Re: [UNIKRAFT PATCH 3/3] build: Add support for clang

[Simon Kuenzer <simon.kuenzer@xxxxxxxxx>]

On 21.11.20 17:34, Vlad-Andrei Badoiu wrote:
> We condition the gcc specific flags via have_gcc and the
> clang specific flags with have_clang.
>
> Signed-off-by: Alice Suiu <alicesuiu17@xxxxxxxxx>
> Signed-off-by: Vlad-Andrei Badoiu <vlad_andrei.badoiu@xxxxxx>
> ---
>   Makefile.uk                 | 17 ++++++++++++++---
>   arch/x86/x86_64/Makefile.uk |  9 ++++++---
>   2 files changed, 20 insertions(+), 6 deletions(-)
>
> diff --git a/Makefile.uk b/Makefile.uk
> index 4f1c7642..54914b26 100644
> --- a/Makefile.uk
> +++ b/Makefile.uk
> @@ -6,7 +6,9 @@
>   
>   COMPFLAGS    += -nostdinc -nostdlib
>   COMPFLAGS    += -U __linux__ -U __FreeBSD__ -U __sun__
> -COMPFLAGS    += -fno-omit-frame-pointer -fno-tree-sra -fno-split-stack
> +COMPFLAGS    += -fno-omit-frame-pointer
> +COMPFLAGS-$(call have_gcc)     += -fno-tree-sra -fno-split-stack
> +
>   ifneq ($(HAVE_STACKPROTECTOR),y)
>   COMPFLAGS    += -fno-stack-protector
>   endif
> @@ -22,10 +24,17 @@ GOCINCLUDES  += -I$(CONFIG_UK_BASE)/include
>   # Set the text and data sections to be readable and writable. Also,
>   # do not page-align the data segment. If the output format supports
>   # Unix style magic numbers, mark the output as OMAGIC.
> -LIBLDFLAGS  += -nostdinc -nostdlib -Wl,--omagic -Wl,-r -Wl,-d 
> -Wl,--build-id=none
> -LDFLAGS     += -nostdinc -nostdlib -Wl,--omagic -Wl,--build-id=none
> +LIBLDFLAGS     += -nostdlib -Wl,--omagic -Wl,-r -Wl,-d -Wl,--build-id=none
> +LIBLDFLAGS-$(call have_gcc)    += -nostdinc
> +LDFLAGS        += -nostdlib -Wl,--omagic -Wl,--build-id=none
> +LDFLAGS-$(call have_gcc)       += -nostdinc
>   
>   COMPFLAGS-$(CONFIG_OPTIMIZE_NONE)         += -O0 -fno-optimize-sibling-calls -fno-tree-vectorize
> +
> +ifeq ($(CONFIG_COMPILER), clang)
> +COMPFLAGS-$(CONFIG_OPTIMIZE_NONE):=$(filter-out 
> -fno-tree-sra,$(COMPFLAGS-$(CONFIG_OPTIMIZE_NONE)))
> +endif
> +
I am not a fan of using filter-out for flags. My concern is that this 
could be easily missed when reading and debugging compile flags. But you 
could do something like this instead:
COMPFLAGS-$(CONFIG_OPTIMIZE_NONE) += -O0 -fno-optimize-sibling-calls
ifeq ($(call have_gcc),y)
COMPFLAGS-$(CONFIG_OPTIMIZE_NONE) += -fno-tree-vectorize
endif

>   COMPFLAGS-$(CONFIG_OPTIMIZE_SIZE)         += -Os
>   COMPFLAGS-$(CONFIG_OPTIMIZE_PERF)         += -O2
>   
> @@ -56,3 +65,5 @@ M4FLAGS      += -DUK_VERSION=$(UK_VERSION).$(UK_SUBVERSION)
>   COMPFLAGS-$(call gcc_version_ge,6,1)  += -no-pie
>   LIBLDFLAGS-$(call gcc_version_ge,6,1) += -no-pie
>   LDFLAGS-$(call gcc_version_ge,6,1)    += -no-pie
> +
> +COMPFLAGS-$(call have_clang)   +=-fno-builtin -fno-PIC
> diff --git a/arch/x86/x86_64/Makefile.uk b/arch/x86/x86_64/Makefile.uk
> index 24919fb8..7af494d0 100644
> --- a/arch/x86/x86_64/Makefile.uk
> +++ b/arch/x86/x86_64/Makefile.uk
> @@ -1,7 +1,9 @@
>   ARCHFLAGS     += -D__X86_64__
> -ARCHFLAGS     += -m64 -mno-red-zone -fno-reorder-blocks 
> -fno-asynchronous-unwind-tables
> +ARCHFLAGS     += -m64 -mno-red-zone -fno-asynchronous-unwind-tables
> +ARCHFLAGS-$(call have_gcc)     += -fno-reorder-blocks
>   ISR_ARCHFLAGS += -D__X86_64__
> -ISR_ARCHFLAGS += -m64 -mno-red-zone -fno-reorder-blocks 
> -fno-asynchronous-unwind-tables
> +ISR_ARCHFLAGS += -m64 -mno-red-zone -fno-asynchronous-unwind-tables
> +ISR_ARCHFLAGS-$(call have_gcc) += -fno-reorder-blocks
>   
>   CINCLUDES   += -I$(CONFIG_UK_BASE)/arch/x86/x86_64/include
>   ASINCLUDES  += -I$(CONFIG_UK_BASE)/arch/x86/x86_64/include
> @@ -9,7 +11,8 @@ CXXINCLUDES += -I$(CONFIG_UK_BASE)/arch/x86/x86_64/include
>   
>   # compiler flags to prevent use of extended (FP, SSE, AVX) registers.
>   # This is for files that contain trap/exception/interrupt handlers
> -ISR_ARCHFLAGS += -mno-80387 -mno-fp-ret-in-387 -mno-mmx -mno-sse -mno-avx
> +ISR_ARCHFLAGS += -mno-80387 -mno-mmx -mno-sse -mno-avx
> +ISR_ARCHFLAGS-$(call have_gcc) += -mno-fp-ret-in-387
>   ISR_ARCHFLAGS-$(call gcc_version_ge,7,1) += -mgeneral-regs-only
>   
>   ARCHFLAGS-$(CONFIG_MARCH_X86_64_GENERIC)        += -mtune=generic