Convert have_ptrace_getregset to a tri-state boolean

have_ptrace_getregset is a tri-state variable (-1, 0, 1), and we have
some conditions like "if (have_ptrace_getregset)", which is not correct.
I'll explain why it is not correct in the following example.  This fix
to this problem to replace the test (have_ptrace_getregset) to test
(have_ptrace_getregset == 1) or (have_ptrace_getregset == -1) etc.
However Doug thinks it hinders readability
https://sourceware.org/ml/gdb-patches/2015-05/msg00692.html so I decide
to add a new enum tribool and change have_ptrace_getregset to it, in
order to make these tests more readable.

have_ptrace_getregset is initialised to -1, and is adjusted to 0 or 1 in
$ARCH_linux_read_description according to the capability of the kernel.
However, it is possible that have_ptrace_getregset is used before it is
set to 0 or 1, which means it is still -1.  This is shown below.

(gdb) run
Starting program: gdb/testsuite/gdb.base/break

Breakpoint 2, amd64_linux_fetch_inferior_registers (ops=0xceaa80, regcache=0xe72000, regnum=16) at git/gdb/amd64-linux-nat.c:128
128	{
top?p have_ptrace_getregset
$1 = TRIBOOL_UNKNOWN
top?c
Continuing.

Breakpoint 2, amd64_linux_fetch_inferior_registers (ops=0xceaa80, regcache=0xe72000, regnum=16) at git/gdb/amd64-linux-nat.c:128
128	{
top?c
Continuing.

Breakpoint 1, x86_linux_read_description (ops=0xceaa80) at git/gdb/x86-linux-nat.c:117
117	{

PTRACE_GETREGSET command is used even GDB doesn't know whether
PTRACE_GETREGSET is supported or not.  It is wrong, but works on x86.
However it doesn't work on arm-linux if the kernel doesn't support
PTRACE_GETREGSET at all.  We'll get:

(gdb) run
Starting program: gdb/testsuite/gdb.base/break
warning: Unable to fetch general register.
PC register is not available

gdb:

2015-06-23  Yao Qi  <yao.qi@linaro.org>

	* amd64-linux-nat.c (amd64_linux_fetch_inferior_registers):
	Check whether have_ptrace_getregset is TRIBOOL_TRUE explicitly.
	(amd64_linux_store_inferior_registers): Likewise.
	* arm-linux-nat.c (fetch_fpregister): Likewise.
	(fetch_fpregs, store_fpregister): Likewise.
	(store_fpregister, store_fpregs): Likewise.
	(fetch_register, fetch_regs): Likewise.
	(store_register, store_regs): Likewise.
	(fetch_vfp_regs, store_vfp_regs): Likewise.
	(arm_linux_read_description): Check have_ptrace_getregset is
	TRIBOOL_UNKNOWN.  Set have_ptrace_getregset to TRIBOOL_TRUE
	or TRIBOOL_FALSE.
	* i386-linux-nat.c (fetch_xstateregs): Check
	have_ptrace_getregset is not TRIBOOL_TRUE.
	(store_xstateregs): Likewise.
	* linux-nat.c (have_ptrace_getregset): Change its type to
	enum tribool.
	* linux-nat.h (tribool): New enum.
	* x86-linux-nat.c (x86_linux_read_description): Use enum tribool.
	Check whether have_ptrace_getregset is TRIBOOL_TRUE.

7 files changed, 53 insertions, 29 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index fd611ad..6e26db0 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,26 @@
+2015-06-23  Yao Qi  <yao.qi@linaro.org>
+
+	* amd64-linux-nat.c (amd64_linux_fetch_inferior_registers):
+	Check whether have_ptrace_getregset is TRIBOOL_TRUE explicitly.
+	(amd64_linux_store_inferior_registers): Likewise.
+	* arm-linux-nat.c (fetch_fpregister): Likewise.
+	(fetch_fpregs, store_fpregister): Likewise.
+	(store_fpregister, store_fpregs): Likewise.
+	(fetch_register, fetch_regs): Likewise.
+	(store_register, store_regs): Likewise.
+	(fetch_vfp_regs, store_vfp_regs): Likewise.
+	(arm_linux_read_description): Check have_ptrace_getregset is
+	TRIBOOL_UNKNOWN.  Set have_ptrace_getregset to TRIBOOL_TRUE
+	or TRIBOOL_FALSE.
+	* i386-linux-nat.c (fetch_xstateregs): Check
+	have_ptrace_getregset is not TRIBOOL_TRUE.
+	(store_xstateregs): Likewise.
+	* linux-nat.c (have_ptrace_getregset): Change its type to
+	enum tribool.
+	* linux-nat.h (tribool): New enum.
+	* x86-linux-nat.c (x86_linux_read_description): Use enum tribool.
+	Check whether have_ptrace_getregset is TRIBOOL_TRUE.
+
 2015-06-19  Doug Evans  <dje@google.com>
 
 	* NEWS: Mention Sun's version of stabs is no longer supported.
diff --git a/gdb/amd64-linux-nat.c b/gdb/amd64-linux-nat.c
index 30892ca..2e1b081 100644
--- a/gdb/amd64-linux-nat.c
+++ b/gdb/amd64-linux-nat.c
@@ -150,7 +150,7 @@ amd64_linux_fetch_inferior_registers (struct target_ops *ops,
     {
       elf_fpregset_t fpregs;
 
-      if (have_ptrace_getregset)
+      if (have_ptrace_getregset == TRIBOOL_TRUE)
 	{
 	  char xstateregs[X86_XSTATE_MAX_SIZE];
 	  struct iovec iov;
@@ -209,7 +209,7 @@ amd64_linux_store_inferior_registers (struct target_ops *ops,
     {
       elf_fpregset_t fpregs;
 
-      if (have_ptrace_getregset)
+      if (have_ptrace_getregset == TRIBOOL_TRUE)
 	{
 	  char xstateregs[X86_XSTATE_MAX_SIZE];
 	  struct iovec iov;
diff --git a/gdb/arm-linux-nat.c b/gdb/arm-linux-nat.c
index 10aea07..c167bce 100644
--- a/gdb/arm-linux-nat.c
+++ b/gdb/arm-linux-nat.c
@@ -95,7 +95,7 @@ fetch_fpregister (struct regcache *regcache, int regno)
   tid = GET_THREAD_ID (inferior_ptid);
 
   /* Read the floating point state.  */
-  if (have_ptrace_getregset)
+  if (have_ptrace_getregset == TRIBOOL_TRUE)
     {
       struct iovec iov;
 
@@ -136,7 +136,7 @@ fetch_fpregs (struct regcache *regcache)
   tid = GET_THREAD_ID (inferior_ptid);
 
   /* Read the floating point state.  */
-  if (have_ptrace_getregset)
+  if (have_ptrace_getregset == TRIBOOL_TRUE)
     {
       struct iovec iov;
 
@@ -176,7 +176,7 @@ store_fpregister (const struct regcache *regcache, int regno)
   tid = GET_THREAD_ID (inferior_ptid);
 
   /* Read the floating point state.  */
-  if (have_ptrace_getregset)
+  if (have_ptrace_getregset == TRIBOOL_TRUE)
     {
       struct iovec iov;
 
@@ -203,7 +203,7 @@ store_fpregister (const struct regcache *regcache, int regno)
   if (regno >= ARM_F0_REGNUM && regno <= ARM_F7_REGNUM)
     collect_nwfpe_register (regcache, regno, fp);
 
-  if (have_ptrace_getregset)
+  if (have_ptrace_getregset == TRIBOOL_TRUE)
     {
       struct iovec iov;
 
@@ -235,7 +235,7 @@ store_fpregs (const struct regcache *regcache)
   tid = GET_THREAD_ID (inferior_ptid);
 
   /* Read the floating point state.  */
-  if (have_ptrace_getregset)
+  if (have_ptrace_getregset == TRIBOOL_TRUE)
     {
       elf_fpregset_t fpregs;
       struct iovec iov;
@@ -263,7 +263,7 @@ store_fpregs (const struct regcache *regcache)
     if (REG_VALID == regcache_register_status (regcache, regno))
       collect_nwfpe_register (regcache, regno, fp);
 
-  if (have_ptrace_getregset)
+  if (have_ptrace_getregset == TRIBOOL_TRUE)
     {
       struct iovec iov;
 
@@ -294,7 +294,7 @@ fetch_register (struct regcache *regcache, int regno)
   /* Get the thread id for the ptrace call.  */
   tid = GET_THREAD_ID (inferior_ptid);
 
-  if (have_ptrace_getregset)
+  if (have_ptrace_getregset == TRIBOOL_TRUE)
     {
       struct iovec iov;
 
@@ -347,7 +347,7 @@ fetch_regs (struct regcache *regcache)
   /* Get the thread id for the ptrace call.  */
   tid = GET_THREAD_ID (inferior_ptid);
 
-  if (have_ptrace_getregset)
+  if (have_ptrace_getregset == TRIBOOL_TRUE)
     {
       struct iovec iov;
 
@@ -397,7 +397,7 @@ store_register (const struct regcache *regcache, int regno)
   tid = GET_THREAD_ID (inferior_ptid);
 
   /* Get the general registers from the process.  */
-  if (have_ptrace_getregset)
+  if (have_ptrace_getregset == TRIBOOL_TRUE)
     {
       struct iovec iov;
 
@@ -424,7 +424,7 @@ store_register (const struct regcache *regcache, int regno)
     regcache_raw_collect (regcache, ARM_PC_REGNUM,
 			 (char *) &regs[ARM_PC_REGNUM]);
 
-  if (have_ptrace_getregset)
+  if (have_ptrace_getregset == TRIBOOL_TRUE)
     {
       struct iovec iov;
 
@@ -453,7 +453,7 @@ store_regs (const struct regcache *regcache)
   tid = GET_THREAD_ID (inferior_ptid);
 
   /* Fetch the general registers.  */
-  if (have_ptrace_getregset)
+  if (have_ptrace_getregset == TRIBOOL_TRUE)
     {
       struct iovec iov;
 
@@ -481,7 +481,7 @@ store_regs (const struct regcache *regcache)
     regcache_raw_collect (regcache, ARM_PS_REGNUM,
 			 (char *) &regs[ARM_CPSR_GREGNUM]);
 
-  if (have_ptrace_getregset)
+  if (have_ptrace_getregset == TRIBOOL_TRUE)
     {
       struct iovec iov;
 
@@ -593,7 +593,7 @@ fetch_vfp_regs (struct regcache *regcache)
   /* Get the thread id for the ptrace call.  */
   tid = GET_THREAD_ID (inferior_ptid);
 
-  if (have_ptrace_getregset)
+  if (have_ptrace_getregset == TRIBOOL_TRUE)
     {
       struct iovec iov;
 
@@ -629,7 +629,7 @@ store_vfp_regs (const struct regcache *regcache)
   /* Get the thread id for the ptrace call.  */
   tid = GET_THREAD_ID (inferior_ptid);
 
-  if (have_ptrace_getregset)
+  if (have_ptrace_getregset == TRIBOOL_TRUE)
     {
       struct iovec iov;
 
@@ -653,7 +653,7 @@ store_vfp_regs (const struct regcache *regcache)
   regcache_raw_collect (regcache, ARM_FPSCR_REGNUM,
 			(char *) regbuf + 32 * 8);
 
-  if (have_ptrace_getregset)
+  if (have_ptrace_getregset == TRIBOOL_TRUE)
     {
       struct iovec iov;
 
@@ -797,7 +797,7 @@ arm_linux_read_description (struct target_ops *ops)
 {
   CORE_ADDR arm_hwcap = 0;
 
-  if (have_ptrace_getregset == -1)
+  if (have_ptrace_getregset == TRIBOOL_UNKNOWN)
     {
       elf_gregset_t gpregs;
       struct iovec iov;
@@ -808,9 +808,9 @@ arm_linux_read_description (struct target_ops *ops)
 
       /* Check if PTRACE_GETREGSET works.  */
       if (ptrace (PTRACE_GETREGSET, tid, NT_PRSTATUS, &iov) < 0)
-	have_ptrace_getregset = 0;
+	have_ptrace_getregset = TRIBOOL_FALSE;
       else
-	have_ptrace_getregset = 1;
+	have_ptrace_getregset = TRIBOOL_TRUE;
     }
 
   if (target_auxv_search (ops, AT_HWCAP, &arm_hwcap) != 1)
diff --git a/gdb/i386-linux-nat.c b/gdb/i386-linux-nat.c
index 4401a2f..349ce68 100644
--- a/gdb/i386-linux-nat.c
+++ b/gdb/i386-linux-nat.c
@@ -327,7 +327,7 @@ fetch_xstateregs (struct regcache *regcache, int tid)
   char xstateregs[X86_XSTATE_MAX_SIZE];
   struct iovec iov;
 
-  if (!have_ptrace_getregset)
+  if (have_ptrace_getregset != TRIBOOL_TRUE)
     return 0;
 
   iov.iov_base = xstateregs;
@@ -350,7 +350,7 @@ store_xstateregs (const struct regcache *regcache, int tid, int regno)
   char xstateregs[X86_XSTATE_MAX_SIZE];
   struct iovec iov;
 
-  if (!have_ptrace_getregset)
+  if (have_ptrace_getregset != TRIBOOL_TRUE)
     return 0;
   
   iov.iov_base = xstateregs;
diff --git a/gdb/linux-nat.c b/gdb/linux-nat.c
index 88f4e3e..be429f8 100644
--- a/gdb/linux-nat.c
+++ b/gdb/linux-nat.c
@@ -166,7 +166,7 @@ blocked.  */
 #endif
 
 /* Does the current host support PTRACE_GETREGSET?  */
-int have_ptrace_getregset = -1;
+enum tribool have_ptrace_getregset = TRIBOOL_UNKNOWN;
 
 /* The single-threaded native GNU/Linux target_ops.  We save a pointer for
    the use of the multi-threaded target.  */
diff --git a/gdb/linux-nat.h b/gdb/linux-nat.h
index 3d766b5..cae263a 100644
--- a/gdb/linux-nat.h
+++ b/gdb/linux-nat.h
@@ -116,7 +116,8 @@ struct lwp_info
 extern struct lwp_info *lwp_list;
 
 /* Does the current host support PTRACE_GETREGSET?  */
-extern int have_ptrace_getregset;
+enum tribool { TRIBOOL_UNKNOWN = -1, TRIBOOL_FALSE = 0, TRIBOOL_TRUE = 1 };
+extern enum tribool have_ptrace_getregset;
 
 /* Iterate over each active thread (light-weight process).  */
 #define ALL_LWPS(LP)							\
diff --git a/gdb/x86-linux-nat.c b/gdb/x86-linux-nat.c
index 5d8f7c7..04917d0 100644
--- a/gdb/x86-linux-nat.c
+++ b/gdb/x86-linux-nat.c
@@ -162,13 +162,13 @@ x86_linux_read_description (struct target_ops *ops)
       if (ptrace (PTRACE_GETFPXREGS, tid, 0, (int) &fpxregs) < 0)
 	{
 	  have_ptrace_getfpxregs = 0;
-	  have_ptrace_getregset = 0;
+	  have_ptrace_getregset = TRIBOOL_FALSE;
 	  return tdesc_i386_mmx_linux;
 	}
     }
 #endif
 
-  if (have_ptrace_getregset == -1)
+  if (have_ptrace_getregset == TRIBOOL_UNKNOWN)
     {
       uint64_t xstateregs[(X86_XSTATE_SSE_SIZE / sizeof (uint64_t))];
       struct iovec iov;
@@ -179,10 +179,10 @@ x86_linux_read_description (struct target_ops *ops)
       /* Check if PTRACE_GETREGSET works.  */
       if (ptrace (PTRACE_GETREGSET, tid,
 		  (unsigned int) NT_X86_XSTATE, &iov) < 0)
-	have_ptrace_getregset = 0;
+	have_ptrace_getregset = TRIBOOL_FALSE;
       else
 	{
-	  have_ptrace_getregset = 1;
+	  have_ptrace_getregset = TRIBOOL_TRUE;
 
 	  /* Get XCR0 from XSAVE extended state.  */
 	  xcr0 = xstateregs[(I386_LINUX_XSAVE_XCR0_OFFSET
@@ -194,7 +194,7 @@ x86_linux_read_description (struct target_ops *ops)
      PTRACE_GETREGSET is not available then set xcr0_features_bits to
      zero so that the "no-features" descriptions are returned by the
      switches below.  */
-  if (have_ptrace_getregset)
+  if (have_ptrace_getregset == TRIBOOL_TRUE)
     xcr0_features_bits = xcr0 & X86_XSTATE_ALL_MASK;
   else
     xcr0_features_bits = 0;