Re: [PATCH v3 3/8] arm64: entry: add unwind info for various kernel entries

[Jens Remus <jremus@linux.ibm.com>]

On 4/6/2026 8:49 PM, Dylan Hatch wrote:
> From: Weinan Liu <wnliu@google.com>
> 
> DWARF CFI (Call Frame Information) specifies how to recover the return
> address and callee-saved registers at each PC in a given function.
> Compilers are able to generate the CFI annotations when they compile
> the code to assembly language. For handcrafted assembly, we need to
> annotate them by hand.
> 
> Annotate CFI unwind info for assembly for interrupt and exception
> handlers.
> 
> Signed-off-by: Weinan Liu <wnliu@google.com>
> Signed-off-by: Dylan Hatch <dylanbhatch@google.com>
> ---
>  arch/arm64/kernel/entry.S | 10 ++++++++++
>  1 file changed, 10 insertions(+)

The added CFI directives somehow cause .eh_frame (instead of
.debug_frame) to be generated in addition to .sframe.  This causes the
following warning when linking vmlinux (.tmp_vmlinux1, .tmp_vmlinux2,
and vmlinux.unstripped):

  LD      vmlinux.unstripped
aarch64-linux-gnu-ld: warning: orphan section `.eh_frame' from `arch/arm64/kernel/entry.o' being placed in section `.eh_frame'

I don't think this can be controlled using compiler options
-fno-asynchronous-unwind-tables -fno-unwind-tables, as entry.S is
only preprocessed and then fed into the assembler.

The following at the top of entry.S would resolve the issue:

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
@@ -30,6 +30,12 @@
 #include <asm/asm-uaccess.h>
 #include <asm/unistd.h>

+/*
+ * Do not generate .eh_frame.  Only generate .debug_frame and optionally
+ * .sframe (via assembler option --gsframe[-N]).
+ */
+	.cfi_sections .debug_frame
+
	.macro	clear_gp_regs
	.irp	n,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29
	mov	x\n, xzr

Regards,
Jens
-- 
Jens Remus
Linux on Z Development (D3303)
jremus@de.ibm.com / jremus@linux.ibm.com

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