Re: [PATCH] lib/test_hexdump: fix failure on big endian cpu

Le 08/08/2018 à 09:25, Michael Ellerman a écrit :

Christophe Leroy [off-list ref] writes:

quoted

diff --git a/lib/test_hexdump.c b/lib/test_hexdump.c
index 3f415d8101f3..626f580b4ff7 100644
--- a/lib/test_hexdump.c
+++ b/lib/test_hexdump.c

@@ -32,16 +32,33 @@ static const char * const test_data_2_le[] __initconst = {
  	"d14c", "9919", "b143", "0caf",
  };
  
+static const char * const test_data_2_be[] __initconst = {
+	"be32", "db7b", "0a18", "93b2",
+	"70ba", "c424", "7d83", "349b",
+	"a69c", "31ad", "9c0f", "ace9",
+	"4cd1", "1999", "43b1", "af0c",
+};
+
  static const char * const test_data_4_le[] __initconst = {
  	"7bdb32be", "b293180a", "24c4ba70", "9b34837d",
  	"ad319ca6", "e9ac0f9c", "9919d14c", "0cafb143",
  };
  
+static const char * const test_data_4_be[] __initconst = {
+	"be32db7b", "0a1893b2", "70bac424", "7d83349b",
+	"a69c31ad", "9c0face9", "4cd11999", "43b1af0c",
+};
+

Is there a reason we can't do it all at compile time?

Codyingstyle suggests to use IS_ENABLED() as much as possible.
I checked symbols inside resulting vmlinux, only the BE ones are there 
so it has
the same effect as an #ifdef

Extract from Documentation/process/codying-style.rst:

Within code, where possible, use the IS_ENABLED macro to convert a Kconfig
symbol into a C boolean expression, and use it in a normal C conditional:

.. code-block:: c

	if (IS_ENABLED(CONFIG_SOMETHING)) {
		...
	}

The compiler will constant-fold the conditional away, and include or exclude
the block of code just as with an #ifdef, so this will not add any runtime
overhead.  However, this approach still allows the C compiler to see the 
code
inside the block, and check it for correctness (syntax, types, symbol
references, etc).  Thus, you still have to use an #ifdef if the code 
inside the
block references symbols that will not exist if the condition is not met.

Christophe

eg:

static const char * const test_data_4[] __initconst = {
#ifdef CONFIG_CPU_LITTLE_ENDIAN
	"7bdb32be", "b293180a", "24c4ba70", "9b34837d",
	"ad319ca6", "e9ac0f9c", "9919d14c", "0cafb143",
#else
	"be32db7b", "0a1893b2", "70bac424", "7d83349b",
	"a69c31ad", "9c0face9", "4cd11999", "43b1af0c",
#endif
};


cheers