Re: [PATCH v2 1/2] riscv: consolidate __ex_table construction

[Kefeng Wang]

On 2021/10/21 23:43, Jisheng Zhang wrote:
> On Thu, 21 Oct 2021 19:38:41 +0800
> Kefeng Wang <wangkefeng.wang@xxxxxxxxxx> wrote:
>
> > On 2021/10/20 22:06, Jisheng Zhang wrote:
> > > From: Jisheng Zhang <jszhang@xxxxxxxxxx>
> > >
> > > Consolidate all the __ex_table constuction code with a _ASM_EXTABLE
> > > helper.
> > >
> > > There should be no functional change as a result of this patch.
> > >
> > > Signed-off-by: Jisheng Zhang <jszhang@xxxxxxxxxx>
> > > ---
> > >    arch/riscv/include/asm/futex.h   | 12 +++-------
> > >    arch/riscv/include/asm/uaccess.h | 40 +++++++++++---------------------
> > >    2 files changed, 17 insertions(+), 35 deletions(-)
> > >
> > > diff --git a/arch/riscv/include/asm/futex.h b/arch/riscv/include/asm/futex.h
> > > index 1b00badb9f87..3191574e135c 100644
> > > --- a/arch/riscv/include/asm/futex.h
> > > +++ b/arch/riscv/include/asm/futex.h
> > > @@ -30,10 +30,7 @@
> > >    	"3:	li %[r],%[e]				\n"	\
> > >    	"	jump 2b,%[t]				\n"	\
> > >    	"	.previous				\n"	\
> > > -	"	.section __ex_table,\"a\"		\n"	\
> > > -	"	.balign " RISCV_SZPTR "			\n"	\
> > > -	"	" RISCV_PTR " 1b, 3b			\n"	\
> > > -	"	.previous				\n"	\
> > > +		_ASM_EXTABLE(1b, 3b)				\
> > >    	: [r] "+r" (ret), [ov] "=&r" (oldval),			\
> > >    	  [u] "+m" (*uaddr), [t] "=&r" (tmp)			\
> > >    	: [op] "Jr" (oparg), [e] "i" (-EFAULT)			\
> > > @@ -103,11 +100,8 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
> > >    	"4:	li %[r],%[e]				\n"
> > >    	"	jump 3b,%[t]				\n"
> > >    	"	.previous				\n"
> > > -	"	.section __ex_table,\"a\"		\n"
> > > -	"	.balign " RISCV_SZPTR "			\n"
> > > -	"	" RISCV_PTR " 1b, 4b			\n"
> > > -	"	" RISCV_PTR " 2b, 4b			\n"
> > > -	"	.previous				\n"
> > > +		_ASM_EXTABLE(1b, 4b)			\
> > > +		_ASM_EXTABLE(2b, 4b)			\
> > >    	: [r] "+r" (ret), [v] "=&r" (val), [u] "+m" (*uaddr), [t] "=&r" (tmp)
> > >    	: [ov] "Jr" (oldval), [nv] "Jr" (newval), [e] "i" (-EFAULT)
> > >    	: "memory");
> > > diff --git a/arch/riscv/include/asm/uaccess.h b/arch/riscv/include/asm/uaccess.h
> > > index f314ff44c48d..35802e72ace8 100644
> > > --- a/arch/riscv/include/asm/uaccess.h
> > > +++ b/arch/riscv/include/asm/uaccess.h
> > > @@ -10,6 +10,12 @@
> > >    
> > >    #include <asm/pgtable.h>		/* for TASK_SIZE */
> > >    
> > > +#define _ASM_EXTABLE(from, to)						\
> > > +	"	.pushsection	__ex_table, \"a\"\n"			\
> > > +	"	.balign "	RISCV_SZPTR "	 \n"			\
> > > +	"	" RISCV_PTR	"(" #from "), (" #to ")\n"		\
> > > +	"	.popsection\n"
> > > +
> >
> > The jump_label mechanism could use this macro too,
> > see arch/riscv/include/asm/jump_label.h, maybe move the above into asm.h
> > and also do some replace in next patch ?
>
> jump_label entry is a bit different with ex_table: two relative offsets and
> a key which should be "long" type.
>
> > Question: the jump label use relative address, but why not trigger the
> > Section mismatch issue?
>
> FWICT, modpost doesn't check __jump_table section

OK, missing that.
> .