[llvm-branch-commits] [llvm] release/18.x: Allow .alt_entry symbols to pass the .cfi nesting check (#82268) (PR #83336)

[via llvm-branch-commits]

https://github.com/llvmbot created https://github.com/llvm/llvm-project/pull/83336

Backport 5b91647e3f82c9747c42c3239b7d7f3ade4542a7

Requested by: @jroelofs

>From faed9cbd490450dba5879f130caf1482a0704838 Mon Sep 17 00:00:00 2001
From: Jon Roelofs <jonathan_roelofs at apple.com>
Date: Wed, 28 Feb 2024 13:03:35 -0800
Subject: [PATCH] Allow .alt_entry symbols to pass the .cfi nesting check
 (#82268)

A symbol with an `N_ALT_ENTRY` attribute may be defined in the middle of
a subsection, so it is reasonable to opt them out of the
`.cfi_{start,end}proc` nesting check.

Fixes: https://github.com/llvm/llvm-project/issues/82261
(cherry picked from commit 5b91647e3f82c9747c42c3239b7d7f3ade4542a7)
---
 llvm/lib/MC/MCParser/AsmParser.cpp            | 4 +++-
 llvm/test/MC/AArch64/cfi-bad-nesting-darwin.s | 6 +++++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/llvm/lib/MC/MCParser/AsmParser.cpp b/llvm/lib/MC/MCParser/AsmParser.cpp
index 8e508dbdb1c69b..026d252ec5bcd7 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 +1951,8 @@ bool AsmParser::parseStatement(ParseStatementInfo &Info,
       Lex();
     }
 
-    if (MAI.hasSubsectionsViaSymbols() && CFIStartProcLoc && Sym->isExternal())
+    if (MAI.hasSubsectionsViaSymbols() && CFIStartProcLoc &&
+        Sym->isExternal() && !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..3a5af86defc592 100644
--- a/llvm/test/MC/AArch64/cfi-bad-nesting-darwin.s
+++ b/llvm/test/MC/AArch64/cfi-bad-nesting-darwin.s
@@ -8,6 +8,10 @@
 	.p2align	2
 _locomotive:
 	.cfi_startproc
+	; An N_ALT_ENTRY symbol can be defined in the middle of a subsection, so
+	; these are opted out of the .cfi_{start,end}proc nesting check.
+	.alt_entry _engineer
+_engineer:
 	ret
 
 	; It is invalid to have a non-private label between .cfi_startproc and
@@ -17,7 +21,7 @@ _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-14]]:2: error: previous .cfi_startproc was here
 	ret
 	.cfi_endproc