Re: [Xen-devel] [PATCH for-4.8 2/2] Config.mk: fix comment for debug option

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, Oct 31, 2016 at 05:09:46PM +0000, Wei Liu wrote:
> Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> ---
> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Cc: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
> Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> Cc: Jan Beulich <jbeulich@xxxxxxxx>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> Cc: Tim Deegan <tim@xxxxxxx>
> Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
> ---
>  Config.mk | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/Config.mk b/Config.mk
> index ebbd9c0..fb836a4 100644
> --- a/Config.mk
> +++ b/Config.mk
> @@ -16,7 +16,8 @@ or       = $(if $(strip $(1)),$(1),$(if $(strip 
> $(2)),$(2),$(if $(strip $(3)),$(
>  
>  -include $(XEN_ROOT)/.config
>  
> -# A debug build of Xen and tools?
> +# A debug build of tools?

For this to hold true, a patch like this is needed:

Please let me know what you think.

---8<---
From 0a96ff9f3610622bc4f7114d6e094bf45ca9305f Mon Sep 17 00:00:00 2001
From: Wei Liu <wei.liu2@xxxxxxxxxx>
Date: Mon, 31 Oct 2016 17:42:25 +0000
Subject: [PATCH] build: make debug option affect tools only

The debug option in Config.mk affects hypervisor, tools and stubdom by
appending different flags to CFLAGS.

It is undesirable because now hypervisor build is affect by both Kconfig
and debug.

Disentangle the semantics of debug by pushing relevant options to
individual sub-systems.

For hypervisor, the flags previously added by debug option is now
controlled by CONFIG_DEBUG.

For tools, flags are moved from config/*.mk into tools/Rules.mk.

For stubdom, it is a bit special because it unilaterally sets debug all
the time, and it also inherits CFLAGS from the source package it tries
to build. It should be fine to not inherit any flags from Xen build
system because they will be overridden by source packages anyway.

Specifically there are some considerations on how the flags are picked:

1. we don't need -fno-optimize-sibling-calls anymore because gcc doc
   indicates that it is not enabled for -O1, which we already set in the
   debug build.
2. for tools we use -O0 -g3 in Rules.mk because they already take
   precedence over the flags set in config/*.mk.
3. for hypervisor we don't add -fno-omit-frame-pointer to debug build
   because that's controlled by CONFIG_FRAME_POINTER.

The debug option in Config.mk will only affect tools components after
this patch is applied.

Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
---
 config/StdGNU.mk | 8 --------
 config/SunOS.mk  | 7 -------
 tools/Rules.mk   | 4 +++-
 xen/Rules.mk     | 6 ++++++
 4 files changed, 9 insertions(+), 16 deletions(-)

diff --git a/config/StdGNU.mk b/config/StdGNU.mk
index 39d36b2..6be8233 100644
--- a/config/StdGNU.mk
+++ b/config/StdGNU.mk
@@ -35,14 +35,6 @@ UTIL_LIBS = -lutil
 SONAME_LDFLAG = -soname
 SHLIB_LDFLAGS = -shared
 
-ifneq ($(debug),y)
-CFLAGS += -O2 -fomit-frame-pointer
-else
-# Less than -O1 produces bad code and large stack frames
-CFLAGS += -O1 -fno-omit-frame-pointer
-CFLAGS-$(gcc) += -fno-optimize-sibling-calls
-endif
-
 ifeq ($(lto),y)
 CFLAGS += -flto
 LDFLAGS-$(clang) += -plugin LLVMgold.so
diff --git a/config/SunOS.mk b/config/SunOS.mk
index 86a384d..0fe5f45 100644
--- a/config/SunOS.mk
+++ b/config/SunOS.mk
@@ -31,12 +31,5 @@ UTIL_LIBS =
 SONAME_LDFLAG = -h
 SHLIB_LDFLAGS = -R $(SunOS_LIBDIR) -shared
 
-ifneq ($(debug),y)
-CFLAGS += -O2 -fno-omit-frame-pointer
-else
-# Less than -O1 produces bad code and large stack frames
-CFLAGS += -O1 -fno-omit-frame-pointer
-endif
-
 CFLAGS += -Wa,--divide -D_POSIX_C_SOURCE=200112L -D__EXTENSIONS__
 
diff --git a/tools/Rules.mk b/tools/Rules.mk
index 5a80fec..0e73690 100644
--- a/tools/Rules.mk
+++ b/tools/Rules.mk
@@ -138,9 +138,11 @@ SHLIB_libxenvchan  = $(SHDEPS_libxenvchan) 
-Wl,-rpath-link=$(XEN_LIBVCHAN)
 
 ifeq ($(debug),y)
 # Disable optimizations and enable debugging information for macros
-CFLAGS += -O0 -g3
+CFLAGS += -O0 -g3 -fno-omit-frame-pointer
 # But allow an override to -O0 in case Python enforces -D_FORTIFY_SOURCE=<n>.
 PY_CFLAGS += $(PY_NOOPT_CFLAGS)
+else
+CFLAGS += -O2 -fomit-frame-pointer
 endif
 
 LIBXL_BLKTAP ?= $(CONFIG_BLKTAP2)
diff --git a/xen/Rules.mk b/xen/Rules.mk
index a9fda71..08cc776 100644
--- a/xen/Rules.mk
+++ b/xen/Rules.mk
@@ -46,6 +46,12 @@ ALL_OBJS-y               += $(BASEDIR)/xsm/built_in.o
 ALL_OBJS-y               += $(BASEDIR)/arch/$(TARGET_ARCH)/built_in.o
 ALL_OBJS-$(CONFIG_CRYPTO)   += $(BASEDIR)/crypto/built_in.o
 
+ifeq ($(CONFIG_DEBUG),y)
+CFLAGS += -O1
+else
+CFLAGS += -O2 -fomit-frame-pointer
+endif
+
 CFLAGS += -nostdinc -fno-builtin -fno-common
 CFLAGS += -Werror -Wredundant-decls -Wno-pointer-arith
 CFLAGS += -pipe -g -D__XEN__ -include $(BASEDIR)/include/xen/config.h
-- 
2.1.4


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