Debug linux binary with enable linux emulation

[Konstantin Belousov]

On Mon, May 11, 2020 at 12:28:23AM +0200, freebsd at sysctl.cz wrote:
> Hi,
> I tried debug with gdb for linux emulation
> and have issue with kernel panic.
> 
> kldload linux64.ko
> gdb ./Discord or other linux binary
> 
> Fatal trap 12: page fault while in kernel mode
> cpuid = 3; apic id = 03
> fault virtual address	= 0x18
> fault code		= supervisor read data, page not present
> instruction pointer	= 0x20:0xffffffff82f5b682
> stack pointer	        = 0x28:0xfffffe00691fd980
> frame pointer	        = 0x28:0xfffffe00691fd9e0
> code segment		= base 0x0, limit 0xfffff, type 0x1b
> 			= DPL 0, pres 1, long 1, def32 0, gran 1
> processor eflags	= interrupt enabled, resume, IOPL = 0
> current process		= 17392 (fish)
> trap number		= 12
> panic: page fault
> cpuid = 3
> time = 1589132677
> KDB: stack backtrace:
> #0 0xffffffff80c1d2f7 at kdb_backtrace+0x67
> #1 0xffffffff80bd062d at vpanic+0x19d
> #2 0xffffffff80bd0483 at panic+0x43
> #3 0xffffffff810a7dcc at trap_fatal+0x39c
> #4 0xffffffff810a7e19 at trap_pfault+0x49
> #5 0xffffffff810a740f at trap+0x29f
> #6 0xffffffff81081bdc at calltrap+0x8
> #7 0xffffffff82f503d1 at linux_thread_detach+0x21
Show the line number for linux_thread_detach+0x21.
Or better, compile with INVARIANTS, it should fire an assertion.
Then get a core dump.

> #8 0xffffffff80be5acf at thread_suspend_check+0x41f
> #9 0xffffffff80c32ed9 at ast+0x3b9
> #10 0xffffffff810850e9 at doreti_ast+0x1f
> Uptime: 2h56m24s
> Dumping 1146 out of 8042
> MB:..2%..12%..21%..31%..41%..51%..62%..72%..81%..91%---<<BOOT>>---
> Copyright (c) 1992-2019 The FreeBSD Project.
> 
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> Reading symbols from /boot/kernel/kernel...
> (No debugging symbols found in /boot/kernel/kernel)
> 0xffffffff80c01eda in sched_switch ()
> (kgdb)
> (kgdb)
> (kgdb) bt
> #0  0xffffffff80c01eda in sched_switch ()
> #1  0xffffffff80bdbfa2 in mi_switch ()
> #2  0xffffffff80c2bb75 in sleepq_catch_signals ()
> #3  0xffffffff80c2be64 in sleepq_timedwait_sig ()
> #4  0xffffffff80bdb9a5 in _sleep ()
> #5  0xffffffff80bf1ee3 in umtxq_sleep ()
> #6  0xffffffff80bf1c90 in do_wait ()
> #7  0xffffffff80bef8fe in __umtx_op_wait_uint_private ()
> #8  0xffffffff810a8984 in amd64_syscall ()
> #9  <signal handler called>
> #10 0x000000080974dedc in ?? ()
> Backtrace stopped: Cannot access memory at address 0x7fffffffddc8
> 
> I have now kernel without debug symbols.
> 
> M.
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