fix(romlib): wrap indirectly included functions

The problem that this resolves is a bit involved; the following
must be met at the same time for some function <to_be_wrapped>:

 * to_be_wrapped must be specified as part of the romlib
 * to_be_wrapped must _not_ be referenced by any translation unit
   in TF-A
 * to_be_wrapped must be referenced by a translation unit in a
   dependent library, mbedtls for example.

Under these circumstances, to_be_wrapped will not be wrapped, and
will instead reference its original definition while simultaneously
residing in romlib.

This is a side effect of two issues with romlib prior to this patch:

 1 to_be_wrapped is expected to wrap by duplicating its definition.
    This causes any condition that links against both the base and
    wrapper functions to be a link error (duplicate symbol definition).
 2 to_be_wrapped is in its own translation unit
    This causes the wrappers to be used by TF-A in an as needed.

The duplicate function definitions can be worked around using the
linker's `--wrap` flag, which redirects all references to a symbol
to resolve to `__wrap_<symbol>` and the original symbol to be
available as `__real_<symbol>`. Most of the changes handle creating
this arguments and passing them to the linker.

Further, once you use the linker's wrap, you will encounter another
issue: if TF-A does not use a function, its wrapper is not present.
This causes link issues when a library and not TF-A uses the wrapper.
Note that this issue would have been resolved previously by ignoring
the wrapper and using the base definition.

This further issue is worked around by concatenating the assembly for
all of the wrappers into a single translation unit. It's possible to
work around this issue in a few other ways, including reordering the
libraries passed to the linker to place libwrapper.a last or grouping
the libraries so that symbols from later libraries may be resolved
with prior libraries.

I chose the translation unit concatenation approach as it revealed
that a jumptable has duplicate symbols within it.

Change-Id: Ie57b5ae69bde2fc8705bdc7a93fae3ddb5341ed9
Signed-off-by: Jimmy Brisson <jimmy.brisson@arm.com>

docs/components/romlib-design.rst

@@ -71,6 +71,15 @@ image(s) is replaced with the wrapper function.
 The "library at ROM" contains a necessary init function that initialises the
 global variables defined by the functions inside "library at ROM".
 
+Wrapper functions are specified at the link stage of compilation and cannot
+interpose uppon functions within the same translation unit. For example, if
+function ``fn_a`` calls ``fn_b`` within translation unit ``functions.c`` and
+the romlib jump table includes an entry for ``fn_b``, ``fn_a`` will include
+a reference to ``fn_b``'s original program text instead of the wrapper. Thus
+the jumptable author must take care to include public entry points into
+translation units to avoid paying the program text cost twice, once in the
+original executable and once in romlib.
+
 Script
 ~~~~~~
 
@@ -86,7 +95,7 @@ files for the "library at ROM" to work. It implements multiple functions:
 
 3. ``romlib_generator.py genwrappers [args]`` - Generates a wrapper function for
    each entry in the index file except for the ones that contain the keyword
-   ``patch``. The generated wrapper file is called ``<fn_name>.s``.
+   ``patch``. The generated wrapper file is called ``wrappers.s``.
 
 4. ``romlib_generator.py pre [args]`` - Preprocesses the index file which means
    it resolves all the include commands in the file recursively. It can also

lib/romlib/Makefile

@@ -44,7 +44,7 @@ endif
 
 .PHONY: all clean distclean
 
-all: $(BUILD_DIR)/romlib.bin $(LIB_DIR)/libwrappers.a
+all: $(BUILD_DIR)/romlib.bin $(BUILD_DIR)/romlib.ldflags $(LIB_DIR)/libwrappers.a
 
 %.o: %.s
 	$(s)echo "  AS      $@"
@@ -88,6 +88,10 @@ $(BUILD_DIR)/jmptbl.s: $(BUILD_DIR)/jmptbl.i
 	$(s)echo "  TBL     $@"
 	$(q)$(ROMLIB_GEN) gentbl --output $@ --bti=$(ENABLE_BTI) $<
 
+$(BUILD_DIR)/romlib.ldflags: ../../$(PLAT_DIR)/jmptbl.i
+	$(s)echo "  LDFLAGS $@"
+	$(q)$(ROMLIB_GEN) link-flags $< > $@
+
 clean:
 	$(q)rm -f $(BUILD_DIR)/*
 

lib/romlib/romlib_generator.py

@@ -182,6 +182,22 @@ class TableGenerator(RomlibApplication):
                 template_name = "jmptbl_entry_" + item["type"] + bti + ".S"
                 output_file.write(self.build_template(template_name, item, True))
 
+class LinkArgs(RomlibApplication):
+    """ Generates the link arguments to wrap functions. """
+
+    def __init__(self, prog):
+        RomlibApplication.__init__(self, prog)
+        self.args.add_argument("file", help="Input file")
+
+    def main(self):
+        index_file_parser = IndexFileParser()
+        index_file_parser.parse(self.config.file)
+
+        fns = [item["function_name"] for item in index_file_parser.items
+               if not item["patch"] and item["type"] != "reserved"]
+
+        print(" ".join("-Wl,--wrap " + f for f in fns))
+
 class WrapperGenerator(RomlibApplication):
     """
     Generates a wrapper function for each entry in the index file except for the ones that contain
@@ -214,21 +230,19 @@ class WrapperGenerator(RomlibApplication):
             if item["type"] == "reserved" or item["patch"]:
                 continue
 
-            asm = self.config.b + "/" + item["function_name"] + ".s"
-            if self.config.list:
-                # Only listing files
-                files.append(asm)
-            else:
-                with open(asm, "w") as asm_file:
-                    # The jump instruction is 4 bytes but BTI requires and extra instruction so
-                    # this makes it 8 bytes per entry.
-                    function_offset = item_index * (8 if self.config.bti else 4)
+            if not self.config.list:
+                # The jump instruction is 4 bytes but BTI requires and extra instruction so
+                # this makes it 8 bytes per entry.
+                function_offset = item_index * (8 if self.config.bti else 4)
 
-                    item["function_offset"] = function_offset
-                    asm_file.write(self.build_template("wrapper" + bti + ".S", item))
+                item["function_offset"] = function_offset
+                files.append(self.build_template("wrapper" + bti + ".S", item))
 
         if self.config.list:
-            print(" ".join(files))
+            print(self.config.b + "/wrappers.s")
+        else:
+            with open(self.config.b + "/wrappers.s", "w") as asm_file:
+                asm_file.write("\n".join(files))
 
 class VariableGenerator(RomlibApplication):
     """ Generates the jump table global variable with the absolute address in ROM. """
@@ -258,7 +272,8 @@ class VariableGenerator(RomlibApplication):
 
 if __name__ == "__main__":
     APPS = {"genvar": VariableGenerator, "pre": IndexPreprocessor,
-            "gentbl": TableGenerator, "genwrappers": WrapperGenerator}
+            "gentbl": TableGenerator, "genwrappers": WrapperGenerator,
+            "link-flags": LinkArgs}
 
     if len(sys.argv) < 2 or sys.argv[1] not in APPS:
         print("usage: romlib_generator.py [%s] [args]" % "|".join(APPS.keys()), file=sys.stderr)

lib/romlib/templates/wrapper.S

@@ -3,8 +3,9 @@
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
-	.globl	${function_name}
-${function_name}:
+	.section .text.__wrap_${function_name}
+	.globl	__wrap_${function_name}
+__wrap_${function_name}:
 	ldr	x17, =jmptbl
 	mov	x16, #${function_offset}
 	ldr	x17, [x17]

lib/romlib/templates/wrapper_bti.S

@@ -3,8 +3,9 @@
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
-	.globl	${function_name}
-${function_name}:
+	.section .text.__wrap_${function_name}
+	.globl	__wrap_${function_name}
+__wrap_${function_name}:
 	bti	jc
 	ldr	x17, =jmptbl
 	mov	x16, #${function_offset}

make_helpers/build_macros.mk

@@ -479,6 +479,10 @@ define linker_script_path
         $(patsubst %.S,$(BUILD_DIR)/%,$(1))
 endef
 
+ifeq ($(USE_ROMLIB),1)
+WRAPPER_FLAGS := @${BUILD_PLAT}/romlib/romlib.ldflags
+endif
+
 # MAKE_BL macro defines the targets and options to build each BL image.
 # Arguments:
 #   $(1) = BL stage
@@ -548,11 +552,11 @@ ifeq ($($(ARCH)-ld-id),arm-link)
 		--map --list="$(MAPFILE)" --scatter=${PLAT_DIR}/scat/${1}.scat \
 		$(LDPATHS) $(LIBWRAPPER) $(LDLIBS) $(BL_LIBS) $(OBJS)
 else ifeq ($($(ARCH)-ld-id),gnu-gcc)
-	$$(q)$($(ARCH)-ld) -o $$@ $$(TF_LDFLAGS) $$(LDFLAGS) $(BL_LDFLAGS) -Wl,-Map=$(MAPFILE) \
+	$$(q)$($(ARCH)-ld) -o $$@ $$(TF_LDFLAGS) $$(LDFLAGS) $$(WRAPPER_FLAGS) $(BL_LDFLAGS) -Wl,-Map=$(MAPFILE) \
 		$(addprefix -Wl$(comma)--script$(comma),$(LINKER_SCRIPTS)) -Wl,--script,$(DEFAULT_LINKER_SCRIPT) \
 		$(OBJS) $(LDPATHS) $(LIBWRAPPER) $(LDLIBS) $(BL_LIBS)
 else
-	$$(q)$($(ARCH)-ld) -o $$@ $$(TF_LDFLAGS) $$(LDFLAGS) $(BL_LDFLAGS) -Map=$(MAPFILE) \
+	$$(q)$($(ARCH)-ld) -o $$@ $$(TF_LDFLAGS) $$(LDFLAGS) $$(WRAPPER_FLAGS) $(BL_LDFLAGS) -Map=$(MAPFILE) \
 		$(addprefix -T ,$(LINKER_SCRIPTS)) --script $(DEFAULT_LINKER_SCRIPT) \
 		$(OBJS) $(LDPATHS) $(LIBWRAPPER) $(LDLIBS) $(BL_LIBS)
 endif