The recommended optimisation level for debugging is -Og, and is what tools
such as gdb prefer.  In practice, it equates to -01 with a few specific
optimisations turned off.

abi-dumper in particular wants the libraries it inspects in this form.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Ian Jackson <iwj@xenproject.org>
CC: Wei Liu <wl@xen.org>
CC: Juergen Gross <jgross@suse.com>
---
 tools/Rules.mk | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/tools/Rules.mk b/tools/Rules.mk
index f61da81f4a..2907ed2d39 100644
--- a/tools/Rules.mk
+++ b/tools/Rules.mk
@@ -106,8 +106,9 @@ endif
 CFLAGS_libxenlight += $(CFLAGS_libxenctrl)
 
 ifeq ($(debug),y)
-# Disable optimizations
-CFLAGS += -O0 -fno-omit-frame-pointer
+# Use -Og if available, -O0 otherwise
+dbg_opt_level := $(call cc-option,$(CC),-Og,-O0)
+CFLAGS += $(dbg_opt_level) -fno-omit-frame-pointer
 # But allow an override to -O0 in case Python enforces -D_FORTIFY_SOURCE=<n>.
 PY_CFLAGS += $(PY_NOOPT_CFLAGS)
 else
-- 
2.11.0

On 12.02.2021 16:39, Andrew Cooper wrote:
> The recommended optimisation level for debugging is -Og, and is what tools
> such as gdb prefer.  In practice, it equates to -01 with a few specific
> optimisations turned off.
> 
> abi-dumper in particular wants the libraries it inspects in this form.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

Reviewed-by: Jan Beulich <jbeulich@suse.com>

> --- a/tools/Rules.mk
> +++ b/tools/Rules.mk
> @@ -106,8 +106,9 @@ endif
>  CFLAGS_libxenlight += $(CFLAGS_libxenctrl)
>  
>  ifeq ($(debug),y)
> -# Disable optimizations
> -CFLAGS += -O0 -fno-omit-frame-pointer
> +# Use -Og if available, -O0 otherwise
> +dbg_opt_level := $(call cc-option,$(CC),-Og,-O0)
> +CFLAGS += $(dbg_opt_level) -fno-omit-frame-pointer

I wonder if we shouldn't do something similar for the hypervisor,
where we use -O1 for debug builds right now. At least when
DEBUG_INFO is also enabled, -Og may be better.

Jan

On 12/02/2021 16:04, Jan Beulich wrote:
> On 12.02.2021 16:39, Andrew Cooper wrote:
>> The recommended optimisation level for debugging is -Og, and is what tools
>> such as gdb prefer.  In practice, it equates to -01 with a few specific
>> optimisations turned off.
>>
>> abi-dumper in particular wants the libraries it inspects in this form.
>>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
> Reviewed-by: Jan Beulich <jbeulich@suse.com>

Thanks,

>
>> --- a/tools/Rules.mk
>> +++ b/tools/Rules.mk
>> @@ -106,8 +106,9 @@ endif
>>  CFLAGS_libxenlight += $(CFLAGS_libxenctrl)
>>  
>>  ifeq ($(debug),y)
>> -# Disable optimizations
>> -CFLAGS += -O0 -fno-omit-frame-pointer
>> +# Use -Og if available, -O0 otherwise
>> +dbg_opt_level := $(call cc-option,$(CC),-Og,-O0)
>> +CFLAGS += $(dbg_opt_level) -fno-omit-frame-pointer
> I wonder if we shouldn't do something similar for the hypervisor,
> where we use -O1 for debug builds right now. At least when
> DEBUG_INFO is also enabled, -Og may be better.

I also made that work... its rather more invasive in terms of changes -
all for "maybe uninitialised" warnings.

$ git diff e2bab84984^ --stat
 xen/Makefile                    | 3 ++-
 xen/arch/arm/domain_build.c     | 2 +-
 xen/arch/x86/irq.c              | 2 +-
 xen/arch/x86/mm/shadow/common.c | 2 +-
 xen/arch/x86/pv/shim.c          | 6 +++---
 xen/arch/x86/sysctl.c           | 4 ++--
 xen/common/efi/boot.c           | 2 +-
 7 files changed, 11 insertions(+), 10 deletions(-)

is what is required to make Gitlab happy.  I was planning to defer it to
4.16 at this point.

~Andrew

On 12.02.2021 17:09, Andrew Cooper wrote:
> On 12/02/2021 16:04, Jan Beulich wrote:
>> On 12.02.2021 16:39, Andrew Cooper wrote:
>>> --- a/tools/Rules.mk
>>> +++ b/tools/Rules.mk
>>> @@ -106,8 +106,9 @@ endif
>>>  CFLAGS_libxenlight += $(CFLAGS_libxenctrl)
>>>  
>>>  ifeq ($(debug),y)
>>> -# Disable optimizations
>>> -CFLAGS += -O0 -fno-omit-frame-pointer
>>> +# Use -Og if available, -O0 otherwise
>>> +dbg_opt_level := $(call cc-option,$(CC),-Og,-O0)
>>> +CFLAGS += $(dbg_opt_level) -fno-omit-frame-pointer
>> I wonder if we shouldn't do something similar for the hypervisor,
>> where we use -O1 for debug builds right now. At least when
>> DEBUG_INFO is also enabled, -Og may be better.
> 
> I also made that work... its rather more invasive in terms of changes -
> all for "maybe uninitialised" warnings.
> 
> $ git diff e2bab84984^ --stat
>  xen/Makefile                    | 3 ++-
>  xen/arch/arm/domain_build.c     | 2 +-
>  xen/arch/x86/irq.c              | 2 +-
>  xen/arch/x86/mm/shadow/common.c | 2 +-
>  xen/arch/x86/pv/shim.c          | 6 +++---
>  xen/arch/x86/sysctl.c           | 4 ++--
>  xen/common/efi/boot.c           | 2 +-
>  7 files changed, 11 insertions(+), 10 deletions(-)
> 
> is what is required to make Gitlab happy.

Oh, good to know. Thanks!

>  I was planning to defer it to 4.16 at this point.

Of course.

Jan

Jan Beulich writes ("Re: [PATCH 07/10] tools: Use -Og for debug builds when available"):
> On 12.02.2021 16:39, Andrew Cooper wrote:
> > The recommended optimisation level for debugging is -Og, and is what tools
> > such as gdb prefer.  In practice, it equates to -01 with a few specific
> > optimisations turned off.
> > 
> > abi-dumper in particular wants the libraries it inspects in this form.
> > 
> > Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
> 
> Reviewed-by: Jan Beulich <jbeulich@suse.com>

Acked-by: Ian Jackson <iwj@xenproject.org>

Andrew Cooper writes ("[PATCH 07/10] tools: Use -Og for debug builds when available"):
> The recommended optimisation level for debugging is -Og, and is what tools
> such as gdb prefer.  In practice, it equates to -01 with a few specific
> optimisations turned off.
> 
> abi-dumper in particular wants the libraries it inspects in this form.

Release-Acked-by: Ian Jackson <iwj@xenproject.org>

I would prefer to have this in 4.15 now than to backport it later...

Ian.