[PATCH 2/2] x86: Discard .note.gnu.property sections in vmlinux

H.J. Lu
2020-01-24T18:18:26Z

With the command-line option, -mx86-used-note=yes, the x86 assembler
in binutils 2.32 and above generates a program property note in a note
section, .note.gnu.property, to encode used x86 ISAs and features.
But x86 kernel linker script only contains a signle NOTE segment:

PHDRS {
text PT_LOAD FLAGS(5);
data PT_LOAD FLAGS(6);
percpu PT_LOAD FLAGS(6);
init PT_LOAD FLAGS(7);
note PT_NOTE FLAGS(0);
}
SECTIONS
{
...
.notes : AT(ADDR(.notes) - 0xffffffff80000000) { __start_notes = .; KEEP(*(.not
e.*)) __stop_notes = .; } :text :note
...
}

which may not be incompatible with note.gnu.property sections. Since
note.gnu.property section in kernel image is unused, this patch discards
.note.gnu.property sections in kernel linker script by adding

/DISCARD/ : {
*(.note.gnu.property)
}

before .notes sections. Since .exit.text and .exit.data sections are
discarded at runtime, it undefines EXIT_TEXT and EXIT_DATA to exclude
.exit.text and .exit.data sections from default discarded sections.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
---
arch/x86/kernel/vmlinux.lds.S | 11 +++++++++++
1 file changed, 11 insertions(+)

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 3a1a819da137..6c6cc26b0177 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -150,6 +150,11 @@ SECTIONS
_etext = .;
. = ALIGN(PAGE_SIZE);

+ /* .note.gnu.property sections should be discarded */
+ /DISCARD/ : {
+ *(.note.gnu.property)
+ }
+
X86_ALIGN_RODATA_BEGIN
RO_DATA(PAGE_SIZE)
X86_ALIGN_RODATA_END
@@ -413,6 +418,12 @@ SECTIONS
STABS_DEBUG
DWARF_DEBUG

+ /* Sections to be discarded. EXIT_TEXT and EXIT_DATA discard at runtime.
+ * not link time. */
+#undef EXIT_TEXT
+#define EXIT_TEXT
+#undef EXIT_DATA
+#define EXIT_DATA
DISCARDS
/DISCARD/ : {
*(.eh_frame)
--
2.24.1