Subject: libebl: Add sym_func_value hook.
From: Mark Wielaard <[email-masked]>
Date: Sun, 15 Jun 2014 11:30:35 +0200

The ARM EABI says that the zero bit of function symbol st_value indicates
whether the symbol points to a THUMB or ARM function. Add a new ebl hook
to adjust the st_value in such a case so that we get the actual value that
the symbol points to. It isn't easily possible to reuse the existing
resolve_sym_value for this purpose, so we end up with another hook that
can be used from dwfl_module_getsym and elflint.

Rebase arm_func_value.patch from 0.159 to 0.160
Signed-off-by: Hongxu Jia <[email-masked]>
---
 backends/arm_init.c          |    1 +
 backends/arm_symbol.c        |    8 ++++++++
 libdwfl/dwfl_module_getsym.c |    2 +-
 libebl/Makefile.am           |    3 ++-
 libebl/ebl-hooks.h           |    3 +++
 libebl/eblsymfuncval.c       |   43 ++++++++++++++++++++++++++++++++++++++++++
 libebl/libebl.h              |   11 +++++++++++
 7 files changed, 69 insertions(+), 2 deletions(-)

diff --git a/backends/arm_init.c b/backends/arm_init.c
index 7171186..9f03630 100644
--- a/backends/arm_init.c
+++ b/backends/arm_init.c
@@ -78,6 +78,7 @@ arm_init (elf, machine, eh, ehlen)
     eh->return_value_location = arm_return_value_location_hard;
   HOOK (eh, abi_cfi);
   HOOK (eh, check_reloc_target_type);
+  HOOK (eh, sym_func_value);
   HOOK (eh, symbol_type_name);
 
   /* We only unwind the core integer registers.  */
diff --git a/backends/arm_symbol.c b/backends/arm_symbol.c
index da4a50a..ccea03b 100644
--- a/backends/arm_symbol.c
+++ b/backends/arm_symbol.c
@@ -130,6 +130,14 @@ arm_check_reloc_target_type (Ebl *ebl __attribute__ ((unused)), Elf64_Word sh_ty
   return sh_type == SHT_ARM_EXIDX;
 }
 
+/* ARM EABI says that the low bit indicates whether the function
+   symbol value is a THUMB function or not.  Mask it off.  */
+GElf_Addr
+arm_sym_func_value (Ebl *ebl __attribute__ ((unused)), GElf_Addr val)
+{
+  return val & ~(GElf_Addr)1;
+}
+
 const char *
 arm_symbol_type_name (int type,
 		      char *buf __attribute__ ((unused)),
diff --git a/libdwfl/dwfl_module_getsym.c b/libdwfl/dwfl_module_getsym.c
index 42d2b67..fb192d7 100644
--- a/libdwfl/dwfl_module_getsym.c
+++ b/libdwfl/dwfl_module_getsym.c
@@ -119,7 +119,7 @@ __libdwfl_getsym (Dwfl_Module *mod, int ndx, GElf_Sym *sym, GElf_Addr *addr,
      descriptors).  */
 
   char *ident;
-  GElf_Addr st_value = sym->st_value & ebl_func_addr_mask (mod->ebl);
+  GElf_Addr st_value = ebl_sym_func_value (mod->ebl, sym->st_value);
   *resolved = false;
   if (! adjust_st_value && mod->e_type != ET_REL && alloc
       && (GELF_ST_TYPE (sym->st_info) == STT_FUNC
diff --git a/libebl/Makefile.am b/libebl/Makefile.am
index ec4477b..889c21b 100644
--- a/libebl/Makefile.am
+++ b/libebl/Makefile.am
@@ -55,7 +55,8 @@ gen_SOURCES = eblopenbackend.c eblclosebackend.c eblstrtab.c \
 	      eblsysvhashentrysize.c eblauxvinfo.c eblcheckobjattr.c \
 	      ebl_check_special_section.c ebl_syscall_abi.c eblabicfi.c \
 	      eblstother.c eblinitreg.c ebldwarftoregno.c eblnormalizepc.c \
-	      eblunwind.c eblresolvesym.c eblcheckreloctargettype.c
+	      eblunwind.c eblresolvesym.c eblcheckreloctargettype.c \
+	      eblsymfuncval.c
 
 libebl_a_SOURCES = $(gen_SOURCES)
 
diff --git a/libebl/ebl-hooks.h b/libebl/ebl-hooks.h
index 2e31446..9df945d 100644
--- a/libebl/ebl-hooks.h
+++ b/libebl/ebl-hooks.h
@@ -191,5 +191,8 @@ bool EBLHOOK(unwind) (Ebl *ebl, Dwarf_Addr pc, ebl_tid_registers_t *setfunc,
    (e.g. function descriptor resolving)  */
 bool EBLHOOK(resolve_sym_value) (Ebl *ebl, GElf_Addr *addr);
 
+/* Returns the real value of a symbol function address or offset.  */
+GElf_Addr EBLHOOK(sym_func_value) (Ebl *ebl, GElf_Addr val);
+
 /* Destructor for ELF backend handle.  */
 void EBLHOOK(destr) (struct ebl *);
diff --git a/libebl/eblsymfuncval.c b/libebl/eblsymfuncval.c
new file mode 100644
index 0000000..c0b322f
--- /dev/null
+++ b/libebl/eblsymfuncval.c
@@ -0,0 +1,43 @@
+/* Turn a symbol function value into a real function address or offset.
+   Copyright (C) 2014 Red Hat, Inc.
+   This file is part of elfutils.
+
+   This file is free software; you can redistribute it and/or modify
+   it under the terms of either
+
+     * the GNU Lesser General Public License as published by the Free
+       Software Foundation; either version 3 of the License, or (at
+       your option) any later version
+
+   or
+
+     * the GNU General Public License as published by the Free
+       Software Foundation; either version 2 of the License, or (at
+       your option) any later version
+
+   or both in parallel, as here.
+
+   elfutils is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received copies of the GNU General Public License and
+   the GNU Lesser General Public License along with this program.  If
+   not, see <http://www.gnu.org/licenses/>.  */
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#include <libeblP.h>
+#include <assert.h>
+
+GElf_Addr
+ebl_sym_func_value (Ebl *ebl, GElf_Addr val)
+{
+  if (ebl == NULL || ebl->sym_func_value == NULL)
+    return val;
+
+  return ebl->sym_func_value (ebl, val);
+}
diff --git a/libebl/libebl.h b/libebl/libebl.h
index 7dbf460..96c076b 100644
--- a/libebl/libebl.h
+++ b/libebl/libebl.h
@@ -472,6 +472,17 @@ extern bool ebl_unwind (Ebl *ebl, Dwarf_Addr pc, ebl_tid_registers_t *setfunc,
 extern bool ebl_resolve_sym_value (Ebl *ebl, GElf_Addr *addr)
    __nonnull_attribute__ (2);
 
+/* Returns the real value of a symbol function address or offset
+   (e.g. when the st_value contains some flag bits that need to be
+   masked off).  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_sym_func_value is called to turn the given value into the a
+   real address or offset (the original value might not be a real
+   address).  This works for both ET_REL when the value is a section
+   offset or ET_EXEC or ET_DYN symbol values, which are addresses.  */
+extern GElf_Addr ebl_sym_func_value (Ebl *ebl, GElf_Addr val);
+
 #ifdef __cplusplus
 }
 #endif