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

Kyrill Tkachov kyrylo.tkachov@foss.arm.com
Fri Aug 30 09:31:00 GMT 2019 

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.

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
>

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