scripts/decode_stacktrace.sh: optionally use LLVM utilities

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/

Link: https://lkml.kernel.org/r/20230929034836.403735-1-cmllamas@google.com
Signed-off-by: Carlos Llamas <cmllamas@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Elliot Berman <quic_eberman@quicinc.com>
Tested-by: Justin Stitt <justinstitt@google.com>
Cc: Will Deacon <will@kernel.org>
Cc: John Stultz <jstultz@google.com>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Tom Rix <trix@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/scripts/decode_stacktrace.sh b/scripts/decode_stacktrace.sh
index cb980b1..fa5be6f 100755 (executable)
--- 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