Re: [Xen-devel] [PATCH 00/12] xen/arm: Add support to build with clang

[Artem Mygaiev <Artem_Mygaiev@xxxxxxxx>]

Hello Julien, Stefano

On Wed, 2019-04-17 at 10:42 +0100, Julien Grall wrote:
> Hi,
> 
> On 16/04/2019 23:43, Stefano Stabellini wrote:
> > On Fri, 29 Mar 2019, Julien Grall wrote:
> > > On 28/03/2019 11:27, Artem Mygaiev wrote:
> > > > Hi Julien,
> > > 
> > > Hi Artem,
> > > 
> > > > On Wed, 2019-03-27 at 18:45 +0000, Julien Grall wrote:
> > > > > Hi all,
> > > > > 
> > > > > This series adds support to build Xen Arm with clang. This series was
> > > > > tested
> > > > > with clang 8.0.
> > > > > 
> > > > > Note that I only did build for arm64. I still need to look at the 
> > > > > arm32
> > > > > build.
> > > > > 
> > > > 
> > > > I wonder if you have time to try the series with Arm Compiler 6? I am
> > > > asking because AFAIK it is based on clang/llvm [1] and there's a
> > > > safety-compliant version of it certified by TUV [2]. I don't have a
> > > > license yet so cannot try it myself but maybe you have access.
> > > I gave a quick try to the Arm Compiler. I had to hack a bit 
> > > config/StdGNU.mk
> > > to pass armclang and the appropriate target option.
> > > 
> > > I also had a linking issue at the end where __2snprintf was not found. It
> > > seems the compiler replace snprintf with __2snprintf, I haven't figured 
> > > out
> > > why yet.
> > 
> > But after these changes, does it work?
> 
> I haven't tried to fix the linking issues. I only gave a quick try because 
> Artem 
> asked. I have no plan at the moment to go further than that for now.
> 
> Patches are welcomed to add support for armclang.
> 

I have implemented a bunch of HACKs [1] so can build Xen master with
armclang 6.12. Not even "smoke"-tested, just trying to identify missing
parameters and proper linker configuration.

Not yet fixed section placement, lots of warnings from linker like:
Warning: L6170W: Mapping symbol #40 '$x.20' in
.altinstr_replacement(ns16550.o:42) identifies code, but is in a
section not marked as executable.

Also armlink sometimes fails with Internal fault: [0xe81a5a:6120001]


[1] Diff below just for reference with xen master + Julien's clang
patch series applied
---

diff --git a/Config.mk b/Config.mk
index 417039d7f6..0fc84293f9 100644
--- a/Config.mk
+++ b/Config.mk
@@ -221,7 +221,9 @@ CFLAGS += -Wall -Wstrict-prototypes
 
 $(call cc-option-add,HOSTCFLAGS,HOSTCC,-Wdeclaration-after-statement)
 $(call cc-option-add,CFLAGS,CC,-Wdeclaration-after-statement)
+ifneq ($(armds),y)
 $(call cc-option-add,CFLAGS,CC,-Wno-unused-but-set-variable)
+endif
 $(call cc-option-add,CFLAGS,CC,-Wno-unused-local-typedefs)
 
 LDFLAGS += $(foreach i, $(EXTRA_LIB), -L$(i)) 
@@ -234,9 +236,15 @@ endif
 APPEND_LDFLAGS += $(foreach i, $(APPEND_LIB), -L$(i))
 APPEND_CFLAGS += $(foreach i, $(APPEND_INCLUDES), -I$(i))
 
-EMBEDDED_EXTRA_CFLAGS := -nopie -fno-stack-protector -fno-stack-
protector-all
+EMBEDDED_EXTRA_CFLAGS := -fno-stack-protector -fno-stack-protector-all
 EMBEDDED_EXTRA_CFLAGS += -fno-exceptions
 
+ifeq ($(armds),y)
+EMBEDDED_EXTRA_CFLAGS += -fno-ropi -fno-rwpi
+else
+EMBEDDED_EXTRA_CFLAGS += -nopie
+endif
+
 XEN_EXTFILES_URL ?= http://xenbits.xen.org/xen-extfiles
 # All the files at that location were downloaded from elsewhere on
 # the internet.  The original download URL is preserved as a comment
diff --git a/config/StdGNU.mk b/config/StdGNU.mk
index 48c50b5ad7..585d076d4f 100644
--- a/config/StdGNU.mk
+++ b/config/StdGNU.mk
@@ -1,6 +1,15 @@
 AS         = $(CROSS_COMPILE)as
+AR         = $(CROSS_COMPILE)ar
 LD         = $(CROSS_COMPILE)ld
 ifeq ($(clang),y)
+ifeq ($(armds),y)
+CC         = armclang
+CXX        = armclang
+LD_LTO     = armlink
+LD         = armlink -v
+AS         = armasm
+AR         = armar
+else
 ifneq ($(CROSS_COMPILE),)
 CC         = clang -target $(CROSS_COMPILE:-=)
 CXX        = clang++ -target $(CROSS_COMPILE:-=)
@@ -9,13 +18,13 @@ CC         = clang
 CXX        = clang++
 endif
 LD_LTO     = $(CROSS_COMPILE)llvm-ld
+endif
 else
 CC         = $(CROSS_COMPILE)gcc
 CXX        = $(CROSS_COMPILE)g++
 LD_LTO     = $(CROSS_COMPILE)ld
 endif
 CPP        = $(CC) -E
-AR         = $(CROSS_COMPILE)ar
 RANLIB     = $(CROSS_COMPILE)ranlib
 NM         = $(CROSS_COMPILE)nm
 STRIP      = $(CROSS_COMPILE)strip
diff --git a/config/arm32.mk b/config/arm32.mk
index f95228e3c0..5afed07357 100644
--- a/config/arm32.mk
+++ b/config/arm32.mk
@@ -4,12 +4,14 @@ CONFIG_ARM_$(XEN_OS) := y
 
 CONFIG_XEN_INSTALL_SUFFIX :=
 
-# -march= -mcpu=
-
 # Explicitly specifiy 32-bit ARM ISA since toolchain default can be
-mthumb:
-CFLAGS += -marm
-
+ifeq ($(armds),y)
+# VE needed
+CFLAGS += --target=arm-arm-none-eabi -march=armv7-a
+else
+CFLAGS += -marm # -march= -mcpu=
 # Use only if calling $(LD) directly.
 LDFLAGS_DIRECT += -EL
+endif
 
 IOEMU_CPU_ARCH ?= arm
diff --git a/config/arm64.mk b/config/arm64.mk
index aa45772b61..46b203d384 100644
--- a/config/arm64.mk
+++ b/config/arm64.mk
@@ -4,10 +4,14 @@ CONFIG_ARM_$(XEN_OS) := y
 
 CONFIG_XEN_INSTALL_SUFFIX :=
 
+ifeq ($(armds),y)
+# VE needed
+CFLAGS += --target=aarch64-arm-none-eabi -march=armv8.1-a+nofp+nosimd
+else
 CFLAGS += #-marm -march= -mcpu= etc
-
 # Use only if calling $(LD) directly.
 LDFLAGS_DIRECT += -EL
+endif
 
 IOEMU_CPU_ARCH ?= aarch64
 
diff --git a/xen/Rules.mk b/xen/Rules.mk
index a151b3f625..72b34451d2 100644
--- a/xen/Rules.mk
+++ b/xen/Rules.mk
@@ -76,9 +76,11 @@ AFLAGS-y                += -D__ASSEMBLY__
 # Older clang's built-in assembler doesn't understand .skip with
labels:
 # https://bugs.llvm.org/show_bug.cgi?id=27369
 ifeq ($(clang),y)
+ifneq ($(armds),y)
 $(call as-option-add,CFLAGS,CC,".L0:\n.L1:\n.skip (.L1 - .L0)",,\
                      -no-integrated-as)
 endif
+endif
 
 ALL_OBJS := $(ALL_OBJS-y)
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