[llvm] Allow .alt_entry symbols to pass the .cfi nesting check (PR #82268)

[Jon Roelofs via llvm-commits]

https://github.com/jroelofs created https://github.com/llvm/llvm-project/pull/82268

Fixes: https://github.com/llvm/llvm-project/issues/82261

>From b695bdf5e095212b3d081c59deb952792d55834d Mon Sep 17 00:00:00 2001
From: Jon Roelofs <jonathan_roelofs at apple.com>
Date: Mon, 19 Feb 2024 10:20:32 -0800
Subject: [PATCH] Allow .alt_entry symbols to pass the .cfi nesting check

Fixes: https://github.com/llvm/llvm-project/issues/82261
---
 llvm/lib/MC/MCParser/AsmParser.cpp            | 5 ++++-
 llvm/test/MC/AArch64/cfi-bad-nesting-darwin.s | 4 +++-
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/llvm/lib/MC/MCParser/AsmParser.cpp b/llvm/lib/MC/MCParser/AsmParser.cpp
index 8e508dbdb1c69b..e8dc078c9610c2 100644
--- a/llvm/lib/MC/MCParser/AsmParser.cpp
+++ b/llvm/lib/MC/MCParser/AsmParser.cpp
@@ -44,6 +44,7 @@
 #include "llvm/MC/MCSection.h"
 #include "llvm/MC/MCStreamer.h"
 #include "llvm/MC/MCSymbol.h"
+#include "llvm/MC/MCSymbolMachO.h"
 #include "llvm/MC/MCTargetOptions.h"
 #include "llvm/MC/MCValue.h"
 #include "llvm/Support/Casting.h"
@@ -1950,7 +1951,9 @@ bool AsmParser::parseStatement(ParseStatementInfo &Info,
       Lex();
     }
 
-    if (MAI.hasSubsectionsViaSymbols() && CFIStartProcLoc && Sym->isExternal())
+    if (MAI.hasSubsectionsViaSymbols() && CFIStartProcLoc &&
+        Sym->isExternal() &&
+        (!isa<MCSymbolMachO>(Sym) || !cast<MCSymbolMachO>(Sym)->isAltEntry()))
       return Error(StartTokLoc, "non-private labels cannot appear between "
                                 ".cfi_startproc / .cfi_endproc pairs") &&
              Error(*CFIStartProcLoc, "previous .cfi_startproc was here");
diff --git a/llvm/test/MC/AArch64/cfi-bad-nesting-darwin.s b/llvm/test/MC/AArch64/cfi-bad-nesting-darwin.s
index 235b7d44809929..6a4dda3a77f05a 100644
--- a/llvm/test/MC/AArch64/cfi-bad-nesting-darwin.s
+++ b/llvm/test/MC/AArch64/cfi-bad-nesting-darwin.s
@@ -8,6 +8,8 @@
 	.p2align	2
 _locomotive:
 	.cfi_startproc
+	.alt_entry _engineer
+_engineer:
 	ret
 
 	; It is invalid to have a non-private label between .cfi_startproc and
@@ -17,7 +19,7 @@ _locomotive:
 	.p2align	2
 _caboose:
 ; DARWIN: [[#@LINE-1]]:1: error: non-private labels cannot appear between .cfi_startproc / .cfi_endproc pairs
-; DARWIN: [[#@LINE-10]]:2: error: previous .cfi_startproc was here
+; DARWIN: [[#@LINE-12]]:2: error: previous .cfi_startproc was here
 	ret
 	.cfi_endproc