[PATCH 2/3] BaseTools/tools_def ARM CLANG35: work around -mno-movt option name change

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

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.biesheuvel@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
 *_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