Re: tdep/2561: MMX register number to register value mapping is incorrect

Re: tdep/2561: MMX register number to register value mapping is incorrect

[Tom Honermann]

The following reply was made to PR tdep/2561; it has been noted by GNATS.

From: Tom Honermann <tom.honermann@oracle.com>
To: gdb-gnats@sources.redhat.com
Cc:  
Subject: Re: tdep/2561: MMX register number to register value mapping is incorrect
Date: Sun, 07 Dec 2008 22:34:16 -0800

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 Attached is a better test case for this bug report.
 
 Tom.
 
 gdb-gnats@sources.redhat.com wrote:
 > Thank you very much for your problem report.
 > It has the internal identification `tdep/2561'.
 > The individual assigned to look at your
 > report is: unassigned. 
 >
 >   
 >> Category:       tdep
 >> Responsible:    unassigned
 >> Synopsis:       MMX register number to register value mapping is incorrect
 >> Arrival-Date:   Mon Dec 08 05:58:01 UTC 2008
 >>     
 
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 --------------040908000103080301060504--

Re: tdep/2561: MMX register number to register value mapping is incorrect

[Tom Honermann]

The following reply was made to PR tdep/2561; it has been noted by GNATS.

From: Tom Honermann <tom.honermann@oracle.com>
To: gdb-gnats@sources.redhat.com
Cc:  
Subject: Re: tdep/2561: MMX register number to register value mapping is incorrect
Date: Mon, 08 Dec 2008 13:10:31 -0800

 Ok, so I'm not very familiar with the GDB bug reporting app (gnatsweb).  
 It seems the UI doesn't offer a way to attach new files.  I added a note 
 previously via email with an attachment and the attachment was included 
 in Base64 format.  I suspect some users might not know how to turn the 
 Base64 encoded content back into a file they can work with, so I'm 
 adding the updated test case again with some instructions for how to get 
 the original .tar.gz archive.
 
 To re-create the test case files on a Linux system, save the content 
 below starting with 'begin-base64' and ending with '====' in a file (ie, 
 'test-gdb-mmx-bug.b64'), and then run 'uudecode test-gdb-mmx-bug.b64'.  
 This will create a new file named 'test-gdb-mmx-bug.tar.gz' which can be 
 unarchived by running 'tar -zxvf test-gdb-mmx-bug.tar.gz'.  A new 
 directory named 'test-gdb-mmx-bug' will be created that contains the 
 test case.
 
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 ====

tdep/2561: MMX register number to register value mapping is incorrect

[tom.honermann]

>Number:         2561
>Category:       tdep
>Synopsis:       MMX register number to register value mapping is incorrect
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          change-request
>Submitter-Id:   net
>Arrival-Date:   Mon Dec 08 05:58:01 UTC 2008
>Closed-Date:
>Last-Modified:
>Originator:     Tom Honermann
>Release:        gdb-6.8
>Organization:
>Environment:
Linux 2.6.9 - Oracle Enterprise Linux 4u4 (Equiv to RedHat 4u4)
>Description:
Intel MMX registers (mm0-mm7) are aliased to the x87 floating point registers (st0-st7).  The x87 floating point registers comprise a register stack that revolves as values are pushed onto it.  The MMX registers however are directly mapped to the backing store for the floating point registers (r0-r7).  Thus, mm0==r0, mm1==r1, ...mm7=r7 but st0 is not necessarily equal to r0.  When displaying MMX registers, gdb computes the association between the MMX and x87 data registers incorrectly.
>How-To-Repeat:
Compile the attached program as a 32bit x86 Linux program  (Makefile included).  Run it and it will display what the MMX register values should be.  The program will then generate a SIGSEGV to break into gdb at a good point for analyzing the x87 and MMX registers.  Run the program in GDB and when the SIGSEGV is received, run 'info all-reg' to see all registers.  Compare the GDB mm0-mm7 register values to those displayed by the program.  The values to register number mapping will be off.
>Fix:
The problem is in 'i386_mmx_regnum_to_fp_regnum' in gdb-6.8/gdb/i386-tdep.c.  The current code for computing the association is:

    fpreg = (mmxreg + tos) % 8;

This should be:

    fpreg = ((8 + mmxreg) - tos) % 8;
>Release-Note:
>Audit-Trail:
>Unformatted:
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