Re: [fsverity-utils PATCH 1/2] Use pkg-config to get libcrypto build flags

[Eric Biggers <ebiggers@kernel.org>]

On Thu, Oct 22, 2020 at 06:59:33PM +0100, luca.boccassi@gmail.com wrote:
> From: Luca Boccassi <luca.boccassi@microsoft.com>
> 
> Especially when cross-compiling or other such cases, it might be necessary
> to pass additional compiler flags. This is commonly done via pkg-config,
> so use it if available, and fall back to the hardcoded -lcrypto if not.
> 
> Signed-off-by: Luca Boccassi <luca.boccassi@microsoft.com>
> ---
>  Makefile | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/Makefile b/Makefile
> index 3fc1bec..122c0a2 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -58,6 +58,7 @@ BINDIR          ?= $(PREFIX)/bin
>  INCDIR          ?= $(PREFIX)/include
>  LIBDIR          ?= $(PREFIX)/lib
>  DESTDIR         ?=
> +PKGCONF         ?= pkg-config
>  
>  # Rebuild if a user-specified setting that affects the build changed.
>  .build-config: FORCE
> @@ -69,7 +70,8 @@ DESTDIR         ?=
>  
>  DEFAULT_TARGETS :=
>  COMMON_HEADERS  := $(wildcard common/*.h)
> -LDLIBS          := -lcrypto
> +LDLIBS          := $(shell $(PKGCONF) libcrypto --libs 2>/dev/null || echo -lcrypto)
> +CFLAGS          += $(shell $(PKGCONF) libcrypto --cflags 2>/dev/null || echo)

There should be a way to prevent pkg-config from being used if someone wants to
link to a local copy of libcrypto.  One might expect setting PKGCONF to an empty
string to work, and it kind of does, but then the shell command executes
"libcrypto", which is strange.  How about quoting "$(PKGCONF)" so that the shell
command is guaranteed to fail as expected in that case?

- Eric