[PATCH 1/2] Cygwin: cache IsWow64Process2 host arch in wincap.

[Jeremy Drake]

This was already used in the FAST_CWD check, and could be used in a
couple other places.

I found the "emulated"/process value returned from the function largely
useless, so I did not cache it.  It is useless because, as the docs say,
it is set to IMAGE_FILE_MACHINE_UNKNOWN (0) if the process is not
running under WOW64, but Microsoft also doesn't consider x64-on-ARM64 to
be WOW64, so it is set to 0 regardless if the process is ARM64 or x64.
You can tell the difference via
GetProcessInformation(ProcessMachineTypeInfo), but for the current
process even that's overkill: what we really want to know is the
IMAGE_FILE_MACHINE_* constant for the Cygwin dll itself, which is
conveniently located in memory already, so make an accessor function to
access that.  (It could also be cached in a member variable for a
simpler accessor, and looked up in init).
---
Note the elif defined (__i386__) case won't compile because it references
the no-longer-present `wow64` value.  This was written and tested against
3.3.6, and the __i386__ case could just go away here...

 winsup/cygwin/local_includes/wincap.h |  3 +++
 winsup/cygwin/path.cc                 |  6 ++----
 winsup/cygwin/wincap.cc               | 28 +++++++++++++++++++++++++++
 3 files changed, 33 insertions(+), 4 deletions(-)

diff --git a/winsup/cygwin/local_includes/wincap.h b/winsup/cygwin/local_includes/wincap.h
index c14872787c..41d0e2c041 100644
--- a/winsup/cygwin/local_includes/wincap.h
+++ b/winsup/cygwin/local_includes/wincap.h
@@ -42,6 +42,7 @@ class wincapc
   RTL_OSVERSIONINFOEXW	version;
   char			osnam[40];
   const void		*caps;
+  USHORT		host_mach;
   bool			_is_server;

 public:
@@ -61,6 +62,8 @@ public:
 		     { return (size_t) system_info.dwAllocationGranularity; }
   const char *osname () const { return osnam; }
   const DWORD build_number () const { return version.dwBuildNumber; }
+  const USHORT host_machine () const { return host_mach; }
+  const USHORT current_module_machine () const;

 #define IMPLEMENT(cap) cap() const { return ((wincaps *) this->caps)->cap; }

diff --git a/winsup/cygwin/path.cc b/winsup/cygwin/path.cc
index 5cfcbc0f2f..869383c836 100644
--- a/winsup/cygwin/path.cc
+++ b/winsup/cygwin/path.cc
@@ -4617,14 +4617,12 @@ find_fast_cwd_pointer ()
 static fcwd_access_t **
 find_fast_cwd ()
 {
-  USHORT emulated, hosted;
   fcwd_access_t **f_cwd_ptr;

-  /* First check if we're running in WOW64 on ARM64 emulating AMD64.  Skip
+  /* First check if we're running on an ARM64 system.  Skip
      fetching FAST_CWD pointer as long as there's no solution for finding
      it on that system. */
-  if (IsWow64Process2 (GetCurrentProcess (), &emulated, &hosted)
-      && hosted == IMAGE_FILE_MACHINE_ARM64)
+  if (wincap.host_machine () == IMAGE_FILE_MACHINE_ARM64)
     return NULL;

   /* Fetch the pointer but don't set the global fast_cwd_ptr yet.  First
diff --git a/winsup/cygwin/wincap.cc b/winsup/cygwin/wincap.cc
index 30d9c14e8d..76c10168d6 100644
--- a/winsup/cygwin/wincap.cc
+++ b/winsup/cygwin/wincap.cc
@@ -238,6 +238,8 @@ wincapc wincap __attribute__((section (".cygwin_dll_common"), shared));
 void
 wincapc::init ()
 {
+  USHORT emul_mach;
+
   if (caps)
     return;		// already initialized

@@ -282,4 +284,30 @@ wincapc::init ()

   __small_sprintf (osnam, "NT-%d.%d", version.dwMajorVersion,
 		   version.dwMinorVersion);
+
+  if (!IsWow64Process2 (GetCurrentProcess (), &emul_mach, &host_mach))
+    {
+      /* assume the only way IsWow64Process2 fails for the current process is
+	 that we're running on an OS version where it's not implemented yet.
+	 As such, the only two realistic options are AMD64 or I386 */
+#if defined (__x86_64__)
+      host_mach = IMAGE_FILE_MACHINE_AMD64;
+#elif defined (__i386__)
+      host_mach = wow64 ? IMAGE_FILE_MACHINE_AMD64 : IMAGE_FILE_MACHINE_I386;
+#else
+      /* this should not happen */
+      host_mach = IMAGE_FILE_MACHINE_UNKNOWN;
+#endif
+    }
+}
+
+extern const IMAGE_DOS_HEADER
+dosheader __asm__ ("__image_base__");
+
+const USHORT
+wincapc::current_module_machine () const
+{
+  PIMAGE_NT_HEADERS ntheader = (PIMAGE_NT_HEADERS)((LPBYTE) &dosheader
+                                                   + dosheader.e_lfanew);
+  return ntheader->FileHeader.Machine;
 }
-- 
2.47.0.windows.2