[ELF][MIPS] Use MIPS R6 `sigrie` as a trap instruction

[atanasyan]

Summary

Current value using as a trap instruction (0xefefefef) is not a good choice for MIPS because it's a valid MIPS instruction swc3 $15,-4113(ra). This patch replaces 0xefefefef by 0x04170001. For all MIPS ISA revisions before R6, this value is just invalid instruction. Starting from MIPS R6 it's a valid instruction sigrie 1 which signals a Reserved Instruction exception.

mips-traps.s test case is added to test trap encoding. Other test cases are modified to remove redundant checking.

[ruiu]

LGTM

[jrtc27]

ELF/Arch/Mips.cpp

61

Maybe I'm being stupid, but won't this do the wrong thing on a big-endian host? If, say, we're building for mips64 on mips64, Config->IsLE and sys::IsLittleEndianHost will both be false, so we'll take the write32le path, which will write 0x04170001 (represented in-memory natively as big-endian) as a little-endian value, i.e. incorrectly byte-swapping? It seems to me like this should be just a check for if (Config->IsLE)?

[atanasyan]

ELF/Arch/Mips.cpp

61

Thanks a lot. The only remaining question - how could I write this nice piece of code? :)

[ruiu]

Maybe we probably should change the type of TrapInstr from uint32_t to uint8_t[4]?

[jrtc27]

ELF/Arch/Mips.cpp

61

I went and verified this because, despite having many dealings with it, it's too easy to get confused about endianness-related code. So, yes, my belief was correct, and I didn't inadvertently mislead you :) Running on powerpc64-linux-gnu:

-- Testing: 1 tests, 1 threads --
FAIL: lld :: ELF/mips-got16-relocatable.s (1 of 1)
******************** TEST 'lld :: ELF/mips-got16-relocatable.s' FAILED ********************
Script:
--
: 'RUN: at line 5';   /home/jrtc27/src/llvm/Build/bin/llvm-mc -filetype=obj -triple=mips-unknown-linux -mcpu=mips32r6 -o /home/jrtc27/src/llvm/Build/tools/lld/test/ELF/Output/mips-got16-relocatable.s.tmp.o /home/jrtc27/src/llvm/llvm/tools/lld/test/ELF/mips-got16-relocatable.s
: 'RUN: at line 6';   /home/jrtc27/src/llvm/Build/bin/ld.lld -r -o /home/jrtc27/src/llvm/Build/tools/lld/test/ELF/Output/mips-got16-relocatable.s.tmp /home/jrtc27/src/llvm/Build/tools/lld/test/ELF/Output/mips-got16-relocatable.s.tmp.o /home/jrtc27/src/llvm/Build/tools/lld/test/ELF/Output/mips-got16-relocatable.s.tmp.o
: 'RUN: at line 7';   /home/jrtc27/src/llvm/Build/bin/llvm-objdump -d -r /home/jrtc27/src/llvm/Build/tools/lld/test/ELF/Output/mips-got16-relocatable.s.tmp | /home/jrtc27/src/llvm/Build/bin/FileCheck -check-prefix=OBJ /home/jrtc27/src/llvm/llvm/tools/lld/test/ELF/mips-got16-relocatable.s
: 'RUN: at line 8';   /home/jrtc27/src/llvm/Build/bin/ld.lld -shared -o /home/jrtc27/src/llvm/Build/tools/lld/test/ELF/Output/mips-got16-relocatable.s.tmp.so /home/jrtc27/src/llvm/Build/tools/lld/test/ELF/Output/mips-got16-relocatable.s.tmp
: 'RUN: at line 9';   /home/jrtc27/src/llvm/Build/bin/llvm-objdump -d /home/jrtc27/src/llvm/Build/tools/lld/test/ELF/Output/mips-got16-relocatable.s.tmp.so | /home/jrtc27/src/llvm/Build/bin/FileCheck -check-prefix=SO /home/jrtc27/src/llvm/llvm/tools/lld/test/ELF/mips-got16-relocatable.s
--
Exit Code: 1

Command Output (stderr):
--
/home/jrtc27/src/llvm/llvm/tools/lld/test/ELF/mips-got16-relocatable.s:17:13: error: OBJ-NEXT: expected string not found in input
# OBJ-NEXT: 8: 04 17 00 01 sigrie 1
            ^
<stdin>:10:2: note: scanning from here
 8: 01 00 17 04 <unknown>
 ^

--

********************
Testing Time: 0.22s
********************
Failing Tests (1):
    lld :: ELF/mips-got16-relocatable.s

  Unexpected Failures: 1

[jrtc27]

In D54154#1289531, @ruiu wrote:

Maybe we probably should change the type of TrapInstr from uint32_t to uint8_t[4]?

That would make sense to clearly convey it's in the target endianness rather than the host; it's certainly a little surprising to have a uint32_t in the "wrong" endianness floating around. My only concern with making it an array is whether it's clear that you need to *repeat* the trap instruction if it's 1 or 2 bytes, but that same argument could be made for the current uint32_t, so probably irrelevant.

[ruiu]

Yeah, we could alternatively represent a trap instruction as an ArrayRef<uint8_t> which can vary in size, but that's somewhat minor point, and I believe always writing 4 bytes using memcpy is much faster than copying ArrayRef contents because the former can be highly optimized by a compiler that can inline memcpy function.

[jrtc27]

In D54154#1289551, @ruiu wrote:

Yeah, we could alternatively represent a trap instruction as an ArrayRef<uint8_t> which can vary in size, but that's somewhat minor point, and I believe always writing 4 bytes using memcpy is much faster than copying ArrayRef contents because the former can be highly optimized by a compiler that can inline memcpy function.

Yeah, I considered that as a possibility, but it doesn't seem worth it. Your uint8_t[4] proposal seems like the best option overall to me, and can always be revisited if it turns out to be a problem (I don't suppose we'll be seeing an IA-64 backend needing 16 bytes for its instruction!).

ELF/Arch/Mips.cpp

61

... and finally if I change this line to just if (Config->IsLE) it does indeed pass as expected on powerpc64-linux-gnu, so LGTM from my (unimportant) point of view once that's fixed. Alternatively you could use your Config->IsLE == sys::IsLittleEndianHost check, but explicitly do the byte swapping when they don't match (i.e. your write32le becomes the identity, and write32be becomes a byte swap, but both inlined and constant propagated), like the PPC64 target.

[ruiu]

Or maybe std::array<uint8_t, 4> as it allows you to initialize it by writing TrapInstr = {0xcc, 0xcc, 0xcc, 0xcc} (which you cannot do if TrapInstr is a uint8_t[4]).

[jrtc27]

In D54154#1289602, @ruiu wrote:

Or maybe std::array<uint8_t, 4> as it allows you to initialize it by writing TrapInstr = {0xcc, 0xcc, 0xcc, 0xcc} (which you cannot do if TrapInstr is a uint8_t[4]).

Ah, right, of course, I regard that as the same proposal just with nicer syntax! Happy to do the tiny amount of grunt work for that tomorrow if you both have better things to do with your time.

[atanasyan]

• Add a separate test case to check trap instruction encoding in case of bi and little endian.
• Use TrapInstr array.

[ruiu]

ELF/Arch/Mips.cpp

61

Let's not handle four byte sequence as one integer because it is very confusing. I'd write

if (Config->IsLE)
  TrapInstr = {....};
else
  TrapInstr = {....};

[jrtc27]

ELF/Arch/Mips.cpp

61

To me this actually seems the most sensible way of writing it; you don't have to care about endianness, and just write the instruction as a literal integer. This is exactly like how you write the PLT entry on various architectures, and both are writing instructions to byte arrays.

[ruiu]

ELF/Arch/Mips.cpp

61

OK, then LGTM.

[atanasyan]

Thanks for review.

ELF/Arch/Mips.cpp

template <class ELFT> MIPS<ELFT>::MIPS() {
   GotPltEntrySize = sizeof(typename ELFT::uint);
   GotBaseSymInGotPlt = false;
   PltEntrySize = 16;
   PltHeaderSize = 32;
   CopyRel = R_MIPS_COPY;
   NoneRel = R_MIPS_NONE;
   PltRel = R_MIPS_JUMP_SLOT;
   NeedsThunks = true;
-  TrapInstr = {0xef, 0xef, 0xef, 0xef};
+
+  // Set `sigrie 1` as a trap instruction.
+  write32(TrapInstr.data(), 0x04170001);
 
   if (ELFT::Is64Bits) {
     RelativeRel = (R_MIPS_64 << 8) | R_MIPS_REL32;
     TlsGotRel = R_MIPS_TLS_TPREL64;
     TlsModuleIndexRel = R_MIPS_TLS_DTPMOD64;
     TlsOffsetRel = R_MIPS_TLS_DTPREL64;
   } else {
     RelativeRel = R_MIPS_REL32;

test/ELF/mips-got16-relocatable.s

 # REQUIRES: mips
 # Check writing updated addend for R_MIPS_GOT16 relocation,
 # when produce a relocatable output.
 
 # RUN: llvm-mc -filetype=obj -triple=mips-unknown-linux -o %t.o %s
 # RUN: ld.lld -r -o %t %t.o %t.o
 # RUN: llvm-objdump -d -r %t | FileCheck -check-prefix=OBJ %s
 # RUN: ld.lld -shared -o %t.so %t
 # RUN: llvm-objdump -d %t.so | FileCheck -check-prefix=SO %s
 
 # OBJ:      Disassembly of section .text:
 # OBJ-NEXT: .text:
 # OBJ-NEXT:        0:       8f 99 00 00     lw      $25, 0($gp)
 # OBJ-NEXT:                         00000000:  R_MIPS_GOT16 .data
 # OBJ-NEXT:        4:       27 24 00 00     addiu   $4, $25, 0
 # OBJ-NEXT:                         00000004:  R_MIPS_LO16  .data
-# OBJ-NEXT:        8:       ef ef ef ef     <unknown>
-# OBJ-NEXT:        c:       ef ef ef ef     <unknown>
-# OBJ-NEXT:       10:       8f 99 00 00     lw      $25, 0($gp)
+# OBJ:            10:       8f 99 00 00     lw      $25, 0($gp)
 # OBJ-NEXT:                         00000010:  R_MIPS_GOT16 .data
 # OBJ-NEXT:       14:       27 24 00 10     addiu   $4, $25, 16
 # OBJ-NEXT:                         00000014:  R_MIPS_LO16  .data
 
 # SO:      Disassembly of section .text:
 # SO-NEXT: .text:
 # SO-NEXT:    10000:       8f 99 80 18     lw      $25, -32744($gp)
 # SO-NEXT:    10004:       27 24 00 00     addiu   $4, $25, 0
-# SO-NEXT:    10008:       ef ef ef ef     <unknown>
-# SO-NEXT:    1000c:       ef ef ef ef     <unknown>
-# SO-NEXT:    10010:       8f 99 80 18     lw      $25, -32744($gp)
+# SO:         10010:       8f 99 80 18     lw      $25, -32744($gp)
 # SO-NEXT:    10014:       27 24 00 10     addiu   $4, $25, 16
 
   .text
   lw     $t9, %got(.data)($gp)
   addiu  $a0, $t9, %lo(.data)
 
   .data
 data:
   .word 0

test/ELF/mips-npic-call-pic-os.s

 # RUN: llvm-objdump -d %t.exe | FileCheck %s
 
 # CHECK: Disassembly of section .text:
 # CHECK-NEXT: __LA25Thunk_foo1a:
 # CHECK-NEXT:    20000:       3c 19 00 02     lui     $25, 2
 # CHECK-NEXT:    20004:       08 00 80 08     j       131104 <foo1a>
 # CHECK-NEXT:    20008:       27 39 00 20     addiu   $25, $25, 32
 # CHECK-NEXT:    2000c:       00 00 00 00     nop
+
 # CHECK: __LA25Thunk_foo1b:
 # CHECK-NEXT:    20010:       3c 19 00 02     lui     $25, 2
 # CHECK-NEXT:    20014:       08 00 80 09     j       131108 <foo1b>
 # CHECK-NEXT:    20018:       27 39 00 24     addiu   $25, $25, 36
 # CHECK-NEXT:    2001c:       00 00 00 00     nop
+
 # CHECK: foo1a:
 # CHECK-NEXT:    20020:       00 00 00 00     nop
+
 # CHECK: foo1b:
 # CHECK-NEXT:    20024:       00 00 00 00     nop
+
 # CHECK: __LA25Thunk_foo2:
 # CHECK-NEXT:    20028:       3c 19 00 02     lui     $25, 2
 # CHECK-NEXT:    2002c:       08 00 80 10     j       131136 <foo2>
 # CHECK-NEXT:    20030:       27 39 00 40     addiu   $25, $25, 64
 # CHECK-NEXT:    20034:       00 00 00 00     nop
-# CHECK-NEXT:    20038:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    2003c:       ef ef ef ef     <unknown>
+
 # CHECK: foo2:
 # CHECK-NEXT:    20040:       00 00 00 00     nop
+
 # CHECK: __LA25Thunk_fpic:
 # CHECK-NEXT:    20044:       3c 19 00 02     lui     $25, 2
 # CHECK-NEXT:    20048:       08 00 80 18     j       131168 <fpic>
 # CHECK-NEXT:    2004c:       27 39 00 60     addiu   $25, $25, 96
 # CHECK-NEXT:    20050:       00 00 00 00     nop
-# CHECK-NEXT:    20054:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20058:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    2005c:       ef ef ef ef     <unknown>
+
 # CHECK: fpic:
 # CHECK-NEXT:    20060:       00 00 00 00     nop
-# CHECK-NEXT:    20064:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20068:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    2006c:       ef ef ef ef     <unknown>
+
 # CHECK: fnpic:
 # CHECK-NEXT:    20070:       00 00 00 00     nop
 # CHECK-NEXT: Disassembly of section differentos:
 # CHECK-NEXT: __start:
 # CHECK-NEXT:    20074:       0c 00 80 00     jal     131072 <__LA25Thunk_foo1a>
 # CHECK-NEXT:    20078:       00 00 00 00     nop
 # CHECK-NEXT:    2007c:       0c 00 80 0a     jal     131112 <__LA25Thunk_foo2>
 # CHECK-NEXT:    20080:       00 00 00 00     nop

 # RUN: llvm-objdump -d %t.exe | FileCheck -check-prefix=REVERSE %s
 
 # REVERSE: Disassembly of section .text:
 # REVERSE-NEXT: __LA25Thunk_foo1a:
 # REVERSE-NEXT:    20000:       3c 19 00 02     lui     $25, 2
 # REVERSE-NEXT:    20004:       08 00 80 08     j       131104 <foo1a>
 # REVERSE-NEXT:    20008:       27 39 00 20     addiu   $25, $25, 32
 # REVERSE-NEXT:    2000c:       00 00 00 00     nop
+
 # REVERSE: __LA25Thunk_foo1b:
 # REVERSE-NEXT:    20010:       3c 19 00 02     lui     $25, 2
 # REVERSE-NEXT:    20014:       08 00 80 09     j       131108 <foo1b>
 # REVERSE-NEXT:    20018:       27 39 00 24     addiu   $25, $25, 36
 # REVERSE-NEXT:    2001c:       00 00 00 00     nop
+
 # REVERSE: foo1a:
 # REVERSE-NEXT:    20020:       00 00 00 00     nop
+
 # REVERSE: foo1b:
 # REVERSE-NEXT:    20024:       00 00 00 00     nop
+
 # REVERSE: __LA25Thunk_foo2:
 # REVERSE-NEXT:    20028:       3c 19 00 02     lui     $25, 2
 # REVERSE-NEXT:    2002c:       08 00 80 10     j       131136 <foo2>
 # REVERSE-NEXT:    20030:       27 39 00 40     addiu   $25, $25, 64
 # REVERSE-NEXT:    20034:       00 00 00 00     nop
-# REVERSE-NEXT:    20038:       ef ef ef ef     <unknown>
-# REVERSE-NEXT:    2003c:       ef ef ef ef     <unknown>
+
 # REVERSE: foo2:
 # REVERSE-NEXT:    20040:       00 00 00 00     nop
-# REVERSE-NEXT:    20044:       ef ef ef ef     <unknown>
-# REVERSE-NEXT:    20048:       ef ef ef ef     <unknown>
-# REVERSE-NEXT:    2004c:       ef ef ef ef     <unknown>
+
 # REVERSE: __LA25Thunk_fpic:
 # REVERSE-NEXT:    20050:       3c 19 00 02     lui     $25, 2
 # REVERSE-NEXT:    20054:       08 00 80 18     j       131168 <fpic>
 # REVERSE-NEXT:    20058:       27 39 00 60     addiu   $25, $25, 96
 # REVERSE-NEXT:    2005c:       00 00 00 00     nop
+
 # REVERSE: fpic:
 # REVERSE-NEXT:    20060:       00 00 00 00     nop
-# REVERSE-NEXT:    20064:       ef ef ef ef     <unknown>
-# REVERSE-NEXT:    20068:       ef ef ef ef     <unknown>
-# REVERSE-NEXT:    2006c:       ef ef ef ef     <unknown>
+
 # REVERSE: fnpic:
 # REVERSE-NEXT:    20070:       00 00 00 00     nop
-# REVERSE-NEXT: Disassembly of section differentos:
+
+# REVERSE: Disassembly of section differentos:
 # REVERSE-NEXT: __start:
 # REVERSE-NEXT:    20074:       0c 00 80 00     jal     131072 <__LA25Thunk_foo1a>
 # REVERSE-NEXT:    20078:       00 00 00 00     nop
 # REVERSE-NEXT:    2007c:       0c 00 80 0a     jal     131112 <__LA25Thunk_foo2>
 # REVERSE-NEXT:    20080:       00 00 00 00     nop
 # REVERSE-NEXT:    20084:       0c 00 80 04     jal     131088 <__LA25Thunk_foo1b>
 # REVERSE-NEXT:    20088:       00 00 00 00     nop
 # REVERSE-NEXT:    2008c:       0c 00 80 0a     jal     131112 <__LA25Thunk_foo2>

test/ELF/mips-npic-call-pic-script.s

 # RUN: llvm-objdump -d %t.exe | FileCheck %s
 
 # CHECK: Disassembly of section .out:
 # CHECK-NEXT: __LA25Thunk_foo1a:
 # CHECK-NEXT:    20000:       3c 19 00 02     lui     $25, 2
 # CHECK-NEXT:    20004:       08 00 80 08     j       131104 <foo1a>
 # CHECK-NEXT:    20008:       27 39 00 20     addiu   $25, $25, 32
 # CHECK-NEXT:    2000c:       00 00 00 00     nop
+
 # CHECK: __LA25Thunk_foo1b:
 # CHECK-NEXT:    20010:       3c 19 00 02     lui     $25, 2
 # CHECK-NEXT:    20014:       08 00 80 09     j       131108 <foo1b>
 # CHECK-NEXT:    20018:       27 39 00 24     addiu   $25, $25, 36
 # CHECK-NEXT:    2001c:       00 00 00 00     nop
+
 # CHECK: foo1a:
 # CHECK-NEXT:    20020:       00 00 00 00     nop
+
 # CHECK: foo1b:
 # CHECK-NEXT:    20024:       00 00 00 00     nop
+
 # CHECK: __LA25Thunk_foo2:
 # CHECK-NEXT:    20028:       3c 19 00 02     lui     $25, 2
 # CHECK-NEXT:    2002c:       08 00 80 10     j       131136 <foo2>
 # CHECK-NEXT:    20030:       27 39 00 40     addiu   $25, $25, 64
 # CHECK-NEXT:    20034:       00 00 00 00     nop
-# CHECK-NEXT:    20038:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    2003c:       ef ef ef ef     <unknown>
+
 # CHECK: foo2:
 # CHECK-NEXT:    20040:       00 00 00 00     nop
-# CHECK-NEXT:    20044:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20048:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    2004c:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20050:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20054:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20058:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    2005c:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20060:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20064:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20068:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    2006c:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20070:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20074:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20078:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    2007c:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20080:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20084:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20088:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    2008c:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20090:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20094:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20098:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    2009c:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    200a0:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    200a4:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    200a8:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    200ac:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    200b0:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    200b4:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    200b8:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    200bc:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    200c0:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    200c4:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    200c8:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    200cc:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    200d0:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    200d4:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    200d8:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    200dc:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    200e0:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    200e4:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    200e8:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    200ec:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    200f0:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    200f4:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    200f8:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    200fc:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20100:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20104:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20108:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    2010c:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20110:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20114:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20118:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    2011c:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20120:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20124:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20128:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    2012c:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20130:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20134:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20138:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    2013c:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20140:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20144:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20148:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    2014c:       ef ef ef ef     <unknown>
+
 # CHECK: __start:
 # CHECK-NEXT:    20150:       0c 00 80 00     jal     131072 <__LA25Thunk_foo1a>
 # CHECK-NEXT:    20154:       00 00 00 00     nop
 # CHECK-NEXT:    20158:       0c 00 80 0a     jal     131112 <__LA25Thunk_foo2>
 # CHECK-NEXT:    2015c:       00 00 00 00     nop
 # CHECK-NEXT:    20160:       0c 00 80 04     jal     131088 <__LA25Thunk_foo1b>
 # CHECK-NEXT:    20164:       00 00 00 00     nop
 # CHECK-NEXT:    20168:       0c 00 80 0a     jal     131112 <__LA25Thunk_foo2>
 # CHECK-NEXT:    2016c:       00 00 00 00     nop
 # CHECK-NEXT:    20170:       0c 00 80 60     jal     131456 <__LA25Thunk_fpic>
 # CHECK-NEXT:    20174:       00 00 00 00     nop
 # CHECK-NEXT:    20178:       0c 00 80 68     jal     131488 <fnpic>
 # CHECK-NEXT:    2017c:       00 00 00 00     nop
+
 # CHECK: __LA25Thunk_fpic:
 # CHECK-NEXT:    20180:       3c 19 00 02     lui     $25, 2
 # CHECK-NEXT:    20184:       08 00 80 64     j       131472 <fpic>
 # CHECK-NEXT:    20188:       27 39 01 90     addiu   $25, $25, 400
 # CHECK-NEXT:    2018c:       00 00 00 00     nop
+
 # CHECK: fpic:
 # CHECK-NEXT:    20190:       00 00 00 00     nop
-# CHECK-NEXT:    20194:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20198:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    2019c:       ef ef ef ef     <unknown>
+
 # CHECK: fnpic:
 # CHECK-NEXT:    201a0:       00 00 00 00     nop
 
   .text
   .globl __start
 __start:
   jal foo1a
   jal foo2
   jal foo1b
   jal foo2
   jal fpic
   jal fnpic
 
 # Test script with orphans added to existing OutputSection, the .text.1 and
 # .text.2 sections will be added to .text
 # RUN: echo "SECTIONS { .text 0x20000 : { *(.text) }  }" > %t2.script
 # RUN: ld.lld --script %t2.script %t-npic.o %t-pic.o %t-sto-pic.o -o %t2.exe
 # RUN: llvm-objdump -d %t2.exe | FileCheck -check-prefix=ORPH1 %s
+
 # ORPH1: Disassembly of section .text:
 # ORPH1-NEXT: __start:
 # ORPH1-NEXT:    20000:       0c 00 80 15     jal     131156 <__LA25Thunk_foo1a>
 # ORPH1-NEXT:    20004:       00 00 00 00     nop
 # ORPH1-NEXT:    20008:       0c 00 80 22     jal     131208 <__LA25Thunk_foo2>
 # ORPH1-NEXT:    2000c:       00 00 00 00     nop
 # ORPH1-NEXT:    20010:       0c 00 80 19     jal     131172 <__LA25Thunk_foo1b>
 # ORPH1-NEXT:    20014:       00 00 00 00     nop
 # ORPH1-NEXT:    20018:       0c 00 80 22     jal     131208 <__LA25Thunk_foo2>
 # ORPH1-NEXT:    2001c:       00 00 00 00     nop
 # ORPH1-NEXT:    20020:       0c 00 80 0c     jal     131120 <__LA25Thunk_fpic>
 # ORPH1-NEXT:    20024:       00 00 00 00     nop
 # ORPH1-NEXT:    20028:       0c 00 80 14     jal     131152 <fnpic>
 # ORPH1-NEXT:    2002c:       00 00 00 00     nop
+
 # ORPH1: __LA25Thunk_fpic:
 # ORPH1-NEXT:    20030:       3c 19 00 02     lui     $25, 2
 # ORPH1-NEXT:    20034:       08 00 80 10     j       131136 <fpic>
 # ORPH1-NEXT:    20038:       27 39 00 40     addiu   $25, $25, 64
 # ORPH1-NEXT:    2003c:       00 00 00 00     nop
+
 # ORPH1: fpic:
 # ORPH1-NEXT:    20040:       00 00 00 00     nop
-# ORPH1-NEXT:    20044:       ef ef ef ef     <unknown>
-# ORPH1-NEXT:    20048:       ef ef ef ef     <unknown>
-# ORPH1-NEXT:    2004c:       ef ef ef ef     <unknown>
+
 # ORPH1: fnpic:
 # ORPH1-NEXT:    20050:       00 00 00 00     nop
+
 # ORPH1: __LA25Thunk_foo1a:
 # ORPH1-NEXT:    20054:       3c 19 00 02     lui     $25, 2
 # ORPH1-NEXT:    20058:       08 00 80 20     j       131200 <foo1a>
 # ORPH1-NEXT:    2005c:       27 39 00 80     addiu   $25, $25, 128
 # ORPH1-NEXT:    20060:       00 00 00 00     nop
+
 # ORPH1: __LA25Thunk_foo1b:
 # ORPH1-NEXT:    20064:       3c 19 00 02     lui     $25, 2
 # ORPH1-NEXT:    20068:       08 00 80 21     j       131204 <foo1b>
 # ORPH1-NEXT:    2006c:       27 39 00 84     addiu   $25, $25, 132
 # ORPH1-NEXT:    20070:       00 00 00 00     nop
-# ORPH1-NEXT:    20074:       ef ef ef ef     <unknown>
-# ORPH1-NEXT:    20078:       ef ef ef ef     <unknown>
-# ORPH1-NEXT:    2007c:       ef ef ef ef     <unknown>
+
 # ORPH1: foo1a:
 # ORPH1-NEXT:    20080:       00 00 00 00     nop
+
 # ORPH1: foo1b:
 # ORPH1-NEXT:    20084:       00 00 00 00     nop
+
 # ORPH1: __LA25Thunk_foo2:
 # ORPH1-NEXT:    20088:       3c 19 00 02     lui     $25, 2
 # ORPH1-NEXT:    2008c:       08 00 80 28     j       131232 <foo2>
 # ORPH1-NEXT:    20090:       27 39 00 a0     addiu   $25, $25, 160
 # ORPH1-NEXT:    20094:       00 00 00 00     nop
-# ORPH1-NEXT:    20098:       ef ef ef ef     <unknown>
-# ORPH1-NEXT:    2009c:       ef ef ef ef     <unknown>
+
 # ORPH1: foo2:
 # ORPH1-NEXT:    200a0:       00 00 00 00     nop
 
 # Test script with orphans added to new OutputSection, the .text.1 and
 # .text.2 sections will form a new OutputSection .text
 # RUN: echo "SECTIONS { .out 0x20000 : { *(.text) }  }" > %t3.script
 # RUN: ld.lld --script %t3.script %t-npic.o %t-pic.o %t-sto-pic.o -o %t3.exe
 # RUN: llvm-objdump -d %t3.exe | FileCheck -check-prefix=ORPH2 %s
+
 # ORPH2: Disassembly of section .out:
 # ORPH2-NEXT: __start:
 # ORPH2-NEXT:    20000:       0c 00 80 18     jal     131168 <__LA25Thunk_foo1a>
 # ORPH2-NEXT:    20004:       00 00 00 00     nop
 # ORPH2-NEXT:    20008:       0c 00 80 22     jal     131208 <__LA25Thunk_foo2>
 # ORPH2-NEXT:    2000c:       00 00 00 00     nop
 # ORPH2-NEXT:    20010:       0c 00 80 1c     jal     131184 <__LA25Thunk_foo1b>
 # ORPH2-NEXT:    20014:       00 00 00 00     nop
 # ORPH2-NEXT:    20018:       0c 00 80 22     jal     131208 <__LA25Thunk_foo2>
 # ORPH2-NEXT:    2001c:       00 00 00 00     nop
 # ORPH2-NEXT:    20020:       0c 00 80 0c     jal     131120 <__LA25Thunk_fpic>
 # ORPH2-NEXT:    20024:       00 00 00 00     nop
 # ORPH2-NEXT:    20028:       0c 00 80 14     jal     131152 <fnpic>
 # ORPH2-NEXT:    2002c:       00 00 00 00     nop
+
 # ORPH2: __LA25Thunk_fpic:
 # ORPH2-NEXT:    20030:       3c 19 00 02     lui     $25, 2
 # ORPH2-NEXT:    20034:       08 00 80 10     j       131136 <fpic>
 # ORPH2-NEXT:    20038:       27 39 00 40     addiu   $25, $25, 64
 # ORPH2-NEXT:    2003c:       00 00 00 00     nop
+
 # ORPH2: fpic:
 # ORPH2-NEXT:    20040:       00 00 00 00     nop
-# ORPH2-NEXT:    20044:       ef ef ef ef     <unknown>
-# ORPH2-NEXT:    20048:       ef ef ef ef     <unknown>
-# ORPH2-NEXT:    2004c:       ef ef ef ef     <unknown>
+
 # ORPH2: fnpic:
 # ORPH2-NEXT:    20050:       00 00 00 00     nop
 # ORPH2-NEXT: Disassembly of section .text:
+
 # ORPH2-NEXT: __LA25Thunk_foo1a:
 # ORPH2-NEXT:    20060:       3c 19 00 02     lui     $25, 2
 # ORPH2-NEXT:    20064:       08 00 80 20     j       131200 <foo1a>
 # ORPH2-NEXT:    20068:       27 39 00 80     addiu   $25, $25, 128
 # ORPH2-NEXT:    2006c:       00 00 00 00     nop
+
 # ORPH2: __LA25Thunk_foo1b:
 # ORPH2-NEXT:    20070:       3c 19 00 02     lui     $25, 2
 # ORPH2-NEXT:    20074:       08 00 80 21     j       131204 <foo1b>
 # ORPH2-NEXT:    20078:       27 39 00 84     addiu   $25, $25, 132
 # ORPH2-NEXT:    2007c:       00 00 00 00     nop
+
 # ORPH2: foo1a:
 # ORPH2-NEXT:    20080:       00 00 00 00     nop
+
 # ORPH2: foo1b:
 # ORPH2-NEXT:    20084:       00 00 00 00     nop
+
 # ORPH2: __LA25Thunk_foo2:
 # ORPH2-NEXT:    20088:       3c 19 00 02     lui     $25, 2
 # ORPH2-NEXT:    2008c:       08 00 80 28     j       131232 <foo2>
 # ORPH2-NEXT:    20090:       27 39 00 a0     addiu   $25, $25, 160
 # ORPH2-NEXT:    20094:       00 00 00 00     nop
-# ORPH2-NEXT:    20098:       ef ef ef ef     <unknown>
-# ORPH2-NEXT:    2009c:       ef ef ef ef     <unknown>
+
 # ORPH2: foo2:
 # ORPH2-NEXT:    200a0:       00 00 00 00     nop

test/ELF/mips-npic-call-pic.s

 # CHECK: foo1b:
 # CHECK-NEXT:    20054:       00 00 00 00     nop
 
 # CHECK: __LA25Thunk_foo2:
 # CHECK-NEXT:    20058:       3c 19 00 02     lui     $25, 2
 # CHECK-NEXT:    2005c:       08 00 80 1c     j       131184 <foo2>
 # CHECK-NEXT:    20060:       27 39 00 70     addiu   $25, $25, 112
 # CHECK-NEXT:    20064:       00 00 00 00     nop
-# CHECK-NEXT:    20068:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    2006c:       ef ef ef ef     <unknown>
 
 # CHECK: foo2:
 # CHECK-NEXT:    20070:       00 00 00 00     nop
 
 # CHECK: __LA25Thunk_fpic:
 # CHECK-NEXT:    20074:       3c 19 00 02     lui     $25, 2
 # CHECK-NEXT:    20078:       08 00 80 24     j       131216 <fpic>
 # CHECK-NEXT:    2007c:       27 39 00 90     addiu   $25, $25, 144
 # CHECK-NEXT:    20080:       00 00 00 00     nop
-# CHECK-NEXT:    20084:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20088:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    2008c:       ef ef ef ef     <unknown>
 
 # CHECK: fpic:
 # CHECK-NEXT:    20090:       00 00 00 00     nop
-# CHECK-NEXT:    20094:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    20098:       ef ef ef ef     <unknown>
-# CHECK-NEXT:    2009c:       ef ef ef ef     <unknown>
 
 # CHECK: fnpic:
 # CHECK-NEXT:    200a0:       00 00 00 00     nop
 
 # Make sure the thunks are created properly no matter how
 # objects are laid out.
 #
 # RUN: ld.lld %t-pic.o %t-npic.o %t-sto-pic.o -o %t.exe
 # RUN: llvm-objdump -d %t.exe | FileCheck -check-prefix=REVERSE %s
 
 # REVERSE: Disassembly of section .text:
 # REVERSE-NEXT: __LA25Thunk_foo1a:
 # REVERSE-NEXT:    20000:       3c 19 00 02     lui     $25, 2
 # REVERSE-NEXT:    20004:       08 00 80 08     j       131104 <foo1a>
 # REVERSE-NEXT:    20008:       27 39 00 20     addiu   $25, $25, 32
 # REVERSE-NEXT:    2000c:       00 00 00 00     nop
+
 # REVERSE: __LA25Thunk_foo1b:
 # REVERSE-NEXT:    20010:       3c 19 00 02     lui     $25, 2
 # REVERSE-NEXT:    20014:       08 00 80 09     j       131108 <foo1b>
 # REVERSE-NEXT:    20018:       27 39 00 24     addiu   $25, $25, 36
 # REVERSE-NEXT:    2001c:       00 00 00 00     nop
+
 # REVERSE: foo1a:
 # REVERSE-NEXT:    20020:       00 00 00 00     nop
+
 # REVERSE: foo1b:
 # REVERSE-NEXT:    20024:       00 00 00 00     nop
+
 # REVERSE: __LA25Thunk_foo2:
 # REVERSE-NEXT:    20028:       3c 19 00 02     lui     $25, 2
 # REVERSE-NEXT:    2002c:       08 00 80 10     j       131136 <foo2>
 # REVERSE-NEXT:    20030:       27 39 00 40     addiu   $25, $25, 64
 # REVERSE-NEXT:    20034:       00 00 00 00     nop
-# REVERSE-NEXT:    20038:       ef ef ef ef     <unknown>
-# REVERSE-NEXT:    2003c:       ef ef ef ef     <unknown>
+
 # REVERSE: foo2:
 # REVERSE-NEXT:    20040:       00 00 00 00     nop
-# REVERSE-NEXT:    20044:       ef ef ef ef     <unknown>
-# REVERSE-NEXT:    20048:       ef ef ef ef     <unknown>
-# REVERSE-NEXT:    2004c:       ef ef ef ef     <unknown>
+
 # REVERSE: __start:
 # REVERSE-NEXT:    20050:       0c 00 80 00     jal     131072 <__LA25Thunk_foo1a>
 # REVERSE-NEXT:    20054:       00 00 00 00     nop
 # REVERSE-NEXT:    20058:       0c 00 80 0a     jal     131112 <__LA25Thunk_foo2>
 # REVERSE-NEXT:    2005c:       00 00 00 00     nop
 # REVERSE-NEXT:    20060:       0c 00 80 04     jal     131088 <__LA25Thunk_foo1b>
 # REVERSE-NEXT:    20064:       00 00 00 00     nop
 # REVERSE-NEXT:    20068:       0c 00 80 0a     jal     131112 <__LA25Thunk_foo2>
 # REVERSE-NEXT:    2006c:       00 00 00 00     nop
 # REVERSE-NEXT:    20070:       0c 00 80 20     jal     131200 <__LA25Thunk_fpic>
 # REVERSE-NEXT:    20074:       00 00 00 00     nop
 # REVERSE-NEXT:    20078:       0c 00 80 28     jal     131232 <fnpic>
 # REVERSE-NEXT:    2007c:       00 00 00 00     nop
+
 # REVERSE: __LA25Thunk_fpic:
 # REVERSE-NEXT:    20080:       3c 19 00 02     lui     $25, 2
 # REVERSE-NEXT:    20084:       08 00 80 24     j       131216 <fpic>
 # REVERSE-NEXT:    20088:       27 39 00 90     addiu   $25, $25, 144
 # REVERSE-NEXT:    2008c:       00 00 00 00     nop
+
 # REVERSE: fpic:
 # REVERSE-NEXT:    20090:       00 00 00 00     nop
-# REVERSE-NEXT:    20094:       ef ef ef ef     <unknown>
-# REVERSE-NEXT:    20098:       ef ef ef ef     <unknown>
-# REVERSE-NEXT:    2009c:       ef ef ef ef     <unknown>
+
 # REVERSE: fnpic:
 # REVERSE-NEXT:    200a0:       00 00 00 00     nop
 
   .text
   .globl __start
 __start:
   jal foo1a
   jal foo2
   jal foo1b
   jal foo2
   jal fpic
   jal fnpic

test/ELF/mips-traps.s

+# Check trap instruction encoding.
+
+# REQUIRES: mips
+
+# RUN: llvm-mc -filetype=obj -triple=mips-unknown-linux -mcpu=mips32r6 -o %t.o %s
+# RUN: ld.lld -r -o %t %t.o %t.o
+# RUN: llvm-objdump -d -r %t | FileCheck --check-prefix=EB %s
+
+# RUN: llvm-mc -filetype=obj -triple=mipsel-unknown-linux -mcpu=mips32r6 -o %t.o %s
+# RUN: ld.lld -r -o %t %t.o %t.o
+# RUN: llvm-objdump -d -r %t | FileCheck --check-prefix=EL %s
+
+# EB:        8:       04 17 00 01     sigrie 1
+# EL:        8:       01 00 17 04     sigrie 1
+
+  .text
+  lw     $t9, %got(.data)($gp)
+  addiu  $a0, $t9, %lo(.data)
+
+  .data
+data:
+  .word 0