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Re: [XEN PATCH v9 03/30] build: fix exported variable name CFLAGS_stack_boundary
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Anthony PERARD <anthony.perard@xxxxxxxxxx>
- Date: Fri, 28 Jan 2022 15:04:55 +0000
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Fri, 28 Jan 2022 15:06:35 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Fri, Jan 28, 2022 at 12:14:58PM +0100, Jan Beulich wrote:
> On 25.01.2022 12:00, Anthony PERARD wrote:
> > Exporting a variable with a dash doesn't work reliably, they may be
> > striped from the environment when calling a sub-make or sub-shell.
> >
> > CFLAGS-stack-boundary start to be removed from env in patch "build:
> > set ALL_OBJS in main Makefile; move prelink.o to main Makefile" when
> > running `make "ALL_OBJS=.."` due to the addition of the quote. At
> > least in my empirical tests.
> >
> > Fixes: 2740d96efd ("xen/build: have the root Makefile generates the CFLAGS")
> > Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
>
> While I did commit this, I'm still somewhat confused. How would quoting
> of elements on a make command line make a difference to which variables
> get exported?
I don't know, maybe without quote, make run sub-make directly, but with
double-quote, a shell is used.
But after reading the manual, I didn't expect the variable to be passed
down sub-make at all:
5.7.2 Communicating Variables to a Sub-make
Except by explicit request, make exports a variable only if it is
either defined in the environment initially or set on the command
line, and if its name consists only of letters, numbers, and
underscores.
But somehow, sub-makes also export the non-shell-exportable variables,
unless the command line in a recipe invoking make has double-quotes.
I've tried again, and checked the process list:
- when running `$(MAKE) -C foo`; make just execute make
- when running `$(MAKE) -C 'foo'`; make just execute make
- when running `$(MAKE) -C "foo"`; make execute /bin/sh -c ...
- when running `$(MAKE) -C foo | tee`; make execute /bin/sh -c ...
So, CFLAGS-stack-boundary disappear when /bin/sh is involved.
> In any event I understand the description that prior to the subsequent
> change there's not actually any issue. Hence I'm not going to queue
> this for backporting despite the Fixes: tag. Unless of course I'm told
> otherwise (with justification).
Justification would be that it's not supposed to work, based on
information from make's manual.
Thanks,
--
Anthony PERARD
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