[llvm] r269126 - ARM: report an error when attempting to target a misalgined BLX

[Tim Northover via llvm-commits]

Author: tnorthover
Date: Tue May 10 16:48:48 2016
New Revision: 269126

URL: http://llvm.org/viewvc/llvm-project?rev=269126&view=rev
Log:
ARM: report an error when attempting to target a misalgined BLX

The CodeGen problem was fixed in r269101, but we still miscompiled assembly
that tried the same thing.

Added:
    llvm/trunk/test/MC/ARM/aligned-blx.s
    llvm/trunk/test/MC/ARM/misaligned-blx.s
Modified:
    llvm/trunk/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp

Modified: llvm/trunk/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp?rev=269126&r1=269125&r2=269126&view=diff
==============================================================================
--- llvm/trunk/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp (original)
+++ llvm/trunk/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp Tue May 10 16:48:48 2016
@@ -83,7 +83,9 @@ const MCFixupKindInfo &ARMAsmBackend::ge
       {"fixup_arm_condbl", 0, 24, MCFixupKindInfo::FKF_IsPCRel},
       {"fixup_arm_blx", 0, 24, MCFixupKindInfo::FKF_IsPCRel},
       {"fixup_arm_thumb_bl", 0, 32, MCFixupKindInfo::FKF_IsPCRel},
-      {"fixup_arm_thumb_blx", 0, 32, MCFixupKindInfo::FKF_IsPCRel},
+      {"fixup_arm_thumb_blx", 0, 32,
+       MCFixupKindInfo::FKF_IsPCRel |
+           MCFixupKindInfo::FKF_IsAlignedDownTo32Bits},
       {"fixup_arm_thumb_cb", 0, 16, MCFixupKindInfo::FKF_IsPCRel},
       {"fixup_arm_thumb_cp", 0, 8,
        MCFixupKindInfo::FKF_IsPCRel |
@@ -131,7 +133,9 @@ const MCFixupKindInfo &ARMAsmBackend::ge
       {"fixup_arm_condbl", 8, 24, MCFixupKindInfo::FKF_IsPCRel},
       {"fixup_arm_blx", 8, 24, MCFixupKindInfo::FKF_IsPCRel},
       {"fixup_arm_thumb_bl", 0, 32, MCFixupKindInfo::FKF_IsPCRel},
-      {"fixup_arm_thumb_blx", 0, 32, MCFixupKindInfo::FKF_IsPCRel},
+      {"fixup_arm_thumb_blx", 0, 32,
+       MCFixupKindInfo::FKF_IsPCRel |
+           MCFixupKindInfo::FKF_IsAlignedDownTo32Bits},
       {"fixup_arm_thumb_cb", 0, 16, MCFixupKindInfo::FKF_IsPCRel},
       {"fixup_arm_thumb_cp", 8, 8,
        MCFixupKindInfo::FKF_IsPCRel |
@@ -535,7 +539,12 @@ unsigned ARMAsmBackend::adjustFixupValue
     //
     // Note that the halfwords are stored high first, low second; so we need
     // to transpose the fixup value here to map properly.
-    uint32_t offset = (Value - 2) >> 2;
+    if (Ctx && Value  % 4 != 0) {
+      Ctx->reportError(Fixup.getLoc(), "misaligned ARM call destination");
+      return 0;
+    }
+
+    uint32_t offset = (Value - 4) >> 2;
     if (const MCSymbolRefExpr *SRE =
             dyn_cast<MCSymbolRefExpr>(Fixup.getValue()))
       if (SRE->getKind() == MCSymbolRefExpr::VK_TLSCALL)

Added: llvm/trunk/test/MC/ARM/aligned-blx.s
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/MC/ARM/aligned-blx.s?rev=269126&view=auto
==============================================================================
--- llvm/trunk/test/MC/ARM/aligned-blx.s (added)
+++ llvm/trunk/test/MC/ARM/aligned-blx.s Tue May 10 16:48:48 2016
@@ -0,0 +1,34 @@
+@ RUN: llvm-mc -triple thumbv7-apple-ios -filetype=obj %s -o %t
+@ RUN: llvm-objdump -macho -d %t | FileCheck %s
+
+        @ Size: 2 bytes
+        .thumb_func _f1
+        .thumb
+        .globl _f1
+_f1:
+        bx lr
+
+        @ A properly aligned ARM function
+        .globl _aligned
+        .p2align 2
+        .arm
+_aligned:
+        bx lr
+
+        @ Align this Thumb function so we can predict the outcome of
+        @ "Align(PC, 4)" during blx operation.
+        .thumb_func _test
+        .thumb
+        .p2align 2
+        .globl _test
+_test:
+        blx _elsewhere
+        blx _aligned    @ PC=0 (mod 4)
+        blx _aligned    @ PC=0 (mod 4)
+        movs r0, r0
+        blx _aligned    @ PC=2 (mod 4)
+
+@ CHECK: blx _elsewhere
+@ CHECK: ff f7 fa ef blx _aligned
+@ CHECK: ff f7 f8 ef blx _aligned
+@ CHECK: ff f7 f6 ef blx _aligned

Added: llvm/trunk/test/MC/ARM/misaligned-blx.s
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/MC/ARM/misaligned-blx.s?rev=269126&view=auto
==============================================================================
--- llvm/trunk/test/MC/ARM/misaligned-blx.s (added)
+++ llvm/trunk/test/MC/ARM/misaligned-blx.s Tue May 10 16:48:48 2016
@@ -0,0 +1,40 @@
+@ RUN: not llvm-mc -triple thumbv7-apple-ios -filetype=obj %s -o /dev/null 2>&1 | FileCheck %s
+        @ Size: 2 bytes
+        .thumb_func _f1
+        .thumb
+        .globl _f1
+_f1:
+        bx lr
+
+        @ A misalgined ARM destination.
+        .arm
+        .globl _misaligned
+_misaligned:
+        bx lr
+
+        @ And a properly aligned one.
+        .globl _aligned
+        .p2align 2
+        .arm
+_aligned:
+        bx lr
+
+        @ Align this Thumb function so we can predict the outcome of
+        @ "Align(PC, 4)" during blx operation.
+        .thumb_func _test
+        .thumb
+        .p2align 2
+        .globl _test
+_test:
+        blx _misaligned       @ PC=0 (mod 4)
+        movs r0, r0
+        blx _misaligned       @ PC=2 (mod 4)
+        movs r0, r0
+        blx _aligned          @ PC=0 (mod 4)
+        movs r0, r0
+        blx _aligned          @ PC=2 (mod 4)
+
+@ CHECK: error: misaligned ARM call destination
+@ CHECK:   blx _misaligned
+@ CHECK: error: misaligned ARM call destination
+@ CHECK:   blx _misaligned