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Change the ARM assembler to require a :lower16: or :upper16 on non-constant

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expressions for mov instructions instead of silently truncating by default.

For the ARM assembler, we want to avoid misleadingly allowing something
like "mov r0, <symbol>" especially when we turn it into a movw and the
expression <symbol> does not have a :lower16: or :upper16" as part of the
expression.  We don't want the behavior of silently truncating, which can be
unexpected and lead to bugs that are difficult to find since this is an easy
mistake to make.

This does change the previous behavior of llvm but actually matches an
older gnu assembler that would not allow this but print less useful errors
of like “invalid constant (0x927c0) after fixup” and “unsupported relocation on
symbol foo”.  The error for llvm is "immediate expression for mov requires
:lower16: or :upper16" with correct location information on the operand
as shown in the added test cases.

rdar://12342160

llvm-svn: 206669
This commit is contained in:
Kevin Enderby 2014-04-18 23:06:39 +00:00
parent 555df34e16
commit 2bb5aba324
6 changed files with 55 additions and 12 deletions
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24
lib/Target/ARM/AsmParser/ARMAsmParser.cpp
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@ -5863,6 +5863,30 @@ validateInstruction(MCInst &Inst,
return Error(Operands[Op]->getStartLoc(), "branch target out of range");
break;
}
case ARM::MOVi16:
case ARM::t2MOVi16:
case ARM::t2MOVTi16:
{
// We want to avoid misleadingly allowing something like "mov r0, <symbol>"
// especially when we turn it into a movw and the expression <symbol> does
// not have a :lower16: or :upper16 as part of the expression. We don't
// want the behavior of silently truncating, which can be unexpected and
// lead to bugs that are difficult to find since this is an easy mistake
// to make.
int i = (Operands[3]->isImm()) ? 3 : 4;
ARMOperand *Op = static_cast<ARMOperand*>(Operands[i]);
const MCConstantExpr *CE = dyn_cast<MCConstantExpr>(Op->getImm());
if (CE) break;
const MCExpr *E = dyn_cast<MCExpr>(Op->getImm());
if (!E) break;
const ARMMCExpr *ARM16Expr = dyn_cast<ARMMCExpr>(E);
if (!ARM16Expr || (ARM16Expr->getKind() != ARMMCExpr::VK_ARM_HI16 &&
ARM16Expr->getKind() != ARMMCExpr::VK_ARM_LO16)) {
return Error(Op->getStartLoc(),
"immediate expression for mov requires :lower16: or :upper16");
break;
}
}
}
return false;

10
lib/Target/ARM/MCTargetDesc/ARMMCCodeEmitter.cpp
View File

@ -1040,12 +1040,12 @@ ARMMCCodeEmitter::getHiLo16ImmOpValue(const MCInst &MI, unsigned OpIdx,
return 0;
}
// If the expression doesn't have :upper16: or :lower16: on it,
// it's just a plain immediate expression, and those evaluate to
// it's just a plain immediate expression, previously those evaluated to
// the lower 16 bits of the expression regardless of whether
// we have a movt or a movw.
Kind = MCFixupKind(isThumb2(STI) ? ARM::fixup_t2_movw_lo16
: ARM::fixup_arm_movw_lo16);
Fixups.push_back(MCFixup::Create(0, E, Kind, MI.getLoc()));
// we have a movt or a movw, but that led to misleadingly results.
// This is now disallowed in the the AsmParser in validateInstruction()
// so this should never happen.
assert(0 && "expression without :upper16: or :lower16:");
return 0;
}

6
test/MC/ARM/arm_fixups.s
View File

@ -26,9 +26,9 @@
@ CHECK-BE: movt r9, :upper16:_foo @ encoding: [0xe3,0b0100AAAA,0x90'A',A]
@ CHECK-BE: @ fixup A - offset: 0, value: _foo, kind: fixup_arm_movt_hi16
mov r2, fred
mov r2, :lower16:fred
@ CHECK: movw r2, fred @ encoding: [A,0x20'A',0b0000AAAA,0xe3]
@ CHECK: movw r2, :lower16:fred @ encoding: [A,0x20'A',0b0000AAAA,0xe3]
@ CHECK: @ fixup A - offset: 0, value: fred, kind: fixup_arm_movw_lo16
@ CHECK-BE: movw r2, fred @ encoding: [0xe3,0b0000AAAA,0x20'A',A]
@ CHECK-BE: movw r2, :lower16:fred @ encoding: [0xe3,0b0000AAAA,0x20'A',A]
@ CHECK-BE: @ fixup A - offset: 0, value: fred, kind: fixup_arm_movw_lo16

8
test/MC/ARM/complex-operands.s
View File

@ -21,20 +21,20 @@ return:
.global arm_function
.type arm_function,%function
arm_function:
mov r0, #(.L_table_end - .L_table_begin) >> 2
mov r0, #:lower16:((.L_table_end - .L_table_begin) >> 2)
blx return
@ CHECK-LABEL: arm_function
@ CHECK: movw r0, #(.L_table_end-.L_table_begin)>>2
@ CHECK: movw r0, :lower16:((.L_table_end-.L_table_begin)>>2)
@ CHECK: blx return
.global thumb_function
.type thumb_function,%function
thumb_function:
mov r0, #(.L_table_end - .L_table_begin) >> 2
mov r0, #:lower16:((.L_table_end - .L_table_begin) >> 2)
blx return
@ CHECK-LABEL: thumb_function
@ CHECK: movw r0, #(.L_table_end-.L_table_begin)>>2
@ CHECK: movw r0, :lower16:((.L_table_end-.L_table_begin)>>2)
@ CHECK: blx return

8
test/MC/ARM/diagnostics.s
View File

@ -465,3 +465,11 @@
ldm sp!, {r0}^
@ CHECK-ERRORS: error: system STM cannot have writeback register
@ CHECK-ERRORS: error: writeback register only allowed on system LDM if PC in register-list
foo2:
mov r0, foo2
movw r0, foo2
@ CHECK-ERRORS: error: immediate expression for mov requires :lower16: or :upper16
@ CHECK-ERRORS: ^
@ CHECK-ERRORS: error: immediate expression for mov requires :lower16: or :upper16
@ CHECK-ERRORS: ^

11
test/MC/ARM/thumb2-diagnostics.s
View File

@ -70,3 +70,14 @@
@ CHECK-ERRORS: error: branch target out of range
@ CHECK-ERRORS: error: branch target out of range
@ CHECK-ERRORS: error: branch target out of range
foo2:
mov r0, foo2
movw r0, foo2
movt r0, foo2
@ CHECK-ERRORS: error: immediate expression for mov requires :lower16: or :upper16
@ CHECK-ERRORS: ^
@ CHECK-ERRORS: error: immediate expression for mov requires :lower16: or :upper16
@ CHECK-ERRORS: ^
@ CHECK-ERRORS: error: immediate expression for mov requires :lower16: or :upper16
@ CHECK-ERRORS: ^