The value of AT_BASE should be the offset between where the ELF inter…

…preter

expected to be loaded (as expressed in the ELF headers) and where it was
actually loaded, and not (as valgrind was doing) the absolute value of the
load address for the interpreter.

Note that when prelink is not in use the two are normally the same, as the
intpreter (like all shared libraries) is normally linked with a zero load
address. When prelinked that is no longer true.

With that fixed, the hack to patch out AT_BASE to avoid confusing gdb on
systems where prelink is in use is no longer needed.

Fixes BZ#329612


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13768 a5019735-40e9-0310-863c-91ae7b9d1cf9

NEWS

@@ -40,6 +40,7 @@ where XXXXXX is the bug number as listed below.
 328205  Implement additional Xen hypercalls
 328455  s390x: SIGILL after emitting wrong register pair for ldxbr
 328711  valgrind.1 manpage "memcheck options" section is badly generated
+329612  Incorrect handling of AT_BASE for image execution 
 
 Release 3.9.0 (31 October 2013)
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

coregrind/m_initimg/initimg-linux.c

@@ -664,19 +664,7 @@ Addr setup_client_stack( void*  init_sp,
             break;
 
          case AT_BASE:
-            /* When gdbserver sends the auxv to gdb, the AT_BASE has
-               to be ignored, as otherwise gdb adds this offset
-               to loaded shared libs, causing wrong address
-               relocation e.g. when inserting breaks.
-               However, ignoring AT_BASE makes V crash on Android 4.1.
-               So, keep the AT_BASE on android for now.
-               ??? Need to dig in depth about AT_BASE/GDB interaction */
-#           if !defined(VGPV_arm_linux_android) \
-               && !defined(VGPV_x86_linux_android) \
-               && !defined(VGPV_mips32_linux_android)
-            auxv->a_type = AT_IGNORE;
-#           endif
-            auxv->u.a_val = info->interp_base;
+            auxv->u.a_val = info->interp_offset;
             break;
 
          case AT_PLATFORM:

coregrind/m_ume/elf.c

@@ -310,11 +310,6 @@ Int VG_(load_ELF)(Int fd, const HChar* name, /*MOD*/ExeInfo* info)
    void *entry;
    ESZ(Addr) ebase = 0;
 
-   /* The difference between where the interpreter got mapped and
-      where it asked to be mapped.  Needed for computing the ppc64 ELF
-      entry point and initial tocptr (R2) value. */
-   ESZ(Word) interp_offset = 0;
-
 #  if defined(HAVE_PIE)
    ebase = info->exe_base;
 #  endif
@@ -500,8 +495,7 @@ Int VG_(load_ELF)(Int fd, const HChar* name, /*MOD*/ExeInfo* info)
       VG_(close)(interp->fd);
 
       entry = (void *)(advised - interp_addr + interp->e.e_entry);
-      info->interp_base = (ESZ(Addr))advised;
-      interp_offset = advised - interp_addr;
+      info->interp_offset = advised - interp_addr;
 
       VG_(free)(interp->p);
       VG_(free)(interp);
@@ -518,12 +512,11 @@ Int VG_(load_ELF)(Int fd, const HChar* name, /*MOD*/ExeInfo* info)
       is the static chain value. */
    info->init_ip  = ((ULong*)entry)[0];
    info->init_toc = ((ULong*)entry)[1];
-   info->init_ip  += interp_offset;
-   info->init_toc += interp_offset;
+   info->init_ip  += info->interp_offset;
+   info->init_toc += info->interp_offset;
 #else
    info->init_ip  = (Addr)entry;
    info->init_toc = 0; /* meaningless on this platform */
-   (void) interp_offset; /* stop gcc complaining it is unused */
 #endif
    VG_(free)(e->p);
    VG_(free)(e);

coregrind/pub_core_ume.h

@@ -52,10 +52,10 @@ typedef
       Addr exe_end;      // INOUT: highest (allowed) address
 
 #if !defined(VGO_darwin)
-      Addr phdr;         // OUT: address phdr was mapped at
-      Int  phnum;        // OUT: number of phdrs
-      UInt stack_prot;   // OUT: stack permissions
-      Addr interp_base;  // OUT: where interpreter (ld.so) was mapped
+      Addr     phdr;          // OUT: address phdr was mapped at
+      Int      phnum;         // OUT: number of phdrs
+      UInt     stack_prot;    // OUT: stack permissions
+      PtrdiffT interp_offset; // OUT: relocation offset for ld.so
 #else
       Addr  stack_start;      // OUT: address of start of stack segment (hot)
       Addr  stack_end;        // OUT: address of end of stack segment (cold)