[V2 PATCH 0/3] powerpc: Fix Little Endian Bugs in Single Step Code

[V2 PATCH 0/3] powerpc: Fix Little Endian Bugs in Single Step Code

[Tom]

From: Tom Musta <tommusta@gmail.com>

This patch series addresses bugs in the PowerPC single-step emulation
code (arch/powerpc/lib/sstep.c) pertaining to Little Endian.

The existing code has a chicken switch for little endian.  The first
patch softens the restriction so that only cross-endian modes are not
supported.

There is a general problem with unaligned little endian loads and stores.
This is addressed by the second patch.

Finally, there is a problem with unaligned single precision floating point
loads and stores which is addressed by the third patch.

V2: fixed bug in MSR[LE] check identified by Andreas Schwab and
Geert Uytterhoeven.

Tom Musta (3):
  powerpc: Enable emulate_step In Little Endian Mode
  powerpc: Fix Unaligned Fixed Point Loads and Stores
  powerpc: Fix Unaligned LE Floating Point Loads and Stores

 arch/powerpc/lib/sstep.c |  109 +++++++++++++++++++++++++++++++++++++++------
 1 files changed, 94 insertions(+), 15 deletions(-)

[V2 PATCH 1/3] powerpc: Enable emulate_step In Little Endian Mode

[Tom]

From: Tom Musta <tommusta@gmail.com>

This patch modifies the endian chicken switch in the single step
emulation code (emulate_step()).  The old (big endian) code bailed
early if a load or store instruction was to be emulated in little
endian mode.

The new code modifies the check and only bails in a cross-endian
situation (LE mode in a kernel compiled for BE and vice verse).

V2: fixed bug in MSR[LE] check identified by Andreas Schwab and
Geert Uytterhoeven.

Signed-off-by: Tom Musta <tommusta@gmail.com>
---
 arch/powerpc/lib/sstep.c |   12 +++++++++---
 1 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c
index b1faa15..7bfaa9d 100644
--- a/arch/powerpc/lib/sstep.c
+++ b/arch/powerpc/lib/sstep.c
@@ -1222,12 +1222,18 @@ int __kprobes emulate_step(struct pt_regs *regs, unsigned int instr)
 	}
 
 	/*
-	 * Following cases are for loads and stores, so bail out
-	 * if we're in little-endian mode.
+	 * Following cases are for loads and stores and this
+	 * implementation does not support cross-endian.  So
+	 * bail out if this is the case.
 	 */
+#ifdef __BIG_ENDIAN__
 	if (regs->msr & MSR_LE)
 		return 0;
-
+#endif
+#ifdef __LITTLE_ENDIAN__
+	if (!(regs->msr & MSR_LE))
+		return 0;
+#endif
 	/*
 	 * Save register RA in case it's an update form load or store
 	 * and the access faults.
-- 
1.7.1

[V2 PATCH 2/3] powerpc: Fix Unaligned Fixed Point Loads and Stores

[Tom]

From: Tom Musta <tommusta@gmail.com>

This patch modifies the unaligned access routines of the sstep.c
module so that it properly reverses the bytes of storage operands
in the little endian kernel kernel.

Signed-off-by: Tom Musta <tommusta@gmail.com>
---
 arch/powerpc/lib/sstep.c |   45 +++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 45 insertions(+), 0 deletions(-)

diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c
index 7bfaa9d..c8743e1 100644
--- a/arch/powerpc/lib/sstep.c
+++ b/arch/powerpc/lib/sstep.c
@@ -212,11 +212,19 @@ static int __kprobes read_mem_unaligned(unsigned long *dest, unsigned long ea,
 {
 	int err;
 	unsigned long x, b, c;
+#ifdef __LITTLE_ENDIAN__
+	int len = nb; /* save a copy of the length for byte reversal */
+#endif
 
 	/* unaligned, do this in pieces */
 	x = 0;
 	for (; nb > 0; nb -= c) {
+#ifdef __LITTLE_ENDIAN__
+		c = 1;
+#endif
+#ifdef __BIG_ENDIAN__
 		c = max_align(ea);
+#endif
 		if (c > nb)
 			c = max_align(nb);
 		err = read_mem_aligned(&b, ea, c);
@@ -225,7 +233,24 @@ static int __kprobes read_mem_unaligned(unsigned long *dest, unsigned long ea,
 		x = (x << (8 * c)) + b;
 		ea += c;
 	}
+#ifdef __LITTLE_ENDIAN__
+	switch (len) {
+	case 2:
+		*dest = byterev_2(x);
+		break;
+	case 4:
+		*dest = byterev_4(x);
+		break;
+#ifdef __powerpc64__
+	case 8:
+		*dest = byterev_8(x);
+		break;
+#endif
+	}
+#endif
+#ifdef __BIG_ENDIAN__
 	*dest = x;
+#endif
 	return 0;
 }
 
@@ -273,9 +298,29 @@ static int __kprobes write_mem_unaligned(unsigned long val, unsigned long ea,
 	int err;
 	unsigned long c;
 
+#ifdef __LITTLE_ENDIAN__
+	switch (nb) {
+	case 2:
+		val = byterev_2(val);
+		break;
+	case 4:
+		val = byterev_4(val);
+		break;
+#ifdef __powerpc64__
+	case 8:
+		val = byterev_8(val);
+		break;
+#endif
+	}
+#endif
 	/* unaligned or little-endian, do this in pieces */
 	for (; nb > 0; nb -= c) {
+#ifdef __LITTLE_ENDIAN__
+		c = 1;
+#endif
+#ifdef __BIG_ENDIAN__
 		c = max_align(ea);
+#endif
 		if (c > nb)
 			c = max_align(nb);
 		err = write_mem_aligned(val >> (nb - c) * 8, ea, c);
-- 
1.7.1

[V2 PATCH 3/3] powerpc: Fix Unaligned LE Floating Point Loads and Stores

[Tom]

From: Tom Musta <tommusta@gmail.com>

This patch addresses unaligned single precision floating point loads
and stores in the single-step code.  The old implementation
improperly treated an 8 byte structure as an array of two 4 byte
words, which is a classic little endian bug.

Signed-off-by: Tom Musta <tommusta@gmail.com>
---
 arch/powerpc/lib/sstep.c |   52 +++++++++++++++++++++++++++++++++++----------
 1 files changed, 40 insertions(+), 12 deletions(-)

diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c
index c8743e1..1cfd150 100644
--- a/arch/powerpc/lib/sstep.c
+++ b/arch/powerpc/lib/sstep.c
@@ -355,22 +355,36 @@ static int __kprobes do_fp_load(int rn, int (*func)(int, unsigned long),
 				struct pt_regs *regs)
 {
 	int err;
-	unsigned long val[sizeof(double) / sizeof(long)];
+	union {
+		double dbl;
+		unsigned long ul[2];
+		struct {
+#ifdef __BIG_ENDIAN__
+			unsigned _pad_;
+			unsigned word;
+#endif
+#ifdef __LITTLE_ENDIAN__
+			unsigned word;
+			unsigned _pad_;
+#endif
+		} single;
+	} data;
 	unsigned long ptr;
 
 	if (!address_ok(regs, ea, nb))
 		return -EFAULT;
 	if ((ea & 3) == 0)
 		return (*func)(rn, ea);
-	ptr = (unsigned long) &val[0];
+	ptr = (unsigned long) &data.ul;
 	if (sizeof(unsigned long) == 8 || nb == 4) {
-		err = read_mem_unaligned(&val[0], ea, nb, regs);
-		ptr += sizeof(unsigned long) - nb;
+		err = read_mem_unaligned(&data.ul[0], ea, nb, regs);
+		if (nb == 4)
+			ptr = (unsigned long)&(data.single.word);
 	} else {
 		/* reading a double on 32-bit */
-		err = read_mem_unaligned(&val[0], ea, 4, regs);
+		err = read_mem_unaligned(&data.ul[0], ea, 4, regs);
 		if (!err)
-			err = read_mem_unaligned(&val[1], ea + 4, 4, regs);
+			err = read_mem_unaligned(&data.ul[1], ea + 4, 4, regs);
 	}
 	if (err)
 		return err;
@@ -382,28 +396,42 @@ static int __kprobes do_fp_store(int rn, int (*func)(int, unsigned long),
 				 struct pt_regs *regs)
 {
 	int err;
-	unsigned long val[sizeof(double) / sizeof(long)];
+	union {
+		double dbl;
+		unsigned long ul[2];
+		struct {
+#ifdef __BIG_ENDIAN__
+			unsigned _pad_;
+			unsigned word;
+#endif
+#ifdef __LITTLE_ENDIAN__
+			unsigned word;
+			unsigned _pad_;
+#endif
+		} single;
+	} data;
 	unsigned long ptr;
 
 	if (!address_ok(regs, ea, nb))
 		return -EFAULT;
 	if ((ea & 3) == 0)
 		return (*func)(rn, ea);
-	ptr = (unsigned long) &val[0];
+	ptr = (unsigned long) &data.ul[0];
 	if (sizeof(unsigned long) == 8 || nb == 4) {
-		ptr += sizeof(unsigned long) - nb;
+		if (nb == 4)
+			ptr = (unsigned long)&(data.single.word);
 		err = (*func)(rn, ptr);
 		if (err)
 			return err;
-		err = write_mem_unaligned(val[0], ea, nb, regs);
+		err = write_mem_unaligned(data.ul[0], ea, nb, regs);
 	} else {
 		/* writing a double on 32-bit */
 		err = (*func)(rn, ptr);
 		if (err)
 			return err;
-		err = write_mem_unaligned(val[0], ea, 4, regs);
+		err = write_mem_unaligned(data.ul[0], ea, 4, regs);
 		if (!err)
-			err = write_mem_unaligned(val[1], ea + 4, 4, regs);
+			err = write_mem_unaligned(data.ul[1], ea + 4, 4, regs);
 	}
 	return err;
 }
-- 
1.7.1

Re: [V2 PATCH 1/3] powerpc: Enable emulate_step In Little Endian Mode

[Paul Mackerras]

On Thu, Oct 31, 2013 at 01:38:56PM -0500, Tom wrote:
> From: Tom Musta <tommusta@gmail.com>
> 
> This patch modifies the endian chicken switch in the single step

"Chicken switch" is IBM jargon, perhaps best avoided where possible in
commit messages.

> emulation code (emulate_step()).  The old (big endian) code bailed
> early if a load or store instruction was to be emulated in little
> endian mode.
> 
> The new code modifies the check and only bails in a cross-endian
> situation (LE mode in a kernel compiled for BE and vice verse).

The patch adds #ifdefs inside code, which is generally frowned upon
in kernel code as it can make the code flow harder to see.  Perhaps
you could do something like

	if ((regs->msr & MSR_LE) != (MSR_KERNEL & MSR_LE))

as an alternative that wouldn't require an #ifdef.  Or, define a
symbol that is 0 in a BE kernel and MSR_LE in a LE kernel, and compare
to that.

Paul.

Re: [V2 PATCH 2/3] powerpc: Fix Unaligned Fixed Point Loads and Stores

[Benjamin Herrenschmidt]

On Thu, 2013-10-31 at 13:38 -0500, Tom wrote:
> From: Tom Musta <tommusta@gmail.com>
> 
> This patch modifies the unaligned access routines of the sstep.c
> module so that it properly reverses the bytes of storage operands
> in the little endian kernel kernel.

Do that patch differ from v1 ? (I already merged v1)

Cheers,
Ben.
 
> Signed-off-by: Tom Musta <tommusta@gmail.com>
> ---
>  arch/powerpc/lib/sstep.c |   45 +++++++++++++++++++++++++++++++++++++++++++++
>  1 files changed, 45 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c
> index 7bfaa9d..c8743e1 100644
> --- a/arch/powerpc/lib/sstep.c
> +++ b/arch/powerpc/lib/sstep.c
> @@ -212,11 +212,19 @@ static int __kprobes read_mem_unaligned(unsigned long *dest, unsigned long ea,
>  {
>  	int err;
>  	unsigned long x, b, c;
> +#ifdef __LITTLE_ENDIAN__
> +	int len = nb; /* save a copy of the length for byte reversal */
> +#endif
>  
>  	/* unaligned, do this in pieces */
>  	x = 0;
>  	for (; nb > 0; nb -= c) {
> +#ifdef __LITTLE_ENDIAN__
> +		c = 1;
> +#endif
> +#ifdef __BIG_ENDIAN__
>  		c = max_align(ea);
> +#endif
>  		if (c > nb)
>  			c = max_align(nb);
>  		err = read_mem_aligned(&b, ea, c);
> @@ -225,7 +233,24 @@ static int __kprobes read_mem_unaligned(unsigned long *dest, unsigned long ea,
>  		x = (x << (8 * c)) + b;
>  		ea += c;
>  	}
> +#ifdef __LITTLE_ENDIAN__
> +	switch (len) {
> +	case 2:
> +		*dest = byterev_2(x);
> +		break;
> +	case 4:
> +		*dest = byterev_4(x);
> +		break;
> +#ifdef __powerpc64__
> +	case 8:
> +		*dest = byterev_8(x);
> +		break;
> +#endif
> +	}
> +#endif
> +#ifdef __BIG_ENDIAN__
>  	*dest = x;
> +#endif
>  	return 0;
>  }
>  
> @@ -273,9 +298,29 @@ static int __kprobes write_mem_unaligned(unsigned long val, unsigned long ea,
>  	int err;
>  	unsigned long c;
>  
> +#ifdef __LITTLE_ENDIAN__
> +	switch (nb) {
> +	case 2:
> +		val = byterev_2(val);
> +		break;
> +	case 4:
> +		val = byterev_4(val);
> +		break;
> +#ifdef __powerpc64__
> +	case 8:
> +		val = byterev_8(val);
> +		break;
> +#endif
> +	}
> +#endif
>  	/* unaligned or little-endian, do this in pieces */
>  	for (; nb > 0; nb -= c) {
> +#ifdef __LITTLE_ENDIAN__
> +		c = 1;
> +#endif
> +#ifdef __BIG_ENDIAN__
>  		c = max_align(ea);
> +#endif
>  		if (c > nb)
>  			c = max_align(nb);
>  		err = write_mem_aligned(val >> (nb - c) * 8, ea, c);

Re: [V2 PATCH 3/3] powerpc: Fix Unaligned LE Floating Point Loads and Stores

[Benjamin Herrenschmidt]

On Thu, 2013-10-31 at 13:38 -0500, Tom wrote:
> From: Tom Musta <tommusta@gmail.com>
> 
> This patch addresses unaligned single precision floating point loads
> and stores in the single-step code.  The old implementation
> improperly treated an 8 byte structure as an array of two 4 byte
> words, which is a classic little endian bug.

Do that patch differ from v1 ? I also already merged v1 of this
one (the only one I didn't merge is the emulate_step one)

Cheers,
Ben.

> Signed-off-by: Tom Musta <tommusta@gmail.com>
> ---
>  arch/powerpc/lib/sstep.c |   52 +++++++++++++++++++++++++++++++++++----------
>  1 files changed, 40 insertions(+), 12 deletions(-)
> 
> diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c
> index c8743e1..1cfd150 100644
> --- a/arch/powerpc/lib/sstep.c
> +++ b/arch/powerpc/lib/sstep.c
> @@ -355,22 +355,36 @@ static int __kprobes do_fp_load(int rn, int (*func)(int, unsigned long),
>  				struct pt_regs *regs)
>  {
>  	int err;
> -	unsigned long val[sizeof(double) / sizeof(long)];
> +	union {
> +		double dbl;
> +		unsigned long ul[2];
> +		struct {
> +#ifdef __BIG_ENDIAN__
> +			unsigned _pad_;
> +			unsigned word;
> +#endif
> +#ifdef __LITTLE_ENDIAN__
> +			unsigned word;
> +			unsigned _pad_;
> +#endif
> +		} single;
> +	} data;
>  	unsigned long ptr;
>  
>  	if (!address_ok(regs, ea, nb))
>  		return -EFAULT;
>  	if ((ea & 3) == 0)
>  		return (*func)(rn, ea);
> -	ptr = (unsigned long) &val[0];
> +	ptr = (unsigned long) &data.ul;
>  	if (sizeof(unsigned long) == 8 || nb == 4) {
> -		err = read_mem_unaligned(&val[0], ea, nb, regs);
> -		ptr += sizeof(unsigned long) - nb;
> +		err = read_mem_unaligned(&data.ul[0], ea, nb, regs);
> +		if (nb == 4)
> +			ptr = (unsigned long)&(data.single.word);
>  	} else {
>  		/* reading a double on 32-bit */
> -		err = read_mem_unaligned(&val[0], ea, 4, regs);
> +		err = read_mem_unaligned(&data.ul[0], ea, 4, regs);
>  		if (!err)
> -			err = read_mem_unaligned(&val[1], ea + 4, 4, regs);
> +			err = read_mem_unaligned(&data.ul[1], ea + 4, 4, regs);
>  	}
>  	if (err)
>  		return err;
> @@ -382,28 +396,42 @@ static int __kprobes do_fp_store(int rn, int (*func)(int, unsigned long),
>  				 struct pt_regs *regs)
>  {
>  	int err;
> -	unsigned long val[sizeof(double) / sizeof(long)];
> +	union {
> +		double dbl;
> +		unsigned long ul[2];
> +		struct {
> +#ifdef __BIG_ENDIAN__
> +			unsigned _pad_;
> +			unsigned word;
> +#endif
> +#ifdef __LITTLE_ENDIAN__
> +			unsigned word;
> +			unsigned _pad_;
> +#endif
> +		} single;
> +	} data;
>  	unsigned long ptr;
>  
>  	if (!address_ok(regs, ea, nb))
>  		return -EFAULT;
>  	if ((ea & 3) == 0)
>  		return (*func)(rn, ea);
> -	ptr = (unsigned long) &val[0];
> +	ptr = (unsigned long) &data.ul[0];
>  	if (sizeof(unsigned long) == 8 || nb == 4) {
> -		ptr += sizeof(unsigned long) - nb;
> +		if (nb == 4)
> +			ptr = (unsigned long)&(data.single.word);
>  		err = (*func)(rn, ptr);
>  		if (err)
>  			return err;
> -		err = write_mem_unaligned(val[0], ea, nb, regs);
> +		err = write_mem_unaligned(data.ul[0], ea, nb, regs);
>  	} else {
>  		/* writing a double on 32-bit */
>  		err = (*func)(rn, ptr);
>  		if (err)
>  			return err;
> -		err = write_mem_unaligned(val[0], ea, 4, regs);
> +		err = write_mem_unaligned(data.ul[0], ea, 4, regs);
>  		if (!err)
> -			err = write_mem_unaligned(val[1], ea + 4, 4, regs);
> +			err = write_mem_unaligned(data.ul[1], ea + 4, 4, regs);
>  	}
>  	return err;
>  }

Re: [V2 PATCH 2/3] powerpc: Fix Unaligned Fixed Point Loads and Stores

[Paul Mackerras]

On Thu, Oct 31, 2013 at 01:38:57PM -0500, Tom wrote:
> From: Tom Musta <tommusta@gmail.com>
> 
> This patch modifies the unaligned access routines of the sstep.c
> module so that it properly reverses the bytes of storage operands
> in the little endian kernel kernel.

This has rather a lot of #ifdefs inside function definitions, and for
little-endian it does the unaligned accesses one byte at a time.  You
could avoid all the #ifdefs if you define the combining function in an
endian-dependant way and make read_mem_unaligned look something like
this:

#ifdef __LITTLE_ENDIAN__
#define combine_pieces(x, b, c, nd)	((x) + ((b) << (8 * (nd))))
#else
#define combine_pieces(x, b, c, nd)	(((x) << (8 * (c))) + (b))
#endif

static int __kprobes read_mem_unaligned(unsigned long *dest, unsigned long ea,
					int nb, struct pt_regs *regs)
{
	int err;
	int nd;
	unsigned long x, b, c;

	/* unaligned, do this in pieces */
	x = 0;
	for (nd = 0; nd < nb; nd += c) {
		c = max_align(ea);
		if (c > nb - nd)
			c = max_align(nb - nd);
		err = read_mem_aligned(&b, ea, c);
		if (err)
			return err;
		x = combine_pieces(x, b, c, nd);
		ea += c;
	}
	*dest = x;
	return 0;
}

and do something analogous for write_mem_unaligned().

Paul.

Re: [V2 PATCH 3/3] powerpc: Fix Unaligned LE Floating Point Loads and Stores

[Tom Musta]

On 11/3/2013 8:34 PM, Benjamin Herrenschmidt wrote:
> On Thu, 2013-10-31 at 13:38 -0500, Tom wrote:
>> From: Tom Musta <tommusta@gmail.com>
>>
>> This patch addresses unaligned single precision floating point loads
>> and stores in the single-step code.  The old implementation
>> improperly treated an 8 byte structure as an array of two 4 byte
>> words, which is a classic little endian bug.
> 
> Do that patch differ from v1 ? I also already merged v1 of this
> one (the only one I didn't merge is the emulate_step one)
> 
> Cheers,
> Ben.
>

Ben:  Only patch 1/3 (Enable emulate_step in Little Endian Mode) differs in V2.

Re: [V2 PATCH 3/3] powerpc: Fix Unaligned LE Floating Point Loads and Stores

[Paul Mackerras]

On Thu, Oct 31, 2013 at 01:38:58PM -0500, Tom wrote:
> From: Tom Musta <tommusta@gmail.com>
> 
> This patch addresses unaligned single precision floating point loads
> and stores in the single-step code.  The old implementation
> improperly treated an 8 byte structure as an array of two 4 byte
> words, which is a classic little endian bug.
> 
> Signed-off-by: Tom Musta <tommusta@gmail.com>
> ---
>  arch/powerpc/lib/sstep.c |   52 +++++++++++++++++++++++++++++++++++----------
>  1 files changed, 40 insertions(+), 12 deletions(-)
> 
> diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c
> index c8743e1..1cfd150 100644
> --- a/arch/powerpc/lib/sstep.c
> +++ b/arch/powerpc/lib/sstep.c
> @@ -355,22 +355,36 @@ static int __kprobes do_fp_load(int rn, int (*func)(int, unsigned long),
>  				struct pt_regs *regs)
>  {
>  	int err;
> -	unsigned long val[sizeof(double) / sizeof(long)];
> +	union {
> +		double dbl;
> +		unsigned long ul[2];
> +		struct {
> +#ifdef __BIG_ENDIAN__
> +			unsigned _pad_;
> +			unsigned word;
> +#endif
> +#ifdef __LITTLE_ENDIAN__
> +			unsigned word;
> +			unsigned _pad_;
> +#endif
> +		} single;
> +	} data;
>  	unsigned long ptr;
>  
>  	if (!address_ok(regs, ea, nb))
>  		return -EFAULT;
>  	if ((ea & 3) == 0)
>  		return (*func)(rn, ea);
> -	ptr = (unsigned long) &val[0];
> +	ptr = (unsigned long) &data.ul;
>  	if (sizeof(unsigned long) == 8 || nb == 4) {
> -		err = read_mem_unaligned(&val[0], ea, nb, regs);
> -		ptr += sizeof(unsigned long) - nb;
> +		err = read_mem_unaligned(&data.ul[0], ea, nb, regs);
> +		if (nb == 4)
> +			ptr = (unsigned long)&(data.single.word);
>  	} else {
>  		/* reading a double on 32-bit */
> -		err = read_mem_unaligned(&val[0], ea, 4, regs);
> +		err = read_mem_unaligned(&data.ul[0], ea, 4, regs);
>  		if (!err)
> -			err = read_mem_unaligned(&val[1], ea + 4, 4, regs);
> +			err = read_mem_unaligned(&data.ul[1], ea + 4, 4, regs);

This breaks 32-bit big-endian (as well as making the code longer and
more complex).

In fact, to make this work for 64-bit little-endian, all you really
needed to do was ifdef out the statement:

		ptr += sizeof(unsigned long) - nb;

Paul.

Re: [V2 PATCH 3/3] powerpc: Fix Unaligned LE Floating Point Loads and Stores

[Paul Mackerras]

On Wed, Dec 11, 2013 at 02:54:40PM +1100, Paul Mackerras wrote:
> On Thu, Oct 31, 2013 at 01:38:58PM -0500, Tom wrote:
> > From: Tom Musta <tommusta@gmail.com>
> > 
> > This patch addresses unaligned single precision floating point loads
> > and stores in the single-step code.  The old implementation
> > improperly treated an 8 byte structure as an array of two 4 byte
> > words, which is a classic little endian bug.
> > 
> > Signed-off-by: Tom Musta <tommusta@gmail.com>
> > ---
> >  arch/powerpc/lib/sstep.c |   52 +++++++++++++++++++++++++++++++++++----------
> >  1 files changed, 40 insertions(+), 12 deletions(-)
> > 
> > diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c
> > index c8743e1..1cfd150 100644
> > --- a/arch/powerpc/lib/sstep.c
> > +++ b/arch/powerpc/lib/sstep.c
> > @@ -355,22 +355,36 @@ static int __kprobes do_fp_load(int rn, int (*func)(int, unsigned long),
> >  				struct pt_regs *regs)
> >  {
> >  	int err;
> > -	unsigned long val[sizeof(double) / sizeof(long)];
> > +	union {
> > +		double dbl;
> > +		unsigned long ul[2];
> > +		struct {
> > +#ifdef __BIG_ENDIAN__
> > +			unsigned _pad_;
> > +			unsigned word;
> > +#endif
> > +#ifdef __LITTLE_ENDIAN__
> > +			unsigned word;
> > +			unsigned _pad_;
> > +#endif
> > +		} single;
> > +	} data;
> >  	unsigned long ptr;
> >  
> >  	if (!address_ok(regs, ea, nb))
> >  		return -EFAULT;
> >  	if ((ea & 3) == 0)
> >  		return (*func)(rn, ea);
> > -	ptr = (unsigned long) &val[0];
> > +	ptr = (unsigned long) &data.ul;
> >  	if (sizeof(unsigned long) == 8 || nb == 4) {
> > -		err = read_mem_unaligned(&val[0], ea, nb, regs);
> > -		ptr += sizeof(unsigned long) - nb;
> > +		err = read_mem_unaligned(&data.ul[0], ea, nb, regs);
> > +		if (nb == 4)
> > +			ptr = (unsigned long)&(data.single.word);
> >  	} else {
> >  		/* reading a double on 32-bit */
> > -		err = read_mem_unaligned(&val[0], ea, 4, regs);
> > +		err = read_mem_unaligned(&data.ul[0], ea, 4, regs);
> >  		if (!err)
> > -			err = read_mem_unaligned(&val[1], ea + 4, 4, regs);
> > +			err = read_mem_unaligned(&data.ul[1], ea + 4, 4, regs);
> 
> This breaks 32-bit big-endian (as well as making the code longer and
> more complex).

And in fact none of this code will get executed in little-endian mode
anyway, since we still have this in the middle of emulate_step():

	/*
	 * Following cases are for loads and stores, so bail out
	 * if we're in little-endian mode.
	 */
	if (regs->msr & MSR_LE)
		return 0;

Paul.

Re: [V2 PATCH 3/3] powerpc: Fix Unaligned LE Floating Point Loads and Stores

[Tom Musta]

On 12/10/2013 10:57 PM, Paul Mackerras wrote:
> On Wed, Dec 11, 2013 at 02:54:40PM +1100, Paul Mackerras wrote:

>> This breaks 32-bit big-endian (as well as making the code longer and
>> more complex).
> 
> And in fact none of this code will get executed in little-endian mode
> anyway, since we still have this in the middle of emulate_step():
> 
> 	/*
> 	 * Following cases are for loads and stores, so bail out
> 	 * if we're in little-endian mode.
> 	 */
> 	if (regs->msr & MSR_LE)
> 		return 0;
> 
> Paul.
> 

See patch 1/3 to explain how it becomes relevant in LE.

I will take another look at the change.

Re: [V2 PATCH 3/3] powerpc: Fix Unaligned LE Floating Point Loads and Stores

[Tom Musta]

On 12/12/2013 9:08 AM, Tom Musta wrote:
> On 12/10/2013 10:57 PM, Paul Mackerras wrote:
>> On Wed, Dec 11, 2013 at 02:54:40PM +1100, Paul Mackerras wrote:
> 
>>> This breaks 32-bit big-endian (as well as making the code longer and
>>> more complex).
>>
>> And in fact none of this code will get executed in little-endian mode
>> anyway, since we still have this in the middle of emulate_step():
>>
>> 	/*
>> 	 * Following cases are for loads and stores, so bail out
>> 	 * if we're in little-endian mode.
>> 	 */
>> 	if (regs->msr & MSR_LE)
>> 		return 0;
>>
>> Paul.
>>
> 
> See patch 1/3 to explain how it becomes relevant in LE.
> 
> I will take another look at the change.
> 

It appears that patch 1/3 never got picked up, even though I thought Ben & I
had worked through that.

And I agree that the code could be simpler.  I will work up a patch to address
these two issues.

Re: [V2 PATCH 3/3] powerpc: Fix Unaligned LE Floating Point Loads and Stores

[Paul Mackerras]

On Thu, Dec 12, 2013 at 02:33:36PM -0600, Tom Musta wrote:
> On 12/12/2013 9:08 AM, Tom Musta wrote:
> > On 12/10/2013 10:57 PM, Paul Mackerras wrote:
> >> On Wed, Dec 11, 2013 at 02:54:40PM +1100, Paul Mackerras wrote:
> > 
> >>> This breaks 32-bit big-endian (as well as making the code longer and
> >>> more complex).
> >>
> >> And in fact none of this code will get executed in little-endian mode
> >> anyway, since we still have this in the middle of emulate_step():
> >>
> >> 	/*
> >> 	 * Following cases are for loads and stores, so bail out
> >> 	 * if we're in little-endian mode.
> >> 	 */
> >> 	if (regs->msr & MSR_LE)
> >> 		return 0;
> >>
> >> Paul.
> >>
> > 
> > See patch 1/3 to explain how it becomes relevant in LE.
> > 
> > I will take another look at the change.
> > 
> 
> It appears that patch 1/3 never got picked up, even though I thought Ben & I
> had worked through that.
> 
> And I agree that the code could be simpler.  I will work up a patch to address
> these two issues.

The other thing that's important for us to know is how you are testing
these changes.  For something like this I'd like to see a description
of the tests you have done in the commit message.

I have been hacking on sstep.c pretty heavily myself recently, so we
will need to coordinate on the changes.

Paul.