Re: [ARM/FDPIC v5 11/21] [ARM] FDPIC: Add support to unwind FDPIC signal frame

[Kyrill Tkachov <kyrylo.tkachov@foss.arm.com>]

Hi Christophe,

On 5/15/19 1:39 PM, Christophe Lyon wrote:
> 2019-XX-XX  Christophe Lyon <christophe.lyon@st.com>
>         Mickaël Guêné <mickael.guene@st.com>
>
>         libgcc/
>         * unwind-arm-common.inc (ARM_SET_R7_RT_SIGRETURN)
>         (THUMB2_SET_R7_RT_SIGRETURN, FDPIC_LDR_R12_WITH_FUNCDESC)
>         (FDPIC_LDR_R9_WITH_GOT, FDPIC_LDR_PC_WITH_RESTORER)
>         (FDPIC_FUNCDESC_OFFSET, ARM_NEW_RT_SIGFRAME_UCONTEXT)
>         (ARM_UCONTEXT_SIGCONTEXT, ARM_SIGCONTEXT_R0, 
> FDPIC_T2_LDR_R12_WITH_FUNCDESC)
>         (FDPIC_T2_LDR_R9_WITH_GOT, FDPIC_T2_LDR_PC_WITH_RESTORER): New.
>         (__gnu_personality_sigframe_fdpic): New.
>         (get_eit_entry): Add FDPIC signal frame support.
>

At this point I'm looking that the code is FDPIC-specific and thus won't 
break other targets.

I'll have to trust your testing that this is correct for FDPIC.

Ok.

Thanks,

Kyrill


> Change-Id: I7f9527cc50665dd1a731b7badf71c319fb38bf57
>
> diff --git a/libgcc/unwind-arm-common.inc b/libgcc/unwind-arm-common.inc
> index 0bacc11..c9a82b7 100644
> --- a/libgcc/unwind-arm-common.inc
> +++ b/libgcc/unwind-arm-common.inc
> @@ -30,6 +30,26 @@
>  #include <sys/sdt.h>
>  #endif
>
> +#if __FDPIC__
> +/* Load r7 with rt_sigreturn value.  */
> +#define ARM_SET_R7_RT_SIGRETURN 0xe3a070ad      /* mov   r7, #0xad */
> +#define THUMB2_SET_R7_RT_SIGRETURN     0x07adf04f      /* mov.w r7, 
> #0xad */
> +
> +/* FDPIC jump to restorer sequence.  */
> +#define FDPIC_LDR_R12_WITH_FUNCDESC    0xe59fc004      /* ldr   r12, 
> [pc, #4] */
> +#define FDPIC_LDR_R9_WITH_GOT          0xe59c9004      /* ldr   r9, 
> [r12, #4] */
> +#define FDPIC_LDR_PC_WITH_RESTORER     0xe59cf000      /* ldr   pc, 
> [r12] */
> +#define FDPIC_T2_LDR_R12_WITH_FUNCDESC  0xc008f8df     /* ldr.w r12, 
> [pc, #8] */
> +#define FDPIC_T2_LDR_R9_WITH_GOT       0x9004f8dc      /* ldr.w r9, 
> [r12, #4] */
> +#define FDPIC_T2_LDR_PC_WITH_RESTORER   0xf000f8dc     /* ldr.w pc, 
> [r12] */
> +#define FDPIC_FUNCDESC_OFFSET          12
> +
> +/* Signal frame offsets.  */
> +#define ARM_NEW_RT_SIGFRAME_UCONTEXT   0x80
> +#define ARM_UCONTEXT_SIGCONTEXT                0x14
> +#define ARM_SIGCONTEXT_R0              0xc
> +#endif
> +
>  /* We add a prototype for abort here to avoid creating a dependency on
>     target headers.  */
>  extern void abort (void);
> @@ -199,6 +219,45 @@ search_EIT_table (const __EIT_entry * table, int 
> nrec, _uw return_address)
>      }
>  }
>
> +#if __FDPIC__
> +/* VFP is not restored, but this is sufficient to allow unwinding.  */
> +static _Unwind_Reason_Code
> +__gnu_personality_sigframe_fdpic (_Unwind_State state,
> +                                 _Unwind_Control_Block *ucbp,
> +                                 _Unwind_Context *context)
> +{
> +    unsigned int sp;
> +    unsigned int pc;
> +    unsigned int funcdesc;
> +    unsigned int handler;
> +    unsigned int first_handler_instruction;
> +    int i;
> +
> +    _Unwind_VRS_Get (context, _UVRSC_CORE, R_SP, _UVRSD_UINT32, &sp);
> +    _Unwind_VRS_Get (context, _UVRSC_CORE, R_PC, _UVRSD_UINT32, &pc);
> +
> +    funcdesc = *(unsigned int *)((pc & ~1) + FDPIC_FUNCDESC_OFFSET);
> +    handler = *(unsigned int *)(funcdesc);
> +    first_handler_instruction = *(unsigned int *)(handler & ~1);
> +
> +    /* Adjust SP to point to the start of registers according to
> +       signal type.  */
> +    if (first_handler_instruction == ARM_SET_R7_RT_SIGRETURN
> +       || first_handler_instruction == THUMB2_SET_R7_RT_SIGRETURN)
> +       sp += ARM_NEW_RT_SIGFRAME_UCONTEXT
> +         + ARM_UCONTEXT_SIGCONTEXT
> +         + ARM_SIGCONTEXT_R0;
> +    else
> +       sp += ARM_UCONTEXT_SIGCONTEXT
> +         + ARM_SIGCONTEXT_R0;
> +    /* Restore regs saved on stack by the kernel.  */
> +    for (i = 0; i < 16; i++)
> +       _Unwind_VRS_Set (context, _UVRSC_CORE, i, _UVRSD_UINT32, sp + 
> 4 * i);
> +
> +    return _URC_CONTINUE_UNWIND;
> +}
> +#endif
> +
>  /* Find the exception index table eintry for the given address.
>     Fill in the relevant fields of the UCB.
>     Returns _URC_FAILURE if an error occurred, _URC_OK on success.  */
> @@ -222,6 +281,27 @@ get_eit_entry (_Unwind_Control_Block *ucbp, _uw 
> return_address)
> &nrec);
>        if (!eitp)
>          {
> +#if __FDPIC__
> +         /* If we are unwinding a signal handler then perhaps we have
> +            reached a trampoline.  Try to detect jump to restorer
> +            sequence.  */
> +         _uw *pc = (_uw *)((return_address+2) & ~1);
> +         if ((pc[0] == FDPIC_LDR_R12_WITH_FUNCDESC
> +              && pc[1] == FDPIC_LDR_R9_WITH_GOT
> +              && pc[2] == FDPIC_LDR_PC_WITH_RESTORER)
> +             || (pc[0] == FDPIC_T2_LDR_R12_WITH_FUNCDESC
> +                 && pc[1] == FDPIC_T2_LDR_R9_WITH_GOT
> +                 && pc[2] == FDPIC_T2_LDR_PC_WITH_RESTORER))
> +           {
> +             struct funcdesc_t *funcdesc
> +               = (struct funcdesc_t *) &__gnu_personality_sigframe_fdpic;
> +
> +             UCB_PR_ADDR (ucbp) = funcdesc->ptr;
> +             UCB_PR_GOT (ucbp) = funcdesc->got;
> +
> +             return _URC_OK;
> +           }
> +#endif
>            UCB_PR_ADDR (ucbp) = 0;
>            return _URC_FAILURE;
>          }
> @@ -236,6 +316,27 @@ get_eit_entry (_Unwind_Control_Block *ucbp, _uw 
> return_address)
>
>    if (!eitp)
>      {
> +#if __FDPIC__
> +      /* If we are unwinding a signal handler then perhaps we have
> +        reached a trampoline.  Try to detect jump to restorer
> +        sequence.  */
> +      _uw *pc = (_uw *)((return_address+2) & ~1);
> +      if ((pc[0] == FDPIC_LDR_R12_WITH_FUNCDESC
> +          && pc[1] == FDPIC_LDR_R9_WITH_GOT
> +          && pc[2] == FDPIC_LDR_PC_WITH_RESTORER)
> +         || (pc[0] == FDPIC_T2_LDR_R12_WITH_FUNCDESC
> +             && pc[1] == FDPIC_T2_LDR_R9_WITH_GOT
> +             && pc[2] == FDPIC_T2_LDR_PC_WITH_RESTORER))
> +       {
> +         struct funcdesc_t *funcdesc
> +           = (struct funcdesc_t *) &__gnu_personality_sigframe_fdpic;
> +
> +         UCB_PR_ADDR (ucbp) = funcdesc->ptr;
> +         UCB_PR_GOT (ucbp) = funcdesc->got;
> +
> +         return _URC_OK;
> +       }
> +#endif
>        UCB_PR_ADDR (ucbp) = 0;
>        return _URC_FAILURE;
>      }
> @@ -244,6 +345,27 @@ get_eit_entry (_Unwind_Control_Block *ucbp, _uw 
> return_address)
>    /* Can this frame be unwound at all?  */
>    if (eitp->content == EXIDX_CANTUNWIND)
>      {
> +#if __FDPIC__
> +      /* If we are unwinding a signal handler then perhaps we have
> +        reached a trampoline.  Try to detect jump to restorer
> +        sequence.  */
> +      _uw *pc = (_uw *)((return_address+2) & ~1);
> +      if ((pc[0] == FDPIC_LDR_R12_WITH_FUNCDESC
> +          && pc[1] == FDPIC_LDR_R9_WITH_GOT
> +          && pc[2] == FDPIC_LDR_PC_WITH_RESTORER)
> +         || (pc[0] == FDPIC_T2_LDR_R12_WITH_FUNCDESC
> +             && pc[1] == FDPIC_T2_LDR_R9_WITH_GOT
> +             && pc[2] == FDPIC_T2_LDR_PC_WITH_RESTORER))
> +       {
> +         struct funcdesc_t *funcdesc
> +           = (struct funcdesc_t *) &__gnu_personality_sigframe_fdpic;
> +
> +         UCB_PR_ADDR (ucbp) = funcdesc->ptr;
> +         UCB_PR_GOT (ucbp) = funcdesc->got;
> +
> +         return _URC_OK;
> +       }
> +#endif
>        UCB_PR_ADDR (ucbp) = 0;
>        return _URC_END_OF_STACK;
>      }
> -- 
> 2.6.3
>