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Bug#969739: Segmentation fault on startup

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  Bug#969739: Segmentation fault on startup Bernhard Übelacker <bernhardu@mailbox.org> - 2020-09-23 22:40 +0200
    Bug#969739: Segmentation fault on startup Michel Dänzer <michel@daenzer.net> - 2020-09-24 10:40 +0200

#1026207 — Bug#969739: Segmentation fault on startup

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Dear Maintainer,
I could not reproduce the crash, but I could modify the process under
gdb to reach a point of execution, which prints a similar backtrace.

Therefore I guess the crash described in Christophe's first message
is really located in [1], caused by "xf86_platform_devices[i].pdev"
containing a null pointer.

[1] https://sources.debian.org/src/xorg-server/2:1.20.9-1/hw/xfree86/common/xf86platformBus.c/#L367


But second and more fundamentally, I guess too that the backtrace
generating function in Xorg seems not to be reliable.

If I am right the following backtraces should show the same addresses, but for
some reason the Xorg output seems to be kind of misleading on some frames.
Would that be worth to track in a separate bug?

Kind regards,
Bernhard

With debug symbols:
    #0  0x000055555560ae10 in xf86MergeOutputClassOptions () at ../../../../../../hw/xfree86/common/xf86platformBus.c:367
    #1  0x00005555555ee197 in xf86CollectOptions () at ../../../../../../hw/xfree86/common/xf86Option.c:83
    #2  0x00007ffff6993d2e in PreInit () at ../../../../../../../hw/xfree86/drivers/modesetting/driver.c:972
    #3  0x00005555555f185e in InitOutput () at ../../../../../../hw/xfree86/common/xf86Init.c:522
    #4  0x00005555555b331c in dix_main () at ../../../../dix/main.c:193
    #5  0x00007ffff72dbcca in __libc_start_main () at ../csu/libc-start.c:308
    #6  0x000055555559cc9a in _start ()

Without debug symbols:
    #0  0x000055555560ae10 in ?? ()
    #1  0x00005555555ee197 in xf86CollectOptions ()
    #2  0x00007ffff6993d2e in ?? () from /usr/lib/xorg/modules/drivers/modesetting_drv.so
    #3  0x00005555555f185e in InitOutput ()
    #4  0x00005555555b331c in ?? ()
    #5  0x00007ffff72dbcca in __libc_start_main () at ../csu/libc-start.c:308
    #6  0x000055555559cc9a in _start ()

From Xorg:
    (EE) Backtrace:
    (EE) 0: /usr/lib/xorg/Xorg (OsLookupColor+0x135) [0x555555712f35]
    (EE) 1: /lib/x86_64-linux-gnu/libpthread.so.0 (funlockfile+0x50) [0x7ffff749018f]
    (EE) 2: /usr/lib/xorg/Xorg (xf86PlatformMatchDriver+0x5c0) [0x55555560b2b0]
    (EE) 3: /usr/lib/xorg/Xorg (xf86CollectOptions+0x77) [0x5555555ee197]
    (EE) unw_get_proc_name failed: no unwind info found [-10]
    (EE) 4: /usr/lib/xorg/modules/drivers/modesetting_drv.so (?+0x0) [0x7ffff6993940]
    (EE) 5: /usr/lib/xorg/Xorg (InitOutput+0x9ae) [0x5555555f185e]
    (EE) 6: /usr/lib/xorg/Xorg (InitFonts+0x1cc) [0x5555555b335c]
    (EE) 7: /lib/x86_64-linux-gnu/libc.so.6 (__libc_start_main+0xea) [0x7ffff72dbcca]
    (EE) 8: /usr/lib/xorg/Xorg (_start+0x2a) [0x55555559cc9a]
    (EE) 
    (EE) Segmentation fault at address 0x124

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#1026253

On 2020-09-23 10:38 p.m., Bernhard Übelacker wrote:
> Dear Maintainer,
> I could not reproduce the crash, but I could modify the process under
> gdb to reach a point of execution, which prints a similar backtrace.
> 
> Therefore I guess the crash described in Christophe's first message
> is really located in [1], caused by "xf86_platform_devices[i].pdev"
> containing a null pointer.
> 
> [1] https://sources.debian.org/src/xorg-server/2:1.20.9-1/hw/xfree86/common/xf86platformBus.c/#L367

https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/508 should 
help then.


-- 
Earthling Michel Dänzer               |               https://redhat.com
Libre software enthusiast             |             Mesa and X developer

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