Re: [PATCH v7 8/8] [DO NOT MERGE] x86/kexec: Add CFI type information to relocate_kernel()

[David Woodhouse]

On Fri, 2025-03-14 at 10:52 -0700, Josh Poimboeuf wrote:
> 
> IIRC, the reasons were the patched alternative, and also you wanted to
> disassemble (but note that's still possible with gdb).

It's meaningful output from 'objdump -S' that I miss. But OK.

> Here was a patch to make it work:
> 
>   https://lore.kernel.org/20241218212326.44qff3i5n6cxuu5d@jpoimboe

I've reworked that and the CR4 filtering, and now it doesn't like me
using SYM_TYPED_FUNC_START() to add the CFI information for the
relocate_kernel() function.

  LD      vmlinux.o
vmlinux.o: warning: objtool: bad call to elf_init_reloc_text_sym() for
data symbol .data..relocate_kernel
 ...

  SORTTAB vmlinux
incomplete ORC unwind tables in file: vmlinux
Failed to sort kernel tables

This happens when I build with (clang and) CONFIG_CFI_CLANG, with and
updated version of your patch above, and this on top of it. This is at
https://git.infradead.org/users/dwmw2/linux.git/shortlog/refs/heads/kexec-debug

From 0f08a44613764e9b38a1c3332812685b61c99c2e Mon Sep 17 00:00:00 2001
From: David Woodhouse <dwmw@xxxxxxxxxxxx>
Date: Mon, 16 Dec 2024 10:26:24 +0000
Subject: [PATCH] x86/kexec: Add CFI type information to relocate_kernel()

A previous commit added __nocfi to machine_kexec() because it makes an
indirect call to relocate_kernel() which lacked CFI type information,
and caused the system to crash.

Use SYM_TYPED_FUNC_START() to ensure that the type information is
present, and remove the __nocfi tag.

Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
---
 arch/x86/kernel/machine_kexec_64.c   | 2 +-
 arch/x86/kernel/relocate_kernel_64.S | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
index 016862d2b544..e1f5fc858aee 100644
--- a/arch/x86/kernel/machine_kexec_64.c
+++ b/arch/x86/kernel/machine_kexec_64.c
@@ -396,7 +396,7 @@ void machine_kexec_cleanup(struct kimage *image)
  * Do not allocate memory (or fail in any way) in machine_kexec().
  * We are past the point of no return, committed to rebooting now.
  */
-void __nocfi machine_kexec(struct kimage *image)
+void machine_kexec(struct kimage *image)
 {
 	unsigned long reloc_start = (unsigned long)__relocate_kernel_start;
 	relocate_kernel_fn *relocate_kernel_ptr;
diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index 814af7fa6318..c859fbe507e8 100644
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -5,6 +5,7 @@
  */
 
 #include <linux/linkage.h>
+#include <linux/cfi_types.h>
 #include <linux/stringify.h>
 #include <asm/alternative.h>
 #include <asm/page_types.h>
@@ -68,7 +69,7 @@ SYM_DATA_END(kexec_debug_idt)
  * opinions about it.
  */
 	.code64
-SYM_CODE_START_NOALIGN(relocate_kernel)
+SYM_TYPED_FUNC_START(relocate_kernel)
 	/*
 	 * %rdi indirection_page
 	 * %rsi pa_control_page
-- 
2.48.1

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