Ignore read-only mappings of ELF files at non-fixed addresses.

Such a mapping is likely part of some transient operation by the dynamic
linker, such as parsing the ELF header while loading an object.  If the
address of that mapping is recycled it may trigger disposal of the
corresponding debug info since it overlaps with a new mapping.  The
result of this is that valgrind is unable to hook malloc() calls in the
client, so memcheck reports zero heap usage.

Fix the problem by ignoring read-only non-fixed ELF file mappings.  This
might not be the best way to address the problem, but it seems to work.
Older versions of valgrind ignored read-only mappings completely.

coregrind/m_aspacemgr/aspacemgr-linux.c

@@ -1493,7 +1493,8 @@ static void init_nsegment ( /*OUT*/NSegment* seg )
    seg->mode     = 0;
    seg->offset   = 0;
    seg->fnIdx    = -1;
-   seg->hasR = seg->hasW = seg->hasX = seg->hasT = seg->isCH = False;
+   seg->hasR     = seg->hasW = seg->hasX = seg->hasT
+                 = seg->isCH = seg->isFF = False;
 }
 
 /* Make an NSegment which holds a reservation. */
@@ -2211,6 +2212,7 @@ VG_(am_notify_client_mmap)( Addr a, SizeT len, UInt prot, UInt flags,
       if (ML_(am_resolve_filename)(fd, buf, VKI_PATH_MAX)) {
          seg.fnIdx = ML_(am_allocate_segname)( buf );
       }
+      seg.isFF = (flags & VKI_MAP_FIXED);
    }
    add_segment( &seg );
    AM_SANITY_CHECK;
@@ -2452,6 +2454,7 @@ SysRes VG_(am_mmap_named_file_fixed_client_flags)
    } else if (ML_(am_resolve_filename)(fd, buf, VKI_PATH_MAX)) {
       seg.fnIdx = ML_(am_allocate_segname)( buf );
    }
+   seg.isFF = (flags & VKI_MAP_FIXED);
    add_segment( &seg );
 
    AM_SANITY_CHECK;
@@ -2762,6 +2765,7 @@ static SysRes VG_(am_mmap_file_float_valgrind_flags) ( SizeT length, UInt prot,
    if (ML_(am_resolve_filename)(fd, buf, VKI_PATH_MAX)) {
       seg.fnIdx = ML_(am_allocate_segname)( buf );
    }
+   seg.isFF = (flags & VKI_MAP_FIXED);
    add_segment( &seg );
 
    AM_SANITY_CHECK;

coregrind/m_debuginfo/debuginfo.c

@@ -1205,6 +1205,10 @@ ULong VG_(di_notify_mmap)( Addr a, Bool allow_SkFileV, Int use_fd )
    /* Ignore mappings with permissions we can't possibly be interested in. */
    if (!(is_rx_map || is_rw_map || is_ro_map))
       return 0;
+   /* Ignore non-fixed read-only mappings.  The dynamic linker may be
+    * mapping something for its own transient purposes. */
+   if (!seg->isFF && is_ro_map)
+      return 0;
 
    /* Peer at the first few bytes of the file, to see if it is an ELF */
    /* object file. Ignore the file if we do not have read permission. */

include/pub_tool_aspacemgr.h

@@ -112,6 +112,7 @@ typedef
       Bool    hasT;     // True --> translations have (or MAY have)
                         // been taken from this segment
       Bool    isCH;     // True --> is client heap (SkAnonC ONLY)
+      Bool    isFF;     // True --> is a fixed file mapping
    }
    NSegment;