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[ARM/FDPIC v6 11/24] [ARM] FDPIC: Add support to unwind FDPIC signal frame

From: Christophe Lyon <christophe dot lyon at st dot com>
To: <gcc-patches at gcc dot gnu dot org>
Date: Mon, 9 Sep 2019 17:44:53 +0200
Subject: [ARM/FDPIC v6 11/24] [ARM] FDPIC: Add support to unwind FDPIC signal frame
References: <20190909154526.11630-1-christophe.lyon@st.com>

From: Christophe Lyon <christophe.lyon@linaro.org>

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.

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

References:
- [ARM/FDPIC v6 00/24] FDPIC ABI for ARM
  - From: Christophe Lyon

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