From 8628117143d73743c6b6d5a3e47613d488858b26 Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Sun, 2 Feb 2020 15:32:34 -0800
Subject: [PATCH] Issue an error for GC on __patchable_function_entries section

__patchable_function_entries section is generated by a compiler with
-fpatchable-function-entry=XX.  The assembly code looks like this:

---
	.text
	.globl	_start
	.type	_start, %function
_start:
	.section __patchable_function_entries,"aw",%progbits
	.dc.a	.LPFE1
	.text
.LPFE1:
	.byte 0
---

But --gc-sections will silently remove __patchable_function_entries
section and generate corrupt result.  The linker bug will be fixed
by implementing the 'o' section flag with linked-to section:

https://sourceware.org/bugzilla/show_bug.cgi?id=25381

In the meantime, this patch disallows garbage collection on
__patchable_function_entries section without linked-to section.

bfd/

 	PR ld/25490
	* elflink.c (_bfd_elf_gc_mark_extra_sections): Issue an error
	for garbage collection on __patchable_function_entries section
	without linked-to section.

ld/

 	PR ld/25490
	* testsuite/ld-elf/pr25490-1.d: New file.
	* testsuite/ld-elf/pr25490-1.d: Likewise.
---
 bfd/elflink.c                   | 7 +++++++
 ld/testsuite/ld-elf/pr25490-1.d | 2 ++
 ld/testsuite/ld-elf/pr25490-1.s | 9 +++++++++
 3 files changed, 18 insertions(+)
 create mode 100644 ld/testsuite/ld-elf/pr25490-1.d
 create mode 100644 ld/testsuite/ld-elf/pr25490-1.s

diff --git a/bfd/elflink.c b/bfd/elflink.c
index 5217528a79b..e4d92952aaf 100644
--- a/bfd/elflink.c
+++ b/bfd/elflink.c
@@ -13350,6 +13350,13 @@ _bfd_elf_gc_mark_extra_sections (struct bfd_link_info *info,
 	      && (isec->flags & SEC_DEBUGGING)
 	      && CONST_STRNEQ (isec->name, ".debug_line."))
 	    debug_frag_seen = TRUE;
+	  else if (strcmp (bfd_section_name (isec),
+			   "__patchable_function_entries") == 0
+		   && elf_linked_to_section (isec) == NULL)
+	      info->callbacks->einfo (_("%F%P: %pB(%pA): error: "
+					"need linked-to section "
+					"for --gc-sections\n"),
+				      isec->owner, isec);
 	}
 
       /* If no non-note alloc section in this file will be kept, then
diff --git a/ld/testsuite/ld-elf/pr25490-1.d b/ld/testsuite/ld-elf/pr25490-1.d
new file mode 100644
index 00000000000..7cc2e6aaa1c
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr25490-1.d
@@ -0,0 +1,2 @@
+#ld: --gc-sections -e _start
+#error: .*\(__patchable_function_entries\): error: need linked-to section for --gc-sections
diff --git a/ld/testsuite/ld-elf/pr25490-1.s b/ld/testsuite/ld-elf/pr25490-1.s
new file mode 100644
index 00000000000..51ba1ea8014
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr25490-1.s
@@ -0,0 +1,9 @@
+	.text
+	.globl	_start
+	.type	_start, %function
+_start:
+	.section	__patchable_function_entries,"aw",%progbits
+	.dc.a	.LPFE1
+	.text
+.LPFE1:
+	.byte 0
-- 
2.24.1