T0b1/wasmtime
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

x86_32: fix stack_addr encoding.

Browse Source 
Consider this testcase:

    target i686
    function u0:0() -> i32 system_v {
        ss0 = explicit_slot 0
    block0:
        v2 = stack_addr.i32 ss0
        return v2
    }

Before this commit, in 32-bit mode the x86 backend would generate
incorrect code for stack addresses:

     0:   55                      push    ebp
     1:   89 e5                   mov     ebp, esp
     3:   83 ec 08                sub     esp, 8
     6:   8d 44 24 00             lea     eax, [esp]
     a:   00 00                   add     byte ptr [eax], al
     c:   00 83 c4 08 5d c3       add     byte ptr [ebx - 0x3ca2f73c], al

This happened because the ModRM byte indicated a disp8 encoding, but
the instruction actually used a disp32 encoding. After this commit,
correct code is generated:

     0:   55                      push    ebp
     1:   89 e5                   mov     ebp, esp
     3:   83 ec 08                sub     esp, 8
     6:   8d 84 24 00 00 00 00    lea     eax, [esp]
     d:   83 c4 08                add     esp, 8
    10:   5d                      pop     ebp
    11:   c3                      ret
This commit is contained in:
whitequark
2020-05-29 15:27:34 +00:00
committed by iximeow
parent 09ccdc9285
commit a180b5b393
3 changed files with 37 additions and 21 deletions
Download Patch File Download Diff File Expand all files Collapse all files

7
cranelift/codegen/meta/src/isa/x86/encodings.rs
View File

@@ -2270,8 +2270,7 @@ fn define_entity_ref(
let rec_gvaddr8 = r.template("gvaddr8");
let rec_pcrel_fnaddr8 = r.template("pcrel_fnaddr8");
let rec_pcrel_gvaddr8 = r.template("pcrel_gvaddr8");
let rec_spaddr4_id = r.template("spaddr4_id");
let rec_spaddr8_id = r.template("spaddr8_id");
let rec_spaddr_id = r.template("spaddr_id");
// Predicates shorthands.
let all_ones_funcaddrs_and_not_is_pic =
@@ -2359,8 +2358,8 @@ fn define_entity_ref(
//
// TODO: Add encoding rules for stack_load and stack_store, so that they
// don't get legalized to stack_addr + load/store.
e.enc32(stack_addr.bind(I32), rec_spaddr4_id.opcodes(&LEA));
e.enc64(stack_addr.bind(I64), rec_spaddr8_id.opcodes(&LEA).rex().w());
e.enc64(stack_addr.bind(I64), rec_spaddr_id.opcodes(&LEA).rex().w());
e.enc32(stack_addr.bind(I32), rec_spaddr_id.opcodes(&LEA));
// Constant addresses (PIC).
e.enc64(const_addr.bind(I64), rec_const_addr.opcodes(&LEA).rex().w());