Patchwork PATCH: PR other/48007: Unwind library doesn't work with UNITS_PER_WORD > sizeof (void *)

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Submitter H.J. Lu
Date April 10, 2011, 1:52 a.m.
Message ID <BANLkTikNYq7dydcZq+quFqiOw+sHvXdguw@mail.gmail.com>
Download mbox | patch
Permalink /patch/90491/
State New
Headers show

Comments

H.J. Lu - April 10, 2011, 1:52 a.m.
On Thu, Mar 24, 2011 at 12:15 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Wed, Mar 23, 2011 at 12:22 PM, Ulrich Weigand <uweigand@de.ibm.com> wrote:
>> Richard Henderson wrote:
>>> Because, really, if we consider the structure truly public, we can't even
>>> change the number of registers for a given port to support new features of
>>> the cpu.
>>
>> Indeed, and I remember we got bitten by that a long time ago, which is why
>> s390.h now has this comment:
>>
>> /* Number of hardware registers that go into the DWARF-2 unwind info.
>>   To avoid ABI incompatibility, this number must not change even as
>>   'fake' hard registers are added or removed.  */
>> #define DWARF_FRAME_REGISTERS 34
>>
>>> I don't suppose there's any way that we can declare these old
>>> programs Just Broken, and drop this compatibility stuff?
>>
>> I wouldn't like that ... we did run into this problem in the wild, and
>> some s390 users really run very old programs for some reason.
>>
>> However, I'm wondering: this bug that leaked the implementation of
>> _Unwind_Context only ever affected the *original* version of the
>> structure -- it was fixed before the extended context was ever
>> added, right?
>>
>> If this is true, we'd still need to keep the original context format
>> unchanged, but we'd be free to modify the *extended* format at any
>> time, without ABI considerations and need for further versioning ...
>>
>
> From what I can tell, the issues are:
>
> 1. _Unwind_Context is supposed to be opaque and we are free to
> change it.  We should be able to extend DWARF_FRAME_REGISTERS
> to support the new hard registers if needed, without breaking binary
> compatibility.
> 2.  _Unwind_Context was leaked and wasn't really opaque.  To
> provide backward binary compatibility, we are stuck with what we
> had.
>
> Is that possible to implement something along the line:
>
> 1. Add some bits to _Unwind_Context so that we can detect
> the leaked _Unwind_Context.
> 2. When a leaked _Unwind_Context is detected at run-time,
> as a compile time option, a target can either provide binary
> compatibility or issue a run-time error.

This is the attempt to implement it.  Any comments?

Thanks.

Patch

diff --git a/gcc/unwind-dw2.c b/gcc/unwind-dw2.c
index 25990b4..5fa2723 100644
--- a/gcc/unwind-dw2.c
+++ b/gcc/unwind-dw2.c
@@ -59,6 +59,12 @@ 
 #define DWARF_REG_TO_UNWIND_COLUMN(REGNO) (REGNO)
 #endif
 
+#ifndef UNIQUE_UNWIND_CONTEXT
+#if defined __x86_64 && !defined __LP64__
+# define UNIQUE_UNWIND_CONTEXT
+#endif
+#endif
+
 /* This is the register and unwind state for a particular frame.  This
    provides the information necessary to unwind up past a frame and return
    to its caller.  */
@@ -69,6 +75,15 @@  struct _Unwind_Context
   void *ra;
   void *lsda;
   struct dwarf_eh_bases bases;
+#ifdef UNIQUE_UNWIND_CONTEXT
+  /* Used to check for unique _Unwind_Context.  */
+  void *dwarf_reg_size_table;
+  /* Signal frame context.  */
+#define SIGNAL_FRAME_BIT ((_Unwind_Word) 1 >> 0)
+  _Unwind_Word flags;
+  _Unwind_Word args_size;
+  _Unwind_Word value[DWARF_FRAME_REGISTERS+1];
+#else
   /* Signal frame context.  */
 #define SIGNAL_FRAME_BIT ((~(_Unwind_Word) 0 >> 1) + 1)
   /* Context which has version/args_size/by_value fields.  */
@@ -79,6 +94,7 @@  struct _Unwind_Context
   _Unwind_Word version;
   _Unwind_Word args_size;
   char by_value[DWARF_FRAME_REGISTERS+1];
+#endif
 };
 
 /* Byte size of every register managed by these routines.  */
@@ -144,11 +160,13 @@  _Unwind_SetSignalFrame (struct _Unwind_Context *context, int val)
     context->flags &= ~SIGNAL_FRAME_BIT;
 }
 
+#ifndef UNIQUE_UNWIND_CONTEXT
 static inline _Unwind_Word
 _Unwind_IsExtendedContext (struct _Unwind_Context *context)
 {
   return context->flags & EXTENDED_CONTEXT_BIT;
 }
+#endif
 
 /* Get the value of register INDEX as saved in CONTEXT.  */
 
@@ -168,8 +186,14 @@  _Unwind_GetGR (struct _Unwind_Context *context, int index)
   size = dwarf_reg_size_table[index];
   ptr = context->reg[index];
 
+#ifdef UNIQUE_UNWIND_CONTEXT
+  gcc_assert (context->dwarf_reg_size_table == &dwarf_reg_size_table);
+  if (context->reg[index] == &context->value[index])
+    return context->value[index];
+#else
   if (_Unwind_IsExtendedContext (context) && context->by_value[index])
     return (_Unwind_Word) (_Unwind_Internal_Ptr) ptr;
+#endif
 
   /* This will segfault if the register hasn't been saved.  */
   if (size == sizeof(_Unwind_Ptr))
@@ -207,11 +231,20 @@  _Unwind_SetGR (struct _Unwind_Context *context, int index, _Unwind_Word val)
   gcc_assert (index < (int) sizeof(dwarf_reg_size_table));
   size = dwarf_reg_size_table[index];
 
+#ifdef UNIQUE_UNWIND_CONTEXT
+  gcc_assert (context->dwarf_reg_size_table == &dwarf_reg_size_table);
+  if (context->reg[index] == &context->value[index])
+    {
+      context->value[index] = val;
+      return;
+    }
+#else
   if (_Unwind_IsExtendedContext (context) && context->by_value[index])
     {
       context->reg[index] = (void *) (_Unwind_Internal_Ptr) val;
       return;
     }
+#endif
 
   ptr = context->reg[index];
 
@@ -230,8 +263,10 @@  static inline void *
 _Unwind_GetGRPtr (struct _Unwind_Context *context, int index)
 {
   index = DWARF_REG_TO_UNWIND_COLUMN (index);
+#ifndef UNIQUE_UNWIND_CONTEXT
   if (_Unwind_IsExtendedContext (context) && context->by_value[index])
     return &context->reg[index];
+#endif
   return context->reg[index];
 }
 
@@ -241,8 +276,10 @@  static inline void
 _Unwind_SetGRPtr (struct _Unwind_Context *context, int index, void *p)
 {
   index = DWARF_REG_TO_UNWIND_COLUMN (index);
+#ifndef UNIQUE_UNWIND_CONTEXT
   if (_Unwind_IsExtendedContext (context))
     context->by_value[index] = 0;
+#endif
   context->reg[index] = p;
 }
 
@@ -254,10 +291,15 @@  _Unwind_SetGRValue (struct _Unwind_Context *context, int index,
 {
   index = DWARF_REG_TO_UNWIND_COLUMN (index);
   gcc_assert (index < (int) sizeof(dwarf_reg_size_table));
+#ifdef UNIQUE_UNWIND_CONTEXT
+  gcc_assert (dwarf_reg_size_table[index] == sizeof (_Unwind_Word));
+  context->value[index] = val;
+  context->reg[index] = &context->value[index];
+#else
   gcc_assert (dwarf_reg_size_table[index] == sizeof (_Unwind_Ptr));
-
   context->by_value[index] = 1;
   context->reg[index] = (void *) (_Unwind_Internal_Ptr) val;
+#endif
 }
 
 /* Return nonzero if register INDEX is stored by value rather than
@@ -267,7 +309,11 @@  static inline int
 _Unwind_GRByValue (struct _Unwind_Context *context, int index)
 {
   index = DWARF_REG_TO_UNWIND_COLUMN (index);
+#ifdef UNIQUE_UNWIND_CONTEXT
+  return context->reg[index] == &context->value[index];
+#else
   return context->by_value[index];
+#endif
 }
 
 /* Retrieve the return address for CONTEXT.  */
@@ -1217,7 +1263,11 @@  __frame_state_for (void *pc_target, struct frame_state *state_in)
   int reg;
 
   memset (&context, 0, sizeof (struct _Unwind_Context));
+#ifdef UNIQUE_UNWIND_CONTEXT
+  context.dwarf_reg_size_table = &dwarf_reg_size_table;
+#else
   context.flags = EXTENDED_CONTEXT_BIT;
+#endif
   context.ra = pc_target + 1;
 
   if (uw_frame_state_for (&context, &fs) != _URC_NO_REASON)
@@ -1455,7 +1505,11 @@  uw_init_context_1 (struct _Unwind_Context *context,
 
   memset (context, 0, sizeof (struct _Unwind_Context));
   context->ra = ra;
+#ifdef UNIQUE_UNWIND_CONTEXT
+  context->dwarf_reg_size_table = &dwarf_reg_size_table;
+#else
   context->flags = EXTENDED_CONTEXT_BIT;
+#endif
 
   code = uw_frame_state_for (context, &fs);
   gcc_assert (code == _URC_NO_REASON);
@@ -1537,8 +1591,13 @@  uw_install_context_1 (struct _Unwind_Context *current,
       void *c = current->reg[i];
       void *t = target->reg[i];
 
+#ifdef UNIQUE_UNWIND_CONTEXT
+      gcc_assert (current->reg[i] != &current->value[i]);
+      if (target->reg[i] == &target->value[i] && c)
+#else
       gcc_assert (current->by_value[i] == 0);
       if (target->by_value[i] && c)
+#endif
 	{
 	  _Unwind_Word w;
 	  _Unwind_Ptr p;