scripts/check-local-export fails with some versions of bash.

    CC      scripts/mod/empty.o
  ./scripts/check-local-export: line 54: wait: pid 17328 is not a child of this shell
  make[2]: *** [scripts/mod/empty.o] Error 127
  make[2]: *** Deleting file `scripts/mod/empty.o'
  make[1]: *** [prepare0] Error 2
  make: *** [__sub-make] Error 2

Avoid use of bash's built-in wait command, by saving the output from
nm command into a temporary variable.

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Fixes: 31cb50b5590fe911 ("kbuild: check static EXPORT_SYMBOL* by script instead of modpost")
---
Changes in v2:
  llvm-nm can't use end-of-options argument, reported-by kernel test robot <lkp@intel.com>

 scripts/check-local-export | 29 +++++++++++++----------------
 1 file changed, 13 insertions(+), 16 deletions(-)

diff --git a/scripts/check-local-export b/scripts/check-local-export
index da745e2743b7..850abc150855 100755
--- a/scripts/check-local-export
+++ b/scripts/check-local-export
@@ -11,9 +11,20 @@ set -e
 declare -A symbol_types
 declare -a export_symbols
 
+function die
+{
+    echo "$1" >&2
+    exit 1
+}
+
 exit_code=0
 
-while read value type name
+# If there is no symbol in the object, ${NM} (both GNU nm and llvm-nm)
+# shows 'no symbols' diagnostic and exits with 0. Saving such line into
+# symbol_types is fine because export_symbols will remain empty.
+result=$(${NM} ${1} 2>&1) || die "${result}"
+
+echo "${result}" | while read value type name
 do
 	# Skip the line if the number of fields is less than 3.
 	#
@@ -37,21 +48,7 @@ do
 	if [[ ${name} == __ksymtab_* ]]; then
 		export_symbols+=(${name#__ksymtab_})
 	fi
-
-	# If there is no symbol in the object, ${NM} (both GNU nm and llvm-nm)
-	# shows 'no symbols' diagnostic (but exits with 0). It is harmless and
-	# hidden by '2>/dev/null'. However, it suppresses real error messages
-	# as well. Add a hand-crafted error message here.
-	#
-	# Use --quiet instead of 2>/dev/null when we upgrade the minimum version
-	# of binutils to 2.37, llvm to 13.0.0.
-	#
-	# Then, the following line will be really simple:
-	#   done < <(${NM} --quiet ${1})
-done < <(${NM} ${1} 2>/dev/null || { echo "${0}: ${NM} failed" >&2; false; } )
-
-# Catch error in the process substitution
-wait $!
+done
 
 for name in "${export_symbols[@]}"
 do
-- 
2.18.4

On Tue, Jun 7, 2022 at 7:13 AM Tetsuo Handa
<penguin-kernel@i-love.sakura.ne.jp> wrote:
>
> scripts/check-local-export fails with some versions of bash.
>
>     CC      scripts/mod/empty.o
>   ./scripts/check-local-export: line 54: wait: pid 17328 is not a child of this shell
>   make[2]: *** [scripts/mod/empty.o] Error 127
>   make[2]: *** Deleting file `scripts/mod/empty.o'
>   make[1]: *** [prepare0] Error 2
>   make: *** [__sub-make] Error 2
>
> Avoid use of bash's built-in wait command, by saving the output from
> nm command into a temporary variable.


This patch does not work because you did not avoid
running the while-loop in a subshell.

It is well described in  this page:
https://riptutorial.com/bash/example/26955/to-avoid-usage-of-a-sub-shell



I will send a working patch with a proper commit log.

The part "Saving such line into symbol_types is fine because export_symbols
will remain empty." seems OK with me.
(I was searching for an elegant solution for this, but
I could not come up with a better one.)






> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Fixes: 31cb50b5590fe911 ("kbuild: check static EXPORT_SYMBOL* by script instead of modpost")
> ---









--
Best Regards

Masahiro Yamada

On 2022/06/07 17:34, Masahiro Yamada wrote:
> This patch does not work because you did not avoid
> running the while-loop in a subshell.
> 
> It is well described in  this page:
> https://riptutorial.com/bash/example/26955/to-avoid-usage-of-a-sub-shell
> 

I didn't know that. Then, adding below diff will work.

@@ -24,7 +24,7 @@ exit_code=0
 # symbol_types is fine because export_symbols will remain empty.
 result=$(${NM} ${1} 2>&1) || die "${result}"

-echo "${result}" | while read value type name
+while read value type name
 do
        # Skip the line if the number of fields is less than 3.
        #
@@ -48,7 +48,9 @@ do
        if [[ ${name} == __ksymtab_* ]]; then
                export_symbols+=(${name#__ksymtab_})
        fi
-done
+done <<EOF
+"${result}"
+EOF

 for name in "${export_symbols[@]}"
 do

> 
> 
> I will send a working patch with a proper commit log.

OK. "[PATCH] scripts/check-local-export: avoid 'wait $!' for process substitution" works.

Thank you.