xenctx: Add -n (--display-stack-pages) option to output larger stack

Important: This is the stack size (also known as stack limit) to
display, not the configured stack size.

Note: use with caution (easy to get garbage).

Below is a pictures of a downwards growing configured 3 page stack,
and where the SP currently is.  Each box is a page.

+ pages                     -n 1    -n 2    -n 3

End of Memory
       +------------------+
       |                  |
       |                  |
       |                  |
       |                  |
       |                  |
       +------------------+
...
       +------------------+
       |                  |
       |                  |
       |                  |
       |                  |
MAX+3  |                  |
       +------------------+                   *
       |                  |                   |
       |                  |                   |
       |                  |                   |
       |                  |                   |
MAX+2  |                  |                   |
       +------------------+           *       |
       |                  |           |       |
       |                  |           |       |
       |                  |           |       |
       |                  |           |       |
MAX+1  |                  |           |       |
       +------------------+   *       |       |
       |                  |   |       |       |
SP --> |                  |   *       *       *
       |                  |
       |                  |
MAX    |                  |
       +------------------+
...
       +------------------+
       |                  |
       |                  |
       |                  |
       |                  |
0      |                  |
       +------------------+

Display using "-n 3" since the used stack pages is 3.

At a different time, the SP may be in the 1st page and so "-n 3"
will display garbage.

For example:

$ xenctx -s /boot/System.map-2.6.32-279.2.1.el6.x86_64 3 1 -n 1
...
Call Trace:
                    [<ffffffff81346898>] io_serial_out+0x18 <--
ffff880032bb1310:   [<ffffffff81346f51>] serial8250_console_putchar+0x31
ffff880032bb1330:   [<ffffffff813428de>] uart_console_write+0x3e
ffff880032bb1338:   [<ffffffff8100bc0e>] apic_timer_interrupt+0xe
ffff880032bb1370:   [<ffffffff813472ad>] serial8250_console_write+0xbd
ffff880032bb13c0:   [<ffffffff8106b8f5>] __call_console_drivers+0x75
ffff880032bb13f0:   [<ffffffff8106b95a>] _call_console_drivers+0x4a
ffff880032bb1410:   [<ffffffff8106be6e>] release_console_sem+0x4e
ffff880032bb1450:   [<ffffffff8106c628>] vprintk+0x248
ffff880032bb14f0:   [<ffffffff814fd363>] printk+0x41

$ xenctx -s /boot/System.map-2.6.32-279.2.1.el6.x86_64 3 1 -n 2
...
Call Trace:
                    [<ffffffff81346898>] io_serial_out+0x18 <--
ffff880032bb1310:   [<ffffffff81346f51>] serial8250_console_putchar+0x31
ffff880032bb1330:   [<ffffffff813428de>] uart_console_write+0x3e
ffff880032bb1338:   [<ffffffff8100bc0e>] apic_timer_interrupt+0xe
ffff880032bb1370:   [<ffffffff813472ad>] serial8250_console_write+0xbd
ffff880032bb13c0:   [<ffffffff8106b8f5>] __call_console_drivers+0x75
ffff880032bb13f0:   [<ffffffff8106b95a>] _call_console_drivers+0x4a
ffff880032bb1410:   [<ffffffff8106be6e>] release_console_sem+0x4e
ffff880032bb1450:   [<ffffffff8106c628>] vprintk+0x248
ffff880032bb14f0:   [<ffffffff814fd363>] printk+0x41

$ xenctx -s /boot/System.map-2.6.32-279.2.1.el6.x86_64 3 1 -n 3
...
Call Trace:
                    [<ffffffff81346898>] io_serial_out+0x18 <--
ffff880032bb1310:   [<ffffffff81346f51>] serial8250_console_putchar+0x31
ffff880032bb1330:   [<ffffffff813428de>] uart_console_write+0x3e
ffff880032bb1338:   [<ffffffff8100bc0e>] apic_timer_interrupt+0xe
ffff880032bb1370:   [<ffffffff813472ad>] serial8250_console_write+0xbd
ffff880032bb13c0:   [<ffffffff8106b8f5>] __call_console_drivers+0x75
ffff880032bb13f0:   [<ffffffff8106b95a>] _call_console_drivers+0x4a
ffff880032bb1410:   [<ffffffff8106be6e>] release_console_sem+0x4e
ffff880032bb1450:   [<ffffffff8106c628>] vprintk+0x248
ffff880032bb14f0:   [<ffffffff814fd363>] printk+0x41
ffff880032bb3f20:   [<ffffffff8100204c>] do_one_initcall+0x3c
ffff880032bb3f50:   [<ffffffff810b0eb1>] sys_init_module+0xe1
ffff880032bb3f80:   [<ffffffff8100b0f2>] system_call_fastpath+0x16

Signed-off-by: Don Slutz <Don@CloudSwitch.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

tools/xentrace/xenctx.c

@@ -35,11 +35,14 @@ static struct xenctx {
     int frame_ptrs;
     int stack_trace;
     int disp_all;
+    int nr_stack_pages;
     int all_vcpus;
     int self_paused;
     xc_dominfo_t dominfo;
 } xenctx;
 
+#define DEFAULT_NR_STACK_PAGES 1
+
 #if defined (__i386__) || defined (__x86_64__)
 typedef unsigned long long guest_word_t;
 #define FMT_32B_WORD "%08llx"
@@ -663,7 +666,8 @@ static int print_stack(vcpu_guest_context_any_t *ctx, int vcpu, int width)
     int i;
 
     stack_limit = ((stack_pointer(ctx) + XC_PAGE_SIZE)
-                   & ~((guest_word_t) XC_PAGE_SIZE - 1));
+                   & ~((guest_word_t) XC_PAGE_SIZE - 1))
+                   + (xenctx.nr_stack_pages - 1) * XC_PAGE_SIZE;
     printf("\n");
     printf("Stack:\n");
     for (i=1; i<5 && stack < stack_limit; i++) {
@@ -834,18 +838,24 @@ static void usage(void)
         kernel_start);
     printf("  -a, --all          display more registers\n");
     printf("  -C, --all-vcpus    print info for all vcpus\n");
+    printf("  -n PAGES, --display-stack-pages=PAGES\n");
+    printf("                     Display N pages from the stack pointer. (default %d)\n",
+           DEFAULT_NR_STACK_PAGES);
+    printf("                     Changes stack limit.  Note: use with caution (easy\n");
+    printf("                     to get garbage).\n");
 }
 
 int main(int argc, char **argv)
 {
     int ch;
     int ret;
-    static const char *sopts = "fs:hak:SC";
+    static const char *sopts = "fs:hak:SCn:";
     static const struct option lopts[] = {
         {"stack-trace", 0, NULL, 'S'},
         {"symbol-table", 1, NULL, 's'},
         {"frame-pointers", 0, NULL, 'f'},
         {"kernel-start", 1, NULL, 'k'},
+        {"display-stack-pages", 0, NULL, 'n'},
         {"all", 0, NULL, 'a'},
         {"all-vcpus", 0, NULL, 'C'},
         {"help", 0, NULL, 'h'},
@@ -855,6 +865,8 @@ int main(int argc, char **argv)
 
     int vcpu = 0;
 
+    xenctx.nr_stack_pages = DEFAULT_NR_STACK_PAGES;
+
     while ((ch = getopt_long(argc, argv, sopts, lopts, NULL)) != -1) {
         switch(ch) {
         case 'f':
@@ -869,6 +881,16 @@ int main(int argc, char **argv)
         case 'a':
             xenctx.disp_all = 1;
             break;
+        case 'n':
+            xenctx.nr_stack_pages = strtol(optarg, NULL, 0);
+            if ( xenctx.nr_stack_pages < 1)
+            {
+                fprintf(stderr,
+                        "%s: Unsupported value(%d) for --display-stack-pages '%s'. Needs to be >= 1\n",
+                        argv[0], xenctx.nr_stack_pages, optarg);
+                exit(-1);
+            }
+            break;
         case 'C':
             xenctx.all_vcpus = 1;
             break;