[llvm] [ARMAsmBackend] Add checks for relocation addends in assembler (PR #109969)

[Oliver Stannard via llvm-commits]

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@@ -579,13 +579,24 @@ unsigned ARMAsmBackend::adjustFixupValue(const MCAssembler &Asm,
   case ARM::fixup_arm_uncondbl:
   case ARM::fixup_arm_condbl:
   case ARM::fixup_arm_blx:
+    // Check that the fixup value is legal.
+    Value = Value - 8;
+    if (!isInt<25>(Value)) {
+      Ctx.reportError(Fixup.getLoc(), "Relocation out of range");
+      return 0;
+    }
+    if (Value % 4 != 0) {
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ostannard wrote:

The ARM BLX instruction can branch to Thumb code, so only needs to be 2-byte aligned.

https://github.com/llvm/llvm-project/pull/109969