[PATCH v3 38/58] objtool/klp: Add test for sympos resolved against a linked vmlinux

@@ -0,0 +1,40 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Two translation units with a same-named static, placed so that the linker
+ * puts them in the opposite order to the one they appear in the symbol table.
+ *
+ * VARSEC selects the section the static lands in.  Linking with
+ * --sort-section=name then orders them alphabetically rather than by object
+ * order, so the first symbol in the symbol table ends up at the *higher*
+ * address.  That is the whole point: counting symbol table order and reading
+ * the linked image's addresses now give different answers, which is what makes
+ * it possible to tell which one klp diff used.
+ *
+ * Only use_a is patched, so exactly one sympos is emitted and there is nothing
+ * to attribute.
+ */
+
+#ifndef FUNC_NAME
+#define FUNC_NAME use_a
+#endif
+#ifndef VARSEC
+#define VARSEC ".data.mmm"
+#endif
+
+#ifndef NO_MODINFO
+static const char __modinfo[]
+	__attribute__((section(".modinfo"), used, aligned(1))) = "\0name=vmlinux";
+#endif
+
+/* volatile so it survives as an STT_OBJECT rather than being folded away */
+static volatile int dup_counter __attribute__((section(VARSEC))) = 1;
+
+int FUNC_NAME(int x)
+{
+	dup_counter += x;
+#ifdef PATCHED
+	return dup_counter + 1;
+#else
+	return dup_counter;
+#endif
+}

@@ -0,0 +1,57 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# sympos for vmlinux, which is resolved differently from sympos for a module.
+#
+# A module's .ko preserves symbol table order, so klp diff can count -- that is
+# what test-sympos covers.  vmlinux cannot be counted: the final link reorders
+# sub-sections, so the order in vmlinux.o is not the order the running kernel
+# has.  klp diff bridges that with .klp.symid, a table of { id, address }
+# emitted into vmlinux.o whose addresses the linker resolves, read back out of
+# the linked vmlinux.
+#
+# Getting it wrong points the relocation at a different symbol of the same
+# name.  Nothing fails to build or load; the patched code uses the wrong
+# object.
+#
+# The fixture is arranged so the two answers differ: the static that comes
+# first in the symbol table is placed at the *higher* address, so counting
+# gives 1 and reading the linked image gives 2.  Without that, both paths agree
+# and the test cannot tell them apart.
+
+. "$(dirname "$0")/../lib.sh"
+
+setup
+
+# use_a's static sorts last by section name, use_b's first.  Only use_a is
+# patched, so exactly one sympos comes out.
+build_one sympos_vmlinux.c orig_a.o    -DFUNC_NAME=use_a -DVARSEC='".data.zzz"'
+build_one sympos_vmlinux.c patched_a.o -DFUNC_NAME=use_a -DVARSEC='".data.zzz"' -DPATCHED
+build_one sympos_vmlinux.c b.o         -DFUNC_NAME=use_b -DVARSEC='".data.aaa"' -DNO_MODINFO
+
+make_vmlinux_pair "$workdir/orig_a.o" "$workdir/b.o" \
+	       -- "$workdir/patched_a.o" "$workdir/b.o"
+
+[ "$(count_input_symbols vmlinux.o dup_counter)" = 2 ] ||
+	fail "fixture did not produce two dup_counter symbols"
+has_input_section vmlinux.o .klp.symid ||
+	fail "objtool --klp-symids emitted no .klp.symid table"
+has_input_section vmlinux .klp.symid ||
+	fail ".klp.symid did not survive the link"
+
+# The premise: symbol table order and address order must disagree, or the test
+# proves nothing.
+first_addr="$(in_symbols vmlinux | awk '$8 == "dup_counter" { print $2; exit }')"
+low_addr="$(in_symbols vmlinux | awk '$8 == "dup_counter" { print $2 }' | sort | head -1)"
+[ "$first_addr" != "$low_addr" ] ||
+	probe_skip "linker did not reorder the two statics"
+
+assert_input_symbol dup_counter
+run_diff
+
+# Address order says 2.  Counting symbol table order would say 1.
+assert_klp_sympos dup_counter 2
+out_symbols | grep -q 'dup_counter,1' &&
+	fail "sympos 1 emitted: counted symbol table order instead of reading the linked vmlinux"
+
+pass "vmlinux sympos taken from the linked image, not from symbol table order"