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objtool: Allow STT_NOTYPE -> STT_FUNC+0 sibling-calls

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Teach objtool about STT_NOTYPE -> STT_FUNC+0 sibling calls. Doing do
allows slightly simpler .S files.

There is a slight complication in that we specifically do not want to
allow sibling calls from symbol holes (previously covered by STT_WEAK
symbols) -- such things exist where a weak function has a .cold
subfunction for example.

Additionally, STT_NOTYPE tail-calls are allowed to happen with a
modified stack frame, they don't need to obey the normal rules after
all.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
This commit is contained in:
Peter Zijlstra 2022-07-11 11:49:50 +02:00
parent dbcdbdfdf1
commit 5a9c361a41
1 changed files with 47 additions and 27 deletions
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74
tools/objtool/check.c
View file

@ -129,16 +129,13 @@ static bool is_jump_table_jump(struct instruction *insn)
static bool is_sibling_call(struct instruction *insn)
{
/*
* Assume only ELF functions can make sibling calls. This ensures
* sibling call detection consistency between vmlinux.o and individual
* objects.
* Assume only STT_FUNC calls have jump-tables.
*/
if (!insn_func(insn))
return false;
/* An indirect jump is either a sibling call or a jump to a table. */
if (insn->type == INSN_JUMP_DYNAMIC)
return !is_jump_table_jump(insn);
if (insn_func(insn)) {
/* An indirect jump is either a sibling call or a jump to a table. */
if (insn->type == INSN_JUMP_DYNAMIC)
return !is_jump_table_jump(insn);
}
/* add_jump_destinations() sets insn->call_dest for sibling calls. */
return (is_static_jump(insn) && insn->call_dest);
@ -1400,27 +1397,50 @@ static void add_return_call(struct objtool_file *file, struct instruction *insn,
list_add_tail(&insn->call_node, &file->return_thunk_list);
}
static bool same_function(struct instruction *insn1, struct instruction *insn2)
static bool is_first_func_insn(struct objtool_file *file,
struct instruction *insn, struct symbol *sym)
{
return insn_func(insn1)->pfunc == insn_func(insn2)->pfunc;
}
static bool is_first_func_insn(struct objtool_file *file, struct instruction *insn)
{
if (insn->offset == insn_func(insn)->offset)
if (insn->offset == sym->offset)
return true;
/* Allow direct CALL/JMP past ENDBR */
if (opts.ibt) {
struct instruction *prev = prev_insn_same_sym(file, insn);
if (prev && prev->type == INSN_ENDBR &&
insn->offset == insn_func(insn)->offset + prev->len)
insn->offset == sym->offset + prev->len)
return true;
}
return false;
}
/*
* A sibling call is a tail-call to another symbol -- to differentiate from a
* recursive tail-call which is to the same symbol.
*/
static bool jump_is_sibling_call(struct objtool_file *file,
struct instruction *from, struct instruction *to)
{
struct symbol *fs = from->sym;
struct symbol *ts = to->sym;
/* Not a sibling call if from/to a symbol hole */
if (!fs || !ts)
return false;
/* Not a sibling call if not targeting the start of a symbol. */
if (!is_first_func_insn(file, to, ts))
return false;
/* Disallow sibling calls into STT_NOTYPE */
if (ts->type == STT_NOTYPE)
return false;
/* Must not be self to be a sibling */
return fs->pfunc != ts->pfunc;
}
/*
* Find the destination instructions for all jumps.
*/
@ -1519,18 +1539,18 @@ static int add_jump_destinations(struct objtool_file *file)
strstr(insn_func(jump_dest)->name, ".cold")) {
insn_func(insn)->cfunc = insn_func(jump_dest);
insn_func(jump_dest)->pfunc = insn_func(insn);
} else if (!same_function(insn, jump_dest) &&
is_first_func_insn(file, jump_dest)) {
/*
* Internal sibling call without reloc or with
* STT_SECTION reloc.
*/
add_call_dest(file, insn, insn_func(jump_dest), true);
continue;
}
}
if (jump_is_sibling_call(file, insn, jump_dest)) {
/*
* Internal sibling call without reloc or with
* STT_SECTION reloc.
*/
add_call_dest(file, insn, insn_func(jump_dest), true);
continue;
}
insn->jump_dest = jump_dest;
}
@ -3309,7 +3329,7 @@ static int validate_sibling_call(struct objtool_file *file,
struct instruction *insn,
struct insn_state *state)
{
if (has_modified_stack_frame(insn, state)) {
if (insn_func(insn) && has_modified_stack_frame(insn, state)) {
WARN_FUNC("sibling call from callable instruction with modified stack frame",
insn->sec, insn->offset);
return 1;