[ARM/FDPIC v3 06/21] [ARM] FDPIC: Add support for c++ exceptions

[Christophe Lyon <christophe.lyon@st.com>]

The main difference with existing support is that function addresses
are function descriptor addresses instead. This means that all code
dealing with function pointers now has to cope with function
descriptors instead.

For the same reason, Linux kernel helpers can no longer be called by
dereferencing their address, so we implement the same functionality as
a regular function here.

When restoring a function address, we also have to restore the FDPIC
register value (r9).

2018-XX-XX  Christophe Lyon  <christophe.lyon@st.com>
	Mickaël Guêné <mickael.guene@st.com>

	gcc/
	* ginclude/unwind-arm-common.h (unwinder_cache): Add reserved5
	field.
	(FDPIC_REGNUM): New define.

	libgcc/
	* config/arm/linux-atomic.c (__kernel_cmpxchg): Add FDPIC support.
	(__kernel_dmb): Likewise.
	(__fdpic_cmpxchg): New function.
	(__fdpic_dmb): New function.
	* config/arm/unwind-arm.h (gnu_Unwind_Find_got): New function.
	(_Unwind_decode_typeinfo_ptr): Add FDPIC support.
	* unwindo-arm-common.inc (UCB_PR_GOT): New.
	(funcdesc_t): New struct.
	(get_eit_entry): Add FDPIC support.
	(unwind_phase2): Likewise.
	(unwind_phase2_forced): Likewise.
	(__gnu_Unwind_RaiseException): Likewise.
	(__gnu_Unwind_Resume): Likewise.
	(__gnu_Unwind_Backtrace): Likewise.
	* unwind-pe.h (read_encoded_value_with_base): Likewise.

	libstdc++/
	* libsupc++/eh_personality.cc (get_ttype_entry): Add FDPIC
	support.

Change-Id: I517a49ff18fae21c686cd1c6008ea7974515b347

diff --git a/gcc/ginclude/unwind-arm-common.h b/gcc/ginclude/unwind-arm-common.h
index 8a1a919..f663891 100644
--- a/gcc/ginclude/unwind-arm-common.h
+++ b/gcc/ginclude/unwind-arm-common.h
@@ -91,7 +91,7 @@ extern "C" {
 	  _uw reserved2;  /* Personality routine address */
 	  _uw reserved3;  /* Saved callsite address */
 	  _uw reserved4;  /* Forced unwind stop arg */
-	  _uw reserved5;
+	  _uw reserved5;  /* Personality routine GOT value in FDPIC mode.  */
 	}
       unwinder_cache;
       /* Propagation barrier cache (valid after phase 1): */
@@ -247,4 +247,6 @@ typedef unsigned long _uleb128_t;
 }   /* extern "C" */
 #endif
 
+#define FDPIC_REGNUM 9
+
 #endif /* defined UNWIND_ARM_COMMON_H */
diff --git a/libgcc/config/arm/linux-atomic.c b/libgcc/config/arm/linux-atomic.c
index d334c58..161d1ce 100644
--- a/libgcc/config/arm/linux-atomic.c
+++ b/libgcc/config/arm/linux-atomic.c
@@ -25,11 +25,49 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 
 /* Kernel helper for compare-and-exchange.  */
 typedef int (__kernel_cmpxchg_t) (int oldval, int newval, int *ptr);
+#if __FDPIC__
+/* Non-FDPIC ABIs call __kernel_cmpxchg directly by dereferencing its
+   address, but under FDPIC we would generate a broken call
+   sequence. That's why we have to implement __kernel_cmpxchg and
+   __kernel_dmb here: this way, the FDPIC call sequence works.  */
+#define __kernel_cmpxchg __fdpic_cmpxchg
+#else
 #define __kernel_cmpxchg (*(__kernel_cmpxchg_t *) 0xffff0fc0)
+#endif
 
 /* Kernel helper for memory barrier.  */
 typedef void (__kernel_dmb_t) (void);
+#if __FDPIC__
+#define __kernel_dmb __fdpic_dmb
+#else
 #define __kernel_dmb (*(__kernel_dmb_t *) 0xffff0fa0)
+#endif
+
+#if __FDPIC__
+static int __fdpic_cmpxchg (int oldval, int newval, int *ptr)
+{
+  int result;
+
+  asm volatile ("1: ldrex r3, [%[ptr]]\n\t"
+		"subs  r3, r3, %[oldval]\n\t"
+		"itt eq\n\t"
+		"strexeq r3, %[newval], [%[ptr]]\n\t"
+		"teqeq r3, #1\n\t"
+		"it eq\n\t"
+		"beq 1b\n\t"
+		"rsbs  %[result], r3, #0\n\t"
+		: [result] "=r" (result)
+		: [oldval] "r" (oldval) , [newval] "r" (newval), [ptr] "r" (ptr)
+		: "r3");
+    return result;
+}
+
+static void __fdpic_dmb ()
+{
+  asm volatile ("dmb\n\t");
+}
+
+#endif
 
 /* Note: we implement byte, short and int versions of atomic operations using
    the above kernel helpers; see linux-atomic-64bit.c for "long long" (64-bit)
diff --git a/libgcc/config/arm/unwind-arm.h b/libgcc/config/arm/unwind-arm.h
index 9f7d3f2..db5dfa2 100644
--- a/libgcc/config/arm/unwind-arm.h
+++ b/libgcc/config/arm/unwind-arm.h
@@ -33,9 +33,31 @@
 /* Use IP as a scratch register within the personality routine.  */
 #define UNWIND_POINTER_REG 12
 
+#define STR(x) #x
+#define XSTR(x) STR(x)
+
 #ifdef __cplusplus
 extern "C" {
 #endif
+_Unwind_Ptr __attribute__((weak)) __gnu_Unwind_Find_got (_Unwind_Ptr);
+
+static inline _Unwind_Ptr gnu_Unwind_Find_got (_Unwind_Ptr ptr)
+{
+    _Unwind_Ptr res;
+
+    if (__gnu_Unwind_Find_got)
+	res =  __gnu_Unwind_Find_got (ptr);
+    else
+      {
+	asm volatile ("mov %[result], r" XSTR(FDPIC_REGNUM)
+		      : [result]"=r" (res)
+		      :
+		      :);
+      }
+
+    return res;
+}
+
   /* Decode an R_ARM_TARGET2 relocation.  */
   static inline _Unwind_Word
   _Unwind_decode_typeinfo_ptr (_Unwind_Word base __attribute__ ((unused)),
@@ -48,7 +70,12 @@ extern "C" {
       if (!tmp)
 	return 0;
 
-#if (defined(linux) && !defined(__uClinux__)) || defined(__NetBSD__) \
+#if __FDPIC__
+      /* For FDPIC, we store the offset of the GOT entry.  */
+      /* So, first get GOT from dynamic linker and then use indirect access.  */
+      tmp += gnu_Unwind_Find_got (ptr);
+      tmp = *(_Unwind_Word *) tmp;
+#elif (defined(linux) && !defined(__uClinux__)) || defined(__NetBSD__) \
     || defined(__FreeBSD__) || defined(__fuchsia__)
       /* Pc-relative indirect.  */
 #define _GLIBCXX_OVERRIDE_TTYPE_ENCODING (DW_EH_PE_pcrel | DW_EH_PE_indirect)
diff --git a/libgcc/unwind-arm-common.inc b/libgcc/unwind-arm-common.inc
index 76f8fc3..7187edd 100644
--- a/libgcc/unwind-arm-common.inc
+++ b/libgcc/unwind-arm-common.inc
@@ -62,6 +62,7 @@ __gnu_Unwind_Find_exidx (_Unwind_Ptr, int *);
 #define UCB_PR_ADDR(ucbp) ((ucbp)->unwinder_cache.reserved2)
 #define UCB_SAVED_CALLSITE_ADDR(ucbp) ((ucbp)->unwinder_cache.reserved3)
 #define UCB_FORCED_STOP_ARG(ucbp) ((ucbp)->unwinder_cache.reserved4)
+#define UCB_PR_GOT(ucbp) ((ucbp)->unwinder_cache.reserved5)
 
 /* Unwind descriptors.  */
 
@@ -85,6 +86,15 @@ typedef struct __EIT_entry
   _uw content;
 } __EIT_entry;
 
+#ifdef __FDPIC__
+
+/* Only used in FDPIC case.  */
+struct funcdesc_t {
+    unsigned int ptr;
+    unsigned int got;
+};
+#endif
+
 /* Assembly helper functions.  */
 
 /* Restore core register state.  Never returns.  */
@@ -259,7 +269,21 @@ get_eit_entry (_Unwind_Control_Block *ucbp, _uw return_address)
     {
       /* One of the predefined standard routines.  */
       _uw idx = (*(_uw *) ucbp->pr_cache.ehtp >> 24) & 0xf;
+#if __FDPIC__
+      {
+	struct funcdesc_t *funcdesc
+	  = (struct funcdesc_t *) __gnu_unwind_get_pr_addr (idx);
+	if (funcdesc)
+	  {
+	    UCB_PR_ADDR (ucbp) = funcdesc->ptr;
+	    UCB_PR_GOT (ucbp) = funcdesc->got;
+	  }
+	else
+	  UCB_PR_ADDR (ucbp) = 0;
+      }
+#else
       UCB_PR_ADDR (ucbp) = __gnu_unwind_get_pr_addr (idx);
+#endif
       if (UCB_PR_ADDR (ucbp) == 0)
 	{
 	  /* Failed */
@@ -270,6 +294,10 @@ get_eit_entry (_Unwind_Control_Block *ucbp, _uw return_address)
     {
       /* Execute region offset to PR */
       UCB_PR_ADDR (ucbp) = selfrel_offset31 (ucbp->pr_cache.ehtp);
+#if __FDPIC__
+      UCB_PR_GOT (ucbp)
+	= (unsigned int) gnu_Unwind_Find_got ((_Unwind_Ptr) UCB_PR_ADDR (ucbp));
+#endif
     }
   return _URC_OK;
 }
@@ -291,14 +319,29 @@ unwind_phase2 (_Unwind_Control_Block * ucbp, phase2_vrs * vrs)
       UCB_SAVED_CALLSITE_ADDR (ucbp) = VRS_PC(vrs);
 
       /* Call the pr to decide what to do.  */
+#if __FDPIC__
+      {
+	volatile struct funcdesc_t funcdesc;
+	funcdesc.ptr = UCB_PR_ADDR (ucbp);
+	funcdesc.got = UCB_PR_GOT (ucbp);
+	pr_result = ((personality_routine) &funcdesc)
+	  (_US_UNWIND_FRAME_STARTING, ucbp, (_Unwind_Context *) vrs);
+      }
+#else
       pr_result = ((personality_routine) UCB_PR_ADDR (ucbp))
 	(_US_UNWIND_FRAME_STARTING, ucbp, (_Unwind_Context *) vrs);
+#endif
     }
   while (pr_result == _URC_CONTINUE_UNWIND);
   
   if (pr_result != _URC_INSTALL_CONTEXT)
     abort();
 
+#if __FDPIC__
+  /* r9 could have been lost due to PLT jump.  Restore correct value.  */
+  vrs->core.r[FDPIC_REGNUM] = gnu_Unwind_Find_got (VRS_PC (vrs));
+#endif
+
   uw_restore_core_regs (vrs, &vrs->core);
 }
 
@@ -346,8 +389,18 @@ unwind_phase2_forced (_Unwind_Control_Block *ucbp, phase2_vrs *entry_vrs,
 	  next_vrs = saved_vrs;
 
 	  /* Call the pr to decide what to do.  */
+#if __FDPIC__
+	  {
+	    volatile struct funcdesc_t funcdesc;
+	    funcdesc.ptr = UCB_PR_ADDR (ucbp);
+	    funcdesc.got = UCB_PR_GOT (ucbp);
+	    pr_result = ((personality_routine) &funcdesc)
+	      (action, ucbp, (void *) &next_vrs);
+	  }
+#else
 	  pr_result = ((personality_routine) UCB_PR_ADDR (ucbp))
 	    (action, ucbp, (void *) &next_vrs);
+#endif
 
 	  saved_vrs.prev_sp = VRS_SP (&next_vrs);
 	}
@@ -384,6 +437,11 @@ unwind_phase2_forced (_Unwind_Control_Block *ucbp, phase2_vrs *entry_vrs,
       return _URC_FAILURE;
     }
 
+#if __FDPIC__
+  /* r9 could have been lost due to PLT jump.  Restore correct value.  */
+  saved_vrs.core.r[FDPIC_REGNUM] = gnu_Unwind_Find_got (VRS_PC (&saved_vrs));
+#endif
+
   uw_restore_core_regs (&saved_vrs, &saved_vrs.core);
 }
 
@@ -429,8 +487,18 @@ __gnu_Unwind_RaiseException (_Unwind_Control_Block * ucbp,
 	return _URC_FAILURE;
 
       /* Call the pr to decide what to do.  */
+#if __FDPIC__
+      {
+	volatile struct funcdesc_t funcdesc;
+	funcdesc.ptr = UCB_PR_ADDR (ucbp);
+	funcdesc.got = UCB_PR_GOT (ucbp);
+	pr_result = ((personality_routine) &funcdesc)
+	  (_US_VIRTUAL_UNWIND_FRAME, ucbp, (void *) &saved_vrs);
+      }
+#else
       pr_result = ((personality_routine) UCB_PR_ADDR (ucbp))
 	(_US_VIRTUAL_UNWIND_FRAME, ucbp, (void *) &saved_vrs);
+#endif
     }
   while (pr_result == _URC_CONTINUE_UNWIND);
 
@@ -488,13 +556,27 @@ __gnu_Unwind_Resume (_Unwind_Control_Block * ucbp, phase2_vrs * entry_vrs)
     }
 
   /* Call the cached PR.  */
+#if __FDPIC__
+  {
+    volatile struct funcdesc_t funcdesc;
+    funcdesc.ptr = UCB_PR_ADDR (ucbp);
+    funcdesc.got = UCB_PR_GOT (ucbp);
+    pr_result = ((personality_routine) &funcdesc)
+      (_US_UNWIND_FRAME_RESUME, ucbp, (_Unwind_Context *) entry_vrs);
+  }
+#else
   pr_result = ((personality_routine) UCB_PR_ADDR (ucbp))
 	(_US_UNWIND_FRAME_RESUME, ucbp, (_Unwind_Context *) entry_vrs);
+#endif
 
   switch (pr_result)
     {
     case _URC_INSTALL_CONTEXT:
       /* Upload the registers to enter the landing pad.  */
+#if __FDPIC__
+      /* r9 could have been lost due to PLT jump.  Restore correct value.  */
+      entry_vrs->core.r[FDPIC_REGNUM] = gnu_Unwind_Find_got (VRS_PC (entry_vrs));
+#endif
       uw_restore_core_regs (entry_vrs, &entry_vrs->core);
 
     case _URC_CONTINUE_UNWIND:
@@ -586,9 +668,20 @@ __gnu_Unwind_Backtrace(_Unwind_Trace_Fn trace, void * trace_argument,
 	}
 
       /* Call the pr to decide what to do.  */
+#if __FDPIC__
+      {
+	volatile struct funcdesc_t funcdesc;
+	funcdesc.ptr = UCB_PR_ADDR (ucbp);
+	funcdesc.got = UCB_PR_GOT (ucbp);
+	code = ((personality_routine) &funcdesc)
+	  (_US_VIRTUAL_UNWIND_FRAME | _US_FORCE_UNWIND,
+	   ucbp, (void *) &saved_vrs);
+      }
+#else
       code = ((personality_routine) UCB_PR_ADDR (ucbp))
 	(_US_VIRTUAL_UNWIND_FRAME | _US_FORCE_UNWIND, 
 	 ucbp, (void *) &saved_vrs);
+#endif
     }
   while (code != _URC_END_OF_STACK
 	 && code != _URC_FAILURE);
diff --git a/libgcc/unwind-pe.h b/libgcc/unwind-pe.h
index dd5ae95..9c5177f 100644
--- a/libgcc/unwind-pe.h
+++ b/libgcc/unwind-pe.h
@@ -259,10 +259,27 @@ read_encoded_value_with_base (unsigned char encoding, _Unwind_Ptr base,
 
       if (result != 0)
 	{
+#if __FDPIC__
+	  /* FDPIC relative addresses imply taking the GOT address
+	     into account.  */
+	  if ((encoding & DW_EH_PE_pcrel) && (encoding & DW_EH_PE_indirect))
+	    {
+	      result += gnu_Unwind_Find_got ((_Unwind_Ptr) u);
+	      result = *(_Unwind_Internal_Ptr *) result;
+	    }
+	  else
+	    {
+	      result += ((encoding & 0x70) == DW_EH_PE_pcrel
+			 ? (_Unwind_Internal_Ptr) u : base);
+	      if (encoding & DW_EH_PE_indirect)
+		result = *(_Unwind_Internal_Ptr *) result;
+	    }
+#else
 	  result += ((encoding & 0x70) == DW_EH_PE_pcrel
 		     ? (_Unwind_Internal_Ptr) u : base);
 	  if (encoding & DW_EH_PE_indirect)
 	    result = *(_Unwind_Internal_Ptr *) result;
+#endif
 	}
     }
 
diff --git a/libstdc++-v3/libsupc++/eh_personality.cc b/libstdc++-v3/libsupc++/eh_personality.cc
index 1b336c7..7b26b8d 100644
--- a/libstdc++-v3/libsupc++/eh_personality.cc
+++ b/libstdc++-v3/libsupc++/eh_personality.cc
@@ -93,7 +93,15 @@ get_ttype_entry (lsda_header_info *info, _uleb128_t i)
   _Unwind_Ptr ptr;
 
   i *= size_of_encoded_value (info->ttype_encoding);
-  read_encoded_value_with_base (info->ttype_encoding, info->ttype_base,
+  read_encoded_value_with_base (
+#if __FDPIC__
+				/* Force these flags to nake sure to
+				   take the GOT into account.  */
+				(DW_EH_PE_pcrel | DW_EH_PE_indirect),
+#else
+				info->ttype_encoding,
+#endif
+				info->ttype_base,
 				info->TType - i, &ptr);
 
   return reinterpret_cast<const std::type_info *>(ptr);
-- 
2.6.3