[Support] Prefer AUX vector for page size (llvm#126863)

Prefers the page size to come from the AUX vector, `getpagesize` is
removed from POSIX.1-2001. Also throws in a couple asserts to ensure the
page size is a valid value.

Author: RossComputerGuy

llvm/cmake/config-ix.cmake

@@ -21,6 +21,7 @@ if (ANDROID OR CYGWIN OR CMAKE_SYSTEM_NAME MATCHES "AIX|DragonFly|FreeBSD|Haiku|
   set(HAVE_MACH_MACH_H 0)
   set(HAVE_MALLOC_MALLOC_H 0)
   set(HAVE_PTHREAD_H 1)
+  set(HAVE_SYS_AUXV_H 1)
   set(HAVE_SYS_MMAN_H 1)
   set(HAVE_SYSEXITS_H 1)
   set(HAVE_UNISTD_H 1)
@@ -52,6 +53,7 @@ else()
   check_include_file(mach/mach.h HAVE_MACH_MACH_H)
   check_include_file(malloc/malloc.h HAVE_MALLOC_MALLOC_H)
   check_include_file(pthread.h HAVE_PTHREAD_H)
+  check_include_file(sys/auxv.h HAVE_SYS_AUXV_H)
   check_include_file(sys/mman.h HAVE_SYS_MMAN_H)
   check_include_file(sysexits.h HAVE_SYSEXITS_H)
   check_include_file(unistd.h HAVE_UNISTD_H)

llvm/include/llvm/Config/config.h.cmake

@@ -295,4 +295,6 @@
 
 #cmakedefine HAVE_BUILTIN_THREAD_POINTER ${HAVE_BUILTIN_THREAD_POINTER}
 
+#cmakedefine HAVE_SYS_AUXV_H ${HAVE_SYS_AUXV_H}
+
 #endif

llvm/lib/Support/Unix/Process.inc

@@ -31,6 +31,9 @@
 #ifdef HAVE_MALLOC_MALLOC_H
 #include <malloc/malloc.h>
 #endif
+#ifdef HAVE_SYS_AUXV_H
+#include <sys/auxv.h>
+#endif
 
 //===----------------------------------------------------------------------===//
 //=== WARNING: Implementation here must contain only generic UNIX code that
@@ -63,7 +66,9 @@ Process::Pid Process::getProcessId() {
 // On Cygwin, getpagesize() returns 64k(AllocationGranularity) and
 // offset in mmap(3) should be aligned to the AllocationGranularity.
 Expected<unsigned> Process::getPageSize() {
-#if defined(HAVE_GETPAGESIZE)
+#if defined(HAVE_SYS_AUXV_H)
+  static const int page_size = ::getauxval(AT_PAGESZ);
+#elif defined(HAVE_GETPAGESIZE)
   static const int page_size = ::getpagesize();
 #elif defined(HAVE_SYSCONF)
   static long page_size = ::sysconf(_SC_PAGE_SIZE);
@@ -73,6 +78,8 @@ Expected<unsigned> Process::getPageSize() {
   if (page_size == -1)
     return errorCodeToError(errnoAsErrorCode());
 
+  assert(page_size > 0 && "Page size cannot be 0");
+  assert((page_size % 1024) == 0 && "Page size must be aligned by 1024");
   return static_cast<unsigned>(page_size);
 }