LLEXT: Xtensa: add a Kconfig option to enable -fPIC

Currently when building LLEXT for Xtensa we use the -fPIC compiler
option, but this cannot be used when using detached sections in
extensions. Add a Kconfig option to switch between the two
compilation modes and switch -fPIC off when building relocatable
(partially linked) ELF binaries.

Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>

cmake/compiler/gcc/target_xtensa.cmake

@@ -3,8 +3,6 @@
 # Flags not supported by llext linker
 # (regexps are supported and match whole word)
 set(LLEXT_REMOVE_FLAGS
-  -fno-pic
-  -fno-pie
   -ffunction-sections
   -fdata-sections
   -g.*
@@ -14,7 +12,20 @@ set(LLEXT_REMOVE_FLAGS
 
 # Flags to be added to llext code compilation
 set(LLEXT_APPEND_FLAGS
-  -fPIC
   -nostdlib
   -nodefaultlibs
 )
+
+if(CONFIG_LLEXT_BUILD_PIC)
+set(LLEXT_REMOVE_FLAGS ${LLEXT_REMOVE_FLAGS}
+    -fno-pic
+    -fno-pie
+)
+set(LLEXT_APPEND_FLAGS ${LLEXT_APPEND_FLAGS}
+    -fPIC
+)
+else()
+set(LLEXT_APPEND_FLAGS ${LLEXT_APPEND_FLAGS}
+  -ffreestanding
+)
+endif()

cmake/compiler/xt-clang/target.cmake

@@ -5,8 +5,6 @@ include(${ZEPHYR_BASE}/cmake/compiler/xcc/target.cmake)
 # Flags not supported by llext linker
 # (regexps are supported and match whole word)
 set(LLEXT_REMOVE_FLAGS
-  -fno-pic
-  -fno-pie
   -ffunction-sections
   -fdata-sections
   -g.*
@@ -16,7 +14,20 @@ set(LLEXT_REMOVE_FLAGS
 
 # Flags to be added to llext code compilation
 set(LLEXT_APPEND_FLAGS
-  -fPIC
   -nostdlib
   -nodefaultlibs
 )
+
+if(CONFIG_LLEXT_BUILD_PIC)
+set(LLEXT_REMOVE_FLAGS ${LLEXT_REMOVE_FLAGS}
+  -fno-pic
+  -fno-pie
+)
+set(LLEXT_APPEND_FLAGS ${LLEXT_APPEND_FLAGS}
+  -fPIC
+)
+else()
+set(LLEXT_APPEND_FLAGS ${LLEXT_APPEND_FLAGS}
+  -ffreestanding
+)
+endif()

subsys/llext/Kconfig

@@ -49,6 +49,16 @@ config LLEXT_HEAP_SIZE
 	help
 	  Heap size in kilobytes available to llext for dynamic allocation
 
+config LLEXT_BUILD_PIC
+	bool "Use -fPIC when building LLEXT"
+	depends on XTENSA
+	default y if LLEXT_TYPE_ELF_SHAREDLIB
+	help
+	  By default LLEXT compilation is performed with -fno-pic -fno-pie compiler
+	  flags. Some platforms can benefit from using -fPIC instead, in which case
+	  most internal linking is performed by the linker at build time. Select "y"
+	  to make use of that advantage.
+
 config LLEXT_SHELL
 	bool "llext shell commands"
 	depends on SHELL