Re: m68k: gdbstub crashing setting float register on cfv4e cpu

[KONRAD Frederic]

Le 4/16/20 à 1:18 PM, Laurent Vivier a écrit :
> Le 14/04/2020 à 18:56, Alex Bennée a écrit :
> > Philippe Mathieu-Daudé <address@hidden> writes:
> >
> > > gdbstub/m68k seems broken with floats, previous to refactor commit
> > > a010bdbe719 ("extend GByteArray to read register helpers").
> > >
> > > HEAD at 6fb1603aa2:
> > >
> > > $ qemu-system-m68k -s -S -cpu cfv4e
> > >
> > > ---[GUEST]---
> > >
> > > (gdb) set architecture m68k:cfv4e
> > > The target architecture is assumed to be m68k:cfv4e
> > > (gdb) target remote 172.17.0.1:1234
> > > Remote debugging using 172.17.0.1:1234
> > > (gdb) info float
> > > fp0            -nan(0xfffffffffff7f) (raw 0xffffffffffffff7f)
> > > fp1            -nan(0xfffffffffff7f) (raw 0xffffffffffffff7f)
> > > fp2            -nan(0xfffffffffff7f) (raw 0xffffffffffffff7f)
> > > fp3            -nan(0xfffffffffff7f) (raw 0xffffffffffffff7f)
> > > fp4            -nan(0xfffffffffff7f) (raw 0xffffffffffffff7f)
> > > fp5            -nan(0xfffffffffff7f) (raw 0xffffffffffffff7f)
> > > fp6            -nan(0xfffffffffff7f) (raw 0xffffffffffffff7f)
> > > fp7            -nan(0xfffffffffff7f) (raw 0xffffffffffffff7f)
> > > fpcontrol      0x0                 0
> > > fpstatus       0x0                 0
> > > fpiaddr        0x0                 0x0
> > > (gdb) set $fp0=1
> > > Remote communication error.  Target disconnected.: Connection reset by
> > > peer.
> >
> > With my sha1 debugging test case I get different results depending on
> > the cpu type:
> >
> >    /home/alex/lsrc/qemu.git/tests/guest-debug/run-test.py --gdb 
> > /home/alex/src/tools/binutils-gdb.git/builds/all/install/bin/gdb --qemu 
> > /home/alex/lsrc/qemu.git/builds/user.static/m68k-linux-user/qemu-m68k --qargs 
> > "" --bin tests/tcg/m68k-linux-user/sha1 --test 
> > /home/alex/lsrc/qemu.git/tests/tcg/multiarch/gdbstub/sha1.py
> >    GNU gdb (GDB) 10.0.50.20200414-git
> >    Copyright (C) 2020 Free Software Foundation, Inc.
> >    License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
> >    This is free software: you are free to change and redistribute it.
> >    There is NO WARRANTY, to the extent permitted by law.
> >    Type "show copying" and "show warranty" for details.
> >    This GDB was configured as "x86_64-pc-linux-gnu".
> >    Type "show configuration" for configuration details.
> >    For bug reporting instructions, please see:
> >    <http://www.gnu.org/software/gdb/bugs/>.
> >    Find the GDB manual and other documentation resources online at:
> >        <http://www.gnu.org/software/gdb/documentation/>.
> >
> >    For help, type "help".
> >    Type "apropos word" to search for commands related to "word"...
> >    Executed .gdbinit
> >    Reading symbols from tests/tcg/m68k-linux-user/sha1...
> >    Remote debugging using localhost:1234
> >    warning: Register "fp0" has an unsupported size (96 bits)
> >    warning: Register "fp1" has an unsupported size (96 bits)
> >    warning: Register "fp2" has an unsupported size (96 bits)
> >    warning: Register "fp3" has an unsupported size (96 bits)
> >    warning: Register "fp4" has an unsupported size (96 bits)
> >    warning: Register "fp5" has an unsupported size (96 bits)
> >    warning: Register "fp6" has an unsupported size (96 bits)
> >    warning: Register "fp7" has an unsupported size (96 bits)
> >    Remote 'g' packet reply is too long (expected 148 bytes, got 180 bytes): 
> > 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000408009f000000000800003407fff0000ffffffffffffffff7fff0000ffffffffffffffff7fff0000ffffffffffffffff7fff0000ffffffffffffffff7fff0000ffffffffffffffff7fff0000ffffffffffffffff7fff0000ffffffffffffffff7fff0000ffffffffffffffff000000000000000000000000
>
> This is a bug in GDB that doesn't support 96bit float registers of 680x0
> but only 64bit registers of coldfire.
>
> There was a rework of GDB in the past that has broken that and no one
> noticed. I bisected and found the commit but it was really too complex
> and difficult to fix.

We worked on that recently, actually the registers are supported in GDB but QEMU
doesn't send the right register description to GDB.

I've a local patch for that, will send it to the list.

> To be able to debug remotely m68k I use gdb from etch-m68k in a chroot
> (or from real hardware).
>
> Thanks,
> Laurent