July 2009 - Darwin-dev - lists.apple.com

Re: Using gdb to step through gdb in os x leopard
by Jonas Maebe 08 Jul '09

08 Jul '09

site_archiver(a)lists.apple.com Delivered-To: darwin-dev(a)lists.apple.com On 08 Jul 2009, at 21:42, Aron-Zvi wrote: It works for me with a self-build gdb-908 I still have lying around: Breakpoint 3, main (argc=0, argv=0x0) at gdb.c:31 31 args.argc = argc; (top-gdb) Jonas _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… Either I'm doing something very wrong or there's a bug... I Think I'll try an older version of gdb and see what happens:( firefly:/Data/dev/darwin/10.5/gdb-908/src/gdb jmaebe$ ls -l gdb -rwxr-sr-x 1 jmaebe procmod 3920920 Mar 22 2008 gdb firefly:/Data/dev/darwin/10.5/gdb-908/src/gdb jmaebe$ ./gdb gdb GNU gdb 6.3.50.20050815-cvs (Sat Mar 22 10:18:45 UTC 2008) Copyright 2004 Free Software Foundation, Inc. GDB is free software, covered by the GNU General Public License, and you are welcome to change it and/or distribute copies of it under certain conditions. Type "show copying" to see the conditions. There is absolutely no warranty for GDB. Type "show warranty" for details. This GDB was configured as "--host=i686-apple-darwin9.2.2 -- target="...Reading symbols for shared libraries ........ done Setting up the environment for debugging gdb. During symbol reading, inner block (0x144006-0x1441b4) not inside outer block (0x144006-0x1440a0). Breakpoint 1 at 0x141536: file utils.c, line 932. Breakpoint 2 at 0x8ca4: file cli-cmds.c, line 189. (top-gdb) b main Breakpoint 3 at 0x23e7: file gdb.c, line 31. (top-gdb) r Starting program: /Data/dev/darwin/10.5/gdb-908/src/gdb/gdb Reading symbols for shared libraries +++++++...................... done (this is under Mac OS X 10.5.4 though, haven't updated my laptop in a while) This email sent to site_archiver(a)lists.apple.com

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Re: Using gdb to step through gdb in os x leopard
by Esteban Bodigami 08 Jul '09

08 Jul '09

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Re: Using gdb to step through gdb in os x leopard
by Aron-Zvi 08 Jul '09

08 Jul '09

site_archiver(a)lists.apple.com Delivered-To: darwin-dev(a)lists.apple.com Dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:in-reply-to:references :from:date:message-id:subject:to:cc:content-type; bh=LiCy2i6e7o81YPTBaf5oUCxKhhvSf/Ugj32BnJB7Ckc=; b=UnusB403ZmWAjqb1F95TXm+iueWTdu1i/MFL+pCwX3sMzzbQktV49DhnUpi2R0m17d rTjpAvEtZzBFouYD4QHsAWHVk1527ZBAeqSJPorQi/8cd7qK2JNw5zb2A9c+lbENaCwK mn1NS+pjaSZ28T+S1eZdS0Z0fUspU45uLIME0= Domainkey-signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc:content-type; b=LdHaZaPSAOGQq3CJm1exGKrwjCzSrqn0T29QcAb5IyOumwU7yPAT7oUiKRzltSgflw xC5Zup8wgeF9iQjQa4m/clonzAJEPBxoFXLX3d9IvJTOqNDzpE7VCjOwEmD4Kylv+djP W89++/Fd9vtyl249XwANgA3k5QheRrBifYZ1o= _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… This email sent to site_archiver(a)lists.apple.com

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Re: Using gdb to step through gdb in os x leopard
by Mo McRoberts 08 Jul '09

08 Jul '09

site_archiver(a)lists.apple.com Delivered-To: darwin-dev(a)lists.apple.com On Wed, Jul 8, 2009 at 20:42, Aron-Zvi<aronzvi(a)gmail.com> wrote: > I'm trying to debug gdb-966 downloaded from opensource.apple.com. I've made > no changes whatsoever to the code - Just downloaded and built. I'm debugging > ( or should I say stepping through...) in order to get a better > understanding of how gdb works on OS X. > > I've tried just as you've specified: > As root: > /usr/libexec/gdb/gdb-i386-apple-darwin --args path_to_freshly_built_gdb/gdb > fooprogram Out of sheer curiosity, can either /usr/libexec/gdb/gdb-i386-apple-darwin or path_to_freshly_built_gdb/gdb debug *themselves*? M. -- http://nevali.net _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… This email sent to site_archiver(a)lists.apple.com

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Re: Using gdb to step through gdb in os x leopard
by Aron-Zvi 08 Jul '09

08 Jul '09

site_archiver(a)lists.apple.com Delivered-To: darwin-dev(a)lists.apple.com Dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:in-reply-to:references :from:date:message-id:subject:to:content-type; bh=L0esHiFpj7s4jqtCN2vdKVBhe8kCZ+cBYi6atxlmHQ8=; b=pDVsdKtFlwA4LB9sRAMBdlR2R9enFxZdzvM6BhSlGFU8FwmlKRNkI4W1Gh9Vx+KmKG nejDQp5AIM3ELJzE4VSYsZNVjsT0rU8Rz1dY8cb/mha1h2xWAwwKfTgHKMDDWgwNQFzy mlIidO57W9fF+bSWNa3cB/MiV8YV4JzdYskd8= Domainkey-signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :content-type; b=dnpgynMILbyM1OtrI3jzsmqVT46lI8XXtL1OYYlitSmORrAdMJTKBSoXzon6FU9/9r oKiLN+Dwr8DFHyHTDIf5IxLRyVQwRwmKWLO9flQJqbHJP5RM/nuKQRXWHUlmwK4xsoB5 9Dy1VfI+qwPRf/Y2kWkM9VwOPldXofGJDA9y8= _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… This email sent to site_archiver(a)lists.apple.com

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Re: Using gdb to step through gdb in os x leopard
by Terry Lambert 08 Jul '09

08 Jul '09

site_archiver(a)lists.apple.com Delivered-To: darwin-dev(a)lists.apple.com If the following doesn't work for you, you should write up a bug report: (gdb) b main ... -- Terry Thanks for the detailed reply Terry. How do I get this working? Thanks in advance, Aron-Zvi I'm stepping through gdb with gdb like so: gdb --args ./gdb fooprogram How can I use gdb to step through gdb debugging another process? -- Terry _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… The gdb command itself is a wrapper for /usr/libexec/gdb/*; make sure you are targetting the right binary. I also generally recommend that you default start-with-shell off; there's an historical bug in gdb that may not be fixed in the version you are using/creating where it ptrace's the child, but ends up with the Mach port for the shell instead of the Mach port for the child. This won't cause the symptoms you're claiming here, but it will make it difficult to intercept signals to the child process, since that's done via Mach exception ports, and if they get to ptrace, it's too late, you are going to hit the trampoline in the child whether you want to or not, since a BSD_AST has been raised on the child of the shell at that point. Here's an example; the first gdb is the gdb doing the debugging; the second gdb is the gdb being debugged; the r command passes a parameter as the first argument of the second gdb and starts it running under the second gdb; in this case, /bin/ls; now I am debugging the debugger debugging /bin/ls: # gdb /usr/libexec/gdb/gdb-i386-apple-darwin GNU gdb 6.3.50-20050815 (Apple version gdb-768) (Tue Oct 2 04:11:19 UTC 2007) Copyright 2004 Free Software Foundation, Inc. GDB is free software, covered by the GNU General Public License, and you are welcome to change it and/or distribute copies of it under certain conditions. Type "show copying" to see the conditions. There is absolutely no warranty for GDB. Type "show warranty" for details. This GDB was configured as "i386-apple-darwin"...Reading symbols for shared libraries .......... done (gdb) r /bin/ls Starting program: /usr/libexec/gdb/gdb-i386-apple-darwin /bin/ls Reading symbols for shared libraries ++++++++ + ......................................................................... done GNU gdb 6.3.50-20050815 (Apple version gdb-768) (Tue Oct 2 04:17:32 UTC 2007) Copyright 2004 Free Software Foundation, Inc. GDB is free software, covered by the GNU General Public License, and you are welcome to change it and/or distribute copies of it under certain conditions. Type "show copying" to see the conditions. There is absolutely no warranty for GDB. Type "show warranty" for details. This GDB was configured as "i386-apple-darwin"...Reading symbols for shared libraries .... done I suspect that if you can't do this, you haven't properly integrated Apple's changes to gdb into the gdb you are attempting to debug (so it would make sense that you were trying to debug it...). On Jul 8, 2009, at 3:43 AM, Aron-Zvi wrote: I've tried running the entire thing as root by switching with su before running the command. I've even tried logging in as root. gdb --args ./gdb fooprogram as root still results in "Unable to find Mach task port for process-id pid_of_ fooprogram (os/kern) failure (0x5)" in the debugee gdb when attempting to run fooprogram. Once again, this happens in macosx_ptrace_him() after task_for_pid() . On Wed, Jul 8, 2009 at 9:55 AM, Terry Lambert <tlambert(a)apple.com> wrote: On Jul 7, 2009, at 6:34 PM, Aron-Zvi wrote: Hey guys, I've downloaded and built the most recent gdb available at opensource.apple.com - gdb-966. I'm running OS X Leopard 10.5.7. gdb fails in macosx_ptrace_him() following the task_for_pid() call. task_for_pid() returns 5 which i believe is KERN_FAILURE. The message displayed in the debugger is "Unable to find Mach task port for process-id 8455". When I run just ./gdb fooprogram - everything works fine. gdb's gid is set to procmod. Furthermore, I've even tried running gdb as root with identical results. As a setgid program, you will be unable to debug it unless you run the gdb you are using to debug it as root. This is an intentional security feature in task_for_pid() and in ptrace() to preclude you using the debugger to debug a program with escalated privilege and thus access code, data, or interfaces which you would otherwise not be privileged to access or execute as a privileged user or group. It doesn't matter that the group is the same as gdb itself is running as, what matters is that the credential for that user has been adulterated away from the identity given to the system by DirectoryServices or whatever authentication database you are using to establish the credential in the first place. Credentials are established by escalating privilege, setting up the credential, and dropping privilege. If you run a program that re-escalates privilege, unless it does the little dance to establish its rights to establish a new kernel credential authoritatively, privilege is revoked. In your case, your gdb is only sgid, so it's incapable of obtaining root privilege in order to become an authoritative source of credential information for the kernel. This is also generally why we ask people to rely on login as a gatekeeper, rather than writing their own credential establishing code. This email sent to site_archiver(a)lists.apple.com

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Re: Using gdb to step through gdb in os x leopard
by Jonas Maebe 08 Jul '09

08 Jul '09

site_archiver(a)lists.apple.com Delivered-To: darwin-dev(a)lists.apple.com On 08 Jul 2009, at 12:43, Aron-Zvi wrote: sudo chgrp procamod gdb chmod 2755 gdb Jonas _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… I've tried running the entire thing as root by switching with su before running the command. I've even tried logging in as root. gdb --args ./gdb fooprogram as root still results in "Unable to find Mach task port for process-id *pid_of_ fooprogram *(os/kern) failure (0x5)" in the debugee gdb when attempting to run fooprogram. Once again, this happens in macosx_ptrace_him() after task_for_pid() . I guess you compiled that gdb yourself. On Mac OS X 10.5.x, gdb has to be owned by the procmod group and have mode 2755 to have the appropriate rights to trace other programs. I.e., after compiling gdb, do the following: This email sent to site_archiver(a)lists.apple.com

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Re: Using gdb to step through gdb in os x leopard
by Aron-Zvi 08 Jul '09

08 Jul '09

site_archiver(a)lists.apple.com Delivered-To: darwin-dev(a)lists.apple.com Dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:in-reply-to:references :from:date:message-id:subject:to:content-type; bh=Q10z/vtWRGUwo4Yc9hF0ND15+ZJ4KgZk7nt0tNmHlvc=; b=sEllVFKKdQbmB2uQzgkisAqjuN69n0iJo5fuR2q2kyGd92gDFd8WGvxDfu/6wxs+6P 3l4oN42gMx4ORF8DszJ63ZfFO84YVU4xd/tGs1XL5W/W4L+zu6WGi4wp55fvubRPtate Y4pN5oNgX7p1b8VgjV7zF58NLm4hhNEzqIpwc= Domainkey-signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :content-type; b=QmFffTg4NR3bwDNvfiN8+vLBGP8YPeP9oSKEnmrlDViKLnbju9zAovXpalrPSHYLog OiHzvTuF+W1VyKVbAXSTZ7AlIlwm5j1EG/JRlMoZj2ke6ZkhIF1qL+IYaDecATkx9LyF caJmuzgu/W7KAnF6PLhNVtRnCzqkcBM/oVRI8= _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… This email sent to site_archiver(a)lists.apple.com

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Re: Using gdb to step through gdb in os x leopard
by Terry Lambert 08 Jul '09

08 Jul '09

site_archiver(a)lists.apple.com Delivered-To: darwin-dev(a)lists.apple.com Hey guys, I'm stepping through gdb with gdb like so: gdb --args ./gdb fooprogram -- Terry _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… On Jul 7, 2009, at 6:34 PM, Aron-Zvi wrote: I've downloaded and built the most recent gdb available at opensource.apple.com - gdb-966. I'm running OS X Leopard 10.5.7. gdb fails in macosx_ptrace_him() following the task_for_pid() call. task_for_pid() returns 5 which i believe is KERN_FAILURE. The message displayed in the debugger is "Unable to find Mach task port for process-id 8455". When I run just ./gdb fooprogram - everything works fine. gdb's gid is set to procmod. Furthermore, I've even tried running gdb as root with identical results. How can I use gdb to step through gdb debugging another process? As a setgid program, you will be unable to debug it unless you run the gdb you are using to debug it as root. This is an intentional security feature in task_for_pid() and in ptrace() to preclude you using the debugger to debug a program with escalated privilege and thus access code, data, or interfaces which you would otherwise not be privileged to access or execute as a privileged user or group. It doesn't matter that the group is the same as gdb itself is running as, what matters is that the credential for that user has been adulterated away from the identity given to the system by DirectoryServices or whatever authentication database you are using to establish the credential in the first place. Credentials are established by escalating privilege, setting up the credential, and dropping privilege. If you run a program that re-escalates privilege, unless it does the little dance to establish its rights to establish a new kernel credential authoritatively, privilege is revoked. In your case, your gdb is only sgid, so it's incapable of obtaining root privilege in order to become an authoritative source of credential information for the kernel. This is also generally why we ask people to rely on login as a gatekeeper, rather than writing their own credential establishing code. This email sent to site_archiver(a)lists.apple.com

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Re: Using gdb to step through gdb in os x leopard
by Eli Bach 08 Jul '09

08 Jul '09

site_archiver(a)lists.apple.com Delivered-To: darwin-dev(a)lists.apple.com Dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:received:received:message-id:from:to :in-reply-to:content-type:content-transfer-encoding:subject :mime-version:date:references:x-mailer; bh=u9JaeNhS6fpb9OWYfPb5cNnW44CXT3oNS+FMLa2kiTQ=; b=WH9iU6xURAL0QtEG3xyJRNjz/ASlAa07qcgyrHR1YniNWSnyokkygcu6OcdcnNuQGt chSKwQ+t3uLh++1TkCsduPP5ywozXtxdEgjP8M3Db6Bdz59YeDbYKmZX+RU6e56HnyMv +GruBcS7HHkuN2ekMeFNp6fM3vh/Vfa+/6Chc= Domainkey-signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:from:to:in-reply-to:content-type :content-transfer-encoding:subject:mime-version:date:references :x-mailer; b=iFlSURwMQYv2iVHt4EY5/EPkDgaFufoO95x7V7mWNN6injqnqUnRiU3yUpY+g0O1/N ksYB4qXelpfvirqIyKGnS0BJxzjXO2GU2tW7QvTTGvGHTDLBH8ugX9VfdsOplOeU4Hl0 4PWLSQTLyuwpB5p1s7wcna4AbUiY807I8xu1Y= On Jul 7, 2009, at 7:21 PM, Esteban Bodigami wrote: Eli _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… first of all, gdb stands for what exactly? "g" database? IMO, it looks like a configuration at runtime that can help your fooprogram return no errors... like a "display no errors" flag (assumming it is text/CLI-only software). In this circumstance, it is highly likely that he is referring to the gnu debugger, as modified/published by Apple. Now, I'm not sure if/how gdb supports debugging itself, as it depends on both gdb supporting this feature AND Apple supporting/enabling it (it may also be platform-specific [ppc vs intel]). You may need to add/enable printf-style debugging instead to figure out why gdb is having problems debugging your program... This email sent to site_archiver(a)lists.apple.com

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