[linux] Interpreting segfault messages

Error 4 means "The cause was a user-mode read resulting in no page being found.". There's a tool that decodes it here.

Here's the definition from the kernel. Keep in mind that 4 means that bit 2 is set and no other bits are set. If you convert it to binary that becomes clear.

/*
 * Page fault error code bits
 *      bit 0 == 0 means no page found, 1 means protection fault
 *      bit 1 == 0 means read, 1 means write
 *      bit 2 == 0 means kernel, 1 means user-mode
 *      bit 3 == 1 means use of reserved bit detected
 *      bit 4 == 1 means fault was an instruction fetch
 */
#define PF_PROT         (1<<0)
#define PF_WRITE        (1<<1)
#define PF_USER         (1<<2)
#define PF_RSVD         (1<<3)
#define PF_INSTR        (1<<4)

Now then, "ip 00007f9bebcca90d" means the instruction pointer was at 0x00007f9bebcca90d when the segfault happened.

"libQtWebKit.so.4.5.2[7f9beb83a000+f6f000]" tells you:

  • The object the crash was in: "libQtWebKit.so.4.5.2"
  • The base address of that object "7f9beb83a000"
  • How big that object is: "f6f000"

If you take the base address and subtract it from the ip, you get the offset into that object:

0x00007f9bebcca90d - 0x7f9beb83a000 = 0x49090D

Then you can run addr2line on it:

addr2line -e /usr/lib64/qt45/lib/libQtWebKit.so.4.5.2 -fCi 0x49090D
??
??:0

In my case it wasn't successful, either the copy I installed isn't identical to yours, or it's stripped.

Examples related to linux

grep's at sign caught as whitespace How to prevent Google Colab from disconnecting? "E: Unable to locate package python-pip" on Ubuntu 18.04 How to upgrade Python version to 3.7? Install Qt on Ubuntu Get first line of a shell command's output Cannot connect to the Docker daemon at unix:/var/run/docker.sock. Is the docker daemon running? Run bash command on jenkins pipeline How to uninstall an older PHP version from centOS7 How to update-alternatives to Python 3 without breaking apt?

Examples related to qt

Install Qt on Ubuntu QtCreator: No valid kits found Qt 5.1.1: Application failed to start because platform plugin "windows" is missing Qt: How do I handle the event of the user pressing the 'X' (close) button? "Failed to load platform plugin "xcb" " while launching qt5 app on linux without qt installed How to enable C++11 in Qt Creator? How to install PyQt5 on Windows? How to convert QString to int? qmake: could not find a Qt installation of '' How to create/read/write JSON files in Qt5

Examples related to webkit

com.apple.WebKit.WebContent drops 113 error: Could not find specified service HTML5 Video autoplay on iPhone What does the shrink-to-fit viewport meta attribute do? Chrome / Safari not filling 100% height of flex parent How to style HTML5 range input to have different color before and after slider? What are -moz- and -webkit-? Video auto play is not working in Safari and Chrome desktop browser Rotate and translate Background color not showing in print preview Blurry text after using CSS transform: scale(); in Chrome

Examples related to kernel

How do I convert dmesg timestamp to custom date format? What is the difference between the kernel space and the user space? What is difference between monolithic and micro kernel? What is the difference between the operating system and the kernel? What is the difference between Trap and Interrupt? "FATAL: Module not found error" using modprobe Interpreting segfault messages What is an OS kernel ? How does it differ from an operating system? Linux Process States What is __gxx_personality_v0 for?

Examples related to segmentation-fault

Command failed due to signal: Segmentation fault: 11 Android Fatal signal 11 (SIGSEGV) at 0x636f7d89 (code=1). How can it be tracked down? Counter exit code 139 when running, but gdb make it through segmentation fault : 11 Segmentation Fault - C What causes a Python segmentation fault? How to return a class object by reference in C++? Login with facebook android sdk app crash API 4 Returning pointer from a function Fixing Segmentation faults in C++