* [PATCH] powerpc/4xx: Fix build errors from mfdcr()
@ 2021-02-18 12:30 Michael Ellerman
2021-02-18 13:04 ` Feng Tang
2021-03-14 10:01 ` Michael Ellerman
0 siblings, 2 replies; 3+ messages in thread
From: Michael Ellerman @ 2021-02-18 12:30 UTC (permalink / raw)
To: linuxppc-dev; +Cc: feng.tang
lkp reported a build error in fsp2.o:
CC arch/powerpc/platforms/44x/fsp2.o
{standard input}:577: Error: unsupported relocation against base
Which comes from:
pr_err("GESR0: 0x%08x\n", mfdcr(base + PLB4OPB_GESR0));
Where our mfdcr() macro is stringifying "base + PLB4OPB_GESR0", and
passing that to the assembler, which obviously doesn't work.
The mfdcr() macro already checks that the argument is constant using
__builtin_constant_p(), and if not calls the out-of-line version of
mfdcr(). But in this case GCC is smart enough to notice that "base +
PLB4OPB_GESR0" will be constant, even though it's not something we can
immediately stringify into a register number.
Segher pointed out that passing the register number to the inline asm
as a constant would be better, and in fact it fixes the build error,
presumably because it gives GCC a chance to resolve the value.
While we're at it, change mtdcr() similarly.
Reported-by: kernel test robot <lkp@intel.com>
Suggested-by: Segher Boessenkool <segher@kernel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---
arch/powerpc/include/asm/dcr-native.h | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/arch/powerpc/include/asm/dcr-native.h b/arch/powerpc/include/asm/dcr-native.h
index 7141ccea8c94..a92059964579 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 \
@@ -64,8 +64,8 @@ static inline void mtdcrx(unsigned int reg, unsigned int val)
#define mtdcr(rn, v) \
do { \
if (__builtin_constant_p(rn) && rn < 1024) \
- asm volatile("mtdcr " __stringify(rn) ",%0" \
- : : "r" (v)); \
+ asm volatile("mtdcr %0, %1" \
+ : : "n" (rn), "r" (v)); \
else if (likely(cpu_has_feature(CPU_FTR_INDEXED_DCR))) \
mtdcrx(rn, v); \
else \
--
2.25.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] powerpc/4xx: Fix build errors from mfdcr()
2021-02-18 12:30 [PATCH] powerpc/4xx: Fix build errors from mfdcr() Michael Ellerman
@ 2021-02-18 13:04 ` Feng Tang
2021-03-14 10:01 ` Michael Ellerman
1 sibling, 0 replies; 3+ messages in thread
From: Feng Tang @ 2021-02-18 13:04 UTC (permalink / raw)
To: Michael Ellerman; +Cc: linuxppc-dev
On Thu, Feb 18, 2021 at 11:30:58PM +1100, Michael Ellerman wrote:
> lkp reported a build error in fsp2.o:
>
> CC arch/powerpc/platforms/44x/fsp2.o
> {standard input}:577: Error: unsupported relocation against base
>
> Which comes from:
>
> pr_err("GESR0: 0x%08x\n", mfdcr(base + PLB4OPB_GESR0));
>
> Where our mfdcr() macro is stringifying "base + PLB4OPB_GESR0", and
> passing that to the assembler, which obviously doesn't work.
>
> The mfdcr() macro already checks that the argument is constant using
> __builtin_constant_p(), and if not calls the out-of-line version of
> mfdcr(). But in this case GCC is smart enough to notice that "base +
> PLB4OPB_GESR0" will be constant, even though it's not something we can
> immediately stringify into a register number.
>
> Segher pointed out that passing the register number to the inline asm
> as a constant would be better, and in fact it fixes the build error,
> presumably because it gives GCC a chance to resolve the value.
>
> While we're at it, change mtdcr() similarly.
>
> Reported-by: kernel test robot <lkp@intel.com>
> Suggested-by: Segher Boessenkool <segher@kernel.crashing.org>
> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Acked-by: Feng Tang <feng.tang@intel.com>
Thanks!
> ---
> arch/powerpc/include/asm/dcr-native.h | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/dcr-native.h b/arch/powerpc/include/asm/dcr-native.h
> index 7141ccea8c94..a92059964579 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 \
> @@ -64,8 +64,8 @@ static inline void mtdcrx(unsigned int reg, unsigned int val)
> #define mtdcr(rn, v) \
> do { \
> if (__builtin_constant_p(rn) && rn < 1024) \
> - asm volatile("mtdcr " __stringify(rn) ",%0" \
> - : : "r" (v)); \
> + asm volatile("mtdcr %0, %1" \
> + : : "n" (rn), "r" (v)); \
> else if (likely(cpu_has_feature(CPU_FTR_INDEXED_DCR))) \
> mtdcrx(rn, v); \
> else \
> --
> 2.25.1
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] powerpc/4xx: Fix build errors from mfdcr()
2021-02-18 12:30 [PATCH] powerpc/4xx: Fix build errors from mfdcr() Michael Ellerman
2021-02-18 13:04 ` Feng Tang
@ 2021-03-14 10:01 ` Michael Ellerman
1 sibling, 0 replies; 3+ messages in thread
From: Michael Ellerman @ 2021-03-14 10:01 UTC (permalink / raw)
To: linuxppc-dev, Michael Ellerman; +Cc: feng.tang
On Thu, 18 Feb 2021 23:30:58 +1100, Michael Ellerman wrote:
> lkp reported a build error in fsp2.o:
>
> CC arch/powerpc/platforms/44x/fsp2.o
> {standard input}:577: Error: unsupported relocation against base
>
> Which comes from:
>
> [...]
Applied to powerpc/fixes.
[1/1] powerpc/4xx: Fix build errors from mfdcr()
https://git.kernel.org/powerpc/c/eead089311f4d935ab5d1d8fbb0c42ad44699ada
cheers
^ permalink raw reply [flat|nested] 3+ messages in thread
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2021-02-18 12:30 [PATCH] powerpc/4xx: Fix build errors from mfdcr() Michael Ellerman
2021-02-18 13:04 ` Feng Tang
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