[Buildroot] [PATCH] Fix issue with printvars executing giant shell command
Yann E. MORIN
yann.morin.1998 at free.fr
Mon Sep 10 18:18:37 UTC 2018
Trent, All,
On 2018-09-10 17:45 +0000, Trent Piepho spake thusly:
> On Wed, 2018-08-29 at 22:49 +0200, Yann E. MORIN wrote:
> > On 2018-08-17 16:15 -0700, Trent Piepho spake thusly:
> > >
> > > The solution here is to use $(strip $(foreach ...)), so the command
> > > expands to "@:", which make is smart enough to not even execute and
> > > wouldn't exceed any limits if it did.
>
> > > --- a/Makefile
> > > +++ b/Makefile
> > > @@ -988,13 +988,13 @@ $(BUILD_DIR)/.br2-external.in: $(BUILD_DIR)
> > > # displayed.
> > > .PHONY: printvars
> > > printvars:
> > > - @:$(foreach V, \
> > > + @:$(strip $(foreach V, \
> >
> > Why do we even need an actual command here? It works exactly the same
> > without a rule, and this indeed also gets rid of a call to a shell (and
> > consequently won't exceed the command line length limit).
>
> Not quite exactly the same. There's no longer a recipe at all, only
> the definition of a dependency for printvars, so the output will
> include:
>
> make[1]: Nothing to be done for 'printvars'.
So what about:
diff --git a/Makefile b/Makefile
index 2c6af12989..57e776056c 100644
--- a/Makefile
+++ b/Makefile
@@ -988,7 +988,8 @@ $(BUILD_DIR)/.br2-external.in: $(BUILD_DIR)
# displayed.
.PHONY: printvars
printvars:
- @:$(foreach V, \
+ @:
+ $(foreach V, \
$(sort $(if $(VARS),$(filter $(VARS),$(.VARIABLES)),$(.VARIABLES))), \
$(if $(filter-out environment% default automatic, \
$(origin $V)), \
> Which isn't expected output for something that was parsing printvars.
Which should probably have already called it with 'make -s' because
that is what is also needed when printvars is called from an
out-of-tree build, by the way.
> I'll also mention that we saw this error running buildroot in certain
> docker containers, but not everywhere. Whether or not make will pass a
> giant sequence of whitespace to a shell ends up not being so simple,
> and I couldn't find any precise rules that govern it. So just because
> it works as desired in one test doesn't mean is must work that way
> everywhere.
Before my suggested hange:
$ strace -ff -s 1048576 -o n.log -e trace=process -- make printvars >/dev/null
$ grep execve n.log* |grep ' '
--> hit!
With the above change:
$ strace -ff -s 1048576 -o n.log -e trace=process -- make printvars >/dev/null
$ grep execve n.log* |grep ' '
--> no hit!
In a recipe, a command line that contains only spaces will not be executed
by make.
So with the above, you get the silence from a rule, and no long-shell
commands that break.
> However, it is clearly defined that strip will convert a sequence of
> whitespace to an empty string, so I figured better to relay on that.
I'm just trying to keep it simple.
Regards,
Yann E. MORIN.
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