[llvm] BPF: Emit an error for illegal LD_imm64 insn when LLVM_ENABLE_ASSERTI… (PR #74035)

[via llvm-commits]

https://github.com/yonghong-song created https://github.com/llvm/llvm-project/pull/74035

…ONS=OFF

Jose reported an issue ([1]) where for the below illegal asm code
```
  r0 = 1 + w3 ll
```
clang actually supports it and generates the object code.

Further investigation finds that clang actually intends to reject the above code as well but only when the clang is built with LLVM_ENABLE_ASSERTIONS=ON.

I later found that clang16 (built by redhat and centos) in fedora system has the same issue since they also have LLVM_ENABLE_ASSERTIONS=OFF ([2]).

So let BPF backend report an error for the above case regardless of the LLVM_ENABLE_ASSERTIONS setting.

  [1] https://lore.kernel.org/bpf/87leahx2xh.fsf@oracle.com/#t
  [2] https://lore.kernel.org/bpf/840e33ec-ea4c-4b55-bda1-0be8d1e0324f@linux.dev/

>From 9dcd1f9fd005c2c3ab32ac3f56284d0399c1e3f5 Mon Sep 17 00:00:00 2001
From: Yonghong Song <yonghong.song at linux.dev>
Date: Thu, 30 Nov 2023 19:36:01 -0800
Subject: [PATCH] BPF: Emit an error for illegal LD_imm64 insn when
 LLVM_ENABLE_ASSERTIONS=OFF

Jose reported an issue ([1]) where for the below illegal asm code
  r0 = 1 + w3 ll
clang actually supports it and generates the object code.

Further investigation finds that clang actually intends to
reject the above code as well but only when the clang is
built with LLVM_ENABLE_ASSERTIONS=ON.

I later found that clang16 (built by redhat and centos)
in fedora system has the same issue since they also have
LLVM_ENABLE_ASSERTIONS=OFF ([2]).

So let BPF backend report an error for the above case
regardless of the LLVM_ENABLE_ASSERTIONS setting.

  [1] https://lore.kernel.org/bpf/87leahx2xh.fsf@oracle.com/#t
  [2] https://lore.kernel.org/bpf/840e33ec-ea4c-4b55-bda1-0be8d1e0324f@linux.dev/
---
 llvm/lib/Target/BPF/MCTargetDesc/BPFInstPrinter.cpp | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/llvm/lib/Target/BPF/MCTargetDesc/BPFInstPrinter.cpp b/llvm/lib/Target/BPF/MCTargetDesc/BPFInstPrinter.cpp
index 15ab55f95e69b81..c266538bec7361e 100644
--- a/llvm/lib/Target/BPF/MCTargetDesc/BPFInstPrinter.cpp
+++ b/llvm/lib/Target/BPF/MCTargetDesc/BPFInstPrinter.cpp
@@ -36,15 +36,16 @@ void BPFInstPrinter::printInst(const MCInst *MI, uint64_t Address,
 }
 
 static void printExpr(const MCExpr *Expr, raw_ostream &O) {
-#ifndef NDEBUG
   const MCSymbolRefExpr *SRE;
 
   if (const MCBinaryExpr *BE = dyn_cast<MCBinaryExpr>(Expr))
     SRE = dyn_cast<MCSymbolRefExpr>(BE->getLHS());
   else
     SRE = dyn_cast<MCSymbolRefExpr>(Expr);
-  assert(SRE && "Unexpected MCExpr type.");
+  if (!SRE)
+    report_fatal_error("Unexpected MCExpr type.");
 
+#ifndef NDEBUG
   MCSymbolRefExpr::VariantKind Kind = SRE->getKind();
 
   assert(Kind == MCSymbolRefExpr::VK_None);