[PATCH] i386: multi-column stack backtraces

Print stack backtraces in multiple columns, saving screen space.  Number of
columns is configurable and defaults to one so behavior is
backwards-compatible.

Also removes the brackets around addresses when printing more
that one entry per line so they print as:
    <address>
instead of:
    [<address>]
This helps multiple entries fit better on one line.

Original idea by Dave Jones, taken from x86_64.

Signed-off-by: Chuck Ebbert <76306.1226@compuserve.com>
Signed-off-by: Dave Jones <davej@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 36 insertions, 5 deletions

diff --git a/arch/i386/Kconfig.debug b/arch/i386/Kconfig.debug
index bf32ecc9ad04..00108ba9a78d 100644
--- a/arch/i386/Kconfig.debug
+++ b/arch/i386/Kconfig.debug
@@ -31,6 +31,15 @@ config DEBUG_STACK_USAGE
 
           This option will slow down process creation somewhat.
 
+config STACK_BACKTRACE_COLS
+        int "Stack backtraces per line" if DEBUG_KERNEL
+        range 1 3
+        default 2
+        help
+          Selects how many stack backtrace entries per line to display.
+
+          This can save screen space when displaying traces.
+
 comment "Page alloc debug is incompatible with Software Suspend on i386"
         depends on DEBUG_KERNEL && SOFTWARE_SUSPEND
 
diff --git a/arch/i386/kernel/traps.c b/arch/i386/kernel/traps.c
index b814dbdcc91e..ee61988f61b5 100644
--- a/arch/i386/kernel/traps.c
+++ b/arch/i386/kernel/traps.c
@@ -112,12 +112,30 @@ static inline int valid_stack_ptr(struct thread_info *tinfo, void *p)
                 p < (void *)tinfo + THREAD_SIZE - 3;
 }
 
-static void print_addr_and_symbol(unsigned long addr, char *log_lvl)
+/*
+ * Print CONFIG_STACK_BACKTRACE_COLS address/symbol entries per line.
+ */
+static inline int print_addr_and_symbol(unsigned long addr, char *log_lvl,
+                                        int printed)
 {
-        printk(log_lvl);
+        if (!printed)
+                printk(log_lvl);
+
+#if CONFIG_STACK_BACKTRACE_COLS == 1
         printk(" [<%08lx>] ", addr);
+#else
+        printk(" <%08lx> ", addr);
+#endif
         print_symbol("%s", addr);
-        printk("\n");
+
+        printed = (printed + 1) % CONFIG_STACK_BACKTRACE_COLS;
+
+        if (printed)
+                printk("  ");
+        else
+                printk("\n");
+
+        return printed;
 }
 
 static inline unsigned long print_context_stack(struct thread_info *tinfo,
@@ -125,20 +143,24 @@ static inline unsigned long print_context_stack(struct thread_info *tinfo,
                                 char *log_lvl)
 {
         unsigned long addr;
+        int printed = 0; /* nr of entries already printed on current line */
 
 #ifdef  CONFIG_FRAME_POINTER
         while (valid_stack_ptr(tinfo, (void *)ebp)) {
                 addr = *(unsigned long *)(ebp + 4);
-                print_addr_and_symbol(addr, log_lvl);
+                printed = print_addr_and_symbol(addr, log_lvl, printed);
                 ebp = *(unsigned long *)ebp;
         }
 #else
         while (valid_stack_ptr(tinfo, stack)) {
                 addr = *stack++;
                 if (__kernel_text_address(addr))
-                        print_addr_and_symbol(addr, log_lvl);
+                        printed = print_addr_and_symbol(addr, log_lvl, printed);
         }
 #endif
+        if (printed)
+                printk("\n");
+
         return ebp;
 }