Function calling conventions and other conventions regarding the use of
machine registers and stack slots.
Require Import Coqlib Decidableplus.
Require Import AST Machregs Locations.
Classification of machine registers
Machine registers (type
mreg in module
Locations) are divided in
the following groups:
-
Callee-save registers, whose value is preserved across a function call.
-
Caller-save registers that can be modified during a function call.
We follow the x86-32 and x86-64 application binary interfaces (ABI)
in our choice of callee- and caller-save registers.
(
r:
mreg) :
bool :=
match r with
|
AX |
CX |
DX =>
false
|
BX |
BP =>
true
|
SI |
DI =>
negb Archi.ptr64 (* callee-save in 32 bits but not in 64 bits *)
|
R8 |
R9 |
R10 |
R11 =>
false
|
R12 |
R13 |
R14 |
R15 =>
true
|
X0 |
X1 |
X2 |
X3 |
X4 |
X5 |
X6 |
X7 =>
false
|
X8 |
X9 |
X10 |
X11 |
X12 |
X13 |
X14 |
X15 =>
false
|
FP0 =>
false
end.
Definition int_caller_save_regs :=
if Archi.ptr64
then AX ::
CX ::
DX ::
SI ::
DI ::
R8 ::
R9 ::
R10 ::
R11 ::
nil
else AX ::
CX ::
DX ::
nil.
Definition float_caller_save_regs :=
if Archi.ptr64
then X0 ::
X1 ::
X2 ::
X3 ::
X4 ::
X5 ::
X6 ::
X7 ::
X8 ::
X9 ::
X10 ::
X11 ::
X12 ::
X13 ::
X14 ::
X15 ::
nil
else X0 ::
X1 ::
X2 ::
X3 ::
X4 ::
X5 ::
X6 ::
X7 ::
nil.
Definition int_callee_save_regs :=
if Archi.ptr64
then BX ::
BP ::
R12 ::
R13 ::
R14 ::
R15 ::
nil
else BX ::
SI ::
DI ::
BP ::
nil.
Definition float_callee_save_regs :
list mreg :=
nil.
Definition destroyed_at_call :=
List.filter (
fun r =>
negb (
is_callee_save r))
all_mregs.
Definition dummy_int_reg :=
AX.
(* Used in Regalloc. *)
Definition dummy_float_reg :=
X0.
(* Used in Regalloc. *)
Definition is_float_reg (
r:
mreg) :=
match r with
|
AX |
BX |
CX |
DX |
SI |
DI |
BP
|
R8 |
R9 |
R10 |
R11 |
R12 |
R13 |
R14 |
R15 =>
false
|
X0 |
X1 |
X2 |
X3 |
X4 |
X5 |
X6 |
X7
|
X8 |
X9 |
X10 |
X11 |
X12 |
X13 |
X14 |
X15 |
FP0 =>
true
end.
Function calling conventions
The functions in this section determine the locations (machine registers
and stack slots) used to communicate arguments and results between the
caller and the callee during function calls. These locations are functions
of the signature of the function and of the call instruction.
Agreement between the caller and the callee on the locations to use
is guaranteed by our dynamic semantics for Cminor and RTL, which demand
that the signature of the call instruction is identical to that of the
called function.
Calling conventions are largely arbitrary: they must respect the properties
proved in this section (such as no overlapping between the locations
of function arguments), but this leaves much liberty in choosing actual
locations. To ensure binary interoperability of code generated by our
compiler with libraries compiled by another compiler, we
implement the standard x86-32 and x86-64 conventions.
Location of function result
In 32 bit mode, the result value of a function is passed back to the
caller in registers AX or DX:AX or FP0, depending on the type
of the returned value. We treat a function without result as a
function with one integer result.
Definition loc_result_32 (
s:
signature) :
rpair mreg :=
match s.(
sig_res)
with
|
None =>
One AX
|
Some (
Tint |
Tany32) =>
One AX
|
Some (
Tfloat |
Tsingle) =>
One FP0
|
Some Tany64 =>
One X0
|
Some Tlong =>
Twolong DX AX
end.
In 64 bit mode, he result value of a function is passed back to
the caller in registers AX or X0.
Definition loc_result_64 (
s:
signature) :
rpair mreg :=
match s.(
sig_res)
with
|
None =>
One AX
|
Some (
Tint |
Tlong |
Tany32 |
Tany64) =>
One AX
|
Some (
Tfloat |
Tsingle) =>
One X0
end.
Definition loc_result :=
if Archi.ptr64 then loc_result_64 else loc_result_32.
The result registers have types compatible with that given in the signature.
Lemma loc_result_type:
forall sig,
subtype (
proj_sig_res sig) (
typ_rpair mreg_type (
loc_result sig)) =
true.
Proof.
The result locations are caller-save registers
Lemma loc_result_caller_save:
forall (
s:
signature),
forall_rpair (
fun r =>
is_callee_save r =
false) (
loc_result s).
Proof.
If the result is in a pair of registers, those registers are distinct and have type Tint at least.
Lemma loc_result_pair:
forall sg,
match loc_result sg with
|
One _ =>
True
|
Twolong r1 r2 =>
r1 <>
r2 /\
sg.(
sig_res) =
Some Tlong
/\
subtype Tint (
mreg_type r1) =
true /\
subtype Tint (
mreg_type r2) =
true
/\
Archi.splitlong =
true
end.
Proof.
The location of the result depends only on the result part of the signature
Lemma loc_result_exten:
forall s1 s2,
s1.(
sig_res) =
s2.(
sig_res) ->
loc_result s1 =
loc_result s2.
Proof.
Location of function arguments
In the x86-32 ABI, all arguments are passed on stack. (Snif.)
Fixpoint loc_arguments_32
(
tyl:
list typ) (
ofs:
Z) {
struct tyl} :
list (
rpair loc) :=
match tyl with
|
nil =>
nil
|
ty ::
tys =>
match ty with
|
Tlong =>
Twolong (
S Outgoing (
ofs + 1)
Tint) (
S Outgoing ofs Tint)
|
_ =>
One (
S Outgoing ofs ty)
end
::
loc_arguments_32 tys (
ofs +
typesize ty)
end.
In the x86-64 ABI:
-
The first 6 integer arguments are passed in registers DI, SI, DX, CX, R8, R9.
-
The first 8 floating-point arguments are passed in registers X0 to X7.
-
Extra arguments are passed on the stack, in Outgoing slots.
Consecutive stack slots are separated by 8 bytes, even if only 4 bytes
of data is used in a slot.
:=
DI ::
SI ::
DX ::
CX ::
R8 ::
R9 ::
nil.
Definition float_param_regs :=
X0 ::
X1 ::
X2 ::
X3 ::
X4 ::
X5 ::
X6 ::
X7 ::
nil.
Fixpoint loc_arguments_64
(
tyl:
list typ) (
ir fr ofs:
Z) {
struct tyl} :
list (
rpair loc) :=
match tyl with
|
nil =>
nil
| (
Tint |
Tlong |
Tany32 |
Tany64)
as ty ::
tys =>
match list_nth_z int_param_regs ir with
|
None =>
One (
S Outgoing ofs ty) ::
loc_arguments_64 tys ir fr (
ofs + 2)
|
Some ireg =>
One (
R ireg) ::
loc_arguments_64 tys (
ir + 1)
fr ofs
end
| (
Tfloat |
Tsingle)
as ty ::
tys =>
match list_nth_z float_param_regs fr with
|
None =>
One (
S Outgoing ofs ty) ::
loc_arguments_64 tys ir fr (
ofs + 2)
|
Some freg =>
One (
R freg) ::
loc_arguments_64 tys ir (
fr + 1)
ofs
end
end.
loc_arguments s returns the list of locations where to store arguments
when calling a function with signature s.
Definition loc_arguments (
s:
signature) :
list (
rpair loc) :=
if Archi.ptr64
then loc_arguments_64 s.(
sig_args) 0 0 0
else loc_arguments_32 s.(
sig_args) 0.
size_arguments s returns the number of Outgoing slots used
to call a function with signature s.
Fixpoint size_arguments_32
(
tyl:
list typ) (
ofs:
Z) {
struct tyl} :
Z :=
match tyl with
|
nil =>
ofs
|
ty ::
tys =>
size_arguments_32 tys (
ofs +
typesize ty)
end.
Fixpoint size_arguments_64 (
tyl:
list typ) (
ir fr ofs:
Z) {
struct tyl} :
Z :=
match tyl with
|
nil =>
ofs
| (
Tint |
Tlong |
Tany32 |
Tany64) ::
tys =>
match list_nth_z int_param_regs ir with
|
None =>
size_arguments_64 tys ir fr (
ofs + 2)
|
Some ireg =>
size_arguments_64 tys (
ir + 1)
fr ofs
end
| (
Tfloat |
Tsingle) ::
tys =>
match list_nth_z float_param_regs fr with
|
None =>
size_arguments_64 tys ir fr (
ofs + 2)
|
Some freg =>
size_arguments_64 tys ir (
fr + 1)
ofs
end
end.
Definition size_arguments (
s:
signature) :
Z :=
if Archi.ptr64
then size_arguments_64 s.(
sig_args) 0 0 0
else size_arguments_32 s.(
sig_args) 0.
Argument locations are either caller-save registers or Outgoing
stack slots at nonnegative offsets.
Definition loc_argument_acceptable (
l:
loc) :
Prop :=
match l with
|
R r =>
is_callee_save r =
false
|
S Outgoing ofs ty =>
ofs >= 0 /\ (
typealign ty |
ofs)
|
_ =>
False
end.
Definition loc_argument_32_charact (
ofs:
Z) (
l:
loc) :
Prop :=
match l with
|
S Outgoing ofs'
ty =>
ofs' >=
ofs /\
typealign ty = 1
|
_ =>
False
end.
Definition loc_argument_64_charact (
ofs:
Z) (
l:
loc) :
Prop :=
match l with
|
R r =>
In r int_param_regs \/
In r float_param_regs
|
S Outgoing ofs'
ty =>
ofs' >=
ofs /\ (2 |
ofs')
|
_ =>
False
end.
Remark loc_arguments_32_charact:
forall tyl ofs p,
In p (
loc_arguments_32 tyl ofs) ->
forall_rpair (
loc_argument_32_charact ofs)
p.
Proof.
assert (
X:
forall ofs1 ofs2 l,
loc_argument_32_charact ofs2 l ->
ofs1 <=
ofs2 ->
loc_argument_32_charact ofs1 l).
{
destruct l;
simpl;
intros;
auto.
destruct sl;
auto.
intuition omega. }
induction tyl as [ |
ty tyl];
simpl loc_arguments_32;
intros.
-
contradiction.
-
destruct H.
+
destruct ty;
subst p;
simpl;
omega.
+
apply IHtyl in H.
generalize (
typesize_pos ty);
intros.
destruct p;
simpl in *.
*
eapply X;
eauto;
omega.
*
destruct H;
split;
eapply X;
eauto;
omega.
Qed.
Remark loc_arguments_64_charact:
forall tyl ir fr ofs p,
In p (
loc_arguments_64 tyl ir fr ofs) -> (2 |
ofs) ->
forall_rpair (
loc_argument_64_charact ofs)
p.
Proof.
Lemma loc_arguments_acceptable:
forall (
s:
signature) (
p:
rpair loc),
In p (
loc_arguments s) ->
forall_rpair loc_argument_acceptable p.
Proof.
Hint Resolve loc_arguments_acceptable:
locs.
The offsets of Outgoing arguments are below size_arguments s.
Remark size_arguments_32_above:
forall tyl ofs0,
ofs0 <=
size_arguments_32 tyl ofs0.
Proof.
Remark size_arguments_64_above:
forall tyl ir fr ofs0,
ofs0 <=
size_arguments_64 tyl ir fr ofs0.
Proof.
Lemma size_arguments_above:
forall s,
size_arguments s >= 0.
Proof.
Lemma loc_arguments_32_bounded:
forall ofs ty tyl ofs0,
In (
S Outgoing ofs ty) (
regs_of_rpairs (
loc_arguments_32 tyl ofs0)) ->
ofs +
typesize ty <=
size_arguments_32 tyl ofs0.
Proof.
induction tyl as [ |
t l];
simpl;
intros x IN.
-
contradiction.
-
rewrite in_app_iff in IN;
destruct IN as [
IN|
IN].
+
apply Zle_trans with (
x +
typesize t); [|
apply size_arguments_32_above].
Ltac decomp :=
match goal with
| [
H:
_ \/
_ |-
_ ] =>
destruct H;
decomp
| [
H:
S _ _ _ =
S _ _ _ |-
_ ] =>
inv H
| [
H:
False |-
_ ] =>
contradiction
end.
destruct t;
simpl in IN;
decomp;
simpl;
omega.
+
apply IHl;
auto.
Qed.
Lemma loc_arguments_64_bounded:
forall ofs ty tyl ir fr ofs0,
In (
S Outgoing ofs ty) (
regs_of_rpairs (
loc_arguments_64 tyl ir fr ofs0)) ->
ofs +
typesize ty <=
size_arguments_64 tyl ir fr ofs0.
Proof.
Lemma loc_arguments_bounded:
forall (
s:
signature) (
ofs:
Z) (
ty:
typ),
In (
S Outgoing ofs ty) (
regs_of_rpairs (
loc_arguments s)) ->
ofs +
typesize ty <=
size_arguments s.
Proof.
Lemma loc_arguments_main:
loc_arguments signature_main =
nil.
Proof.