[PATCH v1 1/5] powerpc/32: Do not allow selection of e5500 or e6500 CPUs on PPC32

Commit 0e00a8c9fd92 ("powerpc: Allow CPU selection also on PPC32")
enlarged the CPU selection logic to PPC32 by removing depend to
PPC64, and failed to restrict that depend to E5500_CPU and E6500_CPU.
Fortunately that got unnoticed because -mcpu=8540 will override the
-mcpu=e500mc64 or -mpcu=e6500 as they are ealier, but that's
fragile and may no be right in the future.

Add back the depend PPC64 on E5500_CPU and E6500_CPU.

Fixes: 0e00a8c9fd92 ("powerpc: Allow CPU selection also on PPC32")
Signed-off-by: Christophe Leroy <redacted>
---
 arch/powerpc/platforms/Kconfig.cputype | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
index 383ed4fe6013..9805a2c717b9 100644
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype

@@ -173,11 +173,11 @@ config POWER9_CPU
 
 config E5500_CPU
 	bool "Freescale e5500"
-	depends on E500
+	depends on PPC64 && E500
 
 config E6500_CPU
 	bool "Freescale e6500"
-	depends on E500
+	depends on PPC64 && E500
 
 config 860_CPU
 	bool "8xx family"

-- 
2.36.1

Since commit 4bf4f42a2feb ("powerpc/kbuild: Set default generic
machine type for 32-bit compile"), when building a 32 bits kernel
with a bi-arch version of GCC, or when building a book3s/32 kernel,
the option -mcpu=powerpc is passed to GCC at all time, relying on it
being eventually overriden by a subsequent -mcpu=xxxx.

But when building the same kernel with a 32 bits only version of GCC,
that is not done, relying on gcc being built with the expected default
CPU.

This logic has two problems. First, it is a bit fragile to rely on
whether the GCC version is bi-arch or not, because today we can have
bi-arch versions of GCC configured with a 32 bits default. Second,
there are some versions of GCC which don't support -mcpu=powerpc,
for instance for e500 SPE-only versions.

So, stop relying on this approximative logic and allow the user to
decide whether he/she wants to use the toolchain's default CPU or if
he/she wants to set one, and allow only possible CPUs based on the
selected target.

Reported-by: Pali Rohár <pali@kernel.org>
Tested-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Cc: Segher Boessenkool <redacted>
Signed-off-by: Christophe Leroy <redacted>
---
 arch/powerpc/Makefile                  | 26 +-------------------------
 arch/powerpc/platforms/Kconfig.cputype | 21 ++++++++++++++++++---
 2 files changed, 19 insertions(+), 28 deletions(-)

diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index a0cd70712061..d54e1fe03551 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile

@@ -15,23 +15,6 @@ HAS_BIARCH	:= $(call cc-option-yn, -m32)
 # Set default 32 bits cross compilers for vdso and boot wrapper
 CROSS32_COMPILE ?=
 
-ifeq ($(HAS_BIARCH),y)
-ifeq ($(CROSS32_COMPILE),)
-ifdef CONFIG_PPC32
-# These options will be overridden by any -mcpu option that the CPU
-# or platform code sets later on the command line, but they are needed
-# to set a sane 32-bit cpu target for the 64-bit cross compiler which
-# may default to the wrong ISA.
-KBUILD_CFLAGS		+= -mcpu=powerpc
-KBUILD_AFLAGS		+= -mcpu=powerpc
-endif
-endif
-endif
-
-ifdef CONFIG_PPC_BOOK3S_32
-KBUILD_CFLAGS		+= -mcpu=powerpc
-endif
-
 # If we're on a ppc/ppc64/ppc64le machine use that defconfig, otherwise just use
 # ppc64_defconfig because we have nothing better to go on.
 uname := $(shell uname -m)

@@ -183,6 +166,7 @@ endif
 endif
 
 CFLAGS-$(CONFIG_TARGET_CPU_BOOL) += $(call cc-option,-mcpu=$(CONFIG_TARGET_CPU))
+AFLAGS-$(CONFIG_TARGET_CPU_BOOL) += $(call cc-option,-mcpu=$(CONFIG_TARGET_CPU))
 
 # Altivec option not allowed with e500mc64 in GCC.
 ifdef CONFIG_ALTIVEC

@@ -193,14 +177,6 @@ endif
 CFLAGS-$(CONFIG_E5500_CPU) += $(E5500_CPU)
 CFLAGS-$(CONFIG_E6500_CPU) += $(call cc-option,-mcpu=e6500,$(E5500_CPU))
 
-ifdef CONFIG_PPC32
-ifdef CONFIG_PPC_E500MC
-CFLAGS-y += $(call cc-option,-mcpu=e500mc,-mcpu=powerpc)
-else
-CFLAGS-$(CONFIG_E500) += $(call cc-option,-mcpu=8540 -msoft-float,-mcpu=powerpc)
-endif
-endif
-
 asinstr := $(call as-instr,lis 9$(comma)foo@high,-DHAVE_AS_ATHIGH=1)
 
 KBUILD_CPPFLAGS	+= -I $(srctree)/arch/$(ARCH) $(asinstr)

diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
index 9805a2c717b9..bfea5d8452f8 100644
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype

@@ -135,9 +135,9 @@ config GENERIC_CPU
 	select ARCH_HAS_FAST_MULTIPLIER
 	select PPC_64S_HASH_MMU
 
-config GENERIC_CPU
+config POWERPC_CPU
 	bool "Generic 32 bits powerpc"
-	depends on PPC32 && !PPC_8xx
+	depends on PPC32 && !PPC_8xx && !PPC_85xx
 
 config CELL_CPU
 	bool "Cell Broadband Engine"

@@ -196,11 +196,23 @@ config G4_CPU
 	depends on PPC_BOOK3S_32
 	select ALTIVEC
 
+config E500_CPU
+	bool "e500 (8540)"
+	depends on PPC_85xx && !PPC_E500MC
+
+config E500MC_CPU
+	bool "e500mc"
+	depends on PPC_85xx && PPC_E500MC
+
+config TOOLCHAIN_DEFAULT_CPU
+	bool "Rely on the toolchain's implicit default CPU"
+	depends on PPC32
+
 endchoice
 
 config TARGET_CPU_BOOL
 	bool
-	default !GENERIC_CPU
+	default !GENERIC_CPU && !TOOLCHAIN_DEFAULT_CPU
 
 config TARGET_CPU
 	string

@@ -215,6 +227,9 @@ config TARGET_CPU
 	default "e300c2" if E300C2_CPU
 	default "e300c3" if E300C3_CPU
 	default "G4" if G4_CPU
+	default "8540" if E500_CPU
+	default "e500mc" if E500MC_CPU
+	default "powerpc" if POWERPC_CPU
 
 config PPC_BOOK3S
 	def_bool y

-- 
2.36.1

Building ppc40x_defconfig leads to following error

  CC      arch/powerpc/kernel/process.o
{standard input}: Assembler messages:
{standard input}:626: Error: unrecognized opcode: `wrteei'

Add -mcpu=405 by default.

Signed-off-by: Christophe Leroy <redacted>
---
 arch/powerpc/platforms/Kconfig.cputype | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
index bfea5d8452f8..e14000557ebd 100644
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype

@@ -137,7 +137,7 @@ config GENERIC_CPU
 
 config POWERPC_CPU
 	bool "Generic 32 bits powerpc"
-	depends on PPC32 && !PPC_8xx && !PPC_85xx
+	depends on PPC32 && !PPC_8xx && !PPC_85xx && !40x
 
 config CELL_CPU
 	bool "Cell Broadband Engine"

@@ -179,6 +179,10 @@ config E6500_CPU
 	bool "Freescale e6500"
 	depends on PPC64 && E500
 
+config 405_CPU
+	bool "40x family"
+	depends on 40x
+
 config 860_CPU
 	bool "8xx family"
 	depends on PPC_8xx

@@ -223,6 +227,7 @@ config TARGET_CPU
 	default "power7" if POWER7_CPU
 	default "power8" if POWER8_CPU
 	default "power9" if POWER9_CPU
+	default "405" if 405_CPU
 	default "860" if 860_CPU
 	default "e300c2" if E300C2_CPU
 	default "e300c3" if E300C3_CPU

-- 
2.36.1

Building ppc40x_defconfig leads to following error

  CC      arch/powerpc/kernel/idle.o
{standard input}: Assembler messages:
{standard input}:67: Error: unrecognized opcode: `wrteei'
{standard input}:78: Error: unrecognized opcode: `wrteei'

Add -mcpu=440 by default and alternatively 464 and 476.

Once that's done, -mcpu=powerpc is only for book3s/32 now.

But then comes

  CC      arch/powerpc/kernel/io.o
{standard input}: Assembler messages:
{standard input}:198: Error: unrecognized opcode: `eieio'
{standard input}:230: Error: unrecognized opcode: `eieio'
{standard input}:245: Error: unrecognized opcode: `eieio'
{standard input}:254: Error: unrecognized opcode: `eieio'
{standard input}:273: Error: unrecognized opcode: `eieio'
{standard input}:396: Error: unrecognized opcode: `eieio'
{standard input}:404: Error: unrecognized opcode: `eieio'
{standard input}:423: Error: unrecognized opcode: `eieio'
{standard input}:512: Error: unrecognized opcode: `eieio'
{standard input}:520: Error: unrecognized opcode: `eieio'
{standard input}:539: Error: unrecognized opcode: `eieio'
{standard input}:628: Error: unrecognized opcode: `eieio'
{standard input}:636: Error: unrecognized opcode: `eieio'
{standard input}:655: Error: unrecognized opcode: `eieio'

Fix it by replacing eieio by mbar on booke.

Signed-off-by: Christophe Leroy <redacted>
---
 arch/powerpc/include/asm/barrier.h        |  2 ++
 arch/powerpc/include/asm/nohash/pgtable.h |  2 +-
 arch/powerpc/include/asm/synch.h          |  5 ++++-
 arch/powerpc/mm/nohash/tlb_low.S          |  4 ++--
 arch/powerpc/platforms/Kconfig.cputype    | 17 ++++++++++++++++-
 arch/powerpc/sysdev/fsl_rio.c             | 12 ++++++++++--
 6 files changed, 35 insertions(+), 7 deletions(-)

diff --git a/arch/powerpc/include/asm/barrier.h b/arch/powerpc/include/asm/barrier.h
index f0e687236484..ef2d8b15eaab 100644
--- a/arch/powerpc/include/asm/barrier.h
+++ b/arch/powerpc/include/asm/barrier.h

@@ -42,6 +42,8 @@
 /* The sub-arch has lwsync */
 #if defined(CONFIG_PPC64) || defined(CONFIG_PPC_E500MC)
 #    define SMPWMB      LWSYNC
+#elif defined(CONFIG_BOOKE)
+#    define SMPWMB      mbar
 #else
 #    define SMPWMB      eieio
 #endif

diff --git a/arch/powerpc/include/asm/nohash/pgtable.h b/arch/powerpc/include/asm/nohash/pgtable.h
index ac75f4ab0dba..b499da6c1a99 100644
--- a/arch/powerpc/include/asm/nohash/pgtable.h
+++ b/arch/powerpc/include/asm/nohash/pgtable.h

@@ -193,7 +193,7 @@ static inline void __set_pte_at(struct mm_struct *mm, unsigned long addr,
 	if (IS_ENABLED(CONFIG_PPC32) && IS_ENABLED(CONFIG_PTE_64BIT) && !percpu) {
 		__asm__ __volatile__("\
 			stw%X0 %2,%0\n\
-			eieio\n\
+			mbar\n\
 			stw%X1 %L2,%1"
 		: "=m" (*ptep), "=m" (*((unsigned char *)ptep+4))
 		: "r" (pte) : "memory");

diff --git a/arch/powerpc/include/asm/synch.h b/arch/powerpc/include/asm/synch.h
index 1d67bc8d7bc6..7130176d8cb8 100644
--- a/arch/powerpc/include/asm/synch.h
+++ b/arch/powerpc/include/asm/synch.h

@@ -14,7 +14,10 @@ extern void do_lwsync_fixups(unsigned long value, void *fixup_start,
 
 static inline void eieio(void)
 {
-	__asm__ __volatile__ ("eieio" : : : "memory");
+	if (IS_ENABLED(CONFIG_BOOKE))
+		__asm__ __volatile__ ("mbar" : : : "memory");
+	else
+		__asm__ __volatile__ ("eieio" : : : "memory");
 }
 
 static inline void isync(void)

diff --git a/arch/powerpc/mm/nohash/tlb_low.S b/arch/powerpc/mm/nohash/tlb_low.S
index dd39074de9af..d62b613a0d5d 100644
--- a/arch/powerpc/mm/nohash/tlb_low.S
+++ b/arch/powerpc/mm/nohash/tlb_low.S

@@ -186,7 +186,7 @@ _GLOBAL(_tlbivax_bcast)
 	isync
 	PPC_TLBIVAX(0, R3)
 	isync
-	eieio
+	mbar
 	tlbsync
 BEGIN_FTR_SECTION
 	b	1f

@@ -355,7 +355,7 @@ _GLOBAL(_tlbivax_bcast)
 	rlwimi	r4,r6,MAS6_SIND_SHIFT,MAS6_SIND
 1:	mtspr	SPRN_MAS6,r4		/* assume AS=0 for now */
 	PPC_TLBIVAX(0,R3)
-	eieio
+	mbar
 	tlbsync
 	sync
 	wrtee	r10

diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
index e14000557ebd..3cc8452b8660 100644
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype

@@ -137,7 +137,7 @@ config GENERIC_CPU
 
 config POWERPC_CPU
 	bool "Generic 32 bits powerpc"
-	depends on PPC32 && !PPC_8xx && !PPC_85xx && !40x
+	depends on PPC_BOOK3S_32
 
 config CELL_CPU
 	bool "Cell Broadband Engine"

@@ -183,6 +183,18 @@ config 405_CPU
 	bool "40x family"
 	depends on 40x
 
+config 440_CPU
+	bool "440 (44x family)"
+	depends on 44x
+
+config 464_CPU
+	bool "464 (44x family)"
+	depends on 44x
+
+config 476_CPU
+	bool "476 (47x family)"
+	depends on PPC_47x
+
 config 860_CPU
 	bool "8xx family"
 	depends on PPC_8xx

@@ -228,6 +240,9 @@ config TARGET_CPU
 	default "power8" if POWER8_CPU
 	default "power9" if POWER9_CPU
 	default "405" if 405_CPU
+	default "440" if 440_CPU
+	default "464" if 464_CPU
+	default "476" if 476_CPU
 	default "860" if 860_CPU
 	default "e300c2" if E300C2_CPU
 	default "e300c3" if E300C3_CPU

diff --git a/arch/powerpc/sysdev/fsl_rio.c b/arch/powerpc/sysdev/fsl_rio.c
index 1bfc9afa8a1a..4647c6074f3b 100644
--- a/arch/powerpc/sysdev/fsl_rio.c
+++ b/arch/powerpc/sysdev/fsl_rio.c

@@ -69,10 +69,10 @@
 
 static DEFINE_SPINLOCK(fsl_rio_config_lock);
 
-#define __fsl_read_rio_config(x, addr, err, op)		\
+#define ___fsl_read_rio_config(x, addr, err, op, barrier)	\
 	__asm__ __volatile__(				\
 		"1:	"op" %1,0(%2)\n"		\
-		"	eieio\n"			\
+		"	"barrier"\n"			\
 		"2:\n"					\
 		".section .fixup,\"ax\"\n"		\
 		"3:	li %1,-1\n"			\

@@ -83,6 +83,14 @@ static DEFINE_SPINLOCK(fsl_rio_config_lock);
 		: "=r" (err), "=r" (x)			\
 		: "b" (addr), "i" (-EFAULT), "0" (err))
 
+#ifdef CONFIG_BOOKE
+#define __fsl_read_rio_config(x, addr, err, op)	\
+	___fsl_read_rio_config(x, addr, err, op, "mbar")
+#else
+#define __fsl_read_rio_config(x, addr, err, op)	\
+	___fsl_read_rio_config(x, addr, err, op, "eieio")
+#endif
+
 void __iomem *rio_regs_win;
 void __iomem *rmu_regs_win;
 resource_size_t rio_law_start;

-- 
2.36.1

With GCC 12, corenet64_smp_defconfig leads to the following build errors:

  CC      arch/powerpc/kernel/irq.o
{standard input}: Assembler messages:
{standard input}:3616: Error: unrecognized opcode: `wrteei'
{standard input}:5689: Error: unrecognized opcode: `wrteei'
  CC      arch/powerpc/kernel/pmc.o
{standard input}: Assembler messages:
{standard input}:42: Error: unrecognized opcode: `mfpmr'
{standard input}:53: Error: unrecognized opcode: `mtpmr'
  CC      arch/powerpc/kernel/io.o
{standard input}: Assembler messages:
{standard input}:376: Error: unrecognized opcode: `mbar'
...
  CC      arch/powerpc/mm/nohash/book3e_hugetlbpage.o
{standard input}: Assembler messages:
{standard input}:291: Error: unrecognized opcode: `tlbsx'
{standard input}:482: Error: unrecognized opcode: `tlbwe'
{standard input}:608: Error: unrecognized opcode: `lbarx'
{standard input}:608: Error: unrecognized opcode: `stbcx.'

-mpcu=powerpc64 cannot be used anymore for book3e, it must be a booke CPU.

But then we get:

  CC      arch/powerpc/lib/xor_vmx.o
cc1: error: AltiVec not supported in this target

Altivec is not supported with -mcpu=e5500 so don't allow selection
of altivec when e5500 is selected.

Signed-off-by: Christophe Leroy <redacted>
---
 arch/powerpc/Makefile                  | 8 +-------
 arch/powerpc/platforms/Kconfig.cputype | 8 ++++----
 2 files changed, 5 insertions(+), 11 deletions(-)

diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index d54e1fe03551..02742facf895 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile

@@ -168,13 +168,7 @@ endif
 CFLAGS-$(CONFIG_TARGET_CPU_BOOL) += $(call cc-option,-mcpu=$(CONFIG_TARGET_CPU))
 AFLAGS-$(CONFIG_TARGET_CPU_BOOL) += $(call cc-option,-mcpu=$(CONFIG_TARGET_CPU))
 
-# Altivec option not allowed with e500mc64 in GCC.
-ifdef CONFIG_ALTIVEC
-E5500_CPU := -mcpu=powerpc64
-else
-E5500_CPU := $(call cc-option,-mcpu=e500mc64,-mcpu=powerpc64)
-endif
-CFLAGS-$(CONFIG_E5500_CPU) += $(E5500_CPU)
+CFLAGS-$(CONFIG_E5500_CPU) += $(call cc-option,-mcpu=e500mc64,-mcpu=powerpc64)
 CFLAGS-$(CONFIG_E6500_CPU) += $(call cc-option,-mcpu=e6500,$(E5500_CPU))
 
 asinstr := $(call as-instr,lis 9$(comma)foo@high,-DHAVE_AS_ATHIGH=1)

diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
index 3cc8452b8660..5185d942b455 100644
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype

@@ -126,12 +126,12 @@ choice
 
 config GENERIC_CPU
 	bool "Generic (POWER4 and above)"
-	depends on PPC64 && !CPU_LITTLE_ENDIAN
-	select PPC_64S_HASH_MMU if PPC_BOOK3S_64
+	depends on PPC_BOOK3S_64 && !CPU_LITTLE_ENDIAN
+	select PPC_64S_HASH_MMU
 
 config GENERIC_CPU
 	bool "Generic (POWER8 and above)"
-	depends on PPC64 && CPU_LITTLE_ENDIAN
+	depends on PPC_BOOK3S_64 && CPU_LITTLE_ENDIAN
 	select ARCH_HAS_FAST_MULTIPLIER
 	select PPC_64S_HASH_MMU
 

@@ -358,7 +358,7 @@ config PHYS_64BIT
 
 config ALTIVEC
 	bool "AltiVec Support"
-	depends on PPC_BOOK3S_32 || PPC_BOOK3S_64 || (PPC_E500MC && PPC64)
+	depends on PPC_BOOK3S || (PPC_E500MC && PPC64 && !E5500_CPU)
 	select PPC_FPU
 	help
 	  This option enables kernel support for the Altivec extensions to the

-- 
2.36.1

On Mon, Jul 11, 2022 at 4:19 PM Christophe Leroy
[off-list ref] wrote:

Is there any value in building for -mcpu=440 or -mcpu=464 when targeting a 476?
Maybe add another !PPC_47x dependency for the first two. Ideally we would also
enforce that 440/464 based boards cannot be selected together with 476, though
I guess that is a separate issue.

Is there a practical difference between 440 and 464 when building kernels?
gcc seems to treat them the same way, so maybe one option for both is enough
here.

     Arnd

Oops, I wanted to include Pali and Segher when I sent the series, I 
prepared a script including them but used the wrong script at the end.

Le 11/07/2022 à 17:05, Arnd Bergmann a écrit :

On Mon, Jul 11, 2022 at 4:19 PM Christophe Leroy
[off-list ref] wrote:

quoted

@@ -183,6 +183,18 @@ config 405_CPU
         bool "40x family"
         depends on 40x

+config 440_CPU
+       bool "440 (44x family)"
+       depends on 44x
+
+config 464_CPU
+       bool "464 (44x family)"
+       depends on 44x
+
+config 476_CPU
+       bool "476 (47x family)"
+       depends on PPC_47x

Is there any value in building for -mcpu=440 or -mcpu=464 when targeting a 476?

No idea, maybe not.

Maybe add another !PPC_47x dependency for the first two. Ideally we would also
enforce that 440/464 based boards cannot be selected together with 476, though
I guess that is a separate issue.

Yes can do that.

By the way, 440/464 boards get excluded from kernel/cputable.c when 47x 
is selected

Is there a practical difference between 440 and 464 when building kernels?
gcc seems to treat them the same way, so maybe one option for both is enough
here.

I don't know.

Christophe

Hi!

On Mon, Jul 11, 2022 at 04:19:29PM +0200, Christophe Leroy wrote:

Commit 0e00a8c9fd92 ("powerpc: Allow CPU selection also on PPC32")
enlarged the CPU selection logic to PPC32 by removing depend to
PPC64, and failed to restrict that depend to E5500_CPU and E6500_CPU.
Fortunately that got unnoticed because -mcpu=8540 will override the
-mcpu=e500mc64 or -mpcu=e6500 as they are ealier, but that's
fragile and may no be right in the future.

A later -mcpu= always overrides an earlier one.  This is the same as
with all other GCC option flags, and will not change in the future.


Segher

On Mon, Jul 11, 2022 at 04:19:30PM +0200, Christophe Leroy wrote:

Since commit 4bf4f42a2feb ("powerpc/kbuild: Set default generic
machine type for 32-bit compile"), when building a 32 bits kernel
with a bi-arch version of GCC, or when building a book3s/32 kernel,
the option -mcpu=powerpc is passed to GCC at all time, relying on it
being eventually overriden by a subsequent -mcpu=xxxx.

But when building the same kernel with a 32 bits only version of GCC,
that is not done, relying on gcc being built with the expected default
CPU.

This logic has two problems. First, it is a bit fragile to rely on
whether the GCC version is bi-arch or not, because today we can have
bi-arch versions of GCC configured with a 32 bits default. Second,
there are some versions of GCC which don't support -mcpu=powerpc,
for instance for e500 SPE-only versions.

More fundamentally, the *only* thing you should check biarch for is
for determining if you can use both -m32 and -m64 with the same
compiler.  Everything behaves identically in a biarch and a non-biarch
compiler, other than the latter screams bloody murder if you try to
change the architecture from 32 to 64 bit or vice versa.

So, stop relying on this approximative logic and allow the user to
decide whether he/she wants to use the toolchain's default CPU or if
he/she wants to set one, and allow only possible CPUs based on the
selected target.

Reported-by: Pali Rohár <pali@kernel.org>
Tested-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Cc: Segher Boessenkool <redacted>
Signed-off-by: Christophe Leroy <redacted>

Reviewed-by: Segher Boessenkool <redacted>

Looks good to me.  This untangles/demystifies quite some code :-)


Segher

On Mon, Jul 11, 2022 at 05:05:04PM +0200, Arnd Bergmann wrote:

Is there any value in building for -mcpu=440 or -mcpu=464 when targeting a 476?

The original 440 had a very short pipeline.  Later IBM 4xx have a longer
pipeline.  Getting this right (with -mtune=, or just with -mcpu=) is
important for performance.  So, no?

Maybe add another !PPC_47x dependency for the first two. Ideally we would also
enforce that 440/464 based boards cannot be selected together with 476, though
I guess that is a separate issue.

Is there a practical difference between 440 and 464 when building kernels?
gcc seems to treat them the same way, so maybe one option for both is enough
here.

-mcpu= is used as the default for -mtune=, so that is always a
consideration.  PPC464 is treated the same as PPC440 in binutils as
well, so I don't think there is any issue there.


Segher

Le 11/07/2022 à 18:39, Segher Boessenkool a écrit :

Hi!

On Mon, Jul 11, 2022 at 04:19:29PM +0200, Christophe Leroy wrote:

quoted

Commit 0e00a8c9fd92 ("powerpc: Allow CPU selection also on PPC32")
enlarged the CPU selection logic to PPC32 by removing depend to
PPC64, and failed to restrict that depend to E5500_CPU and E6500_CPU.
Fortunately that got unnoticed because -mcpu=8540 will override the
-mcpu=e500mc64 or -mpcu=e6500 as they are ealier, but that's
fragile and may no be right in the future.

A later -mcpu= always overrides an earlier one.  This is the same as
with all other GCC option flags, and will not change in the future.

By "future" I meant after patch 2.

At the time being, if you select PPC32 and MPC_85xx and E6500_CPU, you 
get -mcpu=e6500 -mcpu=8540.

After patch 2, if you select PPC32 and MPC_85xx and E6500_CPU, you get 
-mcpu=e6500

Christophe

On Mon, 11 Jul 2022 16:19:29 +0200, Christophe Leroy wrote:

Commit 0e00a8c9fd92 ("powerpc: Allow CPU selection also on PPC32")
enlarged the CPU selection logic to PPC32 by removing depend to
PPC64, and failed to restrict that depend to E5500_CPU and E6500_CPU.
Fortunately that got unnoticed because -mcpu=8540 will override the
-mcpu=e500mc64 or -mpcu=e6500 as they are ealier, but that's
fragile and may no be right in the future.

[...]

Applied to powerpc/next.

[1/5] powerpc/32: Do not allow selection of e5500 or e6500 CPUs on PPC32
      https://git.kernel.org/powerpc/c/9be013b2a9ecb29b5168e4b9db0e48ed53acf37c
[2/5] powerpc/32: Don't always pass -mcpu=powerpc to the compiler
      https://git.kernel.org/powerpc/c/446cda1b21d9a6b3697fe399c6a3a00ff4a285f5
[3/5] powerpc/405: Fix build failure with GCC 12 (unrecognized opcode: `wrteei')
      https://git.kernel.org/powerpc/c/ff27d9200a98757efc7c2cdf198904fd79cf4ffd
[4/5] powerpc/44x: Fix build failure with GCC 12 (unrecognized opcode: `wrteei')
      https://git.kernel.org/powerpc/c/2255411d1d0f0661d1e5acd5f6edf4e6652a345a
[5/5] powerpc/64e: Fix build failure with GCC 12 (unrecognized opcode: `wrteei')
      https://git.kernel.org/powerpc/c/d6b551b8f90cc92c7d3c09cf38c748efe305ecb4

cheers

On Monday 11 July 2022 16:19:30 Christophe Leroy wrote:

Since commit 4bf4f42a2feb ("powerpc/kbuild: Set default generic
machine type for 32-bit compile"), when building a 32 bits kernel
with a bi-arch version of GCC, or when building a book3s/32 kernel,
the option -mcpu=powerpc is passed to GCC at all time, relying on it
being eventually overriden by a subsequent -mcpu=xxxx.

But when building the same kernel with a 32 bits only version of GCC,
that is not done, relying on gcc being built with the expected default
CPU.

This logic has two problems. First, it is a bit fragile to rely on
whether the GCC version is bi-arch or not, because today we can have
bi-arch versions of GCC configured with a 32 bits default. Second,
there are some versions of GCC which don't support -mcpu=powerpc,
for instance for e500 SPE-only versions.

So, stop relying on this approximative logic and allow the user to
decide whether he/she wants to use the toolchain's default CPU or if
he/she wants to set one, and allow only possible CPUs based on the
selected target.

Hello! Exactly same issue is still in file arch/powerpc/boot/Makefile:

  ifdef CONFIG_PPC64_BOOT_WRAPPER
  ifdef CONFIG_CPU_LITTLE_ENDIAN
  BOOTCFLAGS	+= -m64 -mcpu=powerpc64le
  else
  BOOTCFLAGS	+= -m64 -mcpu=powerpc64
  endif
  else
  BOOTCFLAGS	+= -m32 -mcpu=powerpc
  endif

It cause compile error:

  make ARCH=powerpc CROSS_COMPILE=powerpc-linux-gnuspe- mpc85xx_smp_defconfig uImage
  ...
    BOOTAS  arch/powerpc/boot/crt0.o
  powerpc-linux-gnuspe-gcc: error: unrecognized argument in option ‘-mcpu=powerpc’
  powerpc-linux-gnuspe-gcc: note: valid arguments to ‘-mcpu=’ are: 8540 8548 native
  make[1]: *** [arch/powerpc/boot/Makefile:231: arch/powerpc/boot/crt0.o] Error 1

Reported-by: Pali Rohár <pali@kernel.org>
Tested-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Cc: Segher Boessenkool <redacted>
Signed-off-by: Christophe Leroy <redacted>
---
 arch/powerpc/Makefile                  | 26 +-------------------------
 arch/powerpc/platforms/Kconfig.cputype | 21 ++++++++++++++++++---
 2 files changed, 19 insertions(+), 28 deletions(-)

On Thursday 18 August 2022 19:46:34 Pali Rohár wrote:

On Monday 11 July 2022 16:19:30 Christophe Leroy wrote:

quoted

Since commit 4bf4f42a2feb ("powerpc/kbuild: Set default generic
machine type for 32-bit compile"), when building a 32 bits kernel
with a bi-arch version of GCC, or when building a book3s/32 kernel,
the option -mcpu=powerpc is passed to GCC at all time, relying on it
being eventually overriden by a subsequent -mcpu=xxxx.

But when building the same kernel with a 32 bits only version of GCC,
that is not done, relying on gcc being built with the expected default
CPU.

This logic has two problems. First, it is a bit fragile to rely on
whether the GCC version is bi-arch or not, because today we can have
bi-arch versions of GCC configured with a 32 bits default. Second,
there are some versions of GCC which don't support -mcpu=powerpc,
for instance for e500 SPE-only versions.

So, stop relying on this approximative logic and allow the user to
decide whether he/she wants to use the toolchain's default CPU or if
he/she wants to set one, and allow only possible CPUs based on the
selected target.

Hello! Exactly same issue is still in file arch/powerpc/boot/Makefile:

  ifdef CONFIG_PPC64_BOOT_WRAPPER
  ifdef CONFIG_CPU_LITTLE_ENDIAN
  BOOTCFLAGS	+= -m64 -mcpu=powerpc64le
  else
  BOOTCFLAGS	+= -m64 -mcpu=powerpc64
  endif
  else
  BOOTCFLAGS	+= -m32 -mcpu=powerpc
  endif

It cause compile error:

  make ARCH=powerpc CROSS_COMPILE=powerpc-linux-gnuspe- mpc85xx_smp_defconfig uImage
  ...
    BOOTAS  arch/powerpc/boot/crt0.o
  powerpc-linux-gnuspe-gcc: error: unrecognized argument in option ‘-mcpu=powerpc’
  powerpc-linux-gnuspe-gcc: note: valid arguments to ‘-mcpu=’ are: 8540 8548 native
  make[1]: *** [arch/powerpc/boot/Makefile:231: arch/powerpc/boot/crt0.o] Error 1

Now I have sent patch for this issue:
https://patchwork.ozlabs.org/project/linuxppc-dev/patch/20220820105200.30425-1-pali@kernel.org/

quoted

Reported-by: Pali Rohár <pali@kernel.org>
Tested-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Cc: Segher Boessenkool <redacted>
Signed-off-by: Christophe Leroy <redacted>
---
 arch/powerpc/Makefile                  | 26 +-------------------------
 arch/powerpc/platforms/Kconfig.cputype | 21 ++++++++++++++++++---
 2 files changed, 19 insertions(+), 28 deletions(-)

On Monday 11 July 2022 16:19:33 Christophe Leroy wrote:

Hello! I think that there is an issue. After removal of E5500_CPU
variable few line above, it cannot be used in CFLAGS-$(CONFIG_E6500_CPU)
assignment, because it is empty.

Le 11/12/2022 à 18:32, Pali Rohár a écrit :

On Monday 11 July 2022 16:19:33 Christophe Leroy wrote:

quoted

With GCC 12, corenet64_smp_defconfig leads to the following build errors:

   CC      arch/powerpc/kernel/irq.o
{standard input}: Assembler messages:
{standard input}:3616: Error: unrecognized opcode: `wrteei'
{standard input}:5689: Error: unrecognized opcode: `wrteei'
   CC      arch/powerpc/kernel/pmc.o
{standard input}: Assembler messages:
{standard input}:42: Error: unrecognized opcode: `mfpmr'
{standard input}:53: Error: unrecognized opcode: `mtpmr'
   CC      arch/powerpc/kernel/io.o
{standard input}: Assembler messages:
{standard input}:376: Error: unrecognized opcode: `mbar'
...
   CC      arch/powerpc/mm/nohash/book3e_hugetlbpage.o
{standard input}: Assembler messages:
{standard input}:291: Error: unrecognized opcode: `tlbsx'
{standard input}:482: Error: unrecognized opcode: `tlbwe'
{standard input}:608: Error: unrecognized opcode: `lbarx'
{standard input}:608: Error: unrecognized opcode: `stbcx.'

-mpcu=powerpc64 cannot be used anymore for book3e, it must be a booke CPU.

But then we get:

   CC      arch/powerpc/lib/xor_vmx.o
cc1: error: AltiVec not supported in this target

Altivec is not supported with -mcpu=e5500 so don't allow selection
of altivec when e5500 is selected.

Signed-off-by: Christophe Leroy <redacted>
---
  arch/powerpc/Makefile                  | 8 +-------
  arch/powerpc/platforms/Kconfig.cputype | 8 ++++----
  2 files changed, 5 insertions(+), 11 deletions(-)

diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index d54e1fe03551..02742facf895 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile

@@ -168,13 +168,7 @@ endif
  CFLAGS-$(CONFIG_TARGET_CPU_BOOL) += $(call cc-option,-mcpu=$(CONFIG_TARGET_CPU))
  AFLAGS-$(CONFIG_TARGET_CPU_BOOL) += $(call cc-option,-mcpu=$(CONFIG_TARGET_CPU))
  
-# Altivec option not allowed with e500mc64 in GCC.
-ifdef CONFIG_ALTIVEC
-E5500_CPU := -mcpu=powerpc64
-else
-E5500_CPU := $(call cc-option,-mcpu=e500mc64,-mcpu=powerpc64)
-endif
-CFLAGS-$(CONFIG_E5500_CPU) += $(E5500_CPU)
+CFLAGS-$(CONFIG_E5500_CPU) += $(call cc-option,-mcpu=e500mc64,-mcpu=powerpc64)
  CFLAGS-$(CONFIG_E6500_CPU) += $(call cc-option,-mcpu=e6500,$(E5500_CPU))

Hello! I think that there is an issue. After removal of E5500_CPU
variable few line above, it cannot be used in CFLAGS-$(CONFIG_E6500_CPU)
assignment, because it is empty.

Ah yes, you are right.

It should be fixed by 
https://github.com/linuxppc/linux/commit/f2636eaac7dee1d7d096cc115ff4f5111b0c508c

Michael, I see the patch is in next-test. Can you add:

Fixes: d6b551b8f90c ("powerpc/64e: Fix build failure with GCC 12 
(unrecognized opcode: `wrteei')")


Thanks
Christophe

Christophe Leroy [off-list ref] writes:

Le 11/12/2022 à 18:32, Pali Rohár a écrit :

quoted

On Monday 11 July 2022 16:19:33 Christophe Leroy wrote:

quoted

With GCC 12, corenet64_smp_defconfig leads to the following build errors:

   CC      arch/powerpc/kernel/irq.o
{standard input}: Assembler messages:
{standard input}:3616: Error: unrecognized opcode: `wrteei'
{standard input}:5689: Error: unrecognized opcode: `wrteei'
   CC      arch/powerpc/kernel/pmc.o
{standard input}: Assembler messages:
{standard input}:42: Error: unrecognized opcode: `mfpmr'
{standard input}:53: Error: unrecognized opcode: `mtpmr'
   CC      arch/powerpc/kernel/io.o
{standard input}: Assembler messages:
{standard input}:376: Error: unrecognized opcode: `mbar'
...
   CC      arch/powerpc/mm/nohash/book3e_hugetlbpage.o
{standard input}: Assembler messages:
{standard input}:291: Error: unrecognized opcode: `tlbsx'
{standard input}:482: Error: unrecognized opcode: `tlbwe'
{standard input}:608: Error: unrecognized opcode: `lbarx'
{standard input}:608: Error: unrecognized opcode: `stbcx.'

-mpcu=powerpc64 cannot be used anymore for book3e, it must be a booke CPU.

But then we get:

   CC      arch/powerpc/lib/xor_vmx.o
cc1: error: AltiVec not supported in this target

Altivec is not supported with -mcpu=e5500 so don't allow selection
of altivec when e5500 is selected.

Signed-off-by: Christophe Leroy <redacted>
---
  arch/powerpc/Makefile                  | 8 +-------
  arch/powerpc/platforms/Kconfig.cputype | 8 ++++----
  2 files changed, 5 insertions(+), 11 deletions(-)

diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index d54e1fe03551..02742facf895 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile

@@ -168,13 +168,7 @@ endif
  CFLAGS-$(CONFIG_TARGET_CPU_BOOL) += $(call cc-option,-mcpu=$(CONFIG_TARGET_CPU))
  AFLAGS-$(CONFIG_TARGET_CPU_BOOL) += $(call cc-option,-mcpu=$(CONFIG_TARGET_CPU))
  
-# Altivec option not allowed with e500mc64 in GCC.
-ifdef CONFIG_ALTIVEC
-E5500_CPU := -mcpu=powerpc64
-else
-E5500_CPU := $(call cc-option,-mcpu=e500mc64,-mcpu=powerpc64)
-endif
-CFLAGS-$(CONFIG_E5500_CPU) += $(E5500_CPU)
+CFLAGS-$(CONFIG_E5500_CPU) += $(call cc-option,-mcpu=e500mc64,-mcpu=powerpc64)
  CFLAGS-$(CONFIG_E6500_CPU) += $(call cc-option,-mcpu=e6500,$(E5500_CPU))

Hello! I think that there is an issue. After removal of E5500_CPU
variable few line above, it cannot be used in CFLAGS-$(CONFIG_E6500_CPU)
assignment, because it is empty.

Ah yes, you are right.

It should be fixed by 
https://github.com/linuxppc/linux/commit/f2636eaac7dee1d7d096cc115ff4f5111b0c508c

Michael, I see the patch is in next-test. Can you add:

Fixes: d6b551b8f90c ("powerpc/64e: Fix build failure with GCC 12 
(unrecognized opcode: `wrteei')")

Yep, will do.

cheers