[bpf,v2] bpf: fix for lex/yacc build error with gcc-5

Fix build error found with Ubuntu shipped gcc-5

~/git/bpf/tools/bpf$ make all

Auto-detecting system features:
...                        libbfd: [ OFF ]
...        disassembler-four-args: [ OFF ]

  CC       bpf_jit_disasm.o
  LINK     bpf_jit_disasm
  CC       bpf_dbg.o
/home/john/git/bpf/tools/bpf/bpf_dbg.c: In function ‘cmd_load’:
/home/john/git/bpf/tools/bpf/bpf_dbg.c:1077:13: warning: ‘cont’ may be used uninitialized in this function [-Wmaybe-uninitialized]
  } else if (matches(subcmd, "pcap") == 0) {
             ^
  LINK     bpf_dbg
  CC       bpf_asm.o
make: *** No rule to make target `bpf_exp.yacc.o', needed by `bpf_asm'.  Stop.

Fixes: 5a8997f20715 ("tools: bpf: respect output directory during build")
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
---
 tools/bpf/Makefile |    2 ++
 1 file changed, 2 insertions(+)

On 04/25/2018 11:22 PM, John Fastabend wrote:
> Fix build error found with Ubuntu shipped gcc-5
> 
> ~/git/bpf/tools/bpf$ make all
> 
> Auto-detecting system features:
> ...                        libbfd: [ OFF ]
> ...        disassembler-four-args: [ OFF ]
> 
>   CC       bpf_jit_disasm.o
>   LINK     bpf_jit_disasm
>   CC       bpf_dbg.o
> /home/john/git/bpf/tools/bpf/bpf_dbg.c: In function ‘cmd_load’:
> /home/john/git/bpf/tools/bpf/bpf_dbg.c:1077:13: warning: ‘cont’ may be used uninitialized in this function [-Wmaybe-uninitialized]
>   } else if (matches(subcmd, "pcap") == 0) {
>              ^
>   LINK     bpf_dbg
>   CC       bpf_asm.o
> make: *** No rule to make target `bpf_exp.yacc.o', needed by `bpf_asm'.  Stop.
> 
> Fixes: 5a8997f20715 ("tools: bpf: respect output directory during build")
> Signed-off-by: John Fastabend <john.fastabend@gmail.com>

Applied to bpf, thanks John! Will see to get that annoying bpf_dbg warn out
of the way if no one beats me to it. ;)

On Wed, 25 Apr 2018 14:22:45 -0700, John Fastabend wrote:
> --- a/tools/bpf/Makefile
> +++ b/tools/bpf/Makefile
> @@ -76,6 +76,8 @@ $(OUTPUT)bpf_asm: $(OUTPUT)bpf_asm.o $(OUTPUT)bpf_exp.yacc.o $(OUTPUT)bpf_exp.le
>  	$(QUIET_LINK)$(CC) $(CFLAGS) -o $@ $^
>  
>  $(OUTPUT)bpf_exp.lex.c: $(OUTPUT)bpf_exp.yacc.c
> +$(OUTPUT)bpf_exp.yacc.o: $(OUTPUT)bpf_exp.yacc.c
> +$(OUTPUT)bpf_exp.lex.o: $(OUTPUT)bpf_exp.lex.c

Looks better than v1, the first dependency is important.

For some reason, I did not need the other two rules.

By the way, make invoked from tools/bpf/ has never really worked, even
before my patchset. This works correctly:

cd tools
make bpf

 Jiri