[MC][ARM] add .w suffixes for BL (T1) and DBG

[nickdesaulniers]

Summary

F1.2 Standard assembler syntax fields
describes .w and .n suffixes for wide and narrow encodings.

arch/arm/probes/kprobes/test-thumb.c tests installing kprobes for
certain instructions using inline asm. There's a few instructions we
fail to assemble due to missing .w t2InstAliases.

Adds .w suffixes for:

• bl (F5.1.25 BL, BLX (immediate) T1)
• dbg (F5.1.42 DBG T1)

[DavidSpickett]

I couldn't find an official rule for allowing ".w" when the instructions only have 32 bit encodings. However GAS does it and we also allow others such as AND (immediate) (see test/MC/ARM/basic-thumb2-instructions.s) so I think it's fine.

llvm/test/MC/ARM/basic-thumb2-instructions.s

657

Also add a predicated one here.

llvm/test/MC/ARM/thumb2-branches.s

104

You could just use an immediate here and not need to check the relocation emitted.

Also I'd add one with a predicate just to check the alias allows that.

I thought that maybe we should use ".w" in the disassembly, however all bl and dbg are 32 bit encodings so there's no ambiguity here. This matches GAS's behavior too.

[DavidSpickett]

llvm/test/MC/ARM/basic-thumb2-instructions.s

657

s/predicated/conditional

llvm/test/MC/ARM/thumb2-branches.s

104

s/predicated/conditional

[nickdesaulniers]

• add predicated test cases, use immediate operand in test

[nickdesaulniers]

In D97236#2581308, @DavidSpickett wrote:

I couldn't find an official rule for allowing ".w" when the instructions only have 32 bit encodings.

My interpretation of "F1.2 Standard assembler syntax fields":

.W Meaning wide, specifies that the assembler must select a 32-bit encoding for the
instruction. If this is not possible, an assembler error is produced.

(and says the same for .N/16b, so an error diagnostic should be produced whenever there is not a corresponding encoding for that suffix).

See also this thread starting from: https://github.com/ClangBuiltLinux/linux/issues/1296#issuecomment-778598573.

[DavidSpickett]

LGTM with nits fixed.

llvm/test/MC/ARM/basic-thumb2-instructions.s

659

nit: indent the @ encoding

llvm/test/MC/ARM/thumb2-branches.s

105

nit: indent the @ encoding

[nickdesaulniers]

llvm/test/MC/ARM/basic-thumb2-instructions.s

659

I think phab is expanding tabs to a different number of spaces then 8. With tabstop=8, the indentation is consistent throughout the file.

[nickdesaulniers]

llvm/test/MC/ARM/basic-thumb2-instructions.s

659

Yeah, if you click "show 20 lines" in phab, you can see what looks like existing cases of curious indentation. It's just phab expanding tabs to a different number of spaces.

llvm/lib/Target/ARM/ARMInstrThumb2.td

def t2BXJ : T2I<(outs), (ins GPRnopc:$func), NoItinerary, "bxj", "\t$func", []>,
   bits<4> func;
   let Inst{31-27} = 0b11110;
   let Inst{26} = 0;
   let Inst{25-20} = 0b111100;
   let Inst{19-16} = func;
   let Inst{15-0} = 0b1000111100000000;
 }
 
+def : t2InstAlias<"bl${p}.w $func", (tBL pred:$p, thumb_bl_target:$func), 0>;
+
 // Compare and branch on zero / non-zero
 let isBranch = 1, isTerminator = 1 in {
   def tCBZ  : T1I<(outs), (ins tGPR:$Rn, thumb_cb_target:$target), IIC_Br,
                   "cbz\t$Rn, $target", []>,
               T1Misc<{0,0,?,1,?,?,?}>,
               Requires<[IsThumb, HasV8MBaseline]>, Sched<[WriteBr]> {
     // A8.6.27
     bits<6> target;
def t2DBG : T2I<(outs), (ins imm0_15:$opt), NoItinerary, "dbg", "\t$opt",
                 [(int_arm_dbg imm0_15:$opt)]> {
   bits<4> opt;
   let Inst{31-20} = 0b111100111010;
   let Inst{19-16} = 0b1111;
   let Inst{15-8} = 0b10000000;
   let Inst{7-4} = 0b1111;
   let Inst{3-0} = opt;
 }
+def : t2InstAlias<"dbg${p}.w $opt", (t2DBG imm0_15:$opt, pred:$p), 0>;
 
 // Secure Monitor Call is a system instruction.
 // Option = Inst{19-16}
 let isCall = 1, Uses = [SP] in
 def t2SMC : T2I<(outs), (ins imm0_15:$opt), NoItinerary, "smc", "\t$opt",
                 []>, Requires<[IsThumb2, HasTrustZone]> {
   let Inst{31-27} = 0b11110;
   let Inst{26-20} = 0b1111111;

llvm/test/MC/ARM/basic-thumb2-instructions.s

 @ CHECK: cps   #0                       @ encoding: [0xaf,0xf3,0x00,0x81]
 
 @------------------------------------------------------------------------------
 @ DBG
 @------------------------------------------------------------------------------
         dbg #5
         dbg #0
         dbg #15
+        dbg.w #0
+        it ne
+        dbgne.w #0
 
 @ CHECK: dbg  #5                      @ encoding: [0xaf,0xf3,0xf5,0x80]
 @ CHECK: dbg  #0                      @ encoding: [0xaf,0xf3,0xf0,0x80]
 @ CHECK: dbg  #15                     @ encoding: [0xaf,0xf3,0xff,0x80]
+@ CHECK: dbg  #0                      @ encoding: [0xaf,0xf3,0xf0,0x80]
+@ CHECK: it  ne                      @ encoding: [0x18,0xbf]
+@ CHECK: dbgne  #0                      @ encoding: [0xaf,0xf3,0xf0,0x80]
 
 
 @------------------------------------------------------------------------------
 @ DMB
 @------------------------------------------------------------------------------
         dmb #0xf
         dmb #0xe
         dmb #0xd

llvm/test/MC/ARM/thumb2-branches.s

 
 @ CHECK: beq  #-256                   @ encoding: [0x80,0xd0]
 @ CHECK: bne  #254                    @ encoding: [0x7f,0xd1]
 
 @------------------------------------------------------------------------------
 @ unconditional branches accept wide suffix and encode to wide encodings
 @------------------------------------------------------------------------------
 
+         bl.w     #256
+         it ne
+         blne.w   #256
          bmi.w    #-256
          bne.w    #254
          blt.w    #-1048576
          bge.w    #1048574
 
+@ CHECK: bl  #256                    @ encoding: [0x00,0xf0,0x80,0xf8]
+@ CHECK: it  ne                      @ encoding: [0x18,0xbf]
+@ CHECK: blne  #256                    @ encoding: [0x00,0xf0,0x80,0xf8]
 @ CHECK: bmi.w  #-256                   @ encoding: [0x3f,0xf5,0x80,0xaf]
 @ CHECK: bne.w  #254                    @ encoding: [0x40,0xf0,0x7f,0x80]
 @ CHECK: blt.w  #-1048576               @ encoding: [0xc0,0xf6,0x00,0x80]
 @ CHECK: bge.w  #1048574                @ encoding: [0xbf,0xf2,0xff,0xaf]
 
 @------------------------------------------------------------------------------
 @ unconditional branches without width suffix encode depending of offset size
 @------------------------------------------------------------------------------