Re: [PATCH 3/7] objtool: Add support for intra-function calls
From: Alexandre Chartre
Date: Thu Apr 02 2020 - 09:22:47 EST
On 4/2/20 2:53 PM, Julien Thierry wrote:
Hi Alexandre,
I ran into the limitation of intra-function call for the arm64
support but didn't take the time to make a clean patch to support
them properly.
Nice to see you've gone through that work :) .
On 4/2/20 9:22 AM, Alexandre Chartre wrote:
Change objtool to support intra-function calls. An intra-function call
is represented in objtool as a push onto the stack (of the return
I have to disagree a bit with that. The push onto the stack is true
on x86, but other architectures might not have that (arm/arm64 have a
link register that gets set by "bl" instructions and do not modify
the stack).
Correct, this is x86 specific.
address), and a jump to the destination address. That way the stack
information is correctly updated and the call flow is still accurate.
Signed-off-by: Alexandre Chartre <alexandre.chartre@xxxxxxxxxx>
---
tools/objtool/check.c | 73 ++++++++++++++++++++++++++++++++++++++++++-
tools/objtool/check.h | 1 +
2 files changed, 73 insertions(+), 1 deletion(-)
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 214809ac2776..0cec91291d46 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -657,6 +657,18 @@ static int add_call_destinations(struct objtool_file *file)
if (insn->type != INSN_CALL)
continue;
+ if (insn->intra_function_call) {
+ dest_off = insn->offset + insn->len + insn->immediate;
+ insn->jump_dest = find_insn(file, insn->sec, dest_off);
+ if (insn->jump_dest)
+ continue;
+
+ WARN_FUNC("can't find call dest at %s+0x%lx",
+ insn->sec, insn->offset,
+ insn->sec->name, dest_off);
+ return -1;
+ }
+
rela = find_rela_by_dest_range(insn->sec, insn->offset,
insn->len);
if (!rela) {
@@ -1289,6 +1301,49 @@ static int read_retpoline_hints(struct objtool_file *file)
return 0;
}
+static int read_intra_function_call(struct objtool_file *file)
+{
+ struct section *sec;
+ struct instruction *insn;
+ struct rela *rela;
+
+ sec = find_section_by_name(file->elf,
+ ".rela.discard.intra_function_call");
I'm wondering, do we really need to annotate the intra_function_call
and group the in a section?
Would it be a problem to consider all (static) call instructions with
a destination that is not the start offset of a symbol to be an
intra-function call (and set insn->intra_function_call and
insn->jump_dest accordingly)?
Correct, we could automatically detect intra-function calls instead of
having to annotate them. However, I choose to annotate them because I don't
think that's not an expected construct in a "normal" code flow (at least
on x86). So objtool would still issue a warning on intra-function calls
by default, and you can annotate them to indicate if they are expected.
If intra-function calls are frequent on arm then I can add an option to
objtool so it automatically detects them. This way, we won't use the option
on x86 and we have to annotate intra-function call on x86, and you can
use it on arm to automatically detect intra-function calls.
Other than that the logic would stay the same.
+ if (!sec)
+ return 0;
+
+ list_for_each_entry(rela, &sec->rela_list, list) {
+ if (rela->sym->type != STT_SECTION) {
+ WARN("unexpected relocation symbol type in %s",
+ sec->name);
+ return -1;
+ }
+
+ insn = find_insn(file, rela->sym->sec, rela->addend);
+ if (!insn) {
+ WARN("bad .discard.intra_function_call entry");
+ return -1;
+ }
+
+ if (insn->type != INSN_CALL) {
+ WARN_FUNC("intra_function_call not a call",
+ insn->sec, insn->offset);
Nit: This could be slightly confusing with INSN_CALL_DYNAMIC. Maybe just:
"unsupported instruction for intra-function call " ?
Right, I will change that: "intra_function_call not a direct call"
+ return -1;
+ }
+
+ insn->intra_function_call = true;
+ /*
+ * For the impact on the stack, make an intra-function
+ * call behaves like a push of an immediate value (the
+ * return address).
+ */
+ insn->stack_op.src.type = OP_SRC_CONST;
+ insn->stack_op.dest.type = OP_DEST_PUSH;
As commented above, this should be arch dependent.
I will add a arch dependent call. I will also do that for the return
trampoline call case (patch 4).
Thanks,
alex.
+ }
+
+ return 0;
+}
+
static void mark_rodata(struct objtool_file *file)
{
struct section *sec;
@@ -1344,6 +1399,10 @@ static int decode_sections(struct objtool_file *file)
if (ret)
return ret;
+ ret = read_intra_function_call(file);
+ if (ret)
+ return ret;
+
ret = add_call_destinations(file);
if (ret)
return ret;
@@ -2092,7 +2151,8 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
return ret;
if (!no_fp && func && !is_fentry_call(insn) &&
- !has_valid_stack_frame(&state)) {
+ !has_valid_stack_frame(&state) &&
+ !insn->intra_function_call) {
WARN_FUNC("call without frame pointer save/setup",
sec, insn->offset);
return 1;
@@ -2101,6 +2161,17 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
if (dead_end_function(file, insn->call_dest))
return 0;
+ if (insn->intra_function_call) {
+ update_insn_state(insn, &state);
+ ret = validate_branch(file, func, insn,
+ insn->jump_dest, state);
+ if (ret) {
+ if (backtrace)
+ BT_FUNC("(intra-call)", insn);
+ return ret;
+ }
+ }
+
break;
case INSN_JUMP_CONDITIONAL:
diff --git a/tools/objtool/check.h b/tools/objtool/check.h
index cffb23d81782..2bd6d2f46baa 100644
--- a/tools/objtool/check.h
+++ b/tools/objtool/check.h
@@ -35,6 +35,7 @@ struct instruction {
unsigned long immediate;
unsigned int alt_group;
bool dead_end, ignore, hint, save, restore, ignore_alts;
+ bool intra_function_call;
bool retpoline_safe;
u8 visited;
struct symbol *call_dest;
Thanks,