[PATCH] Initialise the machine specific part of rtld bootstrap map

[Matthew Fortune <Matthew dot Fortune at imgtec dot com>]

Hi,

This is a long delayed follow up to a patch by Sandra:
https://sourceware.org/ml/libc-alpha/2015-03/msg00704.html

I've reimplemented it to be MIPS specific and lightweight to just
initialise the necessary fields. Tested using mips64el-linux-gnu (n64)
with some manual verification to make sure I saw the loader failures if I
initialised the fpabi to an illegal value instead of zero.

MIPS requires two fields in the machine specific part of the link map to
be zero initialised.  This is natually achieved except when the map is
allocated on the stack.  The only map allocated on the stack is the
bootstrap map which is often the first use of the stack space following
kernel allocation and is therefore zero.  However, if rtld is invoked
such that the stack has already been used then there may be non-zero
data and ABI checks which use the affected fields will spuriously fail.

	* elf/rtld.c (_dl_start) [ifndef DONT_USE_BOOTSTRAP_MAP]: Call
	ELF_MACHINE_INIT_MAP.
	* sysdeps/mips/dl-machine.h (ELF_MACHINE_INIT_MAP): Define macro.

Thanks,
Matthew

---
 elf/rtld.c                | 3 +++
 sysdeps/mips/dl-machine.h | 7 +++++++
 2 files changed, 10 insertions(+)

diff --git a/elf/rtld.c b/elf/rtld.c
index 647661c..31539a4 100644
--- a/elf/rtld.c
+++ b/elf/rtld.c
@@ -364,6 +364,9 @@ _dl_start (void *arg)
      do not have to use the temporary bootstrap_map.  Global variables
      are initialized to zero by default.  */
 #ifndef DONT_USE_BOOTSTRAP_MAP
+# ifdef ELF_MACHINE_INIT_MAP
+  ELF_MACHINE_INIT_MAP (bootstrap_map);
+# endif
 # ifdef HAVE_BUILTIN_MEMSET
   __builtin_memset (bootstrap_map.l_info, '\0', sizeof (bootstrap_map.l_info));
 # else
diff --git a/sysdeps/mips/dl-machine.h b/sysdeps/mips/dl-machine.h
index 8c0b40e..d929477 100644
--- a/sysdeps/mips/dl-machine.h
+++ b/sysdeps/mips/dl-machine.h
@@ -93,6 +93,13 @@ do { if ((l)->l_info[DT_MIPS (RLD_MAP_REL)]) \
 # define ELF_MACHINE_NAN2008 0
 #endif
 
+/* Initialise the machine dependent parts of a map.  This is not normally
+   required unless the map is allocated on the stack.  */
+#define ELF_MACHINE_INIT_MAP(MAP) \
+do { (MAP)->l_mach.fpabi = 0; \
+     (MAP)->l_mach.odd_spreg = 0; \
+   } while (0)
+
 /* Return nonzero iff ELF header is compatible with the running host.  */
 static inline int __attribute_used__
 elf_machine_matches_host (const ElfW(Ehdr) *ehdr)
-- 
2.2.1