[Bug 1914021] Re: qemu: uncaught target signal 4 (Illegal instruction) but gdb remote-debug exited normally

From: Peter Maydell <1914021@bugs.launchpad.net>
To: qemu-devel@nongnu.org
Subject: [Bug 1914021] Re: qemu: uncaught target signal 4 (Illegal instruction) but gdb remote-debug exited normally
Date: Mon, 01 Feb 2021 13:54:47 -0000	[thread overview]
Message-ID: <161218768774.24999.12302418956246053859.malone@wampee.canonical.com> (raw)
In-Reply-To: 161217038744.31620.11534855593258118024.malonedeb@chaenomeles.canonical.com

Oh, your code is trying to use the SYS_HEAPINFO semihosting call to
figure out where the stack and heap are. This is generally a bad idea if
you're using QEMU user-mode emulation: you start with a perfectly good
stack pointer and you should just use the usual Linux syscalls to
allocate heap if you need it.

I have no idea where your code is getting r1 from -- it's too painful to
try to reverse-engineer it from the binary. I can't repro any difference
between with-gdb and without -- for me with current QEMU r1 is 0 whether
running with the gdb stub or not.

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https://bugs.launchpad.net/bugs/1914021

Title:
  qemu: uncaught target signal 4 (Illegal instruction) but gdb remote-
  debug exited normally

Status in QEMU:
  New

Bug description:
  I'm getting Illegal instruction (core dumped) when running the
  attached a.out_err binary in qemu, but when using Gdb to remote-debug
  the program, it exited normally. will appreciate if you can help look
  into this qemu issue.

  readelf -h a.out_err
  ELF Header:
    Magic:   7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00
    Class:                             ELF32
    Data:                              2's complement, little endian
    Version:                           1 (current)
    OS/ABI:                            UNIX - System V
    ABI Version:                       0
    Type:                              EXEC (Executable file)
    Machine:                           ARM
    Version:                           0x1
    Entry point address:               0x8220
    Start of program headers:          52 (bytes into file)
    Start of section headers:          54228 (bytes into file)
    Flags:                             0x5000200, Version5 EABI, soft-float ABI
    Size of this header:               52 (bytes)
    Size of program headers:           32 (bytes)
    Number of program headers:         3
    Size of section headers:           40 (bytes)
    Number of section headers:         16
    Section header string table index: 15

  qemu-arm version 4.0.0

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