[Buildroot] [PATCH] Fix issue with printvars executing giant shell command
Yann E. MORIN
yann.morin.1998 at free.fr
Wed Aug 29 20:49:29 UTC 2018
Trent, All,
On 2018-08-17 16:15 -0700, Trent Piepho spake thusly:
> The underlying problem is that $(foreach V,1 2 3,) does not evaluate to
> an empty string. It evaluates to " ", three empty strings separated by
> whitespace.
>
> A construct of this format, with a giant list in the foreach, is part of
> the printvars command. This means that "@:$(foreach ....)", which is
> intended to expand to a null command, in fact expands to "@: "
> with a great deal of whitespace. Make chooses to execute this command
> with:
> execve("/bin/sh", ["/bin/sh", "-c", ": "]
>
> But with far more whitespace. So much that it can exceed shell command
> line length limits.
>
> 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.
>
> In some cases, make will not invoke a command via "sh -c" and will exec
> it directly. In this case make does command line argument parsing and
> will swallow all the whitespace without overflowing a /bin/sh limit. It
> proved difficult to write a command that ensured make would do this.
>
> Signed-off-by: Trent Piepho <tpiepho at impinj.com>
> ---
> Makefile | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index 0115c4dfcc..b396c56042 100644
> --- 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).
I.e. the following:
diff --git a/Makefile b/Makefile
index 413ec921cd..b7b1257ea6 100644
--- a/Makefile
+++ b/Makefile
@@ -977,7 +977,7 @@ $(BUILD_DIR)/.br2-external.in: $(BUILD_DIR)
# displayed.
.PHONY: printvars
printvars:
- @:$(foreach V, \
+ $(foreach V, \
$(sort $(if $(VARS),$(fil ter $(VARS),$(.VARIABLES)),$(.VARIABLES))), \
$(if $(filter-out environment% default automatic, \
$(origin $V)), \
Do you see a case where that would not work?
FTR I tried to strace it to find the shells;
$ strace -o m.log -ff -e trace=process -- make -s printvars >/dev/null
$ grep execve m.log* |grep ' '
--> nothing
(before the patch above, there was one hit on the grep.)
Regards,
Yann E. MORIN.
> $(sort $(if $(VARS),$(filter $(VARS),$(.VARIABLES)),$(.VARIABLES))), \
> $(if $(filter-out environment% default automatic, \
> $(origin $V)), \
> $(if $(QUOTED_VARS),\
> $(info $V='$(subst ','\'',$(if $(RAW_VARS),$(value $V),$($V)))'), \
> - $(info $V=$(if $(RAW_VARS),$(value $V),$($V))))))
> + $(info $V=$(if $(RAW_VARS),$(value $V),$($V)))))))
> # ' Syntax colouring...
>
> .PHONY: clean
> --
> 2.14.4
>
> _______________________________________________
> buildroot mailing list
> buildroot at busybox.net
> http://lists.busybox.net/mailman/listinfo/buildroot
--
.-----------------.--------------------.------------------.--------------------.
| Yann E. MORIN | Real-Time Embedded | /"\ ASCII RIBBON | Erics' conspiracy: |
| +33 662 376 056 | Software Designer | \ / CAMPAIGN | ___ |
| +33 223 225 172 `------------.-------: X AGAINST | \e/ There is no |
| http://ymorin.is-a-geek.org/ | _/*\_ | / \ HTML MAIL | v conspiracy. |
'------------------------------^-------^------------------^--------------------'
More information about the buildroot
mailing list