On Wed, Nov 15, 2023 at 05:58:30PM +0800, Maria Yu wrote:
> Registers r7 is removed in clobber list, so compiler may choose r7 for
> local variables usage, while r7 will be actually updated by the inline asm
> code. This caused the runtime behavior wrong.
> While those kind of reserved registers cannot be set to clobber list
> because of error like "inline asm clobber list contains reserved
> registers".
> Explicitly reserve r7 by adding attribute no-omit-frame-pointer for needed
> function, then in T32 asm code r7 is used as a frame pointer and is not
> available for use as a general-purpose register.
> Note that "no-omit-frame-pointer" will make the code size a little bigger
> to store the stack frame pointer. So limited to needed functions can have
> the less impact than the full source file.
>
> Fixes: dd12e97f3c72 ("ARM: kprobes: treat R7 as the frame pointer register in Thumb2 builds")
> Signed-off-by: Maria Yu <quic_aiquny@xxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
This causes warnings with clang:
arch/arm/probes/kprobes/actions-thumb.c:441:47: warning: unknown attribute 'optimize' ignored [-Wunknown-attributes]
441 | static unsigned long __kprobes __attribute__((optimize("no-omit-frame-pointer")))
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
arch/arm/probes/kprobes/actions-thumb.c:524:38: warning: unknown attribute 'optimize' ignored [-Wunknown-attributes]
524 | static void __kprobes __attribute__((optimize("no-omit-frame-pointer")))
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
arch/arm/probes/kprobes/actions-thumb.c:560:38: warning: unknown attribute 'optimize' ignored [-Wunknown-attributes]
560 | static void __kprobes __attribute__((optimize("no-omit-frame-pointer")))
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
arch/arm/probes/kprobes/actions-thumb.c:579:38: warning: unknown attribute 'optimize' ignored [-Wunknown-attributes]
579 | static void __kprobes __attribute__((optimize("no-omit-frame-pointer")))
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
4 warnings generated.
Furthermore, as far as I am aware, the optimize attribute has other issues so
its use is discouraged, see commits 080b6f407635 ("bpf: Don't rely on GCC
__attribute__((optimize)) to disable GCSE") and a7223f5bfcae ("powerpc: Avoid
broken GCC __attribute__((optimize))").
Cheers,
Nathan
> ---
> arch/arm/probes/kprobes/actions-thumb.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm/probes/kprobes/actions-thumb.c b/arch/arm/probes/kprobes/actions-thumb.c
> index 51624fc263fc..c2fdaf9f6dba 100644
> --- a/arch/arm/probes/kprobes/actions-thumb.c
> +++ b/arch/arm/probes/kprobes/actions-thumb.c
> @@ -438,7 +438,7 @@ t16_simulate_branch(probes_opcode_t insn,
> regs->ARM_pc = pc + (offset * 2);
> }
>
> -static unsigned long __kprobes
> +static unsigned long __kprobes __attribute__((optimize("no-omit-frame-pointer")))
> t16_emulate_loregs(probes_opcode_t insn,
> struct arch_probes_insn *asi, struct pt_regs *regs)
> {
> @@ -521,7 +521,7 @@ t16_decode_hiregs(probes_opcode_t insn, struct arch_probes_insn *asi,
> return INSN_GOOD;
> }
>
> -static void __kprobes
> +static void __kprobes __attribute__((optimize("no-omit-frame-pointer")))
> t16_emulate_push(probes_opcode_t insn,
> struct arch_probes_insn *asi, struct pt_regs *regs)
> {
> @@ -557,7 +557,7 @@ t16_decode_push(probes_opcode_t insn, struct arch_probes_insn *asi,
> return INSN_GOOD;
> }
>
> -static void __kprobes
> +static void __kprobes __attribute__((optimize("no-omit-frame-pointer")))
> t16_emulate_pop_nopc(probes_opcode_t insn,
> struct arch_probes_insn *asi, struct pt_regs *regs)
> {
> @@ -576,7 +576,7 @@ t16_emulate_pop_nopc(probes_opcode_t insn,
> );
> }
>
> -static void __kprobes
> +static void __kprobes __attribute__((optimize("no-omit-frame-pointer")))
> t16_emulate_pop_pc(probes_opcode_t insn,
> struct arch_probes_insn *asi, struct pt_regs *regs)
> {
>
> base-commit: 9bacdd8996c77c42ca004440be610692275ff9d0
> --
> 2.17.1
>
>
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> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
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