Messages in this thread | | | Date | Wed, 10 Apr 2024 08:35:26 -0700 | From | Nathan Chancellor <> | Subject | Re: [PATCH v2] ARM: Add a memory clobber to the fmrx instruction |
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On Wed, Apr 10, 2024 at 02:31:11PM +0200, Ard Biesheuvel wrote: > On Wed, 10 Apr 2024 at 04:41, zhuqiuer <zhuqiuer1@huawei.com> wrote: > > > > The instruction fmrx is used throughout the kernel, > > where it is sometimes expected to be skipped > > by incrementing the program counter, such as in vfpmodule.c:vfp_init(). > > Therefore, the instruction should not be reordered when it is not intended. > > Adding a barrier() instruction before and after this call cannot prevent > > reordering by the compiler, as the fmrx instruction is constrained > > by '=r', meaning it works on the general register but not on memory. > > To ensure the order of the instruction after compiling, > > adding a memory clobber is necessary. > > > > Below is the code snippet disassembled from the method: > > vfpmodule.c:vfp_init(), compiled by LLVM. > > > > Before the patching: > > xxxxx: xxxxx bl c010c688 <register_undef_hook> > > xxxxx: xxxxx mov r0, r4 > > xxxxx: xxxxx bl c010c6e4 <unregister_undef_hook> > > ... > > xxxxx: xxxxx bl c0791c8c <printk> > > xxxxx: xxxxx movw r5, #23132 ; 0x5a5c > > xxxxx: xxxxx vmrs r4, fpsid <- this is the fmrx instruction > > > > After the patching: > > xxxxx: xxxxx bl c010c688 <register_undef_hook> > > xxxxx: xxxxx mov r0, r4 > > xxxxx: xxxxx vmrs r5, fpsid <- this is the fmrx instruction > > xxxxx: xxxxx bl c010c6e4 <unregister_undef_hook> > > > > Signed-off-by: zhuqiuer <zhuqiuer1@huawei.com> > > This also fixes the issue I observed so > > Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
This can probably go in Russell's patch tracker? Your patch had
Cc: stable@vger.kernel.org
in it, should this one as well?
> > --- > > arch/arm/vfp/vfpinstr.h | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/arch/arm/vfp/vfpinstr.h b/arch/arm/vfp/vfpinstr.h > > index 3c7938fd40aa..ae2c9b9b7701 100644 > > --- a/arch/arm/vfp/vfpinstr.h > > +++ b/arch/arm/vfp/vfpinstr.h > > @@ -68,14 +68,14 @@ > > u32 __v; \ > > asm(".fpu vfpv2\n" \ > > "vmrs %0, " #_vfp_ \ > > - : "=r" (__v) : : "cc"); \ > > + : "=r" (__v) : : "memory", "cc"); \ > > __v; \ > > }) > > > > #define fmxr(_vfp_,_var_) \ > > asm(".fpu vfpv2\n" \ > > "vmsr " #_vfp_ ", %0" \ > > - : : "r" (_var_) : "cc") > > + : : "r" (_var_) : "memory", "cc") > > > > #else > > > > -- > > 2.12.3 > >
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