From 7e0768329ca347e37c7bdb0da16b51cb3e7b7d8b Mon Sep 17 00:00:00 2001
From: =?utf8?q?Martin=20Storsj=C3=B6?= <martin@martin.st>
Date: Sun, 9 May 2021 23:27:35 +0300
Subject: [PATCH] [LLD] [COFF] Fix including the personality function for DWARF
 EH when linking with --gc-sections

Since c579a5b1d92a9bc2046d00ee2d427832e0f5ddec we don't traverse
.eh_frame when doing GC. But the exception handling personality
function needs to be included, and is only referenced from within
.eh_frame.

Differential Revision: https://reviews.llvm.org/D102138
---
 lld/COFF/Driver.cpp         | 19 ++++++++++++++++++-
 lld/test/COFF/gc-dwarf-eh.s | 36 ++++++++++++++++++++++++++++++++++++
 2 files changed, 54 insertions(+), 1 deletion(-)
 create mode 100644 lld/test/COFF/gc-dwarf-eh.s

diff --git a/lld/COFF/Driver.cpp b/lld/COFF/Driver.cpp
index e2374b5..029148c 100644
--- a/lld/COFF/Driver.cpp
+++ b/lld/COFF/Driver.cpp
@@ -2226,8 +2226,25 @@ void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
     config->printSymbolOrder = arg->getValue();
 
   // Identify unreferenced COMDAT sections.
-  if (config->doGC)
+  if (config->doGC) {
+    if (config->mingw) {
+      // markLive doesn't traverse .eh_frame, but the personality function is
+      // only reached that way. The proper solution would be to parse and
+      // traverse the .eh_frame section, like the ELF linker does.
+      // For now, just manually try to retain the known possible personality
+      // functions. This doesn't bring in more object files, but only marks
+      // functions that already have been included to be retained.
+      for (const char *n : {"__gxx_personality_v0", "__gcc_personality_v0"}) {
+        Defined *d = dyn_cast_or_null<Defined>(symtab->findUnderscore(n));
+        if (d && !d->isGCRoot) {
+          d->isGCRoot = true;
+          config->gcroot.push_back(d);
+        }
+      }
+    }
+
     markLive(symtab->getChunks());
+  }
 
   // Needs to happen after the last call to addFile().
   convertResources();
diff --git a/lld/test/COFF/gc-dwarf-eh.s b/lld/test/COFF/gc-dwarf-eh.s
new file mode 100644
index 0000000..757aa67
--- /dev/null
+++ b/lld/test/COFF/gc-dwarf-eh.s
@@ -0,0 +1,36 @@
+# REQUIRES: x86
+
+# RUN: llvm-mc -triple=i686-windows-gnu %s -filetype=obj -o %t.obj
+# RUN: lld-link -lldmingw -lldmap:%t.map -out:%t.exe -opt:ref -entry:main %t.obj -verbose 2>&1 | FileCheck %s
+# RUN: FileCheck %s --check-prefix=MAP --input-file=%t.map
+
+# CHECK: Discarded _unused
+
+# MAP: In Symbol
+# MAP: gc-dwarf-eh.s.tmp.obj:(.text)
+# MAP: {{ ___gxx_personality_v0$}}
+
+	.def	_main; .scl	2; .type	32; .endef
+	.section	.text,"xr",one_only,_main
+	.globl	_main
+	.cfi_startproc
+	.cfi_personality 0, ___gxx_personality_v0
+_main:
+	xorl	%eax, %eax
+	ret
+	.cfi_endproc
+
+	.def	___gxx_personality_v0; .scl	2; .type	32; .endef
+	.section	.text,"xr",one_only,___gxx_personality_v0
+	.globl	___gxx_personality_v0
+___gxx_personality_v0:
+	ret
+
+	.def	_unused; .scl	2; .type	32; .endef
+	.section	.text,"xr",one_only,_unused
+	.globl	_unused
+	.cfi_startproc
+	.cfi_personality 0, ___gxx_personality_v0
+_unused:
+	ret
+	.cfi_endproc
-- 
2.7.4