[PATCH] scripts/decode_stacktrace.sh: optionally use LLVM utilities

Carlos Llamas
2023-09-29T03:49:04Z

GNU's addr2line can have problems parsing a vmlinux built with LLVM,
particularly when LTO was used. In order to decode the traces correctly
this patch adds the ability to switch to LLVM's utilities readelf and
addr2line. The same approach is followed by Will in [1].

Before:
$ scripts/decode_stacktrace.sh vmlinux < kernel.log
[17716.240635] Call trace:
[17716.240646] skb_cow_data (??:?)
[17716.240654] esp6_input (ld-temp.o:?)
[17716.240666] xfrm_input (ld-temp.o:?)
[17716.240674] xfrm6_rcv (??:?)
[...]

After:
$ LLVM=1 scripts/decode_stacktrace.sh vmlinux < kernel.log
[17716.240635] Call trace:
[17716.240646] skb_cow_data (include/linux/skbuff.h:2172 net/core/skbuff.c:4503)
[17716.240654] esp6_input (net/ipv6/esp6.c:977)
[17716.240666] xfrm_input (net/xfrm/xfrm_input.c:659)
[17716.240674] xfrm6_rcv (net/ipv6/xfrm6_input.c:172)
[...]

Note that one could set CROSS_COMPILE=llvm- instead to hack around this
issue. However, doing so can break the decodecode routine as it will
force the selection of other LLVM utilities down the line e.g. llvm-as.

[1] https://lore.kernel.org/all/20230914131225.13415-3-will@kernel.org/

Cc: Will Deacon <will@kernel.org>
Cc: John Stultz <jstultz@google.com>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Carlos Llamas <cmllamas@google.com>
---
scripts/decode_stacktrace.sh | 19 +++++++++++++++++--
1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/scripts/decode_stacktrace.sh b/scripts/decode_stacktrace.sh
index 564c5632e1a2..bfe5a4082d8e 100755
--- a/scripts/decode_stacktrace.sh
+++ b/scripts/decode_stacktrace.sh
@@ -16,6 +16,21 @@ elif type c++filt >/dev/null 2>&1 ; then
cppfilt_opts=-i
fi

+UTIL_SUFFIX=
+if [[ -z ${LLVM:-} ]]; then
+ UTIL_PREFIX=${CROSS_COMPILE:-}
+else
+ UTIL_PREFIX=llvm-
+ if [[ ${LLVM} == */ ]]; then
+ UTIL_PREFIX=${LLVM}${UTIL_PREFIX}
+ elif [[ ${LLVM} == -* ]]; then
+ UTIL_SUFFIX=${LLVM}
+ fi
+fi
+
+READELF=${UTIL_PREFIX}readelf${UTIL_SUFFIX}
+ADDR2LINE=${UTIL_PREFIX}addr2line${UTIL_SUFFIX}
+
if [[ $1 == "-r" ]] ; then
vmlinux=""
basepath="auto"
@@ -75,7 +90,7 @@ find_module() {

if [[ "$modpath" != "" ]] ; then
for fn in $(find "$modpath" -name "${module//_/[-_]}.ko*") ; do
- if readelf -WS "$fn" | grep -qwF .debug_line ; then
+ if ${READELF} -WS "$fn" | grep -qwF .debug_line ; then
echo $fn
return
fi
@@ -169,7 +184,7 @@ parse_symbol() {
if [[ $aarray_support == true && "${cache[$module,$address]+isset}" == "isset" ]]; then
local code=${cache[$module,$address]}
else
- local code=$(${CROSS_COMPILE}addr2line -i -e "$objfile" "$address" 2>/dev/null)
+ local code=$(${ADDR2LINE} -i -e "$objfile" "$address" 2>/dev/null)
if [[ $aarray_support == true ]]; then
cache[$module,$address]=$code
fi
--
2.42.0.582.g8ccd20d70d-goog