netdev - RE: [net-next PATCH V2 2/5] samples/bpf: Makefile verify LLVM compiler avail and bpf target is supported

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Message-ID: <063D6719AE5E284EB5DD2968C1650D6D5F4AB86F@AcuExch.aculab.com>
Date:	Wed, 27 Apr 2016 13:52:49 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Jesper Dangaard Brouer' <brouer@...hat.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:	"linux-kbuild@...r.kernel.org" <linux-kbuild@...r.kernel.org>,
	"bblanco@...mgrid.com" <bblanco@...mgrid.com>,
	"naveen.n.rao@...ux.vnet.ibm.com" <naveen.n.rao@...ux.vnet.ibm.com>,
	"borkmann@...earbox.net" <borkmann@...earbox.net>,
	"alexei.starovoitov@...il.com" <alexei.starovoitov@...il.com>
Subject: RE: [net-next PATCH V2 2/5] samples/bpf: Makefile verify LLVM
 compiler avail and bpf target is supported

From: Jesper Dangaard Brouer
> Sent: 26 April 2016 17:27
> Make compiling samples/bpf more user friendly, by detecting if LLVM
> compiler tool 'llc' is available, and also detect if the 'bpf' target
> is available in this version of LLVM.
...
> diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
> index 5bae9536f100..45859c99f573 100644
> --- a/samples/bpf/Makefile
> +++ b/samples/bpf/Makefile
> @@ -85,6 +85,24 @@ HOSTLOADLIBES_test_overhead += -lelf -lrt
>  #  make samples/bpf/ LLC=~/git/llvm/build/bin/llc
>  LLC ?= llc
> 
> +# Verify LLVM compiler is available and bpf target is supported
> +.PHONY: verify_cmd_llc verify_target_bpf
> +
> +verify_cmd_llc:
> +	@if ! (which "${LLC}" > /dev/null 2>&1); then \

You should use 'type' not 'which'.
'type' is a posix shell builtin, 'which' is a script/program
that tries to emulate a 'csh' builtin.
You want to know whether the shell that make runs can execute ${LLC}
not whether a csh would be able to run it.

You might also want to worry about:
    LLC="/path_to_llc/llc -extra_arg" make fubar

	David