Re: [ARM/FDPIC v5 06/21] [ARM] FDPIC: Add support for c++ exceptions

[Jonathan Wakely <jwakely@redhat.com>]

On 30/08/19 10:02 +0100, Kyrill Tkachov wrote:
>As Richard mentioned in an earlier post the generic libgcc and 
>libstdc++ changes will need approval from the relevant maintainers.
>
>CC'ing the libstdc++ list and the libgcc maintainer.

The libstdc++ change is OK for trunk.


>On 5/15/19 1:39 PM, Christophe Lyon wrote:
>>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 wrappers that directly
>>call the kernel helpers.
>>
>>When restoring a function address, we also have to restore the FDPIC
>>register value (r9).
>>
>>2019-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 (FDPIC_REGNUM): New define.
>>        (gnu_Unwind_Find_got): New function.
>>        (_Unwind_decode_typeinfo_ptr): Add FDPIC support.
>>        * unwind-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: I64b81cfaf390a05f2fd121f44ba1912cb4b47cae
>>
>>diff --git a/gcc/ginclude/unwind-arm-common.h 
>>b/gcc/ginclude/unwind-arm-common.h
>>index 6df783e..d4eb03e 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): */
>>diff --git a/libgcc/config/arm/linux-atomic.c 
>>b/libgcc/config/arm/linux-atomic.c
>>index 06a6d46..565f829 100644
>>--- a/libgcc/config/arm/linux-atomic.c
>>+++ b/libgcc/config/arm/linux-atomic.c
>>@@ -25,11 +25,62 @@ 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);
>>-#define __kernel_cmpxchg (*(__kernel_cmpxchg_t *) 0xffff0fc0)
>>+
>>+#define STR(X) #X
>>+#define XSTR(X) STR(X)
>>+
>>+#define KERNEL_CMPXCHG 0xffff0fc0
>>+
>>+#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 *) KERNEL_CMPXCHG)
>>+#endif
>>
>> /* Kernel helper for memory barrier.  */
>> typedef void (__kernel_dmb_t) (void);
>>-#define __kernel_dmb (*(__kernel_dmb_t *) 0xffff0fa0)
>>+
>>+#define KERNEL_DMB 0xffff0fa0
>>+
>>+#if __FDPIC__
>>+#define __kernel_dmb __fdpic_dmb
>>+#else
>>+#define __kernel_dmb (*(__kernel_dmb_t *) KERNEL_DMB)
>>+#endif
>>+
>>+#if __FDPIC__
>>+static int __fdpic_cmpxchg (int oldval, int newval, int *ptr)
>>+{
>>+  int result;
>>+
>>+  asm volatile (
>>+               "ldr    ip, 1f\n\t"
>>+               "bx     ip\n\t"
>>+               "1:\n\t"
>>+               ".word " XSTR(KERNEL_CMPXCHG) "\n\t"
>>+               : "=r" (result)
>>+               : "r" (oldval) , "r" (newval), "r" (ptr)
>>+               : "r3", "memory");
>>+  /* The result is actually returned by the kernel helper, we need
>>+     this to avoid a warning.  */
>>+  return result;
>>+}
>>+
>>+static void __fdpic_dmb (void)
>>+{
>>+  asm volatile (
>>+               "ldr    ip, 1f\n\t"
>>+               "bx     ip\n\t"
>>+               "1:\n\t"
>>+               ".word " XSTR(KERNEL_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 43c5379..2bf320a 100644
>>--- a/libgcc/config/arm/unwind-arm.h
>>+++ b/libgcc/config/arm/unwind-arm.h
>>@@ -33,9 +33,33 @@
>> /* Use IP as a scratch register within the personality routine.  */
>> #define UNWIND_POINTER_REG 12
>>
>>+#define FDPIC_REGNUM 9
>>+
>>+#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 +72,12 @@ 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 fd572fe..0bacc11 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 +86,16 @@ 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 +270,21 @@ 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 +295,10 @@ 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 +320,29 @@ 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 +390,18 @@ 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 +438,11 @@ 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 +488,18 @@ __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 +557,27 @@ __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 +669,20 @@ __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 4ed1c66..1c9dae5 100644
>>--- a/libgcc/unwind-pe.h
>>+++ b/libgcc/unwind-pe.h
>>@@ -262,10 +262,27 @@ 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 35e4e46..1528ab9 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
>>