Introduce CMAKE_STAGING_PREFIX variable.

This variable can be useful in cross-compiling contexts where the
sysroot is read-only or where the sysroot should otherwise remain
pristine.

If the new CMAKE_STAGING_PREFIX variable is set, it is used instead
of CMAKE_INSTALL_PREFIX when generating the installation rules in
cmake_install.cmake.

This way, the CMAKE_INSTALL_PREFIX variable
always refers to the installation prefix on the target device, regardless
of whether host==target.

If any -rpath paths passed to the linker contain the CMAKE_STAGING_PREFIX,
the matching path fragments are replaced with the CMAKE_INSTALL_PREFIX.
Matching paths in the -rpath-link are not transformed.

The cross-prefix usr-move workaround is assumed not to require extension
regarding CMAKE_STAGING_PREFIX. The staging area is a single prefix, so
there is no scope for cross-prefix symlinks. The CMAKE_INSTALL_PREFIX
is still used to determine the workaround path, and that variable
remains the relevant one even if CMAKE_STAGING_PREFIX is used. If the
generated export files are deployed to the target, the workaround
will still be in place, and still be employed if required.

2 files changed, 17 insertions, 0 deletions

diff --git a/Modules/Platform/UnixPaths.cmake b/Modules/Platform/UnixPaths.cmake
index 7a424c4..eca3280 100644
--- a/Modules/Platform/UnixPaths.cmake
+++ b/Modules/Platform/UnixPaths.cmake
@@ -43,6 +43,12 @@ if (NOT CMAKE_FIND_NO_INSTALL_PREFIX)
     # Project install destination.
     "${CMAKE_INSTALL_PREFIX}"
   )
+  if(CMAKE_STAGING_PREFIX)
+    list(APPEND CMAKE_SYSTEM_PREFIX_PATH
+      # User-supplied staging prefix.
+      "${CMAKE_STAGING_PREFIX}"
+    )
+  endif()
 endif()
 
 # List common include file locations not under the common prefixes.
diff --git a/Modules/Platform/WindowsPaths.cmake b/Modules/Platform/WindowsPaths.cmake
index c231495..3240c23 100644
--- a/Modules/Platform/WindowsPaths.cmake
+++ b/Modules/Platform/WindowsPaths.cmake
@@ -79,6 +79,12 @@ if (NOT CMAKE_FIND_NO_INSTALL_PREFIX)
     # Project install destination.
     "${CMAKE_INSTALL_PREFIX}"
     )
+  if (CMAKE_STAGING_PREFIX)
+    list(APPEND CMAKE_SYSTEM_PREFIX_PATH
+      # User-supplied staging prefix.
+      "${CMAKE_STAGING_PREFIX}"
+    )
+  endif()
 endif()
 
 if(CMAKE_CROSSCOMPILING AND NOT CMAKE_HOST_SYSTEM_NAME MATCHES "Windows")
@@ -94,6 +100,11 @@ if (NOT CMAKE_FIND_NO_INSTALL_PREFIX)
   list(APPEND CMAKE_SYSTEM_LIBRARY_PATH
     "${CMAKE_INSTALL_PREFIX}/bin"
   )
+  if (CMAKE_STAGING_PREFIX)
+    list(APPEND CMAKE_SYSTEM_LIBRARY_PATH
+      "${CMAKE_STAGING_PREFIX}/bin"
+    )
+  endif()
 endif()
 list(APPEND CMAKE_SYSTEM_LIBRARY_PATH
   "${_CMAKE_INSTALL_DIR}/bin"