Re: [Qemu-devel] About QEMU debugging console

[Zhiyuan Shao]

On Tue, 2010-10-26 at 18:59 +0000, Blue Swirl wrote:
> On Tue, Oct 26, 2010 at 12:22 PM, Zhiyuan Shao <address@hidden> wrote:
> > Hi team,
> >
> > I am a Qemu User, and using Qemu 0.13.0 to debugging the linux kernel
> > code (Qemu+GDB).
> >
> > During the usage, I found the Qemu debugging console (i.e., entered by
> > pressing Ctl+Alt+2 in Qemu SDL window or by passing "-monitor stdio" to
> > Qemu in the command line) is rather difficult to use. It can not show
> > some important information, e.g., on i386 platform, which is my major
> > interest, it can not show IDT, GDT information. Regarding the page
> > mapping information, "info tlb" actually do a really bad job.
> 
> How is that bad?
> 
I booted a Linux OS (i386 with PAE support), and has following
virtual-to-physical mappings:
[0xff00-0000,0xffbf-ffff] -> [0x0000-0000, 0x00bf-ffff]
[0x0000-0000,0x00ff-ffff] -> [0x0000-0000, 0x00ff-ffff]

while now, with "info mem" command of Qemu debugging console, the output
is like:
(qemu) info mem
00000000-00400000 00400000 -r-
00c00000-00c08000 00008000 -rw
00c08000-00c09000 00001000 ur-
00c09000-00c0a000 00001000 urw
00c0e000-00c0f000 00001000 urw
00c10000-00c11000 00001000 -r-
00c11000-00c12000 00001000 ur-
00c12000-00c13000 00001000 -r-
00c14000-00c16000 00002000 -r-
00c1b000-00c1e000 00003000 -rw
00c20000-00c40000 00020000 -rw
00c40000-00c41000 00001000 -r-
00c41000-00c42000 00001000 ur-
00c42000-00c43000 00001000 -rw
00c44000-00c60000 0001c000 -rw
00c67000-00c70000 00009000 -rw
00c71000-00c74000 00003000 ur-
00c75000-00c76000 00001000 urw
00c77000-00c78000 00001000 ur-
00c78000-00c79000 00001000 -rw
00c7a000-00d00000 00086000 -rw
00d18000-00d19000 00001000 urw
00d19000-00d1a000 00001000 -rw
00d1d000-00d1e000 00001000 -r-
00d22000-00d23000 00001000 -r-
00d2a000-00d2b000 00001000 -rw
00df0000-00df1000 00001000 -r-
00df1000-00df2000 00001000 urw
00df4000-00df5000 00001000 -r-
00df5000-00df6000 00001000 urw
00df7000-00df8000 00001000 urw
01000000-01400000 00400000 -rw
01400000-01800000 00400000 -r-
01800000-01c00000 00400000 urw
01c00000-02000000 00400000 -rw
04c00000-05000000 00400000 ur-
05c00000-06000000 00400000 -rw
0bc00000-0c000000 00400000 -r-
0c800000-0cc00000 00400000 urw
0d800000-0e000000 00800000 ur-
0e400000-0e800000 00400000 ur-
10400000-10800000 00400000 -rw
12000000-12001000 00001000 -rw
12002000-12003000 00001000 -rw
12004000-12005000 00001000 -rw
12006000-12007000 00001000 -rw
12008000-12009000 00001000 -rw
1200a000-1200b000 00001000 -rw
1200c000-1200d000 00001000 -rw
1200e000-1200f000 00001000 -rw
13bf0000-13bf1000 00001000 -rw
13bf2000-13bf3000 00001000 -rw
13bf4000-13bf5000 00001000 -rw
13bf6000-13bf7000 00001000 -rw
13bf8000-13bf9000 00001000 -rw
13bfa000-13bfb000 00001000 -rw

Donot know what the "active virtual memory mappings" means for "info
mem" command, but the results displayed is not very likely being
correct.

While with "info tlb" command:

(qemu) info tlb 
00000000: 15c00000 -PDA-T--
00c00000: f000f000 G-D-C--W
00c01000: f000f000 G-D-C--W
00c02000: f000e000 --D----W
00c03000: f000f000 G-D-C--W
00c04000: f000f000 G-D-C--W
00c05000: f000f000 G-D-C--W
00c06000: f000f000 G-D-C--W
00c07000: f000f000 G-D-C--W
00c08000: f000f000 ---A--U-
00c09000: f000e000 G-----UW
00c0e000: f000e000 G-D-C-UW
00c10000: c0008000 G--ACT--
00c11000: f000f000 --D--TU-
00c12000: f000f000 --D-----
00c14000: f000e000 G--ACT--
00c15000: f000f000 --D-CT--
00c1b000: f000f000 G-D-C--W
00c1c000: f000f000 G-D-C--W
00c1d000: f000f000 G-D-C--W
00c20000: f000f000 G-D-C--W
00c21000: f000f000 G-D-C--W
00c22000: f000f000 G-D-C--W
00c23000: f000f000 G-D-C--W
00c24000: f000f000 G-D-C--W
00c25000: f000f000 G-D-C--W
00c26000: f000f000 G-D-C--W
00c27000: f000f000 G-D-C--W
00c28000: f000f000 G-D-C--W
00c29000: f000f000 G-D-C--W
00c2a000: f000f000 G-D-C--W
00c2b000: f000f000 G-D-C--W
00c2c000: f000f000 G-D-C--W
00c2d000: f000f000 G-D-C--W
00c2e000: f000f000 G-D-C--W
00c2f000: f000f000 G-D-C--W
00c30000: f000f000 G-D-C--W
00c31000: f000f000 G-D-C--W
00c32000: f000f000 G-D-C--W
00c33000: f000f000 G-D-C--W
00c34000: f000f000 G-D-C--W
00c35000: f000f000 G-D-C--W
00c36000: f000f000 G-D-C--W
00c37000: f000f000 G-D-C--W
00c38000: f000f000 G-D-C--W
00c39000: f000f000 G-D-C--W
00c3a000: f000f000 G-D-C--W
00c3b000: f000f000 G-D-C--W
00c3c000: f000f000 G-D-C--W
00c3d000: f000f000 G-D-C--W
00c3e000: f000f000 G-D-C--W
00c3f000: f000f000 G-D-C--W
00c40000: f000e000 --D-CT--
00c41000: 9fc00000 ---ACTU-
00c42000: f000f000 G-D-C--W
00c44000: f000f000 G-D-C--W
00c45000: f000f000 G-D-C--W
00c46000: f000f000 G-D-C--W
00c47000: f000f000 G-D-C--W
00c48000: f000f000 G-D-C--W
00c49000: f000f000 G-D-C--W
00c4a000: f000f000 G-D-C--W
00c4b000: f000f000 G-D-C--W
00c4c000: f000f000 G-D-C--W
00c4d000: f000f000 G-D-C--W
00c4e000: f000f000 G-D-C--W
00c4f000: f000f000 G-D-C--W
00c50000: f000f000 G-D-C--W
00c51000: f000f000 G-D-C--W
00c52000: f000f000 G-D-C--W
00c53000: f000f000 G-D-C--W
00c54000: f000f000 G-D-C--W
00c55000: f000f000 G-D-C--W
00c56000: f000f000 G-D-C--W
00c57000: f000f000 G-D-C--W
00c58000: f000f000 G-D-C--W
00c59000: f000f000 G-D-C--W
00c5a000: f000f000 G-D-C--W
00c5b000: f000f000 G-D-C--W
00c5c000: f000f000 G-D-C--W
00c5d000: f000f000 G-D-C--W
00c5e000: f000f000 G-D-C--W
00c5f000: f000f000 G-D-C--W
00c67000: f000f000 G-D-C--W
00c68000: f000f000 G-D-C--W
00c69000: f000f000 G-D-C--W
00c6a000: f000f000 G-D-C--W
00c6b000: f000f000 G-D-C--W
00c6c000: f000f000 G-D-C--W
00c6d000: f000f000 G-D-C--W
00c6e000: f000f000 G-D-C--W
00c6f000: f000f000 G-D-C--W
00c71000: f000f000 G-D---U-
00c72000: f000f000 G-D---U-
00c73000: f000f000 G-D---U-
00c75000: f000e000 --DA--UW
00c77000: f000f000 G-D---U-
00c78000: f000f000 G-D-C--W
00c7a000: f000f000 G-D-C--W
00c7b000: f000f000 G-D-C--W
00c7c000: f000f000 G-D-C--W
00c7d000: f000f000 G-D-C--W
00c7e000: f000f000 G-D-C--W
00c7f000: f000f000 G-D-C--W
00c80000: f000f000 G-D-C--W
00c81000: f000f000 G-D-C--W
00c82000: f000f000 G-D-C--W
00c83000: f000f000 G-D-C--W
00c84000: f000f000 G-D-C--W
00c85000: f000f000 G-D-C--W
00c86000: f000f000 G-D-C--W
00c87000: f000f000 G-D-C--W
00c88000: f000f000 G-D-C--W
00c89000: f000f000 G-D-C--W
00c8a000: f000f000 G-D-C--W
00c8b000: f000f000 G-D-C--W
00c8c000: f000f000 G-D-C--W
00c8d000: f000f000 G-D-C--W
00c8e000: f000f000 G-D-C--W
00c8f000: f000f000 G-D-C--W
00c90000: f000f000 G-D-C--W
00c91000: f000f000 G-D-C--W
00c92000: f000f000 G-D-C--W
00c93000: f000f000 G-D-C--W
00c94000: f000f000 G-D-C--W
00c95000: f000f000 G-D-C--W
00c96000: f000f000 G-D-C--W
00c97000: f000f000 G-D-C--W
00c98000: f000f000 G-D-C--W
00c99000: f000f000 G-D-C--W
00c9a000: f000f000 G-D-C--W
00c9b000: f000f000 G-D-C--W
00c9c000: f000f000 G-D-C--W
00c9d000: f000f000 G-D-C--W
00c9e000: f000f000 G-D-C--W
00c9f000: f000f000 G-D-C--W
00ca0000: f000f000 G-D-C--W
00ca1000: f000f000 G-D-C--W
00ca2000: f000f000 G-D-C--W
00ca3000: f000f000 G-D-C--W
00ca4000: f000f000 G-D-C--W
00ca5000: f000f000 G-D-C--W
00ca6000: f000f000 G-D-C--W
00ca7000: f000f000 G-D-C--W
00ca8000: f000f000 G-D-C--W
00ca9000: f000f000 G-D-C--W
00caa000: f000f000 G-D-C--W
00cab000: f000f000 G-D-C--W
00cac000: f000f000 G-D-C--W
00cad000: f000f000 G-D-C--W
00cae000: f000f000 G-D-C--W
00caf000: f000f000 G-D-C--W
00cb0000: f000f000 G-D-C--W
00cb1000: f000f000 G-D-C--W
00cb2000: f000f000 G-D-C--W
00cb3000: f000f000 G-D-C--W
00cb4000: f000f000 G-D-C--W
00cb5000: f000f000 G-D-C--W
00cb6000: f000f000 G-D-C--W
00cb7000: f000f000 G-D-C--W
00cb8000: f000f000 G-D-C--W
00cb9000: f000f000 G-D-C--W
00cba000: f000f000 G-D-C--W
00cbb000: f000f000 G-D-C--W
00cbc000: f000f000 G-D-C--W
00cbd000: f000f000 G-D-C--W
00cbe000: f000f000 G-D-C--W
00cbf000: f000f000 G-D-C--W
00cc0000: f000f000 G-D-C--W
00cc1000: f000f000 G-D-C--W
00cc2000: f000f000 G-D-C--W
00cc3000: f000f000 G-D-C--W
00cc4000: f000f000 G-D-C--W
00cc5000: f000f000 G-D-C--W
00cc6000: f000f000 G-D-C--W
00cc7000: f000f000 G-D-C--W
00cc8000: f000f000 G-D-C--W
00cc9000: f000f000 G-D-C--W
00cca000: f000f000 G-D-C--W
00ccb000: f000f000 G-D-C--W
00ccc000: f000f000 G-D-C--W
00ccd000: f000f000 G-D-C--W
00cce000: f000f000 G-D-C--W
00ccf000: f000f000 G-D-C--W
00cd0000: f000f000 G-D-C--W
00cd1000: f000f000 G-D-C--W
00cd2000: f000f000 G-D-C--W
00cd3000: f000f000 G-D-C--W
00cd4000: f000f000 G-D-C--W
00cd5000: f000f000 G-D-C--W
00cd6000: f000f000 G-D-C--W
00cd7000: f000f000 G-D-C--W
00cd8000: f000f000 G-D-C--W
00cd9000: f000f000 G-D-C--W
00cda000: f000f000 G-D-C--W
00cdb000: f000f000 G-D-C--W
00cdc000: f000f000 G-D-C--W
00cdd000: f000f000 G-D-C--W
00cde000: f000f000 G-D-C--W
00cdf000: f000f000 G-D-C--W
00ce0000: f000f000 G-D-C--W
00ce1000: f000f000 G-D-C--W
00ce2000: f000f000 G-D-C--W
00ce3000: f000f000 G-D-C--W
00ce4000: f000f000 G-D-C--W
00ce5000: f000f000 G-D-C--W
00ce6000: f000f000 G-D-C--W
00ce7000: f000f000 G-D-C--W
00ce8000: f000f000 G-D-C--W
00ce9000: f000f000 G-D-C--W
00cea000: f000f000 G-D-C--W
00ceb000: f000f000 G-D-C--W
00cec000: f000f000 G-D-C--W
00ced000: f000f000 G-D-C--W
00cee000: f000f000 G-D-C--W
00cef000: f000f000 G-D-C--W
00cf0000: f000f000 G-D-C--W
00cf1000: f000f000 G-D-C--W
00cf2000: f000f000 G-D-C--W
00cf3000: f000f000 G-D-C--W
00cf4000: f000f000 G-D-C--W
00cf5000: f000f000 G-D-C--W
00cf6000: f000f000 G-D-C--W
00cf7000: f000f000 G-D-C--W
00cf8000: f000f000 G-D-C--W
00cf9000: f000f000 G-D-C--W
00cfa000: f000f000 G-D-C--W
00cfb000: f000f000 G-D-C--W
00cfc000: f000f000 G-D-C--W
00cfd000: f000f000 G-D-C--W
00cfe000: f000f000 G-D-C--W
00cff000: f000f000 G-D-C--W
00d18000: d4000000 ------UW
00d19000: 00000000 -------W
00d1d000: 00c00000 G-------
00d22000: 00085000 G-DACT--
00d2a000: c0003000 G--A---W
00df0000: fe830000 --------
00df1000: 003f7000 G-DACTUW
00df4000: fe827000 --D-----
00df5000: a87cb000 --DACTUW
00df7000: 00000000 -----TUW
01000000: e4500000 GPDACT-W
01400000: 24500000 -P-A----
01800000: e0200000 GPDACTUW
01c00000: 00e00000 GP---T-W
04c00000: b8a00000 GP---TU-
05c00000: e2000000 GP-----W
0bc00000: 75f00000 GP---T--
0c800000: 13e00000 -PDACTUW
0d800000: 90f00000 GPDA--U-
0dc00000: 00200000 -P---TU-
0e400000: 00000000 -P---TU-
10400000: 90900000 -PDA-T-W
12000000: 002a8000 --DA---W
12002000: 00200000 --DA---W
12004000: 00400000 --DA---W
12006000: 00600000 --DA---W
12008000: 00800000 --DA---W
1200a000: 00a00000 --DA---W
1200c000: 00c00000 --DA---W
1200e000: 00e00000 --DA---W
13bf0000: 002a8000 --DA---W
13bf2000: 00200000 --DA---W
13bf4000: 00400000 --DA---W
13bf6000: 00600000 --DA---W
13bf8000: 00800000 --DA---W
13bfa000: 00a00000 --DA---W
(qemu) 

Is here someone can explain such output?

> > On this side, I think Bochs is good. Unfortunately, it seems do not
> > support gdb-stub debugging and general purpose debugging at the same
> > time.
> >
> > I do not know if the Qemu team had made any plans to improve this? such
> > as embedding the bochs debugging alike functionalities in future Qemu
> > releases?
> 
> Perhaps nobody were aware that there were any lack of functionalities.
> I think these should be very easy to add.
> 

This should be not so hard, and I may have a try in the close future.
The difficulty here is that you have to consider several paging
techniques invented by Intel, such as, i386, PAE, PSE(36), x86_64. And
these works ONLY for the i386 platform.

I just wondering: It is for sure that I am not the very first person who
encounter such problems in the history of Qemu development. Why these
simple functionalities were not added to the main release till now?


Thank!