[tip: objtool/core] scripts/faddr2line: Skip over mapping symbols in output from readelf

[tip-bot2 for Will Deacon]

The following commit has been merged into the objtool/core branch of tip:

Commit-ID:     60fd39af33d3f63c4c94bd06784ebdf0d883f5c9
Gitweb:        https://git.kernel.org/tip/60fd39af33d3f63c4c94bd06784ebdf0d883f5c9
Author:        Will Deacon <will@xxxxxxxxxx>
AuthorDate:    Mon, 02 Oct 2023 17:57:49 +01:00
Committer:     Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
CommitterDate: Mon, 23 Oct 2023 08:36:46 -07:00

scripts/faddr2line: Skip over mapping symbols in output from readelf

Mapping symbols emitted in the readelf output 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 these entries from readelf using a shell reimplementation of
is_mapping_symbol(), so that the size of a symbol is calculated as a
delta to the next symbol present in ksymtab.

Suggested-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
Signed-off-by: Will Deacon <will@xxxxxxxxxx>
Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20231002165750.1661-4-will@xxxxxxxxxx
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
 scripts/faddr2line | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/scripts/faddr2line b/scripts/faddr2line
index 6b82068..587415a 100755
--- a/scripts/faddr2line
+++ b/scripts/faddr2line
@@ -179,6 +179,11 @@ __faddr2line() {
 			local cur_sym_elf_size=${fields[2]}
 			local cur_sym_name=${fields[7]:-}
 
+			# is_mapping_symbol(cur_sym_name)
+			if [[ ${cur_sym_name} =~ ^(\.L|L0|\$) ]]; then
+				continue
+			fi
+
 			if [[ $cur_sym_addr = $sym_addr ]] &&
 			   [[ $cur_sym_elf_size = $sym_elf_size ]] &&
 			   [[ $cur_sym_name = $sym_name ]]; then