powerpc: Provide a suitable AT_PLATFORM value

The glibc folks want to use AT_PLATFORM to select between possible
alternative versions of shared libraries.  This commit makes the kernel
supply an AT_PLATFORM string that indicates what class of processor
we are running on.  Processors with the same set of user-level
instructions and roughly the same instruction scheduling characteristics
are given the same AT_PLATFORM value; for example, 821, 823 and 860
are all reported as "ppc823", and 7447, 7447A, 7448, 7450, 7451, 7455
are all called "ppc7450".

The intention is that the AT_PLATFORM values match the values that
gcc accepts for the -mcpu= option.  For values which are numeric
(e.g. -mcpu=750), "ppc" has been prepended.

This also adds a PPC_FEATURE_BOOKE bit to the AT_HWCAP value and sets
it for the 440 family and the Freescale 85xx family.
Signed-off-by: Paul Mackerras <paulus@samba.org>

include/asm-powerpc/cputable.h

@@ -19,6 +19,7 @@
 #define PPC_FEATURE_POWER5		0x00040000
 #define PPC_FEATURE_POWER5_PLUS		0x00020000
 #define PPC_FEATURE_CELL		0x00010000
+#define PPC_FEATURE_BOOKE		0x00008000
 
 #ifdef __KERNEL__
 #ifndef __ASSEMBLY__
@@ -64,6 +65,9 @@ struct cpu_spec {
 
 	/* Processor specific oprofile operations */
 	enum powerpc_oprofile_type oprofile_type;
+
+	/* Name of processor class, for the ELF AT_PLATFORM entry */
+	char		*platform;
 };
 
 extern struct cpu_spec		*cur_cpu_spec;

include/asm-powerpc/elf.h

@@ -221,20 +221,18 @@ extern int dump_task_fpu(struct task_struct *, elf_fpregset_t *);
    instruction set this cpu supports.  This could be done in userspace,
    but it's not easy, and we've already done it here.  */
 # define ELF_HWCAP	(cur_cpu_spec->cpu_user_features)
-#ifdef __powerpc64__
-# define ELF_PLAT_INIT(_r, load_addr)	do {	\
-	_r->gpr[2] = load_addr; 		\
-} while (0)
-#endif /* __powerpc64__ */
 
 /* This yields a string that ld.so will use to load implementation
    specific libraries for optimization.  This is more specific in
-   intent than poking at uname or /proc/cpuinfo.
+   intent than poking at uname or /proc/cpuinfo.  */
 
-   For the moment, we have only optimizations for the Intel generations,
-   but that could change... */
+#define ELF_PLATFORM	(cur_cpu_spec->platform)
 
-#define ELF_PLATFORM	(NULL)
+#ifdef __powerpc64__
+# define ELF_PLAT_INIT(_r, load_addr)	do {	\
+	_r->gpr[2] = load_addr; 		\
+} while (0)
+#endif /* __powerpc64__ */
 
 #ifdef __KERNEL__