Re: GDB: "/opt/google/chrome/chrome": not in executable format: File truncated

[Denis Glotov]

Hi devs!

If I use 

FEATURES=nostrip emerge-x86-alex chromeos-chrome

to build Chrome within chroot and keep the binary not stripped, gdb cannot load the resulting chrome image:

(cr) ((b4c1382...)) glotov@glotov-z600 ~/trunk/src/scripts $ sudo chroot /build/x86-alex/

bash: /dev/null: Is a directory

glotov-z600 / # gdb

GNU gdb (Gentoo 7.1 p1) 7.1

Copyright (C) 2010 Free Software Foundation, Inc.

License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>

This is free software: you are free to change and redistribute it.

There is NO WARRANTY, to the extent permitted by law.  Type "show copying"

and "show warranty" for details.

This GDB was configured as "i686-pc-linux-gnu".

For bug reporting instructions, please see:

<http://bugs.gentoo.org/>.

(gdb) file /opt/google/chrome/chrome

"/opt/google/chrome/chrome": not in executable format: File truncated

(gdb) quit

glotov-z600 / # which gdb

/usr/bin/gdb

glotov-z600 / # file /usr/bin/gdb

/usr/bin/gdb: ELF 32-bit LSB shared object, Intel 80386, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.9, stripped

If I don't use FEATURES=nostrip, the strip command takes place during the build:

strip: i686-pc-linux-gnu-strip --strip-debug --keep-file-symbols

   opt/google/chrome/libosmesa.so

   opt/google/chrome/libffmpegsumo.so

   opt/google/chrome/chrome-sandbox

and gdb still refuses symbols, although now it have them in /usr/lib/debug/opt/google/chrome/chrome.debug:

Reading symbols from /opt/google/chrome/chrome...`/usr/lib/debug/opt/google/chrome/chrome.debug': can't read symbols: File truncated.

Have anything changed with the way to get symbols for debugging?

Note. My normal defines are:

declare -x BOARD=x86-alex 

declare -x BUILDTYPE=Release

declare -x CHROME_ORIGIN=LOCAL_SOURCE

declare -x FEATURES="-usersandbox" 

declare -x USE="-build_tests internal chrome_internal"

declare -x KEEP_CHROME_DEBUG_SYMBOLS=1

--
Thank you,
Denis

[Daniel Erat]

gdb meant what it said: /opt/google/chrome/chrome is truncated because an unstripped Chrome binary is too large to fit on a default-sized Chrome OS root partition.

With KEEP_CHROME_DEBUG_SYMBOLS enabled, you should at least get (some) function names in gdb backtraces.

I believe that some engineers build unstripped Chrome binaries on their workstations, sshfs-mount the directories on their Chrome OS devices, and run it that way.  I think that I've seen email describing the procedure.

In the recent past, I've copied unstripped Chrome binaries and the related resources and libcros library somewhere under /home/chronos on my device and symlinked /opt/google/chrome to the new directory.  This works too.

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[Scott Byer]

You can actually get an unstripped chrome, with webkit symbols even if you're so inclined, if you have build_image bump out the partition and fs sizes:  --rootfs_partition_size=2048 --rootfs_size=1874 --rootfs_hash_pad=16

Makes the write of the image to the USB stick take longer, but you can get full stack traces and debugging information from a remote attached gdb that way.

A combination of:

http://www.chromium.org/chromium-os/how-tos-and-troubleshooting/debugging-tips/host-file-access

http://www.chromium.org/chromium-os/how-tos-and-troubleshooting/debugging-tips

and

https://sites.google.com/a/chromium.org/dev/chromium-os/how-tos-and-troubleshooting/remote-debugging

also seems to work, I'm still trying to get that process smoother for myself.

-Scott

(putting notes in the docs on what I find once I have things working nicely is on my to-do list)

[Denis Glotov]

I forgot to mention two things (in order to keep the mail concise).

1. I run GDB on the host, chrooted to ~/chromiumos/chroot/build/x86-alex/. So I thing that size restrictions should not harm the debugger, or could they?

2. I compiled with Clang. This must be the main problem. To verify this, I just recompiled everything with g++ in usual way and GDB accepted symbols. So it must be some Clang symbols incompatibility. Currently investigating...

--
Thank you,
Denis

[Rahul Chaturvedi]

I think you might be running into a known issue with remote debugging chrome on cros. There is a workaround for it with the disable_pie flag.

It's not a good idea to keep debug symbols in the binary - you can always load them from the symbol file instead.

Even if you use sshfs to load the unstripped binary, you'll likely run out of memory very quickly.

Instead, if you want to use remote debugging for chrome, follow the following steps and they should work even with a stripped binary,

• Build chromeos-chrome with EXTRA_BUILD_ARGS="disable_pie=1"
• Either build_image to get the chrome binary on a new image or gmerge it

then,

• gdb /path/to/your/unstripped/chrome/binary

once gdb loads,

• set sysroot /path/to/your/build/root/inside/cros/chroot
• set solib-absolute-prefix /path/to/your/build/root/inside/cros/chroot
• directory /path/to/chrome/src
• target remote IP:PORT

and your symbols should work fine.

/rkc

[Scott Byer]

It would be good if you could add this information to 

https://sites.google.com/a/chromium.org/dev/chromium-os/how-tos-and-troubleshooting/building-chromium-browser

and

https://sites.google.com/a/chromium.org/dev/chromium-os/how-tos-and-troubleshooting/remote-debugging

What's there isn't quite complete.

-Scott

[Rahul Chaturvedi]

I've added the information about disable_pie to https://sites.google.com/a/chromium.org/dev/chromium-os/how-tos-and-troubleshooting/remote-debugging

I also added the solib-absolute-prefix setup line to the instructions for gdb, since that should be there for all binaries being remote debugged anyway.