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Subject[PATCH v2 02/14] objtool: Explicitly avoid self modifying code in .altinstr_replacement
Assume ALTERNATIVE()s know what they're doing and do not change, or
cause to change, instructions in .altinstr_replacement sections.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
tools/objtool/check.c | 42 +++++++++++++++++++++++++++++++-----------
1 file changed, 31 insertions(+), 11 deletions(-)

--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -993,18 +993,27 @@ static void remove_insn_ops(struct instr
}
}

-static void add_call_dest(struct objtool_file *file, struct instruction *insn,
- struct symbol *dest, bool sibling)
+static void annotate_call_site(struct objtool_file *file,
+ struct instruction *insn, bool sibling)
{
struct reloc *reloc = insn_reloc(file, insn);
+ struct symbol *sym = insn->call_dest;

- insn->call_dest = dest;
- if (!dest)
+ if (!sym)
+ sym = reloc->sym;
+
+ /*
+ * Alternative replacement code is just template code which is
+ * sometimes copied to the original instruction, For now, don't
+ * annotate it. (In the future we might consider annotating the
+ * original instruction if/when it ever makes sense to do so.).
+ */
+ if (!strcmp(insn->sec->name, ".altinstr_replacement"))
return;

- if (insn->call_dest->static_call_tramp) {
- list_add_tail(&insn->call_node,
- &file->static_call_list);
+ if (sym->static_call_tramp) {
+ list_add_tail(&insn->call_node, &file->static_call_list);
+ return;
}

/*
@@ -1013,7 +1022,7 @@ static void add_call_dest(struct objtool
* text.
*/
if (insn->sec->noinstr &&
- !strncmp(insn->call_dest->name, "__sanitizer_cov_", 16)) {
+ !strncmp(sym->name, "__sanitizer_cov_", 16)) {
if (reloc) {
reloc->type = R_NONE;
elf_write_reloc(file->elf, reloc);
@@ -1025,9 +1034,10 @@ static void add_call_dest(struct objtool
: arch_nop_insn(insn->len));

insn->type = sibling ? INSN_RETURN : INSN_NOP;
+ return;
}

- if (mcount && !strcmp(insn->call_dest->name, "__fentry__")) {
+ if (mcount && !strcmp(sym->name, "__fentry__")) {
if (sibling)
WARN_FUNC("Tail call to __fentry__ !?!?", insn->sec, insn->offset);

@@ -1042,9 +1052,17 @@ static void add_call_dest(struct objtool

insn->type = INSN_NOP;

- list_add_tail(&insn->mcount_loc_node,
- &file->mcount_loc_list);
+ list_add_tail(&insn->mcount_loc_node, &file->mcount_loc_list);
+ return;
}
+}
+
+static void add_call_dest(struct objtool_file *file, struct instruction *insn,
+ struct symbol *dest, bool sibling)
+{
+ insn->call_dest = dest;
+ if (!dest)
+ return;

/*
* Whatever stack impact regular CALLs have, should be undone
@@ -1054,6 +1072,8 @@ static void add_call_dest(struct objtool
* are converted to JUMP, see read_intra_function_calls().
*/
remove_insn_ops(insn);
+
+ annotate_call_site(file, insn, sibling);
}

/*

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