[PATCH] i386nbsd_pc_in_sigtramp robustness

[Jason R Thorpe <thorpej@wasabisystems.com>]

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The strategy of comparing against hard-coded addresses to find the
signal trampoline is a bad one; it is possible for the user to change
the VM layout, and thus the location of the signal trampoline, with a
kernel option.

The following patch changes the i386-netbsd* targets to disassemble to
find the trampoline, as is done for other NetBSD targets.

Committed to trunk.

	* i386nbsd-tdep.c (i386nbsd_sigtramp_offset): New function.
	(i386nbsd_pc_in_sigtramp): Rewrite to use i386nbsd_sigtramp_offset.
	(i386nbsd_init_abi): Don't initialize tdep->sigtramp_start or
	tdep->sigtramp_end.
	(i386nbsd_sigtramp_start, i386nbsd_sigtramp_end): Remove.
	* config/i386/tm-nbsd.h (SIGTRAMP_START, SIGTRAMP_END)
	(i386bsd_sigtramp_start, i386bsd_sigtramp_end): Remove.

-- 
        -- Jason R. Thorpe <thorpej@wasabisystems.com>

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Index: i386nbsd-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/i386nbsd-tdep.c,v
retrieving revision 1.7
diff -c -r1.7 i386nbsd-tdep.c
*** i386nbsd-tdep.c	1 Sep 2002 23:24:19 -0000	1.7
--- i386nbsd-tdep.c	2 Sep 2002 16:26:23 -0000
***************
*** 140,162 ****
    NULL					/* next */
  };
  
! static int
! i386nbsd_pc_in_sigtramp (CORE_ADDR pc, char *name)
  {
!   struct gdbarch_tdep *tdep = gdbarch_tdep (current_gdbarch);
  
!   /* Check for libc-provided signal trampoline.  */
!   if (nbsd_pc_in_sigtramp (pc, name))
!     return 1;
  
!   /* FIXME: sigtramp_start/sigtramp_end need to go away; we should
!      not be assuming the location of the kernel-provided trampoline!  */
  
!   return (pc >= tdep->sigtramp_start && pc < tdep->sigtramp_end);
  }
  
! CORE_ADDR i386nbsd_sigtramp_start = 0xbfbfdf20;
! CORE_ADDR i386nbsd_sigtramp_end = 0xbfbfdff0;
  
  /* From <machine/signal.h>.  */
  int i386nbsd_sc_pc_offset = 44;
--- 140,240 ----
    NULL					/* next */
  };
  
! /* Under NetBSD/i386, signal handler invocations can be identified by the
!    designated code sequence that is used to return from a signal handler.
!    In particular, the return address of a signal handler points to the
!    following code sequence:
! 
! 	leal	0x10(%esp), %eax
! 	pushl	%eax
! 	pushl	%eax
! 	movl	$0x127, %eax		# __sigreturn14
! 	int	$0x80
! 
!    Each instruction has a unique encoding, so we simply attempt to match
!    the instruction the PC is pointing to with any of the above instructions.
!    If there is a hit, we know the offset to the start of the designated
!    sequence and can then check whether we really are executing in the
!    signal trampoline.  If not, -1 is returned, otherwise the offset from the
!    start of the return sequence is returned.  */
! #define RETCODE_INSN1		0x8d
! #define RETCODE_INSN2		0x50
! #define RETCODE_INSN3		0x50
! #define RETCODE_INSN4		0xb8
! #define RETCODE_INSN5		0xcd
! 
! #define RETCODE_INSN2_OFF	4
! #define RETCODE_INSN3_OFF	5
! #define RETCODE_INSN4_OFF	6
! #define RETCODE_INSN5_OFF	11
! 
! static const unsigned char sigtramp_retcode[] =
  {
!   RETCODE_INSN1, 0x44, 0x24, 0x10,
!   RETCODE_INSN2,
!   RETCODE_INSN3,
!   RETCODE_INSN4, 0x27, 0x01, 0x00, 0x00,
!   RETCODE_INSN5, 0x80,
! };
  
! static LONGEST
! i386nbsd_sigtramp_offset (CORE_ADDR pc)
! {
!   unsigned char ret[sizeof(sigtramp_retcode)], insn;
!   LONGEST off;
!   int i;
! 
!   if (read_memory_nobpt (pc, &insn, 1) != 0)
!     return -1;
! 
!   switch (insn)
!     {
!     case RETCODE_INSN1:
!       off = 0;
!       break;
! 
!     case RETCODE_INSN2:
!       /* INSN2 and INSN3 are the same.  Read at the location of PC+1
! 	 to determine if we're actually looking at INSN2 or INSN3.  */
!       if (read_memory_nobpt (pc + 1, &insn, 1) != 0)
! 	return -1;
! 
!       if (insn == RETCODE_INSN3)
! 	off = RETCODE_INSN2_OFF;
!       else
! 	off = RETCODE_INSN3_OFF;
!       break;
! 
!     case RETCODE_INSN4:
!       off = RETCODE_INSN4_OFF;
!       break;
! 
!     case RETCODE_INSN5:
!       off = RETCODE_INSN5_OFF;
!       break;
! 
!     default:
!       return -1;
!     }
! 
!   pc -= off;
! 
!   if (read_memory_nobpt (pc, (char *) ret, sizeof (ret)) != 0)
!     return -1;
  
!   if (memcmp (ret, sigtramp_retcode, sizeof (ret)) == 0)
!     return off;
  
!   return -1;
  }
  
! static int
! i386nbsd_pc_in_sigtramp (CORE_ADDR pc, char *name)
! {
! 
!   return (nbsd_pc_in_sigtramp (pc, name)
! 	  || i386nbsd_sigtramp_offset (pc) >= 0);
! }
  
  /* From <machine/signal.h>.  */
  int i386nbsd_sc_pc_offset = 44;
***************
*** 175,184 ****
  
    /* NetBSD uses -freg-struct-return by default.  */
    tdep->struct_return = reg_struct_return;
- 
-   /* NetBSD uses a different memory layout.  */
-   tdep->sigtramp_start = i386nbsd_sigtramp_start;
-   tdep->sigtramp_end = i386nbsd_sigtramp_end;
  
    /* NetBSD has a `struct sigcontext' that's different from the
       origional 4.3 BSD.  */
--- 253,258 ----
Index: config/i386/tm-nbsd.h
===================================================================
RCS file: /cvs/src/src/gdb/config/i386/tm-nbsd.h,v
retrieving revision 1.13
diff -c -r1.13 tm-nbsd.h
*** config/i386/tm-nbsd.h	30 Jun 2002 17:22:57 -0000	1.13
--- config/i386/tm-nbsd.h	2 Sep 2002 16:26:26 -0000
***************
*** 23,38 ****
  
  #include "i386/tm-i386.h"
  
- /* These defines allow the recognition of sigtramps as a function name
-    <sigtramp>.
- 
-    FIXME: kettenis/2002-05-12: Of course these defines will have to go
-    if we go truly "multi-arch", but I don't know yet how to get rid of
-    them.  */
- 
- #define SIGTRAMP_START(pc) i386bsd_sigtramp_start (pc)
- #define SIGTRAMP_END(pc) i386bsd_sigtramp_end (pc)
- extern CORE_ADDR i386bsd_sigtramp_start (CORE_ADDR pc);
- extern CORE_ADDR i386bsd_sigtramp_end (CORE_ADDR pc);
- 
  #endif /* TM_NBSD_H */
--- 23,26 ----