2000-03-04 Mark Kettenis <kettenis@gnu.org>

	Fix support for Linux/i386 signal trampolines.  The old approach
	didn't work for Linux 2.2 and beyond, and didn't work with recent
	versions of the GNU C library.
	* i386-tdep.c (LINUX_RT_SIGTRAMP_INSN0, LINUX_RT_SIGTRAMP_OFFSET0,
	LINUX_RT_SIGTRAMP_INSN1, LINUX_RT_SIGTRAMP_OFFSET1): New defines.
	(linux_rt_sigtramp_code): New variable.
	(LINUX_RT_SIGTRAMP_LEN): New define.
	(i386_linux_rt_sigtramp_start): New function.  Detect start of
	signal trampolines for RT signals.
	(i386_linux_sigtramp): Removed.
	(i386_linux_in_sigtramp): New function.
	(i386_linux_sigcontext_addr): New function.  Recognize the names
	of the signal tranmpolines used by recent versions of the GNU C
	library, and add support for RT signals.
        (LINUX_SIGCONTEXT_PC_OFFSET, LINUX_SIGCONTEXT_SP_OFFSET):  New
	defines.  Moved here from config/i386/tm-linux.h.
	(i386_linux_sigtramp_saved_pc, i386_linux_sigtramp_saved_sp):
	Reimplement in terms of i386_linux_sigcontext_addr.
	* config/i386/tm-linux.h (LINUX_SIGCONTEXT_SIZE): Removed.
        (LINUX_SIGCONTEXT_PC_OFFSET, LINUX_SIGCONTEXT_SP_OFFSET):
        Moved to i386-tdep.c.
	(IN_SIGTRAMP): Redefine to call i386_linux_in_sigtramp.

1 files changed, 147 insertions, 34 deletions

diff --git a/gdb/i386-tdep.c b/gdb/i386-tdep.c
index c381961..10011f6 100644
--- a/gdb/i386-tdep.c
+++ b/gdb/i386-tdep.c
@@ -781,11 +781,19 @@ i386v4_sigtramp_saved_pc (frame)
 
 #ifdef I386_LINUX_SIGTRAMP
 
-/* When the i386 Linux kernel calls a signal handler, the return
-   address points to a bit of code on the stack.  This function
-   returns whether the PC appears to be within this bit of code.
-
-   The instruction sequence is
+/* Linux has two flavors of signals.  Normal signal handlers, and
+   "realtime" (RT) signals.  The RT signals can provide additional
+   information to the signal handler if the SA_SIGINFO flag is set
+   when establishing a signal handler using `sigaction'.  It is not
+   unlikely that future versions of Linux will support SA_SIGINFO for
+   normal signals too.  */
+
+/* When the i386 Linux kernel calls a signal handler and the
+   SA_RESTORER flag isn't set, the return address points to a bit of
+   code on the stack.  This function returns whether the PC appears to
+   be within this bit of code.
+
+   The instruction sequence for normal signals is
        pop    %eax
        mov    $0x77,%eax
        int    $0x80
@@ -799,7 +807,15 @@ i386v4_sigtramp_saved_pc (frame)
    order to identify a signal trampoline, but there doesn't seem to be
    any other way.  The IN_SIGTRAMP macro in tm-linux.h arranges to
    only call us if no function name could be identified, which should
-   be the case since the code is on the stack.  */
+   be the case since the code is on the stack.
+
+   Detection of signal trampolines for handlers that set the
+   SA_RESTORER flag is in general not possible.  Unfortunately this is
+   what the GNU C Library has been doing for quite some time now.
+   However, as of version 2.1.2, the GNU C Library uses signal
+   trampolines (named __restore and __restore_rt) that are identical
+   to the ones used by the kernel.  Therefore, these trampolines are
+   supported too.  */
 
 #define LINUX_SIGTRAMP_INSN0 (0x58)	/* pop %eax */
 #define LINUX_SIGTRAMP_OFFSET0 (0)
@@ -821,8 +837,7 @@ static const unsigned char linux_sigtramp_code[] =
    the routine.  Otherwise, return 0.  */
 
 static CORE_ADDR
-i386_linux_sigtramp_start (pc)
-     CORE_ADDR pc;
+i386_linux_sigtramp_start (CORE_ADDR pc)
 {
   unsigned char buf[LINUX_SIGTRAMP_LEN];
 
@@ -864,51 +879,149 @@ i386_linux_sigtramp_start (pc)
   return pc;
 }
 
+/* This function does the same for RT signals.  Here the instruction
+   sequence is
+       mov    $0xad,%eax
+       int    $0x80
+   or 0xb8 0xad 0x00 0x00 0x00 0xcd 0x80.
+
+   The effect is to call the system call rt_sigreturn.  */
+
+#define LINUX_RT_SIGTRAMP_INSN0 (0xb8)	/* mov $NNNN,%eax */
+#define LINUX_RT_SIGTRAMP_OFFSET0 (0)
+#define LINUX_RT_SIGTRAMP_INSN1 (0xcd)	/* int */
+#define LINUX_RT_SIGTRAMP_OFFSET1 (5)
+
+static const unsigned char linux_rt_sigtramp_code[] =
+{
+  LINUX_RT_SIGTRAMP_INSN0, 0xad, 0x00, 0x00, 0x00,	/* mov $0xad,%eax */
+  LINUX_RT_SIGTRAMP_INSN1, 0x80				/* int $0x80 */
+};
+
+#define LINUX_RT_SIGTRAMP_LEN (sizeof linux_rt_sigtramp_code)
+
+/* If PC is in a RT sigtramp routine, return the address of the start
+   of the routine.  Otherwise, return 0.  */
+
+static CORE_ADDR
+i386_linux_rt_sigtramp_start (CORE_ADDR pc)
+{
+  unsigned char buf[LINUX_RT_SIGTRAMP_LEN];
+
+  /* We only recognize a signal trampoline if PC is at the start of
+     one of the two instructions.  We optimize for finding the PC at
+     the start, as will be the case when the trampoline is not the
+     first frame on the stack.  We assume that in the case where the
+     PC is not at the start of the instruction sequence, there will be
+     a few trailing readable bytes on the stack.  */
+
+  if (read_memory_nobpt (pc, (char *) buf, LINUX_RT_SIGTRAMP_LEN) != 0)
+    return 0;
+
+  if (buf[0] != LINUX_RT_SIGTRAMP_INSN0)
+    {
+      if (buf[0] != LINUX_RT_SIGTRAMP_INSN1)
+	return 0;
+
+      pc -= LINUX_RT_SIGTRAMP_OFFSET1;
+
+      if (read_memory_nobpt (pc, (char *) buf, LINUX_RT_SIGTRAMP_LEN) != 0)
+	return 0;
+    }
+
+  if (memcmp (buf, linux_rt_sigtramp_code, LINUX_RT_SIGTRAMP_LEN) != 0)
+    return 0;
+
+  return pc;
+}
+
 /* Return whether PC is in a Linux sigtramp routine.  */
 
 int
-i386_linux_sigtramp (pc)
-     CORE_ADDR pc;
+i386_linux_in_sigtramp (CORE_ADDR pc, char *name)
 {
-  return i386_linux_sigtramp_start (pc) != 0;
+  if (name)
+    return STREQ ("__restore", name) || STREQ ("__restore_rt", name);
+  
+  return (i386_linux_sigtramp_start (pc) != 0
+	  || i386_linux_rt_sigtramp_start (pc) != 0);
 }
 
-/* Assuming FRAME is for a Linux sigtramp routine, return the saved
-   program counter.  The Linux kernel will set up a sigcontext
-   structure immediately before the sigtramp routine on the stack.  */
+/* Assuming FRAME is for a Linux sigtramp routine, return the address
+   of the associated sigcontext structure.  */
 
 CORE_ADDR
-i386_linux_sigtramp_saved_pc (frame)
-     struct frame_info *frame;
+i386_linux_sigcontext_addr (struct frame_info *frame)
 {
   CORE_ADDR pc;
 
   pc = i386_linux_sigtramp_start (frame->pc);
-  if (pc == 0)
-    error ("i386_linux_sigtramp_saved_pc called when no sigtramp");
-  return read_memory_integer ((pc
-			       - LINUX_SIGCONTEXT_SIZE
-			       + LINUX_SIGCONTEXT_PC_OFFSET),
-			      4);
+  if (pc)
+    {
+      CORE_ADDR sp;
+
+      if (frame->next)
+	/* If this isn't the top frame, the next frame must be for the
+	   signal handler itself.  The sigcontext structure lives on
+	   the stack, right after the signum argument.  */
+	return frame->next->frame + 12;
+
+      /* This is the top frame.  We'll have to find the address of the
+	 sigcontext structure by looking at the stack pointer.  Keep
+	 in mind that the first instruction of the sigtramp code is
+	 "pop %eax".  If the PC is at this instruction, adjust the
+	 returned value accordingly.  */
+      sp = read_register (SP_REGNUM);
+      if (pc == frame->pc)
+	return sp + 4;
+      return sp;
+    }
+
+  pc = i386_linux_rt_sigtramp_start (frame->pc);
+  if (pc)
+    {
+      if (frame->next)
+	/* If this isn't the top frame, the next frame must be for the
+	   signal handler itself.  The sigcontext structure is part of
+	   the user context.  A pointer to the user context is passed
+	   as the third argument to the signal handler.  */
+	return read_memory_integer (frame->next->frame + 16, 4) + 20;
+
+      /* This is the top frame.  Again, use the stack pointer to find
+	 the address of the sigcontext structure.  */
+      return read_memory_integer (read_register (SP_REGNUM) + 8, 4) + 20;
+    }
+
+  error ("Couldn't recognize signal trampoline.");
+  return 0;
 }
 
+/* Offset to saved PC in sigcontext, from <asm/sigcontext.h>.  */
+#define LINUX_SIGCONTEXT_PC_OFFSET (56)
+
 /* Assuming FRAME is for a Linux sigtramp routine, return the saved
-   stack pointer.  The Linux kernel will set up a sigcontext structure
-   immediately before the sigtramp routine on the stack.  */
+   program counter.  */
 
 CORE_ADDR
-i386_linux_sigtramp_saved_sp (frame)
-     struct frame_info *frame;
+i386_linux_sigtramp_saved_pc (struct frame_info *frame)
 {
-  CORE_ADDR pc;
+  CORE_ADDR addr;
+  addr = i386_linux_sigcontext_addr (frame);
+  return read_memory_integer (addr + LINUX_SIGCONTEXT_PC_OFFSET, 4);
+}
 
-  pc = i386_linux_sigtramp_start (frame->pc);
-  if (pc == 0)
-    error ("i386_linux_sigtramp_saved_sp called when no sigtramp");
-  return read_memory_integer ((pc
-			       - LINUX_SIGCONTEXT_SIZE
-			       + LINUX_SIGCONTEXT_SP_OFFSET),
-			      4);
+/* Offset to saved SP in sigcontext, from <asm/sigcontext.h>.  */
+#define LINUX_SIGCONTEXT_SP_OFFSET (28)
+
+/* Assuming FRAME is for a Linux sigtramp routine, return the saved
+   stack pointer.  */
+
+CORE_ADDR
+i386_linux_sigtramp_saved_sp (struct frame_info *frame)
+{
+  CORE_ADDR addr;
+  addr = i386_linux_sigcontext_addr (frame);
+  return read_memory_integer (addr + LINUX_SIGCONTEXT_SP_OFFSET, 4);
 }
 
 #endif /* I386_LINUX_SIGTRAMP */