netdev - Re: [PATCH iproute2] build: Fix link errors on some systems

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Message-ID: <405e8cce-e2dd-891a-dc8a-7c8b0c77f4c6@nvidia.com>
Date:   Wed, 6 Jan 2021 10:42:35 +0200
From:   Roi Dayan <roid@...dia.com>
To:     Petr Machata <petrm@...dia.com>
CC:     <netdev@...r.kernel.org>, David Ahern <dsahern@...il.com>,
        Petr Machata <me@...chata.org>
Subject: Re: [PATCH iproute2] build: Fix link errors on some systems



On 2021-01-04 6:07 PM, Petr Machata wrote:
> 
> Roi Dayan <roid@...dia.com> writes:
> 
>> Since moving get_rate() and get_size() from tc to lib, on some
>> systems we fail to link because of missing the math lib.
>> Move the link flag from tc makefile to the main makefile.
> 
> Hmm, yeah, it gets optimized out on x86-64. The issue is reproducible
> on any platform with -O0.
> 
>> ../lib/libutil.a(utils.o): In function `get_rate':
>> utils.c:(.text+0x10dc): undefined reference to `floor'
>> ../lib/libutil.a(utils.o): In function `get_size':
>> utils.c:(.text+0x1394): undefined reference to `floor'
>> ../lib/libutil.a(json_print.o): In function `sprint_size':
>> json_print.c:(.text+0x14c0): undefined reference to `rint'
>> json_print.c:(.text+0x14f4): undefined reference to `rint'
>> json_print.c:(.text+0x157c): undefined reference to `rint'
>>
>> Fixes: f3be0e6366ac ("lib: Move get_rate(), get_rate64() from tc here")
>> Fixes: 44396bdfcc0a ("lib: Move get_size() from tc here")
>> Fixes: adbe5de96662 ("lib: Move sprint_size() from tc here, add print_size()")
>> Signed-off-by: Roi Dayan <roid@...dia.com>
>> ---
>>   Makefile    | 1 +
>>   tc/Makefile | 2 +-
>>   2 files changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/Makefile b/Makefile
>> index e64c65992585..2a604ec58905 100644
>> --- a/Makefile
>> +++ b/Makefile
>> @@ -59,6 +59,7 @@ SUBDIRS=lib ip tc bridge misc netem genl tipc devlink rdma dcb man
>>   
>>   LIBNETLINK=../lib/libutil.a ../lib/libnetlink.a
>>   LDLIBS += $(LIBNETLINK)
>> +LDFLAGS += -lm
>>   
>>   all: config.mk
>>   	@set -e; \
>> diff --git a/tc/Makefile b/tc/Makefile
>> index 5a517af20b7c..8d91900716c1 100644
>> --- a/tc/Makefile
>> +++ b/tc/Makefile
>> @@ -110,7 +110,7 @@ ifneq ($(TC_CONFIG_NO_XT),y)
>>   endif
>>   
>>   TCOBJ += $(TCMODULES)
>> -LDLIBS += -L. -lm
>> +LDLIBS += -L.
>>   
>>   ifeq ($(SHARED_LIBS),y)
>>   LDLIBS += -ldl
> 
> This will work, but it will give a libm dependency to all the tools.
> util.c currently tries not to do that:
> 
> 	/* emulate ceil() without having to bring-in -lm and always be >= 1 */
> 	*val = t;
> 	if (*val < t)
> 		*val += 1;
> 
> I think that just adding an unnecessary -lm is more of a tidiness issue
> than anything else. One way to avoid it is to split the -lm deps out
> from util.c / json_print.c to like util_math.c / json_print_math.c. That
> way they will be in an .o of their own, and won't be linked in unless
> the binary in question needs the code. Then the binaries that do call it
> can keep on linking in -lm like they did so far.
> 
> Thoughts?
> 

ok fine by me.