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build(romlib): don't timestamp generated wrappers

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The Makefile rule for the libwrappers object files places a dependency
on a timestamp file. This timestamp file is created by the recipe that
generates the libwrappers sources, and was presumably introduced to
indicate to Make that all of the source files are generated
simultaneously by that rule.

Instead, we can use a grouped target rule, which uses `&:` instead of
`:`. This communicates to Make that all of the targets listed are
generated at once.

To demonstrate, the following two Makefile rules differ in their
behaviour:

    a.x b.x c.x: # targets may be updated independently
        ... # generate a.x, b.x and c.x

    a.x b.x c.x &: # all targets are updated at once
        ... # generate a.x, b.x and c.x

While both recipes do generate all three files, only the second rule
communicates this fact to Make. As such, Make can reason that if one of
the files is up to date then all of them are, and avoid re-running the
rule for any generated file that it has not already run it for.

Change-Id: I10b49eb72b5276c7f9bd933900833b03a61cff2f
Signed-off-by: Chris Kay <chris.kay@arm.com>
This commit is contained in:
Chris Kay 2024-05-23 13:09:39 +00:00
parent d9db846766
commit ae4795261a
1 changed files with 2 additions and 5 deletions
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7
lib/romlib/Makefile
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@ -84,14 +84,11 @@ $(BUILD_DIR)/jmptbl.i: ../../$(PLAT_DIR)/jmptbl.i
@echo " PRE $@"
$(Q)$(ROMLIB_GEN) pre --output $@ --deps $(BUILD_DIR)/jmptbl.d $<
$(BUILD_DIR)/wrappers.stamp: $(BUILD_DIR)/jmptbl.i
$(WRAPPER_SOURCES) &: $(BUILD_DIR)/jmptbl.i
@echo " WRP $<"
$(Q)$(ROMLIB_GEN) genwrappers --bti=$(ENABLE_BTI) -b $(WRAPPER_DIR) $<
@touch $@
$(WRAPPER_SOURCES): $(BUILD_DIR)/wrappers.stamp
$(WRAPPER_OBJS): $(WRAPPER_SOURCES) $(BUILD_DIR)/wrappers.stamp
$(WRAPPER_OBJS): $(WRAPPER_DIR)/%.o: $(WRAPPER_DIR)/%.s
$(BUILD_DIR)/jmptbl.s: $(BUILD_DIR)/jmptbl.i
@echo " TBL $@"