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From: Nathan Chancellor <nathan@kernel.org>
Date: Wed, 07 Feb 2024 17:14:55 -0700
Subject: [PATCH 03/11] s390: vmlinux.lds.S: Explicitly handle '.got' and
 '.plt' sections
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Message-Id: <20240207-s390-lld-and-orphan-warn-v1-3-8a665b3346ab@kernel.org>
References: <20240207-s390-lld-and-orphan-warn-v1-0-8a665b3346ab@kernel.org>
In-Reply-To: <20240207-s390-lld-and-orphan-warn-v1-0-8a665b3346ab@kernel.org>
To: hca@linux.ibm.com, gor@linux.ibm.com, agordeev@linux.ibm.com
Cc: borntraeger@linux.ibm.com, svens@linux.ibm.com, maskray@google.com, 
 ndesaulniers@google.com, linux-s390@vger.kernel.org, 
 linux-kernel@vger.kernel.org, llvm@lists.linux.dev, patches@lists.linux.dev, 
 Nathan Chancellor <nathan@kernel.org>

When building with CONFIG_LD_ORPHAN_WARN after selecting
CONFIG_ARCH_HAS_LD_ORPHAN_WARN, there are a lot of warnings around the
GOT and PLT sections:

  s390-linux-ld: warning: orphan section `.plt' from `arch/s390/kernel/head64.o' being placed in section `.plt'
  s390-linux-ld: warning: orphan section `.got' from `arch/s390/kernel/head64.o' being placed in section `.got'
  s390-linux-ld: warning: orphan section `.got.plt' from `arch/s390/kernel/head64.o' being placed in section `.got.plt'
  s390-linux-ld: warning: orphan section `.iplt' from `arch/s390/kernel/head64.o' being placed in section `.iplt'
  s390-linux-ld: warning: orphan section `.igot.plt' from `arch/s390/kernel/head64.o' being placed in section `.igot.plt'

  s390-linux-ld: warning: orphan section `.iplt' from `arch/s390/boot/head.o' being placed in section `.iplt'
  s390-linux-ld: warning: orphan section `.igot.plt' from `arch/s390/boot/head.o' being placed in section `.igot.plt'
  s390-linux-ld: warning: orphan section `.got' from `arch/s390/boot/head.o' being placed in section `.got'

Currently, only the '.got' section is actually emitted in the final
binary. In a manner similar to other architectures, put the '.got'
section near the '.data' section and coalesce the PLT sections,
checking that the final section is zero sized, which is a safe/tested
approach versus full discard.

Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
 arch/s390/boot/vmlinux.lds.S   | 19 +++++++++++++++++++
 arch/s390/kernel/vmlinux.lds.S | 19 +++++++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/arch/s390/boot/vmlinux.lds.S b/arch/s390/boot/vmlinux.lds.S
index 389df0e0d9e5..4aa2f340c8d9 100644
--- a/arch/s390/boot/vmlinux.lds.S
+++ b/arch/s390/boot/vmlinux.lds.S
@@ -39,6 +39,9 @@ SECTIONS
 		*(.rodata.*)
 		_erodata = . ;
 	}
+	.got : {
+		*(.got)
+	}
 	NOTES
 	.data :	{
 		_data = . ;
@@ -118,6 +121,22 @@ SECTIONS
 	}
 	_end = .;
 
+	/*
+	 * Sections that should stay zero sized, which is safer to
+	 * explicitly check instead of blindly discarding.
+	 */
+	.got.plt : {
+		*(.got.plt)
+	}
+	ASSERT(SIZEOF(.got.plt) == 0, "Unexpected GOT/PLT entries detected!")
+	.plt : {
+		*(.plt)
+		*(.plt.*)
+		*(.iplt)
+		*(.igot .igot.plt)
+	}
+	ASSERT(SIZEOF(.plt) == 0, "Unexpected run-time procedure linkages detected!")
+
 	/* Sections to be discarded */
 	/DISCARD/ : {
 		*(.eh_frame)
diff --git a/arch/s390/kernel/vmlinux.lds.S b/arch/s390/kernel/vmlinux.lds.S
index d231a3faf981..661a487a3048 100644
--- a/arch/s390/kernel/vmlinux.lds.S
+++ b/arch/s390/kernel/vmlinux.lds.S
@@ -62,6 +62,9 @@ SECTIONS
 	.data.rel.ro : {
 		*(.data.rel.ro .data.rel.ro.*)
 	}
+	.got : {
+		*(.got)
+	}
 
 	. = ALIGN(PAGE_SIZE);
 	_sdata = .;		/* Start of data section */
@@ -241,6 +244,22 @@ SECTIONS
 	DWARF_DEBUG
 	ELF_DETAILS
 
+	/*
+	 * Sections that should stay zero sized, which is safer to
+	 * explicitly check instead of blindly discarding.
+	 */
+	.got.plt : {
+		*(.got.plt)
+	}
+	ASSERT(SIZEOF(.got.plt) == 0, "Unexpected GOT/PLT entries detected!")
+	.plt : {
+		*(.plt)
+		*(.plt.*)
+		*(.iplt)
+		*(.igot .igot.plt)
+	}
+	ASSERT(SIZEOF(.plt) == 0, "Unexpected run-time procedure linkages detected!")
+
 	/* Sections to be discarded */
 	DISCARDS
 	/DISCARD/ : {

-- 
2.43.0