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List:       wine-devel
Subject:    Re: What is the meaning of the 200 __clone lines in backtraces?
From:       Daniel Santos <daniel.santos () pobox ! com>
Date:       2015-11-26 22:22:29
Message-ID: 56578625.9000808 () pobox ! com
[Download RAW message or body]

On 11/26/2015 03:40 PM, Qian Hong wrote:
> Hi Bruno,
> 
> On Fri, Nov 27, 2015 at 12:36 AM, Bruno Jesus <00cpxxx@gmail.com> wrote:
> > Up to 200. Is this a bug or it is just not possible to identify when
> > the backtrace ends and 200 is a hard limit or what else could it be?
> 'Up to 200' is limited by WineDbg
> 
> stack.c:
> 185  * Do a backtrace on the current thread
> 186  */
> 187 unsigned stack_fetch_frames(const CONTEXT* _ctx)
> 
> 239         if (nf > 200 || !ret) break;
> 
> There is also:
> dbg.tab.c:/* YYINITDEPTH -- initial size of the parser's stacks.  */
> dbg.tab.c:#ifndef YYINITDEPTH
> dbg.tab.c:# define YYINITDEPTH 200
> 
> However, I'm also curious by repeat of '__clone', I don't understand
> this part, hopefully someone else can explain it ;-)

Funny timing on this question. I've had a patch for this sitting in my local branch \
for a month or so and finally submitted it last night (attached). My guess has always \
been that when a process is forked (since that's how Linux babies are made) that \
something wasn't reading that stack frame correctly and just looped it. The call to \
clone would have happened in the process that spawned us, like /bin/bash if you \
started it from a bash shell.

There's likely a cleaner approach than this patch, but this one at least makes \
"backtrace all" readable for me.

Daniel


["0001-winedbg-suppress-bogus-clone-frames-in-backtrace.txt" (text/plain)]

From d4e80308c347a000db4bae59aeb873d1364f72c8 Mon Sep 17 00:00:00 2001
From: Daniel Santos <daniel.santos@pobox.com>
Date: Fri, 13 Nov 2015 19:36:40 -0600
Subject: winedbg: suppress bogus clone() frames in backtrace

Signed-off-by: Daniel Santos <daniel.santos@pobox.com>
---
 programs/winedbg/stack.c | 27 ++++++++++++++++++++++-----
 1 file changed, 22 insertions(+), 5 deletions(-)

diff --git a/programs/winedbg/stack.c b/programs/winedbg/stack.c
index f49480a..8ef2dbc 100644
--- a/programs/winedbg/stack.c
+++ b/programs/winedbg/stack.c
@@ -307,6 +307,11 @@ static void stack_print_addr_and_args(int nf)
                     im.ModuleName, (DWORD_PTR)(ihsf.InstructionOffset - im.BaseOfImage));
 }
 
+static int addr_is_nonzero(const ADDRESS64 *addr)
+{
+    return addr->Offset && (addr->Mode != AddrModeFlat || addr->Segment);
+}
+
 /******************************************************************
  *		backtrace
  *
@@ -322,12 +327,24 @@ static void backtrace(void)
          dbg_curr_thread->curr_frame < dbg_curr_thread->num_frames;
          dbg_curr_thread->curr_frame++)
     {
-        dbg_printf("%s%d ", 
-                   (cf == dbg_curr_thread->curr_frame ? "=>" : "  "),
-                   dbg_curr_thread->curr_frame);
-        stack_print_addr_and_args(dbg_curr_thread->curr_frame);
+        const unsigned nf     = dbg_curr_thread->curr_frame;
+        const ADDRESS64 *addr = &dbg_curr_thread->frames[nf].addr_frame;
+
+        /* suppress bogus clone() frames from repeating */
+        if (nf > 0
+            && !addr_is_nonzero(addr)
+            && !addr_is_nonzero(&dbg_curr_thread->frames[nf - 1u].addr_frame)
+            && !memcmp(&dbg_curr_thread->frames[nf].addr_pc,
+                       &dbg_curr_thread->frames[nf - 1u].addr_pc,
+                       sizeof(dbg_curr_thread->frames[nf].addr_pc)))
+        {
+            break;
+        }
+
+        dbg_printf("%s%2u ", (cf == nf ? "=>" : "  "), nf);
+        stack_print_addr_and_args(nf);
         dbg_printf(" (");
-        print_bare_address(&dbg_curr_thread->frames[dbg_curr_thread->curr_frame].addr_frame);
+        print_bare_address(addr);
         dbg_printf(")\n");
     }
     /* reset context to current stack frame */
-- 
2.5.1





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