linux-kernel - [PATCH] kbuild: use a pipe rather than process substitution

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Message-Id: <20220610213453.630304-1-alvin@pqrs.dk>
Date:   Fri, 10 Jun 2022 23:34:52 +0200
From:   Alvin Šipraga <alvin@...s.dk>
To:     Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>,
        Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org,
        Alvin Šipraga <alsi@...g-olufsen.dk>,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: [PATCH] kbuild: use a pipe rather than process substitution

From: Alvin Šipraga <alsi@...g-olufsen.dk>

Bash process substitution of the form `foo < <(bar)`, as found in
scripts/check-local-export, can cause issues in chrooted environments
and with tools such as pseudo. The blamed commit started to cause build
errors for me when using the Yocto project's devshell environment;
devshell uses pseudo internally:

.../scripts/check-local-export: line 51: /dev/fd/63: No such file or directory

Replace the process substitution with a simple pipe into the while loop.
This is functionally equivalent and more portable than the former. Note
that pipefail is enabled so that the script terminates when ${NM} fails.

Link: https://bugzilla.yoctoproject.org/show_bug.cgi?id=13288
Fixes: 31cb50b5590f ("kbuild: check static EXPORT_SYMBOL* by script instead of modpost")
Signed-off-by: Alvin Šipraga <alsi@...g-olufsen.dk>
---
 scripts/check-local-export | 28 +++++++++++++---------------
 1 file changed, 13 insertions(+), 15 deletions(-)

diff --git a/scripts/check-local-export b/scripts/check-local-export
index da745e2743b7..42de6f8f2541 100755
--- a/scripts/check-local-export
+++ b/scripts/check-local-export
@@ -7,12 +7,24 @@
 # EXPORT_SYMBOL should be used for global symbols.
 
 set -e
+set -o pipefail
 
 declare -A symbol_types
 declare -a export_symbols
 
 exit_code=0
 
+# 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 ${1})
+(${NM} ${1} 2>/dev/null || { echo "${0}: ${NM} failed" >&2; false; } ) | \
 while read value type name
 do
 	# Skip the line if the number of fields is less than 3.
@@ -37,21 +49,7 @@ 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
-- 
2.36.1