standard_library], [musl],
+  [AC_DEFINE([__MUSL__], [1], [Define to 1 when using musl libc.])])
 
 dnl Add _GNU_SOURCE compile definition because the php_config.h with definitions
 dnl by AC_USE_SYSTEM_EXTENSIONS might be included after the system headers which

ext/posix/config.m4

@@ -44,7 +44,8 @@ if test "$PHP_POSIX" = "yes"; then
 
 dnl Skip pathconf and fpathconf check on musl libc due to limited implementation
 dnl (first argument is not validated and has different error).
-  AS_IF([command -v ldd >/dev/null && ldd --version 2>&1 | grep ^musl >/dev/null 2>&1],
+  PHP_C_STANDARD_LIBRARY
+  AS_VAR_IF([php_cv_c_standard_library], [musl],
     [],
     [AC_CHECK_FUNCS([pathconf fpathconf])])