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  • Re: Xorg segfaults on iMac G3 with Rage 128 Pro

    From Paul Wise@21:1/5 to Ben Westover on Sun Apr 16 05:00:02 2023
    On Sat, 2023-04-15 at 15:46 -0400, Ben Westover wrote:

    My system is up to date as of April 15, 2023; I'm running kernel 6.1.0-7-powerpc with Mesa 22.3.6. Does anyone how to fix this problem?

    I think you will need to do some debugging, there are some tips here:

    https://x.org/wiki/Development/Documentation/ServerDebugging/

    --
    bye,
    pabs

    https://wiki.debian.org/PaulWise

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  • From Ben Westover@21:1/5 to Paul Wise on Sun Apr 16 21:10:01 2023
    Copy: debian-powerpc@lists.debian.org

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  • From Paul Wise@21:1/5 to Ben Westover on Mon Apr 17 04:20:02 2023
    On Sun, 2023-04-16 at 15:08 -0400, Ben Westover wrote:

    I'm probably doing something wrong (never used gdb before), but Xorg
    closes almost instantly after I run it so there's not enough time to
    launch gdb before it's already segfaulted. It sounds like these tips are
    for when Xorg launches and runs for a bit but crashes when a specific
    action is performed.

    There is also the case where you launch Xorg via gdb and then run it.

    $ gdb `which Xorg`
    (gdb) run
    (gdb) bt full

    Also, you will need to either install dbgsym packages beforehand
    (possibly using find-dbgsym-packages from debian-goodies), or install
    and enable libdebuginfod-common to let gdb auto-download debug symbols.

    Apart from running Xorg in gdb directly, another method is to install systemd-coredump, enable the Xorg Option NoTrapSignals to disable Xorg
    handling its own crashes, then load the crash dump file into gdb using
    `sudo coredumpctl debug`.

    PS: I'm subscribed, no need to CC me.

    --
    bye,
    pabs

    https://wiki.debian.org/PaulWise

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  • From Luke Kenneth Casson Leighton@21:1/5 to Ben Westover on Tue Apr 18 10:50:01 2023
    On Tuesday, April 18, 2023, Ben Westover <kwestover.kw@gmail.com> wrote:
    Hello,

    On 4/16/23 10:18 PM, Paul Wise wrote:

    There is also the case where you launch Xorg via gdb and then run it.

    $ gdb `which Xorg`
    (gdb) run
    (gdb) bt full

    Perfect! I was able to get a full backtrace, which is attached. Here's
    the part that I think is important:

    Program received signal SIGSEGV, Segmentation fault.
    0xa6e7cc98 in R128GetConnectorInfoFromBIOS (pScrn=pScrn@entry=0x776620,
    otypes=otypes@entry=0xaffff0f4) at ../../src/r128_output.c:432
    432 ../../src/r128_output.c: No such file or directory.
    (gdb) bt full
    #0 0xa6e7cc98 in R128GetConnectorInfoFromBIOS (pScrn=pScrn@entry=0x776620,
    otypes=otypes@entry=0xaffff0f4) at ../../src/r128_output.c:432
    info = 0x776ed0
    bios_header = <error reading variable bios_header (Cannot
    access memory at address 0x48)>
    offset = <optimized out>
    i = 2

    Here's part of the relevant funtion in r128_output.c [1]:

    void R128GetConnectorInfoFromBIOS(ScrnInfoPtr pScrn, R128OutputType
    *otypes)
    {
    R128InfoPtr info = R128PTR(pScrn);
    uint16_t bios_header, offset;
    uint32_t i;

    for (i = 0; i < R128_MAX_BIOS_CONNECTOR; i++) {
    otypes[i] = OUTPUT_NONE;
    }

    /* non-x86 platform */
    if (!info->VBIOS) {
    otypes[0] = OUTPUT_VGA;
    }

    bios_header = R128_BIOS16(0x48);

    almost certainly a NULL pointer from this macro


    There's more after this, but it seems to crash at that last line,
    failing to read the memory at 0x48 to get the BIOS' connector info.

    see how 0x48 is the same there this tells us R128_BIOS16
    takes a NULL address somehow.

    l.

    --
    ---
    crowd-funded eco-conscious hardware: https://www.crowdsupply.com/eoma68

    <br><br>On Tuesday, April 18, 2023, Ben Westover &lt;<a href="mailto:kwestover.kw@gmail.com">kwestover.kw@gmail.com</a>&gt; wrote:<br>&gt; Hello,<br>&gt;<br>&gt; On 4/16/23 10:18 PM, Paul Wise wrote:<br>&gt;&gt;<br>&gt;&gt; There is also the case where
    you launch Xorg via gdb and then run it.<br>&gt;&gt;<br>&gt;&gt;     $ gdb `which Xorg`<br>&gt;&gt;     (gdb) run<br>&gt;&gt;     (gdb) bt full<br>&gt;<br>&gt; Perfect! I was able to get a full backtrace, which is attached. Here&#39;s<br>&gt; the
    part that I think is important:<br>&gt;<br>&gt;     Program received signal SIGSEGV, Segmentation fault.<br>&gt;     0xa6e7cc98 in R128GetConnectorInfoFromBIOS (pScrn=pScrn@entry=0x776620, otypes=otypes@entry=0xaffff0f4) at ../../src/r128_output.c:
    432<br>&gt;     432     ../../src/r128_output.c: No such file or directory.<br>&gt;     (gdb) bt full<br>&gt;     #0  0xa6e7cc98 in R128GetConnectorInfoFromBIOS (p
  • From Paul Wise@21:1/5 to Luke Kenneth Casson Leighton on Wed Apr 19 04:50:02 2023
    On Tue, 2023-04-18 at 09:42 +0100, Luke Kenneth Casson Leighton wrote:
    On Tuesday, April 18, 2023, Ben Westover wrote:
            /* non-x86 platform */
            if (!info->VBIOS) {
                otypes[0] = OUTPUT_VGA;
            }

            bios_header = R128_BIOS16(0x48);

    almost certainly a NULL pointer from this macro

    These are the macro definitions.

    #define R128_BIOS8(v) ((info->VBIOS[(v)]))
    #define R128_BIOS16(v) ((info->VBIOS[(v)]) | \
    (info->VBIOS[(v) + 1] << 8))
    #define R128_BIOS32(v) ((info->VBIOS[(v)]) | \
    (info->VBIOS[(v) + 1] << 8) | \
    (info->VBIOS[(v) + 2] << 16) | \
    (info->VBIOS[(v) + 3] << 24))

    Please try these gdb commands once you hit the crash point:

    print info
    print info.VBIOS
    print info->VBIOS
    print info->VBIOS[0x48]
    print info->VBIOS[0x49]

    --
    bye,
    pabs

    https://wiki.debian.org/PaulWise

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