On Wed, 12 Dec 2018 at 11:33, Ard Biesheuvel <ard.biesheu...@linaro.org> wrote: > > PE/COFF only has a very limited id space for runtime relocations, and > so it defines only a single relocation for movw/movt instruction pairs, > which can be combined to load a 32-bit symbol reference into a register. > For this to work as expected, these instructions must always appear in > the same order and adjacently, and this is something few compilers take > into account, unless they target PE/COFF explicitly (and this is not the > case for our ELF based toolchains) > > For Clang 3.6 and later, we can pass the -mno-movt option to suppress > movw/movt pairs entirely, which works around the issue. Unfortunately, > for Clang 3.5, the option is called differently (-mllvm -arm-use-movt=0) > and mutually incompatible between 3.5 and 3.6. > > Since it is desirable for the CLANG35 toolchain to be usable on newer > versions of Clang as well (given that it is the only non-LTO alternative > to CLANG38), let's work around this issue in a way that permits versions > 3.5 and newer of Clang to be used with the CLANG35 profile. > > So pass the -mkernel flag instead (and drop the -mno-unaligned-access > in *_CLANG35_ARM_CC_XIPFLAGS which now becomes redundant, and which > Clang complains about). This also inhibits movw/movt generation, along > with some other changes (e.g., long calls) which do affect code generation > but not in a undesirable manner. > > Contributed-under: TianoCore Contribution Agreement 1.1 > Signed-off-by: Ard Biesheuvel <ard.biesheu...@linaro.org> > --- > BaseTools/Conf/tools_def.template | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/BaseTools/Conf/tools_def.template > b/BaseTools/Conf/tools_def.template > index ac2b95e0f5ba..2ba833e1fb06 100755 > --- a/BaseTools/Conf/tools_def.template > +++ b/BaseTools/Conf/tools_def.template > @@ -5249,7 +5249,7 @@ DEFINE CLANG35_AARCH64_CC_FLAGS = > DEF(GCC_AARCH64_CC_FLAGS) DEF(CLANG35_AARCH64 > *_CLANG35_ARM_ASM_FLAGS = DEF(GCC_ASM_FLAGS) > DEF(CLANG35_ARM_TARGET) $(ARCHASM_FLAGS) $(PLATFORM_FLAGS) -Qunused-arguments > *_CLANG35_ARM_DLINK_FLAGS = DEF(CLANG35_ARM_TARGET) > DEF(GCC_ARM_DLINK_FLAGS) > *_CLANG35_ARM_DLINK2_FLAGS = DEF(GCC_DLINK2_FLAGS_COMMON) > -Wl,--defsym=PECOFF_HEADER_SIZE=0x220 > -*_CLANG35_ARM_PLATFORM_FLAGS = -march=armv7-a > +*_CLANG35_ARM_PLATFORM_FLAGS = -march=armv7-a -mkernel -Qunused-arguments
Alternatively, we could switch to armv6 code generation here (except for the .S pieces which us Thumb2 instructions), which also gets rid of the movw/movt pairs. > *_CLANG35_ARM_PP_FLAGS = DEF(GCC_PP_FLAGS) DEF(CLANG35_ARM_TARGET) > $(ARCHCC_FLAGS) $(PLATFORM_FLAGS) > *_CLANG35_ARM_RC_FLAGS = DEF(GCC_ARM_RC_FLAGS) > *_CLANG35_ARM_VFRPP_FLAGS = DEF(GCC_VFRPP_FLAGS) > DEF(CLANG35_ARM_TARGET) $(ARCHCC_FLAGS) $(PLATFORM_FLAGS) > -- > 2.19.2 > _______________________________________________ edk2-devel mailing list edk2-devel@lists.01.org https://lists.01.org/mailman/listinfo/edk2-devel
