bionic: Report linker relocation address to gdb

GDB needs the runtime linker's base address in order to
locate the latter's ".text" and ".plt" sections, for the
purpose of detecting solib trampolines.  It also can
potentially use this to calculate the relocated address
of rtld_db_dlactivity.

Bug: http://code.google.com/p/android/issues/detail?id=34856
Change-Id: I63d3e7ae4e20a684ceb25967f2241e7d58dd685d
Signed-off-by: Ryan V. Bissell <ryan@bissell.org>

1 files changed, 8 insertions, 7 deletions

diff --git a/linker/linker.c b/linker/linker.c
index 54fb22b..c5a8127 100644
--- a/linker/linker.c
+++ b/linker/linker.c
@@ -1640,7 +1640,7 @@ static void parse_preloads(const char *path, char *delim)
  * fixed it's own GOT. It is safe to make references to externs
  * and other non-local data at this point.
  */
-static unsigned __linker_init_post_relocation(unsigned **elfdata)
+static unsigned __linker_init_post_relocation(unsigned **elfdata, unsigned linker_base)
 {
     static soinfo linker_soinfo;
 
@@ -1730,15 +1730,16 @@ sanitize:
     _r_debug.r_map = map;
     r_debug_tail = map;
 
-        /* gdb expects the linker to be in the debug shared object list,
-         * and we need to make sure that the reported load address is zero.
-         * Without this, gdb gets the wrong idea of where rtld_db_dlactivity()
-         * is.  Don't use soinfo_alloc(), because the linker shouldn't
+        /* gdb expects the linker to be in the debug shared object list.
+         * Without this, gdb has trouble locating the linker's ".text"
+         * and ".plt" sections. Gdb could also potentially use this to
+         * relocate the offset of our exported 'rtld_db_dlactivity' symbol.
+         * Don't use soinfo_alloc(), because the linker shouldn't
          * be on the soinfo list.
          */
     strlcpy((char*) linker_soinfo.name, "/system/bin/linker", sizeof linker_soinfo.name);
     linker_soinfo.flags = 0;
-    linker_soinfo.base = 0;     // This is the important part; must be zero.
+    linker_soinfo.base = linker_base;
     insert_soinfo_into_debug_map(&linker_soinfo);
 
         /* extract information passed from the kernel */
@@ -1930,5 +1931,5 @@ unsigned __linker_init(unsigned **elfdata) {
 
     // We have successfully fixed our own relocations. It's safe to run
     // the main part of the linker now.
-    return __linker_init_post_relocation(elfdata);
+    return __linker_init_post_relocation(elfdata, linker_addr);
 }