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[Thumb] Validate branch target for CBZ/CBNZ instructions.

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Summary:
The assembler currently does not check the branch target for CBZ/CBNZ
instructions, which only permit branching forwards with a positive offset. This
adds validation for the branch target to ensure negative PC-relative offsets are
not encoded into the instruction, whether specified as a literal or as an
assembler symbol.

Reviewers: rengolin, t.p.northover

Subscribers: llvm-commits, rengolin

Differential Revision: https://reviews.llvm.org/D23312

llvm-svn: 278659
This commit is contained in:
Prakhar Bahuguna 2016-08-15 07:57:44 +00:00
parent 3fdcf4e64c
commit 2e2846c8af
4 changed files with 47 additions and 0 deletions
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6
lib/Target/ARM/AsmParser/ARMAsmParser.cpp
View File

@ -6684,6 +6684,12 @@ bool ARMAsmParser::validateInstruction(MCInst &Inst,
return Error(Operands[Op]->getStartLoc(), "branch target out of range");
break;
}
case ARM::tCBZ:
case ARM::tCBNZ: {
if (!static_cast<ARMOperand &>(*Operands[2]).isUnsignedOffset<6, 1>())
return Error(Operands[2]->getStartLoc(), "branch target out of range");
break;
}
case ARM::MOVi16:
case ARM::t2MOVi16:
case ARM::t2MOVTi16:

5
lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
View File

@ -578,6 +578,11 @@ unsigned ARMAsmBackend::adjustFixupValue(const MCFixup &Fixup, uint64_t Value,
// Offset by 4, and don't encode the low two bits.
return ((Value - 4) >> 2) & 0xff;
case ARM::fixup_arm_thumb_cb: {
// CB instructions can only branch to offsets in [0, 126] in multiples of 2
if (Ctx && ((int64_t)Value < 0 || Value > 0x3e || Value & 1)) {
Ctx->reportError(Fixup.getLoc(), "out of range pc-relative fixup value");
return 0;
}
// Offset by 4 and don't encode the lower bit, which is always 0.
// FIXME: diagnose if no Thumb2
uint32_t Binary = (Value - 4) >> 1;

19
test/MC/ARM/thumb-cb-negative-offsets.s Normal file
View File

@ -0,0 +1,19 @@
@ RUN: not llvm-mc -triple thumbv7m-none-eabi -filetype=obj -o /dev/null %s 2>&1 | FileCheck %s
@ RUN: not llvm-mc -triple thumbv8m.base-none-eabi -filetype=obj -o /dev/null %s 2>&1 | FileCheck %s
label0:
.word 4
@ CHECK: out of range pc-relative fixup value
cbz r0, label0
@ CHECK: out of range pc-relative fixup value
cbnz r0, label0
@ CHECK: out of range pc-relative fixup value
cbz r0, label1
@ CHECK: out of range pc-relative fixup value
cbnz r0, label1
.space 1000
label1:
.word 4

17
test/MC/ARM/thumb-diagnostics.s
View File

@ -234,6 +234,23 @@ error: invalid operand for instruction
@ CHECK-ERRORS: error: branch target out of range
@ CHECK-ERRORS: error: branch target out of range
@------------------------------------------------------------------------------
@ CBZ/CBNZ - out of range immediates for branches
@------------------------------------------------------------------------------
cbz r0, #-2
cbz r0, #0
cbz r0, #17
cbnz r0, #126
cbnz r0, #128
@ CHECK-ERRORS-V7M: error: branch target out of range
@ CHECK-ERRORS-V7M: error: invalid operand for instruction
@ CHECK-ERRORS-V7M: error: branch target out of range
@ CHECK-ERRORS-V8: error: branch target out of range
@ CHECK-ERRORS-V8: error: invalid operand for instruction
@ CHECK-ERRORS-V8: error: branch target out of range
@------------------------------------------------------------------------------
@ SEV/WFE/WFI/YIELD - are not supported pre v6M or v6T2
@------------------------------------------------------------------------------