libebl: Add ebl_func_addr_mask plus ARM backend implementation.

The ARM EABI says that the zero bit of function symbol st_value indicates
whether the symbol points to a THUMB or ARM function. Also the return
value address in an unwind will contain the same extra bit to indicate
whether to return to a regular ARM or THUMB function. Add a new ebl
function to mask off such bits and turn a function value into a function
address so that we get the actual value that a function symbol or return
address points to. It isn't easily possible to reuse the existing
ebl_resolve_sym_value for this purpose, so we end up with another hook
that can be used from dwfl_module_getsym, handle_cfi and elflint.

Signed-off-by: Mark Wielaard <[email protected]>

5 files changed, 34 insertions, 4 deletions

diff --git a/libebl/ChangeLog b/libebl/ChangeLog
index 7198d5ec..5ec71016 100644
--- a/libebl/ChangeLog
+++ b/libebl/ChangeLog
@@ -1,3 +1,9 @@
+2014-06-17  Mark Wielaard  <[email protected]>
+
+	* eblinitreg.c (ebl_func_addr_mask): New function.
+	* libebl.h (ebl_func_addr_mask): Define.
+	* libeblP.h (struct ebl): Add func_addr_mask.
+
 2014-05-19  Mark Wielaard  <[email protected]>
 
 	* Makefile.am (gen_SOURCES): Add eblcheckreloctargettype.c.
diff --git a/libebl/ebl-hooks.h b/libebl/ebl-hooks.h
index 65c62ec6..e1186f86 100644
--- a/libebl/ebl-hooks.h
+++ b/libebl/ebl-hooks.h
@@ -187,7 +187,7 @@ bool EBLHOOK(unwind) (Ebl *ebl, Dwarf_Addr pc, ebl_tid_registers_t *setfunc,
 		      bool *signal_framep);
 
 /* Returns true if the value can be resolved to an address in an
-   allocated section, which will be returned in *SHNDXP.
+   allocated section, which will be returned in *ADDR.
    (e.g. function descriptor resolving)  */
 bool EBLHOOK(resolve_sym_value) (Ebl *ebl, GElf_Addr *addr);
 
diff --git a/libebl/eblinitreg.c b/libebl/eblinitreg.c
index 8909c500..5729b3cc 100644
--- a/libebl/eblinitreg.c
+++ b/libebl/eblinitreg.c
@@ -1,5 +1,5 @@
 /* Fetch live process Dwfl_Frame from PID.
-   Copyright (C) 2013 Red Hat, Inc.
+   Copyright (C) 2013, 2014 Red Hat, Inc.
    This file is part of elfutils.
 
    This file is free software; you can redistribute it and/or modify
@@ -49,3 +49,10 @@ ebl_frame_nregs (Ebl *ebl)
 {
   return ebl == NULL ? 0 : ebl->frame_nregs;
 }
+
+GElf_Addr
+ebl_func_addr_mask (Ebl *ebl)
+{
+  return ((ebl == NULL || ebl->func_addr_mask == 0)
+	  ? ~(GElf_Addr)0 : ebl->func_addr_mask);
+}
diff --git a/libebl/libebl.h b/libebl/libebl.h
index d05751fa..bb993bf0 100644
--- a/libebl/libebl.h
+++ b/libebl/libebl.h
@@ -1,5 +1,5 @@
 /* Interface for libebl.
-   Copyright (C) 2000-2010, 2013 Red Hat, Inc.
+   Copyright (C) 2000-2010, 2013, 2014 Red Hat, Inc.
    This file is part of elfutils.
 
    This file is free software; you can redistribute it and/or modify
@@ -409,6 +409,17 @@ extern bool ebl_set_initial_registers_tid (Ebl *ebl,
 extern size_t ebl_frame_nregs (Ebl *ebl)
   __nonnull_attribute__ (1);
 
+/* Mask to use for function symbol or unwind return addresses in case
+   the architecture adds some extra non-address bits to it.  This is
+   different from ebl_resolve_sym_value which only works for actual
+   symbol addresses (in non-ET_REL files) that might resolve to an
+   address in a different section.  ebl_func_addr_mask is called to
+   turn a given function value into the a real address or offset (the
+   original value might not be a real address).  This works for all
+   cases where an actual function address (or offset in ET_REL symbol
+   tables) is needed.  */
+extern GElf_Addr ebl_func_addr_mask (Ebl *ebl);
+
 /* Convert *REGNO as is in DWARF to a lower range suitable for
    Dwarf_Frame->REGS indexing.  */
 extern bool ebl_dwarf_to_regno (Ebl *ebl, unsigned *regno)
diff --git a/libebl/libeblP.h b/libebl/libeblP.h
index f91c2a0d..dbd67f3e 100644
--- a/libebl/libeblP.h
+++ b/libebl/libeblP.h
@@ -1,5 +1,5 @@
 /* Internal definitions for interface for libebl.
-   Copyright (C) 2000-2009, 2013 Red Hat, Inc.
+   Copyright (C) 2000-2009, 2013, 2014 Red Hat, Inc.
    This file is part of elfutils.
 
    This file is free software; you can redistribute it and/or modify
@@ -64,6 +64,12 @@ struct ebl
      Ebl architecture can unwind iff FRAME_NREGS > 0.  */
   size_t frame_nregs;
 
+  /* Mask to use to turn a function value into a real function address
+     in case the architecture adds some extra non-address bits to it.
+     If not initialized (0) then ebl_func_addr_mask will return ~0,
+     otherwise it should be the actual mask to use.  */
+  GElf_Addr func_addr_mask;
+
   /* Function descriptor load address and table as used by
      ebl_resolve_sym_value if available for this arch.  */
   GElf_Addr fd_addr;