[5.5/10] arch/arm, cmake: Build FDPIC modules in the normal ELF build.

arch/arm/src/cmake/elf.cmake

@@ -27,17 +27,59 @@ nuttx_mod_compile_options(-fvisibility=hidden -mlong-calls)
 nuttx_elf_compile_options_ifdef(CONFIG_UNWINDER_ARM -fno-unwind-tables
                                 -fno-asynchronous-unwind-tables)
 
-# An ELF module needs r9 as its PIC base, so it must not also have the register
-# fixed: GCC rejects that pair with "unable to use 'r9' for PIC register".  This
-# mirrors CELFFLAGS in common/Toolchain.defs, which filters --fixed-r9 back out
-# of the inherited CFLAGS for the same reason.
+if(CONFIG_FDPIC)
 
-nuttx_elf_compile_options_ifdef(CONFIG_PIC -mpic-register=r9)
+  # An FDPIC module is a shared object whose two segments the loader places
+  # independently.  The stock compiler emits correct FDPIC objects for both C
+  # and C++, so only the link needs the arm-uclinuxfdpiceabi linker: the stock
+  # one carries the armelf emulation alone and would turn every import into a
+  # jump slot where the ABI wants a function descriptor.
 
-nuttx_elf_link_options_ifdef(
-  CONFIG_PIC --unresolved-symbols=ignore-in-object-files --emit-relocs)
+  if(NOT FDPIC_CROSSDEV)
+    set(FDPIC_CROSSDEV arm-uclinuxfdpiceabi-)
+  endif()
+
+  # Say which linker is missing rather than failing later with a command that
+  # cannot be run.
+
+  find_program(FDPIC_LD "${FDPIC_CROSSDEV}ld")
+
+  if(NOT FDPIC_LD)
+    message(
+      FATAL_ERROR
+        "CONFIG_FDPIC needs ${FDPIC_CROSSDEV}ld, which is not on PATH. "
+        "It is in the NuttX CI image, and tools/ci/docker/linux/Dockerfile "
+        "shows how it is built.  Set FDPIC_CROSSDEV to use a different prefix")
+  endif()
+
+  set(CMAKE_ELF_LD
+      "${FDPIC_LD}"
+      CACHE INTERNAL "Linker for FDPIC modules")
+
+  nuttx_elf_compile_options(-mfdpic -fPIC -Wa,--noexecstack)
+
+  nuttx_elf_link_options(-m armelf_linux_fdpiceabi -shared -z now)
 
-nuttx_elf_link_options_ifdef(CONFIG_BINFMT_ELF_RELOCATABLE -r)
+elseif(CONFIG_PIC)
+
+  # An ELF module needs r9 as its PIC base, so it must not also have the
+  # register fixed: GCC rejects that pair with "unable to use 'r9' for PIC
+  # register".  This mirrors CELFFLAGS in common/Toolchain.defs, which filters
+  # --fixed-r9 back out of the inherited CFLAGS for the same reason.
+
+  nuttx_elf_compile_options(-mpic-register=r9)
+
+  nuttx_elf_link_options(--unresolved-symbols=ignore-in-object-files
+                         --emit-relocs)
+
+endif()
+
+# Not with CONFIG_PIC: there the module is linked as an executable, which is
+# what common/Toolchain.defs does too.
+
+if(CONFIG_BINFMT_ELF_RELOCATABLE AND NOT CONFIG_PIC)
+  nuttx_elf_link_options(-r)
+endif()
 
 nuttx_mod_link_options(-r)
 

arch/arm/src/common/Toolchain.defs

@@ -642,11 +642,45 @@ ifeq ($(CONFIG_PIC),y)
   # after including this file, which would discard the flag.
 
   ARCHCFLAGS += --fixed-r9
+
+ifeq ($(CONFIG_FDPIC),y)
+  # An FDPIC module is a shared object whose two segments the loader places
+  # independently.  The stock compiler emits correct FDPIC objects for both C
+  # and C++, so only the link needs the arm-uclinuxfdpiceabi linker: the
+  # stock one carries the armelf emulation alone and would turn every import
+  # into a jump slot where the ABI wants a function descriptor.
+
+  FDPIC_CROSSDEV ?= arm-uclinuxfdpiceabi-
+  MODULELD = $(FDPIC_CROSSDEV)ld
+
+  # Say which linker is missing rather than letting make report a command it
+  # cannot run.  The report is deferred to the link itself rather than made
+  # here, so that a tree configured for FDPIC on a host without the linker can
+  # still be cleaned and reconfigured.
+
+  FDPIC_LD_FOUND := $(shell command -v $(MODULELD) 2> /dev/null)
+
+  ifeq ($(FDPIC_LD_FOUND),)
+    FDPIC_NO_LD_MSG = CONFIG_FDPIC needs $(FDPIC_CROSSDEV)ld, which is not \
+      on PATH.  It is in the NuttX CI image, and \
+      tools/ci/docker/linux/Dockerfile shows how it is built.  Set \
+      FDPIC_CROSSDEV to use a different prefix.
+
+    MODULELD = $(SHELL) -c 'echo "ERROR: $(FDPIC_NO_LD_MSG)" 1>&2; exit 1' --
+  endif
+
+  CELFFLAGS += -mfdpic -fPIC -Wa,--noexecstack
+  CXXELFFLAGS += -mfdpic -fPIC -Wa,--noexecstack
+
+  LDELFFLAGS += -m armelf_linux_fdpiceabi -shared -z now
+else
   CELFFLAGS += $(PICFLAGS) -mpic-register=r9
   CXXELFFLAGS += $(PICFLAGS) -mpic-register=r9
 
   # Generate an executable elf, need to ignore undefined symbols
   LDELFFLAGS += --unresolved-symbols=ignore-in-object-files --emit-relocs
+endif
+
 else
   ifneq ($(CONFIG_BINFMT_ELF_EXECUTABLE),y)
     LDELFFLAGS += -r

cmake/nuttx_add_application.cmake

@@ -149,7 +149,15 @@ function(nuttx_add_application)
         if(TARGET STARTUP_OBJS)
           add_dependencies(${TARGET} STARTUP_OBJS)
         endif()
-        if(NOT "${CMAKE_LD}" MATCHES "gcc$")
+        # A module may need a different linker from the one that links the
+        # firmware: an FDPIC module does, because the stock linker cannot
+        # produce one.  CMAKE_ELF_LD is that linker, and it is the ordinary one
+        # unless the architecture says otherwise.
+
+        if(NOT CMAKE_ELF_LD)
+          set(CMAKE_ELF_LD ${CMAKE_LD})
+        endif()
+        if(NOT "${CMAKE_ELF_LD}" MATCHES "gcc$")
           set(USE_LINKER True)
         endif()
         if(STACKSIZE)
@@ -179,7 +187,7 @@ function(nuttx_add_application)
           POST_BUILD
           COMMAND
             # add default link option
-            ${CMAKE_LD} -T ${NUTTX_BINARY_DIR}/gnu-elf.ld
+            ${CMAKE_ELF_LD} -T ${NUTTX_BINARY_DIR}/gnu-elf.ld
             # add global MOD link option if dynlib link
             $<$<BOOL:${DYNLIB_ELF_MODE}>:$<TARGET_PROPERTY:nuttx_global,NUTTX_MOD_APP_LINK_OPTIONS>>
             # add global ELF link option if m&kernel link

libs/libc/elf/gnu-elf.ld.in

@@ -39,6 +39,34 @@
 #  define SECTIONS_ALIGN 4
 #endif
 
+/* An FDPIC module is a shared object whose read-only and writable segments
+ * the loader places independently: the read-only one runs where the
+ * filesystem already holds it and only the writable one is copied to RAM,
+ * once per running instance.  So the two go into segments of their own, and
+ * .dynamic is named, because a shared object is bound through it.
+ *
+ * Everything else is common, the symbols crt0.c walks included, so a module
+ * is built and entered the same way whichever this is.
+ */
+
+#ifdef CONFIG_FDPIC
+#  define PHDR_TEXT :text
+#  define PHDR_DATA :data
+#  define DATA_ALIGN . = ALIGN(0x1000);
+
+PHDRS
+{
+  text    PT_LOAD FLAGS(5);    /* Read and execute */
+  data    PT_LOAD FLAGS(6);    /* Read and write   */
+  dynamic PT_DYNAMIC FLAGS(6);
+}
+
+#else
+#  define PHDR_TEXT
+#  define PHDR_DATA
+#  define DATA_ALIGN
+#endif
+
 SECTIONS
 {
   .text TEXT :
@@ -53,7 +81,7 @@ SECTIONS
       *(.jcr)
       . = ALIGN(SECTIONS_ALIGN);
       _etext = . ;
-    }
+    } PHDR_TEXT
 
   .rodata :
     {
@@ -64,7 +92,9 @@ SECTIONS
       *(.gnu.linkonce.r*)
       . = ALIGN(SECTIONS_ALIGN);
       _erodata = . ;
-    }
+    } PHDR_TEXT
+
+  DATA_ALIGN
 
   .data DATA :
     {
@@ -75,7 +105,7 @@ SECTIONS
       *(.gnu.linkonce.d*)
       . = ALIGN(SECTIONS_ALIGN);
       _edata = . ;
-    }
+    } PHDR_DATA
 
   .init_array :
     {
@@ -86,7 +116,7 @@ SECTIONS
       . = ALIGN(SECTIONS_ALIGN);
       _einit = .;
       _ectors = .;
-    }
+    } PHDR_DATA
 
   .fini_array :
     {
@@ -98,7 +128,24 @@ SECTIONS
       . = ALIGN(SECTIONS_ALIGN);
       _efini = .;
       _edtors = .;
-    }
+    } PHDR_DATA
+
+#ifdef CONFIG_FDPIC
+  .dynamic :
+    {
+      *(.dynamic)
+    } :data :dynamic
+#endif
+
+  .got :
+    {
+      *(.got*)
+    } PHDR_DATA
+
+  /* .bss holds no file content, so it comes last.  Everything ahead of it
+   * has content, thus the writable segment's p_filesz stops where .bss
+   * starts and the file does not carry it.
+   */
 
   .bss :
     {
@@ -111,12 +158,7 @@ SECTIONS
       *(COMMON)
       . = ALIGN(SECTIONS_ALIGN);
       _ebss = . ;
-    }
-
-  .got :
-    {
-      *(.got*)
-    }
+    } PHDR_DATA
 
     /* Stabs debugging sections.    */