[patch 3/4] x86, ptrace: change interface to newest-to-oldest array

[Markus Metzger <markus.t.metzger@intel.com>]

Change the ptrace user interface to use an array from newest to oldest BTS entry.
This eliminates the need for the GET_INDEX command.

I could further imagine combining ALLOCATE_BUFFER with CONFIG and GET_BUFFER_SIZE with STATUS. This would bring the interface down to 3 commands (config, status, read), but it would require struct to be passed for config and status.

Signed-off-by: Markus Metzger <markus.t.metzger@intel.com>
---

Index: linux-2.6-x86/arch/x86/kernel/ptrace.c
===================================================================
--- linux-2.6-x86.orig/arch/x86/kernel/ptrace.c	2007-12-10 11:14:26.%N +0100
+++ linux-2.6-x86/arch/x86/kernel/ptrace.c	2007-12-10 11:34:20.%N +0100
@@ -479,26 +479,33 @@
 	return ds_get_bts_size((void *)child->thread.ds_area_msr);
 }
 
-static int ptrace_bts_get_index(struct task_struct *child)
-{
-	if (!child->thread.ds_area_msr)
-		return -ENXIO;
-
-	return ds_get_bts_index((void *)child->thread.ds_area_msr);
-}
-
 static int ptrace_bts_read_record(struct task_struct *child,
 				  long index,
 				  struct bts_struct __user *out)
 {
 	struct bts_struct ret;
 	int retval;
+	int bts_size;
+	int bts_index;
 
 	if (!child->thread.ds_area_msr)
 		return -ENXIO;
 
+	if (index < 0)
+		return -EINVAL;
+
+	bts_size = ds_get_bts_size((void *)child->thread.ds_area_msr);
+	if (bts_size <= index)
+		return -EINVAL;
+
+	/* translate the ptrace bts index into the ds bts index */
+	bts_index = ds_get_bts_index((void *)child->thread.ds_area_msr);
+	bts_index -= (index + 1);
+	if (bts_index < 0)
+		bts_index += bts_size;
+
 	retval = ds_read_bts((void *)child->thread.ds_area_msr,
-			     index, &ret);
+			     bts_index, &ret);
 	if (retval)
 		return retval;
 
@@ -813,10 +820,6 @@
 		ret = ptrace_bts_get_buffer_size(child);
 		break;
 
-	case PTRACE_BTS_GET_INDEX:
-		ret = ptrace_bts_get_index(child);
-		break;
-
 	case PTRACE_BTS_READ_RECORD:
 		ret = ptrace_bts_read_record
 			(child, data,
@@ -1017,7 +1020,6 @@
 	case PTRACE_BTS_MAX_BUFFER_SIZE:
 	case PTRACE_BTS_ALLOCATE_BUFFER:
 	case PTRACE_BTS_GET_BUFFER_SIZE:
-	case PTRACE_BTS_GET_INDEX:
 	case PTRACE_BTS_READ_RECORD:
 	case PTRACE_BTS_CONFIG:
 	case PTRACE_BTS_STATUS:
Index: linux-2.6-x86/include/asm-x86/ptrace-abi.h
===================================================================
--- linux-2.6-x86.orig/include/asm-x86/ptrace-abi.h	2007-12-10 11:14:26.%N +0100
+++ linux-2.6-x86/include/asm-x86/ptrace-abi.h	2007-12-10 11:16:27.%N +0100
@@ -99,32 +99,27 @@
    ENXIO........no buffer allocated */
 #define PTRACE_BTS_GET_BUFFER_SIZE 42
 
-/* Return the index of the next bts record to be written,
-   if successful; -1, otherwise.
-   EOPNOTSUPP...processor does not support bts tracing
-   ENXIO........no buffer allocated
-   After the first warp-around, this is the start of the circular bts buffer. */
-#define PTRACE_BTS_GET_INDEX 43
-
-/* Read the DATA'th bts record into a ptrace_bts_record buffer provided in ADDR.
+/* Read the DATA'th bts record into a ptrace_bts_record buffer
+   provided in ADDR.
+   Records are ordered from newest to oldest.
    Return 0, if successful; -1, otherwise
    EOPNOTSUPP...processor does not support bts tracing
    ENXIO........no buffer allocated
    EINVAL.......invalid index */
-#define PTRACE_BTS_READ_RECORD 44
+#define PTRACE_BTS_READ_RECORD 43
 
 /* Configure last branch trace; the configuration is given as a bit-mask of
    PTRACE_BTS_O_* options in DATA; parameter ADDR is ignored.
    Return 0, if successful; -1, otherwise
    EOPNOTSUPP...processor does not support bts tracing
    ENXIO........no buffer allocated */
-#define PTRACE_BTS_CONFIG 45
+#define PTRACE_BTS_CONFIG 44
 
 /* Return the configuration as bit-mask of PTRACE_BTS_O_* options
    if successful; -1, otherwise.
    EOPNOTSUPP...processor does not support bts tracing
    ENXIO........no buffer allocated */
-#define PTRACE_BTS_STATUS 46
+#define PTRACE_BTS_STATUS 45
 
 /* Trace configuration options */
 /* Collect last branch trace */
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