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From: Michael Ellerman <mpe@ellerman.id.au>
To: Segher Boessenkool <segher@kernel.crashing.org>
Cc: Feng Tang <feng.tang@intel.com>,
	Christophe Leroy <christophe.leroy@csgroup.eu>,
	lkp <lkp@intel.com>,
	"kbuild-all@lists.01.org" <kbuild-all@lists.01.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: {standard input}:577: Error: unsupported relocation against base
Date: Wed, 17 Feb 2021 16:43:45 +1100	[thread overview]
Message-ID: <87a6s3uu3y.fsf@mpe.ellerman.id.au> (raw)
In-Reply-To: <20210216220619.GL28121@gate.crashing.org>

Segher Boessenkool <segher@kernel.crashing.org> writes:
> Hi!
>
> On Tue, Feb 16, 2021 at 08:36:02PM +1100, Michael Ellerman wrote:
>> Feng Tang <feng.tang@intel.com> writes:
>> >   {standard input}:577: Error: unsupported relocation against base
>> >   {standard input}:580: Error: unsupported relocation against base
>> >   {standard input}:583: Error: unsupported relocation against base
>
>> > The reason is macro 'mfdcr' requirs an instant number as parameter,
>> > which is not met by show_plbopb_regs().
>> 
>> It doesn't require a constant, it checks if the argument is constant:
>> 
>> #define mfdcr(rn)						\
>> 	({unsigned int rval;					\
>> 	if (__builtin_constant_p(rn) && rn < 1024)		\
>> 		asm volatile("mfdcr %0," __stringify(rn)	\
>> 		              : "=r" (rval));			\
>> 	else if (likely(cpu_has_feature(CPU_FTR_INDEXED_DCR)))	\
>> 		rval = mfdcrx(rn);				\
>> 	else							\
>> 		rval = __mfdcr(rn);				\
>> 	rval;})
>
> It requires a constant number with known (at compile time) value, while
> __builtin_constant_p checks for any constant.  The address of some
> defined symbol is a constant as well normally, for example.
>
> It's better to write that asm as
> 	asm volatile("mfdcr %0,%1" : "=r" (rval) : "n"(rn));
> btw (the "n" constraint means "constant integer with known value" (it
> stands for "numeric"), while the "i" constraint means just "constant
> integer").

Actually that fixes it.

diff --git a/arch/powerpc/include/asm/dcr-native.h b/arch/powerpc/include/asm/dcr-native.h
index 7141ccea8c94..d143308b0f95 100644
--- a/arch/powerpc/include/asm/dcr-native.h
+++ b/arch/powerpc/include/asm/dcr-native.h
@@ -53,8 +53,8 @@ static inline void mtdcrx(unsigned int reg, unsigned int val)
 #define mfdcr(rn)                                              \
        ({unsigned int rval;                                    \
        if (__builtin_constant_p(rn) && rn < 1024)              \
-               asm volatile("mfdcr %0," __stringify(rn)        \
-                             : "=r" (rval));                   \
+               asm volatile("mfdcr %0, %1" : "=r" (rval)       \
+                            : "n" (rn));                       \
        else if (likely(cpu_has_feature(CPU_FTR_INDEXED_DCR)))  \
                rval = mfdcrx(rn);                              \
        else                                                    \


I guess because we give the compiler time to work out the constant,
rather than stringifying it immediately.

cheers

WARNING: multiple messages have this Message-ID (diff)
From: Michael Ellerman <mpe@ellerman.id.au>
To: kbuild-all@lists.01.org
Subject: Re: {standard input}:577: Error: unsupported relocation against base
Date: Wed, 17 Feb 2021 16:43:45 +1100	[thread overview]
Message-ID: <87a6s3uu3y.fsf@mpe.ellerman.id.au> (raw)
In-Reply-To: <20210216220619.GL28121@gate.crashing.org>

[-- Attachment #1: Type: text/plain, Size: 2553 bytes --]

Segher Boessenkool <segher@kernel.crashing.org> writes:
> Hi!
>
> On Tue, Feb 16, 2021 at 08:36:02PM +1100, Michael Ellerman wrote:
>> Feng Tang <feng.tang@intel.com> writes:
>> >   {standard input}:577: Error: unsupported relocation against base
>> >   {standard input}:580: Error: unsupported relocation against base
>> >   {standard input}:583: Error: unsupported relocation against base
>
>> > The reason is macro 'mfdcr' requirs an instant number as parameter,
>> > which is not met by show_plbopb_regs().
>> 
>> It doesn't require a constant, it checks if the argument is constant:
>> 
>> #define mfdcr(rn)						\
>> 	({unsigned int rval;					\
>> 	if (__builtin_constant_p(rn) && rn < 1024)		\
>> 		asm volatile("mfdcr %0," __stringify(rn)	\
>> 		              : "=r" (rval));			\
>> 	else if (likely(cpu_has_feature(CPU_FTR_INDEXED_DCR)))	\
>> 		rval = mfdcrx(rn);				\
>> 	else							\
>> 		rval = __mfdcr(rn);				\
>> 	rval;})
>
> It requires a constant number with known (at compile time) value, while
> __builtin_constant_p checks for any constant.  The address of some
> defined symbol is a constant as well normally, for example.
>
> It's better to write that asm as
> 	asm volatile("mfdcr %0,%1" : "=r" (rval) : "n"(rn));
> btw (the "n" constraint means "constant integer with known value" (it
> stands for "numeric"), while the "i" constraint means just "constant
> integer").

Actually that fixes it.

diff --git a/arch/powerpc/include/asm/dcr-native.h b/arch/powerpc/include/asm/dcr-native.h
index 7141ccea8c94..d143308b0f95 100644
--- a/arch/powerpc/include/asm/dcr-native.h
+++ b/arch/powerpc/include/asm/dcr-native.h
@@ -53,8 +53,8 @@ static inline void mtdcrx(unsigned int reg, unsigned int val)
 #define mfdcr(rn)                                              \
        ({unsigned int rval;                                    \
        if (__builtin_constant_p(rn) && rn < 1024)              \
-               asm volatile("mfdcr %0," __stringify(rn)        \
-                             : "=r" (rval));                   \
+               asm volatile("mfdcr %0, %1" : "=r" (rval)       \
+                            : "n" (rn));                       \
        else if (likely(cpu_has_feature(CPU_FTR_INDEXED_DCR)))  \
                rval = mfdcrx(rn);                              \
        else                                                    \


I guess because we give the compiler time to work out the constant,
rather than stringifying it immediately.

cheers

  reply	other threads:[~2021-02-17  5:44 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-05 10:58 {standard input}:577: Error: unsupported relocation against base kernel test robot
2021-01-05 10:58 ` kernel test robot
2021-01-18 14:24 ` Christophe Leroy
2021-02-05 10:08   ` Feng Tang
2021-02-05 10:08     ` Feng Tang
2021-02-16  9:36     ` Michael Ellerman
2021-02-16  9:36       ` Michael Ellerman
2021-02-16 22:06       ` Segher Boessenkool
2021-02-17  5:43         ` Michael Ellerman [this message]
2021-02-17  5:43           ` Michael Ellerman
2021-02-17 15:37           ` Segher Boessenkool
2021-02-17 10:49       ` Feng Tang
2021-02-17 10:49         ` Feng Tang
2021-02-18 11:08         ` Michael Ellerman
2021-02-18 11:08           ` Michael Ellerman

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