On 11/17/2023 1:36 AM, Ard Biesheuvel wrote:
On Fri, 17 Nov 2023 at 03:24, Nathan Chancellor <nathan@xxxxxxxxxx> wrote:
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))").
Thx for trying this. I was tested with arm-linux-gnueabihf-gcc and not
notice this.
Ah yes, apalogies for missing that. I did a test build with Clang but
I did not spot the errors. So
Unreviewed-by: ....
Maria, please use the Makefile based per-file CFLAGS override that I
suggested before. There is really no reason to make this per-function.
Ok. I will upload a new patchset.
--
Thx and BRs,
Aiqun(Maria) Yu
