ELF loader support for auxvec base platform string

Some IBM POWER-based platforms have the ability to run in a
mode which mostly appears to the OS as a different processor from the
actual hardware.  For example, a Power6 system may appear to be a
Power5+, which makes the AT_PLATFORM value "power5+".  This means that
programs are restricted to the ISA supported by Power5+;
Power6-specific instructions are treated as illegal.

However, some applications (virtual machines, optimized libraries) can
benefit from knowledge of the underlying CPU model.  A new aux vector
entry, AT_BASE_PLATFORM, will denote the actual hardware.  For
example, on a Power6 system in Power5+ compatibility mode, AT_PLATFORM
will be "power5+" and AT_BASE_PLATFORM will be "power6".  The idea is
that AT_PLATFORM indicates the instruction set supported, while
AT_BASE_PLATFORM indicates the underlying microarchitecture.

If the architecture has defined ELF_BASE_PLATFORM, copy that value to
the user stack in the same manner as ELF_PLATFORM.

Signed-off-by: Nathan Lynch <ntl@pobox.com>
Acked-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 5 insertions, 1 deletions

diff --git a/include/linux/auxvec.h b/include/linux/auxvec.h
index 0da17d14fd13..d7afa9dd6635 100644
--- a/include/linux/auxvec.h
+++ b/include/linux/auxvec.h
@@ -26,9 +26,13 @@
 
 #define AT_SECURE 23   /* secure mode boolean */
 
+#define AT_BASE_PLATFORM 24     /* string identifying real platform, may
+                                 * differ from AT_PLATFORM. */
+
 #define AT_EXECFN  31   /* filename of program */
+
 #ifdef __KERNEL__
-#define AT_VECTOR_SIZE_BASE 17 /* NEW_AUX_ENT entries in auxiliary table */
+#define AT_VECTOR_SIZE_BASE 18 /* NEW_AUX_ENT entries in auxiliary table */
   /* number of "#define AT_.*" above, minus {AT_NULL, AT_IGNORE, AT_NOTELF} */
 #endif