[PATCH v2 2/2] scripts/faddr2line: Constrain readelf output to symbols from System.map

[Will Deacon]

Some symbols emitted in the readelf output but filtered from System.map
can confuse the 'faddr2line' symbol size calculation, resulting in the
erroneous rejection of valid offsets. This is especially prevalent when
building an arm64 kernel with CONFIG_CFI_CLANG=y, where most functions
are prefixed with a 32-bit data value in a '$d.n' section. For example:

447538: ffff800080014b80   548 FUNC    GLOBAL DEFAULT    2 do_one_initcall
   104: ffff800080014c74     0 NOTYPE  LOCAL  DEFAULT    2 $x.73
   106: ffff800080014d30     0 NOTYPE  LOCAL  DEFAULT    2 $x.75
   111: ffff800080014da4     0 NOTYPE  LOCAL  DEFAULT    2 $d.78
   112: ffff800080014da8     0 NOTYPE  LOCAL  DEFAULT    2 $x.79
    36: ffff800080014de0   200 FUNC    LOCAL  DEFAULT    2 run_init_process

Adding a warning to do_one_initcall() results in:

  | WARNING: CPU: 0 PID: 1 at init/main.c:1236 do_one_initcall+0xf4/0x260

Which 'faddr2line' refuses to accept:

$ ./scripts/faddr2line vmlinux do_one_initcall+0xf4/0x260
skipping do_one_initcall address at 0xffff800080014c74 due to size mismatch (0x260 != 0x224)
no match for do_one_initcall+0xf4/0x260

Filter out entries from readelf using the 'sysmap-ignored-syms.sed'
script used to construct System.map, so that the size of a symbol is
calculated as a delta to the next symbol present in ksymtab.

Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: John Stultz <jstultz@xxxxxxxxxx>
Signed-off-by: Will Deacon <will@xxxxxxxxxx>
---
 scripts/faddr2line | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/scripts/faddr2line b/scripts/faddr2line
index 62a3fa6f6f59..da734af90036 100755
--- a/scripts/faddr2line
+++ b/scripts/faddr2line
@@ -64,6 +64,7 @@ else
 	UTIL_PREFIX=${CROSS_COMPILE:-}
 fi
 
+IGNORED_SYMS=$(dirname $0)/sysmap-ignored-syms.sed
 READELF="${UTIL_PREFIX}readelf"
 ADDR2LINE="${UTIL_PREFIX}addr2line"
 AWK="awk"
@@ -185,7 +186,7 @@ __faddr2line() {
 				found=2
 				break
 			fi
-		done < <(${READELF} --symbols --wide $objfile | sed 's/\[.*\]//' | ${AWK} -v sec=$sym_sec '$7 == sec' | sort --key=2)
+		done < <(${READELF} --symbols --wide $objfile | sed -f ${IGNORED_SYMS} -e 's/\[.*\]//' | ${AWK} -v sec=$sym_sec '$7 == sec' | sort --key=2)
 
 		if [[ $found = 0 ]]; then
 			warn "can't find symbol: sym_name: $sym_name sym_sec: $sym_sec sym_addr: $sym_addr sym_elf_size: $sym_elf_size"
-- 
2.41.0.487.g6d72f3e995-goog