Re: [PATCH v4 02/63] vmlinux.lds: Unify TEXT_MAIN, DATA_MAIN, and related macros

[Will Deacon <will@kernel.org>]

On Sat, Dec 20, 2025 at 04:25:50PM +0000, Carlos Llamas wrote:
> On Wed, Sep 17, 2025 at 09:03:10AM -0700, Josh Poimboeuf wrote:
> > TEXT_MAIN, DATA_MAIN and friends are defined differently depending on
> > whether certain config options enable -ffunction-sections and/or
> > -fdata-sections.
> > 
> > There's no technical reason for that beyond voodoo coding.  Keeping the
> > separate implementations adds unnecessary complexity, fragments the
> > logic, and increases the risk of subtle bugs.
> > 
> > Unify the macros by using the same input section patterns across all
> > configs.
> > 
> > This is a prerequisite for the upcoming livepatch klp-build tooling
> > which will manually enable -ffunction-sections and -fdata-sections via
> > KCFLAGS.
> > 
> > Cc: Heiko Carstens <hca@linux.ibm.com>
> > Cc: Vasily Gorbik <gor@linux.ibm.com>
> > Cc: Alexander Gordeev <agordeev@linux.ibm.com>
> > Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
> > ---
> >  include/asm-generic/vmlinux.lds.h | 40 ++++++++++---------------------
> >  scripts/module.lds.S              | 12 ++++------
> >  2 files changed, 17 insertions(+), 35 deletions(-)

[...]

> I'm seeing some KP when trying to load modules after this change. I
> believe there is some sort of incompatibility with the SCS (Shadow Call
> Stack) code in arm64? The panic is always on __pi_scs_handle_fde_frame:
> 
>   init: Loading module [...]/drivers/net/wireless/virtual/mac80211_hwsim.ko
>   Unable to handle kernel paging request at virtual address ffffffe6468f0ffc
>   [...]

nit: please don't trim the useful stuff when reporting a crash!

>   pc : __pi_scs_handle_fde_frame+0xd8/0x15c
>   lr : __pi_$x+0x74/0x138
>   sp : ffffffc08005bb10
>   x29: ffffffc08005bb10 x28: ffffffc081873010 x27: 0000000000000000
>   x26: 0000000000000007 x25: 0000000000000000 x24: 0000000000000000
>   x23: 0000000000000001 x22: ffffffe649794fa0 x21: ffffffe6469190b4
>   x20: 000000000000182c x19: 0000000000000001 x18: ffffffc080053000
>   x17: 000000000000002d x16: ffffffe6469190c5 x15: ffffffe6468f1000
>   x14: 000000000000003e x13: ffffffe6469190c6 x12: 00000000d50323bf
>   x11: 00000000d503233f x10: ffffffe649119cb8 x9 : ffffffe6468f1000
>   x8 : 0000000000000100 x7 : 00656d6172665f68 x6 : 0000000000000001
>   x5 : 6372610000000000 x4 : 0000008000000000 x3 : 0000000000000000
>   x2 : ffffffe647e528f4 x1 : 0000000000000001 x0 : 0000000000000004
>   Call trace:
>    __pi_scs_handle_fde_frame+0xd8/0x15c (P)
>    module_finalize+0xfc/0x164
>    post_relocation+0xbc/0xd8
>    load_module+0xfd4/0x11a8
>    __arm64_sys_finit_module+0x23c/0x328
>    invoke_syscall+0x58/0xe4
>    el0_svc_common+0x80/0xdc
>    do_el0_svc+0x1c/0x28
>    el0_svc+0x54/0x1c4
>    el0t_64_sync_handler+0x68/0xdc
>    el0t_64_sync+0x1c4/0x1c8
>   Code: 54fffd4c 1400001f 3707ff63 aa0903ef (b85fcdf0)

Hmm, looks like a translation fault from the load buried here:

	u32 insn = le32_to_cpup((void *)loc);

in scs_patch_loc(), called from the 'DW_CFA_negate_ra_state' case in
scs_handle_fde_frame(). So presumably 'loc' is bogus.

Since you replied to this patch, does reverting it fix the problem for
you?

> This is not a problem if I disable UNWIND_PATCH_PAC_INTO_SCS but I have
> no idea why.

Well, that avoids compiling the code that's crashing :p

> Looking around it seems like this might related:
> 
>   $ cat arch/arm64/include/asm/module.lds.h
>   SECTIONS {
>   [...]
>   #ifdef CONFIG_UNWIND_TABLES
>         /*
>          * Currently, we only use unwind info at module load time, so we can
>          * put it into the .init allocation.
>          */
>         .init.eh_frame : { *(.eh_frame) }
>   #endif

This patch doesn't seem to change that though?

Ard, do you have any ideas here? I wonder whether the addition of
support for 64-bit offsets in 60de7a647fc5 ("arm64/scs: Deal with 64-bit
relative offsets in FDE frames") has introduced padding/alignment
requirements into 'struct eh_frame' and we end up off-by-4 for 'loc' or
something like that? The faulting address looks like an underflow.

Will