linux-kernel - Re: [PATCH 2/3] powerpc: fix build errors

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Date:   Thu, 24 Feb 2022 23:39:16 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Anders Roxell <anders.roxell@...aro.org>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Anders Roxell <anders.roxell@...aro.org>,
        stable@...r.kernel.org, Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH 2/3] powerpc: fix build errors

Hi Anders,

Thanks for these, just a few comments below ...

Anders Roxell <anders.roxell@...aro.org> writes:
> Building tinyconfig with gcc (Debian 11.2.0-16) and assembler (Debian
> 2.37.90.20220207) the following build error shows up:
>
>  {standard input}: Assembler messages:
>  {standard input}:1190: Error: unrecognized opcode: `stbcix'
>  {standard input}:1433: Error: unrecognized opcode: `lwzcix'
>  {standard input}:1453: Error: unrecognized opcode: `stbcix'
>  {standard input}:1460: Error: unrecognized opcode: `stwcix'
>  {standard input}:1596: Error: unrecognized opcode: `stbcix'
>  ...
>
> Rework to add assembler directives [1] around the instruction. Going
> through the them one by one shows that the changes should be safe.  Like
> __get_user_atomic_128_aligned() is only called in p9_hmi_special_emu(),
> which according to the name is specific to power9.  And __raw_rm_read*()
> are only called in things that are powernv or book3s_hv specific.
>
> [1] https://sourceware.org/binutils/docs/as/PowerPC_002dPseudo.html#PowerPC_002dPseudo
>
> Cc: <stable@...r.kernel.org>
> Co-developed-by: Arnd Bergmann <arnd@...db.de>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> Signed-off-by: Anders Roxell <anders.roxell@...aro.org>
> ---
>  arch/powerpc/include/asm/io.h        | 46 +++++++++++++++++++++++-----
>  arch/powerpc/include/asm/uaccess.h   |  3 ++
>  arch/powerpc/platforms/powernv/rng.c |  6 +++-
>  3 files changed, 46 insertions(+), 9 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/io.h b/arch/powerpc/include/asm/io.h
> index beba4979bff9..5ff6dec489f8 100644
> --- a/arch/powerpc/include/asm/io.h
> +++ b/arch/powerpc/include/asm/io.h
> @@ -359,25 +359,37 @@ static inline void __raw_writeq_be(unsigned long v, volatile void __iomem *addr)
>   */
>  static inline void __raw_rm_writeb(u8 val, volatile void __iomem *paddr)
>  {
> -	__asm__ __volatile__("stbcix %0,0,%1"
> +	__asm__ __volatile__(".machine \"push\"\n"
> +			     ".machine \"power6\"\n"
> +			     "stbcix %0,0,%1\n"
> +			     ".machine \"pop\"\n"
>  		: : "r" (val), "r" (paddr) : "memory");

As Segher said it'd be cleaner without the embedded quotes.

> @@ -441,7 +465,10 @@ static inline unsigned int name(unsigned int port)	\
>  	unsigned int x;					\
>  	__asm__ __volatile__(				\
>  		"sync\n"				\
> +		".machine \"push\"\n"			\
> +		".machine \"power6\"\n"			\
>  		"0:"	op "	%0,0,%1\n"		\
> +		".machine \"pop\"\n"			\
>  		"1:	twi	0,%0,0\n"		\
>  		"2:	isync\n"			\
>  		"3:	nop\n"				\
> @@ -465,7 +492,10 @@ static inline void name(unsigned int val, unsigned int port) \
>  {							\
>  	__asm__ __volatile__(				\
>  		"sync\n"				\
> +		".machine \"push\"\n"			\
> +		".machine \"power6\"\n"			\
>  		"0:" op " %0,0,%1\n"			\
> +		".machine \"pop\"\n"			\
>  		"1:	sync\n"				\
>  		"2:\n"					\
>  		EX_TABLE(0b, 2b)			\

It's not visible from the diff, but the above two are __do_in_asm and
__do_out_asm and are inside an ifdef CONFIG_PPC32.

AFAICS they're only used for:

__do_in_asm(_rec_inb, "lbzx")
__do_in_asm(_rec_inw, "lhbrx")
__do_in_asm(_rec_inl, "lwbrx")
__do_out_asm(_rec_outb, "stbx")
__do_out_asm(_rec_outw, "sthbrx")
__do_out_asm(_rec_outl, "stwbrx")

Which are all old instructions, so I don't think we need the machine
power6 for those two macros?

> diff --git a/arch/powerpc/platforms/powernv/rng.c b/arch/powerpc/platforms/powernv/rng.c
> index b4386714494a..5bf30ef6d928 100644
> --- a/arch/powerpc/platforms/powernv/rng.c
> +++ b/arch/powerpc/platforms/powernv/rng.c
> @@ -43,7 +43,11 @@ static unsigned long rng_whiten(struct powernv_rng *rng, unsigned long val)
>  	unsigned long parity;
>  
>  	/* Calculate the parity of the value */
> -	asm ("popcntd %0,%1" : "=r" (parity) : "r" (val));
> +	asm (".machine \"push\"\n"
> +	     ".machine \"power7\"\n"
> +	     "popcntd %0,%1\n"
> +	     ".machine \"pop\"\n"
> +	     : "=r" (parity) : "r" (val));

This was actually present in an older CPU, but it doesn't really matter,
this is fine.

cheers