Hi,
> On 20 Aug 2021, at 11:29, Richard Sandiford <richard.sandif...@arm.com> wrote:
>
>>> Maybe it would be easier to have the makefile fragments determine
>>> something like CODE_MODEL_CFLAGS, which can be "-fPIC", "-mdynamic-no-pic",
>>> etc., and use:
>>>
>>> COMPILER += $(NO_PIE_CFLAGS) $(CODE_MODEL_CFLAGS)
>>
>> OK. I have misgivings about this - the problem is that:
>>
>> -fPIC -fno-PIE != -fno-PIE -fPIC, which is not obvious to many folks - who
>> expect that
>> the “last edition of a flag will be the one in force”.
>>
>> So the PIE-ness and the PIC-ness are decoupled in the configury but they
>> need to be
>> ordered specifically for targets that want PIC code by default (FWIW, I
>> don’t think Darwin
>> is the only default-PIC case here, from discussions on irc).
>
> Yeah, that's what the above was supposed to achieve. In other words,
> if you force non-PIE, you also need to follow that by $(CODE_MODEL_CFLAGS),
> which restates whatever the base code model is.
>
> If it's the decoupling you're worried about, then an alternative would
> be to have:
>
> NO_PIE_CFLAGS="-fno-PIE \$(CODE_MODEL_CFLAGS)”
I’d like to ask a couple of questions (of HJ who introduced the no-PIE logic)
before implementing this.
A. We use no-PIE for cc1* because that is needed to handle the PCH
implementation (which relies on the executables being loaded at the same
addresses each time).
B. It’s certainly not obvious to me why we need to build code to run on $build
to be no-PIE - I don’t see any such dependencies in the generators etc.
- So Question1 - HJ what was the motivation for making the XXX_BUILD_XXX
adopt no-PIE?
——
Independently of this we seem to be building the objects for $host thus:
$(CXX) (NO_PIE_CFLAGS) -c $(ALL_CXXFLAGS) etc.
but we build for $build thus:
$(CXX) -c $(ALL_CXXFLAGS) $(GENERATOR_CFLAGS) -DGENERATOR_FILE
$(BUILD_NO_PIE_CFLAGS) $(BUILD_CPPFLAGS)
which means that code model flags in $ALL_CXXFLAGS are overridden for $build,
but active for $host
^^ this is actually what causes the Darwin build fail - since on Darwin we
cannot build static linked code for user-space processes.
in any event that’s inconsistent (unless there’s a reason that it should be
different).
----
below are extracts from gcc/Makefile *on linux* which demonstrates the
different ordering.
AFAICT,
NO_PIE_CFLAGS_FOR_BUILD, NO_PIE_FLAG_FOR_BUILD are dead variables?
Question 2 : HJ, what was your intention for how a configuration would request
PIC code (for example) for things to run on $build?
thanks
Iain
-------
ALL_CXXFLAGS = $(T_CFLAGS) $(CFLAGS-$@) $(CXXFLAGS) $(INTERNAL_CFLAGS) \
$(COVERAGE_FLAGS) $(ALIASING_FLAGS) $(NOEXCEPTION_FLAGS) \
--
# Native compiler for the build machine and its switches.
CC_FOR_BUILD = $(CC)
CXX_FOR_BUILD = $(CXX)
NO_PIE_CFLAGS_FOR_BUILD =
NO_PIE_FLAG_FOR_BUILD =
BUILD_CFLAGS= $(ALL_CFLAGS) $(GENERATOR_CFLAGS) -DGENERATOR_FILE
BUILD_CXXFLAGS = $(ALL_CXXFLAGS) $(GENERATOR_CFLAGS) -DGENERATOR_FILE
BUILD_NO_PIE_CFLAGS = $(NO_PIE_CFLAGS)
BUILD_CFLAGS += $(BUILD_NO_PIE_CFLAGS)
BUILD_CXXFLAGS += $(BUILD_NO_PIE_CFLAGS)
# Native compiler that we use. This may be C++ some day.
COMPILER_FOR_BUILD = $(CXX_FOR_BUILD)
BUILD_COMPILERFLAGS = $(BUILD_CXXFLAGS)
# Native linker that we use.
LINKER_FOR_BUILD = $(CXX_FOR_BUILD)
BUILD_LINKERFLAGS = $(BUILD_CXXFLAGS)
# Native linker and preprocessor flags. For x-fragment overrides.
BUILD_LDFLAGS=$(LDFLAGS)
BUILD_NO_PIE_FLAG = $(NO_PIE_FLAG)
BUILD_LDFLAGS += $(BUILD_NO_PIE_FLAG)
BUILD_CPPFLAGS= -I. -I$(@D) -I$(srcdir) -I$(srcdir)/$(@D) \
-I$(srcdir)/../include $(CPPINC) $(CPPFLAGS)
--
# This is the variable actually used when we compile. If you change this,
# you probably want to update BUILD_CFLAGS in configure.ac
ALL_CFLAGS = $(T_CFLAGS) $(CFLAGS-$@) \
build/%.o : # dependencies provided by explicit rule later
$(COMPILER_FOR_BUILD) -c $(BUILD_COMPILERFLAGS) $(BUILD_CPPFLAGS) \
-o $@ $<
^^^^ this has
$(CXX) -c $(ALL_CXXFLAGS) $(GENERATOR_CFLAGS) -DGENERATOR_FILE
$(BUILD_NO_PIE_CFLAGS) $(BUILD_CPPFLAGS)
NO_PIE_CFLAGS_FOR_BUILD is apparently ignored
# Rule for the generator programs:
$(genprog:%=build/gen%$(build_exeext)): build/gen%$(build_exeext): build/gen%.o
$(BUILD_LIBDEPS)
+$(LINKER_FOR_BUILD) $(BUILD_LINKERFLAGS) $(BUILD_LDFLAGS) -o $@ \
$(filter-out $(BUILD_LIBDEPS), $^) $(BUILD_LIBS)
--
build/genversion$(build_exeext): build/genversion.o
+$(LINKER_FOR_BUILD) $(BUILD_LINKERFLAGS) $(BUILD_LDFLAGS) \
build/genversion.o -o $@
=========
# The name of the compiler to use.
COMPILER = $(CXX)
COMPILER_FLAGS = $(CXXFLAGS)
# If HOST_LIBS is set, then the user is controlling the libraries to
--
CET_HOST_FLAGS = -fcf-protection
COMPILER += $(CET_HOST_FLAGS)
--
# We don't want to compile the compilers with -fPIE, it make PCH fail.
COMPILER += $(NO_PIE_CFLAGS)
--
# A list of all the language-specific executables.
COMPILERS = gnat1$(exeext) cc1$(exeext) cc1plus$(exeext) d21$(exeext)
f951$(exeext) go1$(exeext) lto1$(exeext) cc1obj$(exeext) cc1objplus$(exeext)
--
# Native compiler that we use. This may be C++ some day.
COMPILER_FOR_BUILD = $(CXX_FOR_BUILD)
BUILD_COMPILERFLAGS = $(BUILD_CXXFLAGS)
--
# This is the variable to use when using $(COMPILER).
ALL_COMPILERFLAGS = $(ALL_CXXFLAGS)
--
COMPILE.base = $(COMPILER) -c $(ALL_COMPILERFLAGS) $(ALL_CPPFLAGS) -o $@
This is :
$(CXX) (NO_PIE_CFLAGS) -c $(ALL_CXXFLAGS) etc.
COMPILE = $(COMPILE.base) -MT $@ -MMD -MP -MF $(@D)/$(DEPDIR)/$(*F).TPo
POSTCOMPILE = @mv $(@D)/$(DEPDIR)/$(*F).TPo $(@D)/$(DEPDIR)/$(*F).Po
.cc.o .c.o:
$(COMPILE) $<
$(POSTCOMPILE)
