[PATCH 0/3] asm-generic/io.h: Silence -Wnull-pointer-arithmetic warning on PCI_IOBASE

[PATCH 0/3] asm-generic/io.h: Silence -Wnull-pointer-arithmetic warning on PCI_IOBASE

[Niklas Schnelle]

Hi,

This is version 5 of my attempt to get rid of a clang
-Wnull-pointer-arithmetic warning for the use of PCI_IOBASE in
asm-generic/io.h. This was originally found on s390 but should apply to
all platforms leaving PCI_IOBASE undefined while making use of the inb()
and friends helpers from asm-generic/io.h.

This applies cleanly and was compile tested on top of v5.12 for the
previously broken ARC, nds32, h8300 and risc-v architecture. It also
applies cleanly on v5.13-rc1 for which I boot tested it on s390.

I did boot test this only on x86_64 and s390x the former implements
inb() itself while the latter would emit a WARN_ONCE() but no drivers
use inb().

Thanks,
Niklas

Changes since v4:
- Added Link to patch 4 (Arnd)
- Improved comment on RISC-V patch mentioning current brokeness (Arnd)

Changes since v3:
- Changed the subject of the last patch to better reflect the actual
  change i.e. the addition of WARN_ONCE() to the helpers not the
  silencing of the clang warning
- Added asm/bug.h to asm-generic/io.h so it doesn't have to be included
  previously by all arches to be available for the WARN_ONCE()
- Added patch for risc-v which defines PCI_IOBASE except when compiled
  for nommu

Changes since v2:
- Improved comment for SPARC PCI_IOBASE definition as suggested
  by David Laight
- Added a patch for ARC which is missing the asm/bug.h include for
  WARN_ONCE() (kernel test robot)
- Added ifdefs to ioport_map() and __pci_ioport_map() since apparently
  at least test configs enable CONFIG_HAS_IOPORT_MAP even on
  architectures which leave PCI_IOBASE unset (kernel test robot for
  nds32 and ARC).

Changes since v1:
- Added patch to explicitly set PCI_IOBASE to 0 on sparc as suggested by
  Arnd Bergmann
- Instead of working around the warning with a uintptr_t PCI_IOBASE make
  inb() and friends explicitly WARN_ONCE() and return 0xff... (Arnd
  Bergmann)

Niklas Schnelle (3):
  sparc: explicitly set PCI_IOBASE to 0
  risc-v: Use generic io.h helpers for nommu
  asm-generic/io.h: warn in inb() and friends with undefined PCI_IOBASE

 arch/riscv/include/asm/io.h |  5 +--
 arch/sparc/include/asm/io.h |  8 +++++
 include/asm-generic/io.h    | 65 ++++++++++++++++++++++++++++++++++---
 3 files changed, 72 insertions(+), 6 deletions(-)

-- 
2.25.1

[PATCH v5--cover-letter 1/3] sparc: explicitly set PCI_IOBASE to 0

[Niklas Schnelle]

Instead of relying on the fallback in asm-generic/io.h which sets
PCI_IOBASE 0 if it is not defined set it explicitly.

Link: https://lore.kernel.org/lkml/CAK8P3a3PK9zyeP4ymELtc2ZYnymECoACiigw9Za+pvSJpCk5=g@mail.gmail.com/
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
---
 arch/sparc/include/asm/io.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/sparc/include/asm/io.h b/arch/sparc/include/asm/io.h
index 2eefa526b38f..c019e50702c1 100644
--- a/arch/sparc/include/asm/io.h
+++ b/arch/sparc/include/asm/io.h
@@ -1,6 +1,14 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 #ifndef ___ASM_SPARC_IO_H
 #define ___ASM_SPARC_IO_H
+
+/*
+ * On LEON PCI addresses below 64k are converted to IO accesses.
+ * io_remap_xxx() returns a kernel virtual address in the PCI window so
+ * inb() doesn't need to add an offset.
+ */
+#define PCI_IOBASE ((void __iomem *)0)
+
 #if defined(__sparc__) && defined(__arch64__)
 #include <asm/io_64.h>
 #else
-- 
2.25.1

[PATCH v5--cover-letter 2/3] risc-v: Use generic io.h helpers for nommu

[Niklas Schnelle]

From: Niklas Schnelle <niklas@komani.de>

Without MMU support PCI_IOBASE is left undefined because PCI_IO_END is
VMEMMAP_START. Nevertheless the in*()/out*() helper macros are left
defined with uses of PCI_IOBASE.

At the moment this only compiles because asm-generic/io.h defines
PCI_IOBASE as 0 if it is undefined and so at macro expansion PCI_IOBASE
is defined. This leads to compilation errors when asm-generic/io.h is
changed to leave PCI_IOBASE undefined.  More importantly it is currently
broken at runtime, as accessing a fixed I/O port number of an ISA device
on NOMMU RISC-V would turn into a NULL pointer dereference.

Instead only define the in*()/out*() helper macros with MMU support and
fall back to the asm-generic/io.h helper stubs otherwise.

Signed-off-by: Niklas Schnelle <niklas@komani.de>
---
 arch/riscv/include/asm/io.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/include/asm/io.h b/arch/riscv/include/asm/io.h
index c025a746a148..31a8b98c0f13 100644
--- a/arch/riscv/include/asm/io.h
+++ b/arch/riscv/include/asm/io.h
@@ -23,12 +23,12 @@
 #include <asm/mmio.h>
 
 /*
- *  I/O port access constants.
+ *  I/O port access constants. Without MMU support leave PCI_IOBASE undefined
+ *  and fall back to generic stubs for I/O access routines.
  */
 #ifdef CONFIG_MMU
 #define IO_SPACE_LIMIT		(PCI_IO_SIZE - 1)
 #define PCI_IOBASE		((void __iomem *)PCI_IO_START)
-#endif /* CONFIG_MMU */
 
 /*
  * Emulation routines for the port-mapped IO space used by some PCI drivers.
@@ -145,6 +145,7 @@ __io_writes_outs(writes, u64, q, __io_bw(), __io_aw())
 __io_writes_outs(outs, u64, q, __io_pbr(), __io_paw())
 #define outsq(addr, buffer, count) __outsq((void __iomem *)addr, buffer, count)
 #endif
+#endif /* CONFIG_MMU */
 
 #include <asm-generic/io.h>
 
-- 
2.25.1

[PATCH v5--cover-letter 3/3] asm-generic/io.h: warn in inb() and friends with undefined PCI_IOBASE

[Niklas Schnelle]

When PCI_IOBASE is not defined, it is set to 0 such that it is ignored
in calls to the readX/writeX primitives. This triggers clang's
-Wnull-pointer-arithmetic warning and will result in illegal accesses on
platforms that do not support I/O ports.

Make things explicit and silence the warning by letting inb() and
friends fail with WARN_ONCE() and a 0xff... return in case PCI_IOBASE is
not defined.

Link: https://lore.kernel.org/lkml/20210421111759.2059976-1-schnelle@linux.ibm.com/
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
---
 include/asm-generic/io.h | 65 +++++++++++++++++++++++++++++++++++++---
 1 file changed, 61 insertions(+), 4 deletions(-)

diff --git a/include/asm-generic/io.h b/include/asm-generic/io.h
index e93375c710b9..7b523683c241 100644
--- a/include/asm-generic/io.h
+++ b/include/asm-generic/io.h
@@ -8,6 +8,7 @@
 #define __ASM_GENERIC_IO_H
 
 #include <asm/page.h> /* I/O is all done through memory accesses */
+#include <linux/bug.h>
 #include <linux/string.h> /* for memset() and memcpy() */
 #include <linux/types.h>
 
@@ -440,10 +441,6 @@ static inline void writesq(volatile void __iomem *addr, const void *buffer,
 #endif
 #endif /* CONFIG_64BIT */
 
-#ifndef PCI_IOBASE
-#define PCI_IOBASE ((void __iomem *)0)
-#endif
-
 #ifndef IO_SPACE_LIMIT
 #define IO_SPACE_LIMIT 0xffff
 #endif
@@ -458,12 +455,17 @@ static inline void writesq(volatile void __iomem *addr, const void *buffer,
 #define _inb _inb
 static inline u8 _inb(unsigned long addr)
 {
+#ifdef PCI_IOBASE
 	u8 val;
 
 	__io_pbr();
 	val = __raw_readb(PCI_IOBASE + addr);
 	__io_par(val);
 	return val;
+#else
+	WARN_ONCE(1, "No I/O port support\n");
+	return ~0;
+#endif
 }
 #endif
 
@@ -471,12 +473,17 @@ static inline u8 _inb(unsigned long addr)
 #define _inw _inw
 static inline u16 _inw(unsigned long addr)
 {
+#ifdef PCI_IOBASE
 	u16 val;
 
 	__io_pbr();
 	val = __le16_to_cpu((__le16 __force)__raw_readw(PCI_IOBASE + addr));
 	__io_par(val);
 	return val;
+#else
+	WARN_ONCE(1, "No I/O port support\n");
+	return ~0;
+#endif
 }
 #endif
 
@@ -484,12 +491,17 @@ static inline u16 _inw(unsigned long addr)
 #define _inl _inl
 static inline u32 _inl(unsigned long addr)
 {
+#ifdef PCI_IOBASE
 	u32 val;
 
 	__io_pbr();
 	val = __le32_to_cpu((__le32 __force)__raw_readl(PCI_IOBASE + addr));
 	__io_par(val);
 	return val;
+#else
+	WARN_ONCE(1, "No I/O port support\n");
+	return ~0;
+#endif
 }
 #endif
 
@@ -497,9 +509,13 @@ static inline u32 _inl(unsigned long addr)
 #define _outb _outb
 static inline void _outb(u8 value, unsigned long addr)
 {
+#ifdef PCI_IOBASE
 	__io_pbw();
 	__raw_writeb(value, PCI_IOBASE + addr);
 	__io_paw();
+#else
+	WARN_ONCE(1, "No I/O port support\n");
+#endif
 }
 #endif
 
@@ -507,9 +523,13 @@ static inline void _outb(u8 value, unsigned long addr)
 #define _outw _outw
 static inline void _outw(u16 value, unsigned long addr)
 {
+#ifdef PCI_IOBASE
 	__io_pbw();
 	__raw_writew((u16 __force)cpu_to_le16(value), PCI_IOBASE + addr);
 	__io_paw();
+#else
+	WARN_ONCE(1, "No I/O port support\n");
+#endif
 }
 #endif
 
@@ -517,9 +537,13 @@ static inline void _outw(u16 value, unsigned long addr)
 #define _outl _outl
 static inline void _outl(u32 value, unsigned long addr)
 {
+#ifdef PCI_IOBASE
 	__io_pbw();
 	__raw_writel((u32 __force)cpu_to_le32(value), PCI_IOBASE + addr);
 	__io_paw();
+#else
+	WARN_ONCE(1, "No I/O port support\n");
+#endif
 }
 #endif
 
@@ -606,7 +630,11 @@ static inline void outl_p(u32 value, unsigned long addr)
 #define insb insb
 static inline void insb(unsigned long addr, void *buffer, unsigned int count)
 {
+#ifdef PCI_IOBASE
 	readsb(PCI_IOBASE + addr, buffer, count);
+#else
+	WARN_ONCE(1, "No I/O port support\n");
+#endif
 }
 #endif
 
@@ -614,7 +642,11 @@ static inline void insb(unsigned long addr, void *buffer, unsigned int count)
 #define insw insw
 static inline void insw(unsigned long addr, void *buffer, unsigned int count)
 {
+#ifdef PCI_IOBASE
 	readsw(PCI_IOBASE + addr, buffer, count);
+#else
+	WARN_ONCE(1, "No I/O port support\n");
+#endif
 }
 #endif
 
@@ -622,7 +654,11 @@ static inline void insw(unsigned long addr, void *buffer, unsigned int count)
 #define insl insl
 static inline void insl(unsigned long addr, void *buffer, unsigned int count)
 {
+#ifdef PCI_IOBASE
 	readsl(PCI_IOBASE + addr, buffer, count);
+#else
+	WARN_ONCE(1, "No I/O port support\n");
+#endif
 }
 #endif
 
@@ -631,7 +667,11 @@ static inline void insl(unsigned long addr, void *buffer, unsigned int count)
 static inline void outsb(unsigned long addr, const void *buffer,
 			 unsigned int count)
 {
+#ifdef PCI_IOBASE
 	writesb(PCI_IOBASE + addr, buffer, count);
+#else
+	WARN_ONCE(1, "No I/O port support\n");
+#endif
 }
 #endif
 
@@ -640,7 +680,11 @@ static inline void outsb(unsigned long addr, const void *buffer,
 static inline void outsw(unsigned long addr, const void *buffer,
 			 unsigned int count)
 {
+#ifdef PCI_IOBASE
 	writesw(PCI_IOBASE + addr, buffer, count);
+#else
+	WARN_ONCE(1, "No I/O port support\n");
+#endif
 }
 #endif
 
@@ -649,7 +693,11 @@ static inline void outsw(unsigned long addr, const void *buffer,
 static inline void outsl(unsigned long addr, const void *buffer,
 			 unsigned int count)
 {
+#ifdef PCI_IOBASE
 	writesl(PCI_IOBASE + addr, buffer, count);
+#else
+	WARN_ONCE(1, "No I/O port support\n");
+#endif
 }
 #endif
 
@@ -1020,18 +1068,27 @@ static inline void __iomem *ioremap_np(phys_addr_t offset, size_t size)
 #define ioport_map ioport_map
 static inline void __iomem *ioport_map(unsigned long port, unsigned int nr)
 {
+#ifdef PCI_IOBASE
 	port &= IO_SPACE_LIMIT;
 	return (port > MMIO_UPPER_LIMIT) ? NULL : PCI_IOBASE + port;
+#else
+	WARN_ONCE(1, "No I/O port support\n");
+	return NULL;
+#endif
 }
 #define __pci_ioport_unmap __pci_ioport_unmap
 static inline void __pci_ioport_unmap(void __iomem *p)
 {
+#ifdef PCI_IOBASE
 	uintptr_t start = (uintptr_t) PCI_IOBASE;
 	uintptr_t addr = (uintptr_t) p;
 
 	if (addr >= start && addr < start + IO_SPACE_LIMIT)
 		return;
 	iounmap(p);
+#else
+	WARN_ONCE(1, "No I/O port support\n");
+#endif
 }
 #endif
 
-- 
2.25.1