linux - tools/objtool/tests/generic/test-switch-rodata.sh

53 lines · 2.0 KiB

1	#!/bin/bash
2	# SPDX-License-Identifier: GPL-2.0
3	#
4	# A Clang switch jump table travels with the function it belongs to.
5	#
6	# For a dense enough switch Clang emits the targets as a table in
7	# .rodata..Lswitch.table.<function>, named after the function but not part of
8	# it. klp diff has to associate the two: the patched function indexes into
9	# that table, so a clone which does not bring it along jumps through whatever
10	# the kernel's copy holds -- which, when the patch changed the switch, is the
11	# wrong set of targets.
12	#
13	# That is an indirect jump to a stale address, not a missing symbol, so nothing
14	# reports it at build or load time.
15	#
16	# objtool has no switch-specific code: the table is carried by the general
17	# mechanism for data a cloned function references. So this is a regression
18	# test on that mechanism reaching a shape it is easy to get wrong, not a guard
19	# on a particular line -- making the table uncorrelated, the nearest sabotage,
20	# does not change the outcome.
21	#
22	# Covers the same ground as corpus/x86_64-llvm-switch-rodata/
23	# clang-switch-rodata-assoc in Joe Lawrence's klp-build unit test corpus.
24
25	. "$(dirname "$0")/../lib.sh"
26
27	clang_only "only Clang emits switch jump tables in their own section"
28
29	setup
30	build_pair switch_rodata.c
31
32	# The premise: this Clang really did build a table rather than a chain of
33	# comparisons, and the added case really did change it.
34	tbl=.rodata..Lswitch.table.status_to_string
35	has_input_section orig.o "$tbl" \|\|
36	probe_skip "this clang built no jump table for the switch"
37	# readelf prefixes each line with "[nn]", which splits into one or two fields
38	# depending on the index, so strip it before counting columns.
39	tbl_size()
40	{
41	in_sections "$1" \| sed 's/^ \[[ 0-9]\] *//' \|
42	awk -v s="$tbl" '$1 == s { print $5 }'
43	}
44	[ "$(tbl_size orig.o)" != "$(tbl_size patched.o)" ] \|\|
45	fail "fixture's added case did not change the jump table"
46
47	run_diff
48
49	assert_patched status_to_string
50	assert_section "$tbl"
51	assert_reloc_sym .text.status_to_string "$tbl"
52
53	pass "Clang switch jump table carried with the function it belongs to"