BPF: Change callx insn encoding (#81546)

Currently, the kernel verifier unsupported callx insn used the 32-bit
imm field to store the target register. On the other hand, gcc used the
dst_reg field to store the target register. The gcc encoding is better.
This patch adjusted the coding to be the same as gcc.

Signed-off-by: Yonghong Song <[email protected]>

Author: yonghong-song

llvm/lib/Target/BPF/AsmParser/BPFAsmParser.cpp

@@ -229,6 +229,7 @@ struct BPFOperand : public MCParsedAsmOperand {
     return StringSwitch<bool>(Name.lower())
         .Case("if", true)
         .Case("call", true)
+        .Case("callx", true)
         .Case("goto", true)
         .Case("gotol", true)
         .Case("*", true)

llvm/lib/Target/BPF/BPFInstrInfo.td

@@ -622,9 +622,9 @@ class CALLX<string OpcodeStr>
                    (ins GPR:$BrDst),
                    !strconcat(OpcodeStr, " $BrDst"),
                    []> {
-  bits<32> BrDst;
+  bits<4> BrDst;
 
-  let Inst{31-0} = BrDst;
+  let Inst{51-48} = BrDst;
   let BPFClass = BPF_JMP;
 }
 

llvm/test/MC/BPF/insn-unit.s

@@ -61,6 +61,9 @@
 // CHECK-32: c3 92 10 00 00 00 00 00 	lock *(u32 *)(r2 + 16) += w9
 // CHECK: db a3 e2 ff 00 00 00 00 	lock *(u64 *)(r3 - 30) += r10
 
+  callx r2
+// CHECK: 8d 02 00 00 00 00 00 00 	callx r2
+
 // ======== BPF_JMP Class ========
   if r1 & r2 goto Llabel0    // BPF_JSET  | BPF_X
   if r1 & 0xffff goto Llabel0    // BPF_JSET  | BPF_K