Merging r195677:

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r195677 | dpeixott | 2013-11-25 11:11:13 -0800 (Mon, 25 Nov 2013) | 41 lines

ARM integrated assembler generates incorrect nop opcode

This patch fixes a bug in the assembler that was causing bad code to
be emitted.  When switching modes in an assembly file (e.g. arm to
thumb mode) we would always emit the opcode from the original mode.

Consider this small example:

$ cat align.s
.code 16
foo:
  add r0, r0
.align 3
  add r0, r0

$ llvm-mc -triple armv7-none-linux align.s -filetype=obj -o t.o
$ llvm-objdump -triple thumbv7 -d t.o
Disassembly of section .text:
foo:
       0:       00 44         add     r0, r0
       2:       00 f0 20 e3   blx #4195904
       6:       00 00         movs    r0, r0
       8:       00 44         add     r0, r0

This shows that we have actually emitted an arm nop (e320f000)
instead of a thumb nop. Unfortunately, this encodes to a thumb
branch which causes bad things to happen when compiling assembly
code with align directives.

The fix is to notify the ARMAsmBackend when we switch mode. The
MCMachOStreamer was already doing this correctly. This patch makes
the same change for the MCElfStreamer.

There is still a bug in the way nops are emitted for alignment
because the MCAlignment fragment does not store the correct mode.
The ARMAsmBackend will emit nops for the last mode it knew about. In
the example above, we still generate an arm nop if we add a `.code
32` to the end of the file.

PR18019

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_34@196001 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/MC/MCELFStreamer.cpp b/lib/MC/MCELFStreamer.cpp
index 3be71ce9b61ecf7a36015e467cb50f8ceb3e7973..e806cb9f1c94de9e6fb1541cce6551135843da0e 100644 (file)
--- a/lib/MC/MCELFStreamer.cpp
+++ b/lib/MC/MCELFStreamer.cpp
@@ -15,6 +15,7 @@
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/MC/MCAssembler.h"
+#include "llvm/MC/MCAsmBackend.h"
 #include "llvm/MC/MCCodeEmitter.h"
 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCELF.h"
@@ -96,6 +97,9 @@ void MCELFStreamer::EmitDebugLabel(MCSymbol *Symbol) {
 }
 
 void MCELFStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
+  // Let the target do whatever target specific stuff it needs to do.
+  getAssembler().getBackend().handleAssemblerFlag(Flag);
+  // Do any generic stuff we need to do.
   switch (Flag) {
   case MCAF_SyntaxUnified: return; // no-op here.
   case MCAF_Code16: return; // Change parsing mode; no-op here.

diff --git a/test/MC/ARM/align_arm_2_thumb.s b/test/MC/ARM/align_arm_2_thumb.s
new file mode 100644 (file)
index 0000000..120e964
--- /dev/null
+++ b/test/MC/ARM/align_arm_2_thumb.s
@@ -0,0 +1,15 @@
+@ RUN: llvm-mc -triple armv7-none-linux -filetype=obj -o %t.o %s
+@ RUN: llvm-objdump -triple thumbv7-none-linux -d %t.o | FileCheck --check-prefix=ARM_2_THUMB %s
+
+@ RUN: llvm-mc -triple armv7-apple-darwin -filetype=obj -o %t_darwin.o %s
+@ RUN: llvm-objdump -triple thumbv7-apple-darwin -d %t_darwin.o | FileCheck --check-prefix=ARM_2_THUMB %s
+
+.syntax unified
+.code 16
+@ ARM_2_THUMB-LABEL: foo
+foo:
+  add r0, r0
+.align 3
+@ ARM_2_THUMB: 2: 00 bf     nop
+  add r0, r0
+

diff --git a/test/MC/ARM/align_thumb_2_arm.s b/test/MC/ARM/align_thumb_2_arm.s
new file mode 100644 (file)
index 0000000..328bfab
--- /dev/null
+++ b/test/MC/ARM/align_thumb_2_arm.s
@@ -0,0 +1,15 @@
+@ RUN: llvm-mc -triple thumbv7-none-linux -filetype=obj -o %t.o %s
+@ RUN: llvm-objdump -triple armv7-none-linux -d %t.o | FileCheck --check-prefix=THUMB_2_ARM %s
+
+@ RUN: llvm-mc -triple thumbv7-apple-darwin -filetype=obj -o %t_darwin.o %s
+@ RUN: llvm-objdump -triple armv7-apple-darwin -d %t_darwin.o | FileCheck --check-prefix=THUMB_2_ARM %s
+
+.syntax unified
+.code 32
+@ THUMB_2_ARM-LABEL: foo
+foo:
+  add r0, r0
+.align 3
+@ THUMB_2_ARM: 4: 00 f0 20 e3    nop
+  add r0, r0
+