Re: unw_step loops forever on MIPS.

[Story, Lenny]

Sergey,

That patch worked great.

Thanks For the super quick response.

-Lenny

---

From: Sergey Korolev <s.korolev@ndmsystems.com>
Sent: Tuesday, June 8, 2021 4:58 PM
To: Story, Lenny <lstory@irobot.com>
Cc: libunwind-devel@nongnu.org <libunwind-devel@nongnu.org>
Subject: Re: unw_step loops forever on MIPS.

 

Lenny, please try an attached patch (https://github.com/keenetic/libunwind/commit/d746635d2b8d44b3dddbc333cfcd32f9fe8b213d).

From d746635d2b8d44b3dddbc333cfcd32f9fe8b213d Mon Sep 17 00:00:00 2001
From: Sergey Korolev <s.korolev@ndmsystems.com>
Date: Tue, 22 Jan 2019 23:56:38 +0300
Subject: [PATCH] mips: fix regression after "Handle Gstep according the N64/N32 ABI"

unw_step should return zero for _MIPS_SIM != _ABI64 when dwarf_step failed
(restore unw_step behaviour before 5eec9a2ecb9a93996d566bbfbcdbe006f64b7e16).
---
 src/mips/Gstep.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/mips/Gstep.c b/src/mips/Gstep.c
index f5a742e1..b967dd89 100644
--- a/src/mips/Gstep.c
+++ b/src/mips/Gstep.c
@@ -208,11 +208,14 @@ unw_step (unw_cursor_t *cursor)
   if (unlikely (ret == -UNW_ESTOPUNWIND))
     return ret;
 
-#if _MIPS_SIM == _ABI64
   if (unlikely (ret < 0))
     {
+#if _MIPS_SIM == _ABI64
       return _step_n64(c);
-    }
+#else
+      return ret;
 #endif
+    }
+
   return (c->dwarf.ip == 0) ? 0 : 1;
 }
--
2.25.1

On Tue, Jun 8, 2021 at 11:39 PM Story, Lenny <lstory@irobot.com> wrote:

Greetings,

I have a test of libunwind running on my mips target.  It seems the the unw_step api always returns > 0. This results in my backtrace loop never terminating.  

Any thoughts on why this would happen ?

Thanks !

-Lenny

I am using 1.5.0.

 [BACKTRACE] (1) main:140

 [BACKTRACE] (1) _init:736

 [BACKTRACE] (1) _init:736

 [BACKTRACE] (1) _init:736

 [BACKTRACE] (1) _init:736

 [BACKTRACE] (1) _init:736

 [BACKTRACE] (1) _init:736

 [BACKTRACE] (1) _init:736

 [BACKTRACE] (1) _init:736

 [BACKTRACE] (1) _init:736

 [BACKTRACE] (1) _init:736

 [BACKTRACE] (1) _init:736

void show_backtrace(void)

{

    char symbol[256];

    unw_cursor_t  cursor;

    unw_context_t context;

   

    unw_getcontext(&context);    

    unw_init_local(&cursor, &context);

   

    int Cursor_Result = 0;

    int n = 0;

   

    while((Cursor_Result = unw_step(&cursor)) > 0)

    {

        unw_word_t ip;

        unw_word_t sp;

        unw_word_t off;

   

        unw_get_reg(&cursor, UNW_REG_IP, &ip);

        unw_get_reg(&cursor, UNW_REG_SP, &sp);              

       

        memset(&symbol, 0, sizeof(symbol));

       

        if (unw_get_proc_name(&cursor, &symbol[0], sizeof(symbol), &off) == 0)

        {

            fprintf(stdout, "[BACKTRACE] (%d) %s:%d \n", Cursor_Result, &symbol[0], off);            

        }        

        if(n++ > 10)

            break;

    }

}

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