Re: [PATCH v7 45/50] drivers/of: Avoid recursively calling unflatten_dt_node()

On Wed, Nov 4, 2015 at 5:07 PM, Rob Herring [off-list ref] wrote:

On Wed, Nov 4, 2015 at 7:12 AM, Gavin Shan [off-list ref] wrote:

quoted

In current implementation, unflatten_dt_node() is called recursively
to unflatten device nodes in FDT blob. It's stress to limited stack
capacity.

Did you actually hit a problem?

Now we have a max depth of 64. Seems like that should be plenty... Any
idea how this compares to when we run out of stack space?

FWIW, on arm64:

drivers/of/fdt.c:443:1: warning: the frame size of 1136 bytes is
larger than 1024 bytes [-Wframe-larger-than=]

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Function populate_node() is used to unflatten FDT blob to device
tree. It supports maximal 64 level of device nodes. There is one
array @fpsizes[64] tracking the full name length of last unflattened
device node in the corresponding level (index of element in the
array - 1). Build warning is seen with CONFIG_FRAME_WARN=1024 like
below on ARM64 as Geert reported. The issue can be reproduced on
PPC64 as well.

  $ make drivers/of/fdt.o
  drivers/of/fdt.c:443:1: warning: the frame size of 1136 bytes is \
  larger than 1024 bytes [-Wframe-larger-than=]

This changes the data type of @fpsizes[i] from "unsigned long" to
"unsigned int" to avoid the build warning. The return value type
of populate_node() and its @fpsize argument is adjusted accordingly.
With this applied, 256 bytes saved from the stack frame on ARM64 and
PPC64 platforms and the above warning isn't seen.

Fixes: 9ffa9eb ("drivers/of: Avoid recursively calling unflatten_dt_node()")
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Gavin Shan <redacted>
---
 drivers/of/fdt.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
index c95054c..34344a8 100644
--- a/drivers/of/fdt.c
+++ b/drivers/of/fdt.c

@@ -264,13 +264,13 @@ static void populate_properties(const void *blob,
 		*pprev = NULL;
 }
 
-static unsigned long populate_node(const void *blob,
-				   int offset,
-				   void **mem,
-				   struct device_node *dad,
-				   unsigned long fpsize,
-				   struct device_node **pnp,
-				   bool dryrun)
+static unsigned int populate_node(const void *blob,
+				  int offset,
+				  void **mem,
+				  struct device_node *dad,
+				  unsigned int fpsize,
+				  struct device_node **pnp,
+				  bool dryrun)
 {
 	struct device_node *np;
 	const char *pathp;

@@ -397,7 +397,7 @@ static int unflatten_dt_nodes(const void *blob,
 	struct device_node *root;
 	int offset = 0, depth = 0;
 #define FDT_MAX_DEPTH	64
-	unsigned long fpsizes[FDT_MAX_DEPTH];
+	unsigned int fpsizes[FDT_MAX_DEPTH];
 	struct device_node *nps[FDT_MAX_DEPTH];
 	void *base = mem;
 	bool dryrun = !base;

-- 
2.1.0

On Fri, May 13, 2016 at 09:31:39PM +1000, Gavin Shan wrote:

Function populate_node() is used to unflatten FDT blob to device
tree. It supports maximal 64 level of device nodes. There is one
array @fpsizes[64] tracking the full name length of last unflattened
device node in the corresponding level (index of element in the
array - 1). Build warning is seen with CONFIG_FRAME_WARN=1024 like
below on ARM64 as Geert reported. The issue can be reproduced on
PPC64 as well.

  $ make drivers/of/fdt.o
  drivers/of/fdt.c:443:1: warning: the frame size of 1136 bytes is \
  larger than 1024 bytes [-Wframe-larger-than=]

This changes the data type of @fpsizes[i] from "unsigned long" to
"unsigned int" to avoid the build warning. The return value type
of populate_node() and its @fpsize argument is adjusted accordingly.
With this applied, 256 bytes saved from the stack frame on ARM64 and
PPC64 platforms and the above warning isn't seen.

Fixes: 9ffa9eb ("drivers/of: Avoid recursively calling unflatten_dt_node()")
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Gavin Shan <redacted>
---
 drivers/of/fdt.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

Applied, thanks.

Rob