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Fix disassembler silent truncation #14136

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9d8bfed
Print undecodable bytes instead of silently truncating disassembly
jlb6740 Aug 14, 2026
48452cc
prtest:full
jlb6740 Aug 14, 2026
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38 changes: 38 additions & 0 deletions cranelift/codegen/src/machinst/mod.rs
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Expand Up @@ -703,6 +703,44 @@ impl<T: CompilePhase> CompiledCodeBase<T> {

writeln!(buf)?;
}

// `disasm_all` stops at the first instruction it cannot decode and
// reports success rather than an error, so without this the rest of
// the block would silently vanish from the listing. That matters
// most for `precise-output` filetests, whose expectations would
// then assert nothing at all about those bytes. Print them as
// `.byte` directives instead, the same form capstone itself
// produces for undecodable s390x instructions.
let decoded: usize = insns.iter().map(|i| i.bytes().len()).sum();
for (chunk_idx, chunk) in buffer[decoded..].chunks(8).enumerate() {
let addr = start as u64 + decoded as u64 + (chunk_idx * 8) as u64;
let chunk_end = addr + chunk.len() as u64;
let contains = |off| addr <= off && off < chunk_end;

write!(buf, " .byte ")?;
for (i, byte) in chunk.iter().enumerate() {
if i > 0 {
write!(buf, ", ")?;
}
write!(buf, "{byte:#04x}")?;
}

for reloc in relocs.iter().filter(|reloc| contains(reloc.offset as u64)) {
write!(
buf,
" ; reloc_external {} {} {}",
reloc.kind,
reloc.target.display(params),
reloc.addend,
)?;
}

if let Some(trap) = traps.iter().find(|trap| contains(trap.offset as u64)) {
write!(buf, " ; trap: {}", trap.code)?;
}

writeln!(buf)?;
}
}

return Ok(buf);
Expand Down
4 changes: 4 additions & 0 deletions cranelift/filetests/filetests/isa/x64/branches.clif
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Expand Up @@ -1003,6 +1003,9 @@ block5(v5: i32):
; movslq (%rcx, %r10, 4), %rax
; addq %rax, %rcx
; jmpq *%rcx
; .byte 0x2f, 0x00, 0x00, 0x00, 0x24, 0x00, 0x00, 0x00
; .byte 0x24, 0x00, 0x00, 0x00, 0x19, 0x00, 0x00, 0x00
; .byte 0x3a, 0x00, 0x00, 0x00
; block2: ; offset 0x38
; jmp 0x48
; block3: ; offset 0x3d
Expand Down Expand Up @@ -1089,6 +1092,7 @@ block1(v5: i32):
; addb %al, (%rax)
; subb $0, %al
; addb %al, (%rax)
; .byte 0x2f, 0x00, 0x00, 0x00, 0x14, 0x00, 0x00, 0x00
; block2: ; offset 0x4d
; movq %r11, %rax
; jmp 0x68
Expand Down
52 changes: 52 additions & 0 deletions cranelift/filetests/filetests/isa/x64/disas-undecodable-bytes.clif
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@@ -0,0 +1,52 @@
test compile precise-output
set unwind_info=false
target x86_64 has_avx has_avx_vnni

;; The bundled capstone build cannot decode AVX-VNNI, and capstone stops at the
;; first instruction it does not recognize rather than reporting an error. The
;; remaining bytes are therefore printed as `.byte` directives so that they stay
;; visible here instead of silently disappearing from this expectation. Note
;; that x86 instruction length cannot be determined without decoding, so there
;; is no way to resynchronize: everything after `vpdpbusd`, including the
;; epilogue, is covered by the byte dump.

function %vpdpbusd_i8x16(i8x16, i8x16, i32x4) -> i32x4 {
block0(v0: i8x16, v1: i8x16, v2: i32x4):
v3 = swiden_low v0
v4 = uwiden_low v1
v5 = imul v3, v4
v6 = swiden_high v0
v7 = uwiden_high v1
v8 = imul v6, v7
v9 = swiden_low v5
v10 = swiden_high v5
v11 = iadd_pairwise v9, v10
v12 = swiden_low v8
v13 = swiden_high v8
v14 = iadd_pairwise v12, v13
v15 = iadd_pairwise v11, v14
v16 = iadd v15, v2
return v16
}

; VCode:
; pushq %rbp
; movq %rsp, %rbp
; block0:
; movdqa %xmm0, %xmm5
; movdqa %xmm2, %xmm0
; vpdpbusd %xmm5, %xmm1, %xmm0
; movq %rbp, %rsp
; popq %rbp
; retq
;
; Disassembled:
; block0: ; offset 0x0
; pushq %rbp
; movq %rsp, %rbp
; block1: ; offset 0x4
; movdqa %xmm0, %xmm5
; movdqa %xmm2, %xmm0
; .byte 0xc4, 0xe2, 0x71, 0x50, 0xc5, 0x48, 0x89, 0xec
; .byte 0x5d, 0xc3

1 change: 1 addition & 0 deletions cranelift/filetests/filetests/isa/x64/f128const.clif
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Expand Up @@ -66,4 +66,5 @@ block0():
; addb %al, (%rax)
; addb %al, (%rax)
; addb %bh, %bh
; .byte 0x3f

8 changes: 8 additions & 0 deletions cranelift/filetests/filetests/isa/x64/fcvt-avx.clif
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Expand Up @@ -154,6 +154,14 @@ block0(v0: i64x2):
; addb %al, (%rax)
; addb %al, (%rax)
; addb %al, (%rax)
; .byte 0xff, 0xff, 0xff, 0xff, 0x00, 0x00, 0x00, 0x00
; .byte 0xff, 0xff, 0xff, 0xff, 0x00, 0x00, 0x00, 0x00
; .byte 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x30, 0x43
; .byte 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x30, 0x43
; .byte 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x30, 0x45
; .byte 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x30, 0x45
; .byte 0x00, 0x00, 0x10, 0x00, 0x00, 0x00, 0x30, 0x45
; .byte 0x00, 0x00, 0x10, 0x00, 0x00, 0x00, 0x30, 0x45

function %i64x2_to_f64x2(i64x2) -> f64x2 {
block0(v0: i64x2):
Expand Down
9 changes: 9 additions & 0 deletions cranelift/filetests/filetests/isa/x64/fcvt.clif
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Expand Up @@ -372,6 +372,7 @@ block0(v0: i32x4):
; addb %al, (%rax)
; addb %al, (%rax)
; addb %dh, (%rax)
; .byte 0x43

function %f12(i32x4) -> f32x4 {
block0(v0: i32x4):
Expand Down Expand Up @@ -1195,6 +1196,14 @@ block0(v0: i64x2):
; addb %al, (%rax)
; addb %al, (%rax)
; addb %al, (%rax)
; .byte 0xff, 0xff, 0xff, 0xff, 0x00, 0x00, 0x00, 0x00
; .byte 0xff, 0xff, 0xff, 0xff, 0x00, 0x00, 0x00, 0x00
; .byte 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x30, 0x43
; .byte 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x30, 0x43
; .byte 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x30, 0x45
; .byte 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x30, 0x45
; .byte 0x00, 0x00, 0x10, 0x00, 0x00, 0x00, 0x30, 0x45
; .byte 0x00, 0x00, 0x10, 0x00, 0x00, 0x00, 0x30, 0x45

function %i64x2_to_f64x2(i64x2) -> f64x2 {
block0(v0: i64x2):
Expand Down
2 changes: 2 additions & 0 deletions cranelift/filetests/filetests/isa/x64/float-avx.clif
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Expand Up @@ -592,6 +592,8 @@ block0(v0: f64x2):
; addb %al, (%rax)
; addb %al, (%rax)
; sarb $0xff, %bh
; .byte 0xff, 0xdf, 0x41, 0x00, 0x00, 0xc0, 0xff, 0xff
; .byte 0xff, 0xdf, 0x41

function %load_and_store_f32(i64, i64) {
block0(v0: i64, v1: i64):
Expand Down
1 change: 1 addition & 0 deletions cranelift/filetests/filetests/isa/x64/i128.clif
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Expand Up @@ -2192,6 +2192,7 @@ block0(v0: i128, v1: i128):
; addb %ah, (%rax, %rax)
; addb %al, (%rax)
; addb %al, (%rax)
; .byte 0x00

function %uadd_overflow_as_i128(i64, i64) -> i64, i64 {
block0(v0: i64, v1: i64):
Expand Down
1 change: 1 addition & 0 deletions cranelift/filetests/filetests/isa/x64/immediates.clif
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Expand Up @@ -59,4 +59,5 @@ block0(v0: i64, v1: i64):
; fstp %st(5)
; outb %al, %dx
; outb %al, %dx
; .byte 0xff, 0xff

1 change: 1 addition & 0 deletions cranelift/filetests/filetests/isa/x64/mul.clif
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Expand Up @@ -698,4 +698,5 @@ block0:
; andb (%rdx), %ah
; andb (%rax), %al
; addb %al, (%rax)
; .byte 0x00

2 changes: 2 additions & 0 deletions cranelift/filetests/filetests/isa/x64/narrowing.clif
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Expand Up @@ -94,6 +94,8 @@ block0(v0: f64x2):
; addb %al, (%rax)
; addb %al, (%rax)
; addb %al, %al
; .byte 0xff, 0xff, 0xff, 0xdf, 0x41, 0x00, 0x00, 0xc0
; .byte 0xff, 0xff, 0xff, 0xdf, 0x41

function %f4(i16x8, i16x8) -> i8x16 {
block0(v0: i16x8, v1: i16x8):
Expand Down
1 change: 1 addition & 0 deletions cranelift/filetests/filetests/isa/x64/select-issue-3744.clif
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Expand Up @@ -40,4 +40,5 @@ block0(v0: f32, v1: f32):
; addb %al, (%rax)
; addb %al, (%rax)
; addb %al, (%rax)
; .byte 0x00

2 changes: 2 additions & 0 deletions cranelift/filetests/filetests/isa/x64/shuffle-avx512.clif
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Expand Up @@ -40,6 +40,7 @@ block0(v0: i8x16, v1: i8x16):
; addb %al, (%rax)
; addb %al, (%rax)
; addb %al, (%rax)
; .byte 0x11

function %f3(i8x16, i8x16) -> i8x16 {
block0(v0: i8x16, v1: i8x16):
Expand Down Expand Up @@ -75,4 +76,5 @@ block0(v0: i8x16, v1: i8x16):
; addb %bl, (%rdi)
; sbbb (%rsi, %rax), %al
; orb $0xb, %al
; .byte 0x17, 0x0d, 0x18, 0x04, 0x02, 0x0f, 0x11, 0x05

41 changes: 41 additions & 0 deletions cranelift/filetests/filetests/isa/x64/simd-arith-avx.clif
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Expand Up @@ -596,6 +596,7 @@ block0(v0: i16x8, v1: i16x8):
; addb %al, (%rax)
; addb %al, -0x7fff8000(%rax)
; addb %al, -0x7fff8000(%rax)
; .byte 0x00, 0x80, 0x00, 0x80

function %i64x2_extmul_high_i32x4_s(i32x4, i32x4) -> i64x2 {
block0(v0: i32x4, v1: i32x4):
Expand Down Expand Up @@ -703,6 +704,7 @@ block0(v0: i32x4):
; addb %al, (%r8)
; addb %al, (%rax)
; addb %al, (%rax)
; .byte 0x30, 0x43

function %f32x4_add(f32x4, f32x4) -> f32x4 {
block0(v0: f32x4, v1: f32x4):
Expand Down Expand Up @@ -1298,6 +1300,7 @@ block0(v0: i16x8):
; addb %al, (%rcx)
; addb %al, (%rcx)
; addb %al, (%rcx)
; .byte 0x00

function %i8x16_splat(i8) -> i8x16 {
block0(v0: i8):
Expand Down Expand Up @@ -1370,6 +1373,10 @@ block0(v0: f64x2):
; addb %al, (%rax)
; addb %al, (%rax)
; loopne 0x33
; .byte 0xff, 0xff, 0xef, 0x41, 0x00, 0x00, 0xe0, 0xff
; .byte 0xff, 0xff, 0xef, 0x41, 0x00, 0x00, 0x00, 0x00
; .byte 0x00, 0x00, 0x30, 0x43, 0x00, 0x00, 0x00, 0x00
; .byte 0x00, 0x00, 0x30, 0x43

function %i8x16_shl(i8x16, i32) -> i8x16 {
block0(v0: i8x16, v1: i32):
Expand Down Expand Up @@ -1410,6 +1417,22 @@ block0(v0: i8x16, v1: i32):
; addb %al, (%rax)
; addb %al, (%rax)
; addb %al, (%rax)
; .byte 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff
; .byte 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff
; .byte 0xfe, 0xfe, 0xfe, 0xfe, 0xfe, 0xfe, 0xfe, 0xfe
; .byte 0xfe, 0xfe, 0xfe, 0xfe, 0xfe, 0xfe, 0xfe, 0xfe
; .byte 0xfc, 0xfc, 0xfc, 0xfc, 0xfc, 0xfc, 0xfc, 0xfc
; .byte 0xfc, 0xfc, 0xfc, 0xfc, 0xfc, 0xfc, 0xfc, 0xfc
; .byte 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8
; .byte 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8
; .byte 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0
; .byte 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0
; .byte 0xe0, 0xe0, 0xe0, 0xe0, 0xe0, 0xe0, 0xe0, 0xe0
; .byte 0xe0, 0xe0, 0xe0, 0xe0, 0xe0, 0xe0, 0xe0, 0xe0
; .byte 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0
; .byte 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0
; .byte 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80
; .byte 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80

function %i8x16_shl_imm(i8x16) -> i8x16 {
block0(v0: i8x16):
Expand Down Expand Up @@ -1443,6 +1466,8 @@ block0(v0: i8x16):
; addb %al, (%rax)
; addb %al, (%rax)
; addb %al, (%rax)
; .byte 0xfe, 0xfe, 0xfe, 0xfe, 0xfe, 0xfe, 0xfe, 0xfe
; .byte 0xfe, 0xfe, 0xfe, 0xfe, 0xfe, 0xfe, 0xfe, 0xfe

function %i16x8_shl(i16x8, i32) -> i16x8 {
block0(v0: i16x8, v1: i32):
Expand Down Expand Up @@ -1648,6 +1673,22 @@ block0(v0: i8x16, v1: i32):
; addb %al, (%rax)
; addb %al, (%rax)
; addb %al, (%rax)
; .byte 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff
; .byte 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff
; .byte 0x7f, 0x7f, 0x7f, 0x7f, 0x7f, 0x7f, 0x7f, 0x7f
; .byte 0x7f, 0x7f, 0x7f, 0x7f, 0x7f, 0x7f, 0x7f, 0x7f
; .byte 0x3f, 0x3f, 0x3f, 0x3f, 0x3f, 0x3f, 0x3f, 0x3f
; .byte 0x3f, 0x3f, 0x3f, 0x3f, 0x3f, 0x3f, 0x3f, 0x3f
; .byte 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f
; .byte 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f
; .byte 0x0f, 0x0f, 0x0f, 0x0f, 0x0f, 0x0f, 0x0f, 0x0f
; .byte 0x0f, 0x0f, 0x0f, 0x0f, 0x0f, 0x0f, 0x0f, 0x0f
; .byte 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07
; .byte 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07
; .byte 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03
; .byte 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03
; .byte 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01
; .byte 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01

function %i8x16_ushr_imm(i8x16) -> i8x16 {
block0(v0: i8x16):
Expand Down
2 changes: 2 additions & 0 deletions cranelift/filetests/filetests/isa/x64/simd-bitselect.clif
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Expand Up @@ -201,6 +201,7 @@ block0(v0: i16x8, v1: i16x8):
; addb %al, (%rax)
; incl (%rax)
; addb %al, (%rax)
; .byte 0xff, 0xff, 0xff, 0x00, 0xff, 0xff

function %bad_const_mask(i8x16, i8x16) -> i8x16 {
block0(v0: i8x16, v1: i8x16):
Expand Down Expand Up @@ -250,4 +251,5 @@ block0(v0: i8x16, v1: i8x16):
; addb %bh, %bh
; addb %al, (%rax)
; addb %al, (%rax)
; .byte 0xff

27 changes: 27 additions & 0 deletions cranelift/filetests/filetests/isa/x64/simd-bitwise-compile.clif
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Original file line number Diff line number Diff line change
Expand Up @@ -362,6 +362,24 @@ block0(v0: i32):
; addb %al, (%rcx)
; addb (%rbx), %al
; addb $5, %al
; .byte 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d
; .byte 0x0e, 0x0f, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff
; .byte 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff
; .byte 0xff, 0xff, 0xfe, 0xfe, 0xfe, 0xfe, 0xfe, 0xfe
; .byte 0xfe, 0xfe, 0xfe, 0xfe, 0xfe, 0xfe, 0xfe, 0xfe
; .byte 0xfe, 0xfe, 0xfc, 0xfc, 0xfc, 0xfc, 0xfc, 0xfc
; .byte 0xfc, 0xfc, 0xfc, 0xfc, 0xfc, 0xfc, 0xfc, 0xfc
; .byte 0xfc, 0xfc, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8
; .byte 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8
; .byte 0xf8, 0xf8, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0
; .byte 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0
; .byte 0xf0, 0xf0, 0xe0, 0xe0, 0xe0, 0xe0, 0xe0, 0xe0
; .byte 0xe0, 0xe0, 0xe0, 0xe0, 0xe0, 0xe0, 0xe0, 0xe0
; .byte 0xe0, 0xe0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0
; .byte 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0
; .byte 0xc0, 0xc0, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80
; .byte 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80
; .byte 0x80, 0x80

function %ishl_i8x16_imm(i8x16) -> i8x16 {
block0(v0: i8x16):
Expand Down Expand Up @@ -395,6 +413,8 @@ block0(v0: i8x16):
; addb %al, (%rax)
; addb %al, (%rax)
; addb %al, (%rax)
; .byte 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0
; .byte 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0

function %ishl_i16x8_imm(i16x8) -> i16x8 {
block0(v0: i16x8):
Expand Down Expand Up @@ -508,6 +528,10 @@ block0:
; addb %al, (%rcx)
; addb (%rbx), %al
; addb $5, %al
; .byte 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d
; .byte 0x0e, 0x0f, 0x7f, 0x7f, 0x7f, 0x7f, 0x7f, 0x7f
; .byte 0x7f, 0x7f, 0x7f, 0x7f, 0x7f, 0x7f, 0x7f, 0x7f
; .byte 0x7f, 0x7f

function %ushr_i16x8_imm(i16x8) -> i16x8 {
block0(v0: i16x8):
Expand Down Expand Up @@ -639,6 +663,8 @@ block0(v0: i32):
; addb %al, (%rcx)
; addb (%rbx), %al
; addb $5, %al
; .byte 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d
; .byte 0x0e, 0x0f

function %sshr_i8x16_imm(i8x16, i32) -> i8x16 {
block0(v0: i8x16, v1: i32):
Expand Down Expand Up @@ -926,4 +952,5 @@ block0(v0: i64x2, v1: i32):
; addb %al, (%rax)
; addb %al, (%rax)
; addb %al, (%rax)
; .byte 0x00, 0x80

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