[PATCH] D156716: [AArch64][PAC] Check authenticated LR value during tail call

[Anatoly Trosinenko via Phabricator via llvm-commits]

atrosinenko added inline comments.


================
Comment at: llvm/lib/Target/AArch64/AArch64PointerAuth.cpp:191
+        .addMemOperand(createCheckMemOperand(MF))
+        .setMIFlags(MachineInstr::FrameDestroy);
+    return MBB;
----------------
kristof.beyls wrote:
> I'm wondering why any/all of the machineinsts created in this function need to have the FrameDestroy flag set? Do you know?
Setting `MachineInstr::FrameDestroy` unconditionally in `checkAuthenticatedRegister` is definitely a mistake, thank you. Maybe I have to pass MI flags as an argument, but it seems that it works as-is, at least for generating DWARF debug info (see Epilogue Begin marker).

Added an explicit assertion that WinCFI is not requested as I don't yet emit any SEH opcodes.

```
$ cat /tmp/tail-call.c 
int caller_indirect(int *n, int (fptr)(int*)) {
  asm volatile ("" ::: "lr");
  *n = 42;
  return fptr(n);
}
$ ./bin/clang -O1 -target aarch64-linux-gnu /tmp/tail-call.c -c -o /tmp/tail-call.o -mbranch-protection=pac-ret -mllvm -aarch64-authenticated-lr-check-method=xpac-hint -g
$ dwarfdump -l /tmp/tail-call.o && llvm-objdump -d /tmp/tail-call.o 

.debug_line: line number info for a single cu
Source lines (from CU-DIE at .debug_info offset 0x0000000c):

            NS new statement, BB new basic block, ET end of text sequence
            PE prologue end, EB epilogue begin
            IS=val ISA number, DI=val discriminator value
<pc>        [lno,col] NS BB ET PE EB IS= DI= uri: "filepath"
0x00000000  [   1, 0] NS uri: "/tmp/tail-call.c"
0x0000000c  [   2, 3] NS PE
0x0000000c  [   3, 6] NS
0x00000010  [   4,10] NS ET EB
0x00000030  [   4,10] NS ET


/tmp/tail-call.o:       file format elf64-littleaarch64

Disassembly of section .text:

0000000000000000 <caller_indirect>:
       0: d503233f      paciasp
       4: f81f0ffe      str     x30, [sp, #-0x10]!
       8: 52800548      mov     w8, #0x2a
       c: b9000008      str     w8, [x0]
      10: f84107fe      ldr     x30, [sp], #0x10
      14: d50323bf      autiasp
      18: aa1e03f0      mov     x16, x30
      1c: d50320ff      xpaclri
      20: eb1e021f      cmp     x16, x30
      24: 54000041      b.ne    0x2c <caller_indirect+0x2c>
      28: d61f0020      br      x1
      2c: d4388e20      brk     #0xc471
```


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D156716/new/

https://reviews.llvm.org/D156716