GCC ICE reporting guide

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A guide to debugging GCC Internal Compiler Errors (ICEs).

This page helps with GCC crashing when building a Gentoo package (or any software) with internal compiler error: Segmentation fault.

To extract useful information from the crash to report a bug requires a few steps. This article lists the steps and provides a few real-world debugging sessions.

Quick guide


  1. Extract self-contained preprocessed file (extracted with -save-temps)
  2. Verify gcc still crashes when ran on preprocessed file
  3. Expand -march=native to flags not dependent on your machine
  4. File a bug on https://bugs.gentoo.org with the following details:
    1. Provide a preprocessed file (or a minimized file)
    2. Provide gcc -v output
    3. Provide emerge --info
    4. Provide -march=native expansion
  5. [optional] Minimize amount of flags needed to trigger the error
  6. [optional] Minimize self-contained example
  7. [optional] File a bug on https://gcc.gnu.org/bugzilla

If you don't know how to all of the above, read on to the detailed guide below!

Detailed guide

Steps to track an ICE (internal compiler errors) down

Rebuilding GCC and glibc with debugging symbols (optional)

This consumes several gigabytes of disk space. Gentoo Wiki's Debugging page contains more explanations on the topic.
Using the installsources FEATURE requires dev-util/debugedit to be installled prior to the following explanations.

To get more detailed GCC crash reports it is suggested to rebuild it with debugging symbols and keeping the full sources. As GCC and glibc are tightly coupled, it is also suggested to do the same for the latter hence you will have more readable traces:

  • Create the following files in the directory /etc/portage/env:
FILE /etc/portage/env/debugsyms
CFLAGS="${CFLAGS} -ggdb3"
FEATURES="${FEATURES} splitdebug compressdebug -nostrip"
FILE /etc/portage/env/installsources
FEATURES="${FEATURES} installsources"
FILE /etc/portage/env/no-builtin-strlen
CFLAGS="${CFLAGS} -fno-builtin-strlen"
  • The next step is to activate those settings for sys-devel/gcc, create the following file in /etc/portage/packages.env:
FILE /etc/portage/package.env/gcc
sys-devel/gcc debugsyms installsources
  • Do the same for The case for sys-libs/glibc, however that latter case depends on if you use Valgrind or not. So create one the following files according to your current use case:
FILE /etc/portage/package.env/glibc(package.env settings for sys-libs/glibc for systems using Valgrind)
# Valgrind requires -fno-builtin-strlen for glibc
sys-libs/glibc no-builtin-strlen debugsyms installsources
FILE /etc/portage/package.env/glibc(package.env settings for sys-libs/glibc for systems without Valgrind))
sys-libs/glibc debugsyms installsources
root #emerge --ask -1 sys-libs/glibc sys-devel/gcc
If your system has several slotted sys-devel/gcc emerge again each of those.

Check if an ICE is reproducible

Sometimes GCC crashes due to external reasons not directly related to GCC:

  • Out-of-memory condition (check dmesg)
  • Bad RAM modules (sys-apps/memtest86+)
  • Unstable overclock of CPU or RAM

Make sure the above is not your case!

Look at build.log with the ICE and try to resume the build to see if the same command causes the same ICE. Usually the command looks something like make --jobs=8 --load-average=8 CPPFLAGS= CFLAGS= LDFLAGS=.

Go to the Working directory (specified in build.log as well) and rerun the build command.

You should see the exact command and the failure.

Our running example will be an ICE on dev-lang/python-3.6.5:

user $cd '/var/tmp/portage/dev-lang/python-3.6.5/work/Python-3.6.5'
user $LANG=C make
running build
running build_ext
INFO: Can't locate Tcl/Tk libs and/or headers
building 'cmath' extension
gcc-7.3.0 -pthread -fPIC -Wno-unused-result -Wsign-compare -DNDEBUG -march=prescott -mfpmath=sse -O2 -pipe -fomit-frame-pointer -fwrapv -std=c99 -Wextra -Wno-unused-result -Wno-unused-parameter -Wno-missing-field-initializers -I./Include -I. -I/var/tmp/portage/dev-lang/python-3.6.5/work/Python-3.6.5/Include -I/var/tmp/portage/dev-lang/python-3.6.5/work/Python-3.6.5 -c /var/tmp/portage/dev-lang/python-3.6.5/work/Python-3.6.5/Modules/cmathmodule.c -o build/temp.linux-i686-3.6/var/tmp/portage/dev-lang/python-3.6.5/work/Python-3.6.5/Modules/cmathmodule.o
In file included from /var/tmp/portage/dev-lang/python-3.6.5/work/Python-3.6.5/Modules/cmathmodule.c:11:0:
/var/tmp/portage/dev-lang/python-3.6.5/work/Python-3.6.5/Modules/clinic/cmathmodule.c.h: In function 'cmath_acos':
/var/tmp/portage/dev-lang/python-3.6.5/work/Python-3.6.5/Modules/clinic/cmathmodule.c.h:45:1: internal compiler error: Segmentation fault
Please submit a full bug report,
with preprocessed source if appropriate.
See <https://bugs.gentoo.org/> for instructions.

The build fails every time LANG=C make is rerun. Yay!

Extract exact command

If the build system already prints exact command, just re-execute it (make sure you are in the correct directory). If the build system does not print the command, you will have to use other methods of getting command like running strace or passing verbose flags manually.

In the case of Python, the command is printed as-is:

user $LANG=C gcc-7.3.0 -pthread -fPIC -Wno-unused-result -Wsign-compare -DNDEBUG -march=prescott -mfpmath=sse -O2 -pipe -fomit-frame-pointer -fwrapv -std=c99 -Wextra -Wno-unused-result -Wno-unused-parameter -Wno-missing-field-initializers -I./Include -I. -I/var/tmp/portage/dev-lang/python-3.6.5/work/Python-3.6.5/Include -I/var/tmp/portage/dev-lang/python-3.6.5/work/Python-3.6.5 -c /var/tmp/portage/dev-lang/python-3.6.5/work/Python-3.6.5/Modules/cmathmodule.c -o build/temp.linux-i686-3.6/var/tmp/portage/dev-lang/python-3.6.5/work/Python-3.6.5/Modules/cmathmodule.o
In file included from /var/tmp/portage/dev-lang/python-3.6.5/work/Python-3.6.5/Modules/cmathmodule.c:11:0:
/var/tmp/portage/dev-lang/python-3.6.5/work/Python-3.6.5/Modules/clinic/cmathmodule.c.h: In function 'cmath_acos':
/var/tmp/portage/dev-lang/python-3.6.5/work/Python-3.6.5/Modules/clinic/cmathmodule.c.h:45:1: internal compiler error: Segmentation fault
Please submit a full bug report,
with preprocessed source if appropriate.
See <https://bugs.gentoo.org/> for instructions.

Extract self-contained source (use -save-temps)

Add -save-temps to the gcc command on the previous step to extract a preprocessed sample. foo.c will create foo.i (or foo.ii for c++).

Obligatory Python example:

user $LANG=C gcc-7.3.0 -pthread -fPIC -Wno-unused-result -Wsign-compare -DNDEBUG -march=prescott -mfpmath=sse -O2 -pipe -fomit-frame-pointer -fwrapv -std=c99 -Wextra -Wno-unused-result -Wno-unused-parameter -Wno-missing-field-initializers -I./Include -I. -I/var/tmp/portage/dev-lang/python-3.6.5/work/Python-3.6.5/Include -I/var/tmp/portage/dev-lang/python-3.6.5/work/Python-3.6.5 -c /var/tmp/portage/dev-lang/python-3.6.5/work/Python-3.6.5/Modules/cmathmodule.c -o build/temp.linux-i686-3.6/var/tmp/portage/dev-lang/python-3.6.5/work/Python-3.6.5/Modules/cmathmodule.o -save-temps

... same failure ...

The preprocessed file is in cmathmodule.i now. You can get more tips at https://gcc.gnu.org/bugs/.

Expand -march=native, exact gcc version and other system-specific options

Some compiler options like -march=native are dependent on the environment. dev-util/debugedit You need to resolve them into exact options. One way to do it is to query gcc for expansion. Pick your arch instead of arch=sandybridge to avoid diff on march= value. That will minimize the diff.

user $arch=sandybridge; for t in param target; do cmd="gcc -Q -O2 -march=$arch --help=$t"; diff -U0 <(LANG=C $cmd) <(LANG=C $cmd -march=native); done
--- /dev/fd/63	2020-06-10 22:26:45.832792880 +0100
+++ /dev/fd/62	2020-06-10 22:26:45.832792880 +0100
@@ -70,3 +70,3 @@
-  --param=l1-cache-line-size= 		32
-  --param=l1-cache-size=      		64
-  --param=l2-cache-size=      		512
+  --param=l1-cache-line-size= 		64
+  --param=l1-cache-size=      		32
+  --param=l2-cache-size=      		8192
--- /dev/fd/61	2020-06-10 22:26:45.856792856 +0100
+++ /dev/fd/60	2020-06-10 22:26:45.856792856 +0100
@@ -16 +16 @@
-  -maes                       		[disabled]
+  -maes                       		[enabled]
@@ -26 +26 @@
-  -mavx                       		[disabled]
+  -mavx                       		[enabled]

Here -march=native is substituted for -march=sandybridge --param=l1-cache-line-size=64 --param=l1-cache-size=32 --param=l2-cache-size=8192 -maes -mavx ....

Make sure bug is reproducible after substitution as well!

Report bug on bugs.gentoo.org

File a bug at https://bugs.gentoo.org/ against toolchain@gentoo.org and provide a few details:

  • gcc -v output
  • Attach .i reproducer

[bonus] minimize needed flags to reproduce failure

You can do similar expansion for optimizer options as well: LANG=C gcc -O2 -Q --help=optimizers

To expand -O3 into -O2 + extra, you can use diff -U0 <(LANG=C gcc -O2 -Q --help=optimizers) <(LANG=C gcc -O3 -Q --help=optimizers)

Try to find minimal set of flags needed to trigger the crash by removing some expanded options.

[bonus] minimize self-contained source using cvise

Now to the fun part! Let's shrink .i down to a manageable size with help of dev-util/cvise.

  1. root #emerge --ask dev-util/cvise
  2. Write a test.sh tester:
    FILE test.sh
    LANG=C gcc-7.3.0 -pthread -fPIC -Wno-unused-result -Wsign-compare -DNDEBUG -march=prescott -mfpmath=sse -O2 -pipe -fomit-frame-pointer -fwrapv -std=c99 -Wextra -Wno-unused-result -Wno-unused-parameter -Wno-missing-field-initializers -I./Include -I. -I/var/tmp/portage/dev-lang/python-3.6.5/work/Python-3.6.5/Include -I/var/tmp/portage/dev-lang/python-3.6.5/work/Python-3.6.5 -c cmathmodule.i -o cmathmodule.o \
    >gcc_out.txt 2>&1
    grep "internal compiler error" gcc_out.txt >/dev/null 2>&1
  3. Validate tester
    user $./test.sh
    user $echo $?
  4. Reduce!
user $cvise test.sh cmathmodule.i
===< 2430 >===
running 4 interestingness tests in parallel
===< pass_includes :: 0 >===
===< pass_unifdef :: 0 >===
===< pass_comments :: 0 >===
===< pass_blank :: 0 >===
(1.2 %, 733906 bytes)
(27.4 %, 539234 bytes)
===< pass_clang_binsrch :: replace-function-def-with-decl >===
(29.5 %, 523834 bytes)
(30.2 %, 518466 bytes)
(32.0 %, 505350 bytes)
          ******** cmathmodule.i ********

typedef struct {
  double a
} b;
b c;
d, e, f;
g() {
  b h;
  if (e)
    h.a = copysign(f, d);
  c = h;


cmathmodule.i contains the same shrunk example.

You can also pass the tester command directly to cvise without creating a shell script, e.g.:

user $LANG=C cvise --commands "gcc-7.3.0 -pthread -fPIC -Wno-unused-result -Wsign-compare -DNDEBUG -march=prescott -mfpmath=sse -O2 -pipe -fomit-frame-pointer -fwrapv -std=c99 -Wextra -Wno-unused-result -Wno-unused-parameter -Wno-missing-field-initializers -I./Include -I. -I/var/tmp/portage/dev-lang/python-3.6.5/work/Python-3.6.5/Include -I/var/tmp/portage/dev-lang/python-3.6.5/work/Python-3.6.5 -c cmathmodule.i -o cmathmodule.o |& fgrep \"internal compiler error\"" cmathmodule.i

[bonus] Check if bug still exists on vanilla gcc master

Building gcc locally could look like:

user $git clone git://gcc.gnu.org/git/gcc.git
user $mkdir -p gcc-build && cd gcc-build
user $../gcc/configure --enable-languages=c,c++ --disable-bootstrap --prefix="$(pwd)/../gcc-installed" --disable-nls CFLAGS="-O1 -ggdb" CXXFLAGS="-O1 -ggdb"
user $make && make install

Look at configure options of Gentoo's gcc -v to get more options to add to defaults. Be careful: some configure options like --enable-default-pie --enable-default-ssp can change code generation enough to trigger or hide a bug.

[bonus] Report bug on gcc.gnu.org/bugzilla

File the bug at https://gcc.gnu.org/bugzilla/ with attached minimal reproducer and gcc -v detals.

[bonus] Extract gcc backtrace

Example session would be:

user $gdb --quiet --args gcc-7.3.0 -fPIC -march=prescott -mfpmath=sse -O1 -c cmathmodule.c -o cmathmodule.o
(gdb) set follow-fork-mode child 
(gdb) break internal_error
(gdb) run
Thread 2.1 "cc1" received signal SIGSEGV, Segmentation fault.
[Switching to process 17286]
0x085375d4 in lra_eliminate_reg_if_possible(rtx_def**) ()
(gdb) bt
#0  0x085375d4 in lra_eliminate_reg_if_possible(rtx_def**) ()

[bonus] Fix gcc bug

By now you have a source tree and a command for how to build it!

A few starting points for you:

Good luck!

LTO example

LTO bugs are harder to track down because there's an extra step (a few) between the compiler and the final binary.

GCC's wiki and LinkTimeOptimization touches on this.

PR105600 is an example of such a GCC bug.


The following example is based on a real case (bug #903868). The first part is to narrow things down to have a minimal set of files then in a second movement, investigate why the error condition is triggered.

Extract the exact compiler command

You might need to manually run make VERBOSE=1 ... if CMake is used to get more details.

Whenever the compilation fails with an LTO error, the very first step is to look at what the file build.log contains and search inside for the string FAILED: (typically, it just precedes the compiler crash dump):

FILE /var/tmp/portage/kde-plasma/xdg-desktop-portal-kde-

Did you notice the two double ampersands (&&) that enclose the full command line? This is our point of interest, copy what is enclosed in-between and keep it somewhere we will use it later in this section. For now, just change the working directory for the failed package's one somewhere under /var/tmp/portage. Here:

root #cd /var/tmp/portage/kde-plasma/xdg-desktop-portal-kde-

From this vantage point of view:

root #ls -l work
total 22
drwxr-xr-x 8 portage portage 17 Apr 13 12:42 xdg-desktop-portal-kde-
drwxr-xr-x 8 portage portage 19 Apr 13 12:42 xdg-desktop-portal-kde-

What we have here is two subdirectories:

  • xdg-desktop-portal-kde- is where the package source files reside (notably)
  • xdg-desktop-portal-kde- is where the object files resulting from the compilation process are put (plus some other things we ignore for the moment).

So from the above GCC command line perspective:

  • All .cpp files relative paths are relative to xdg-desktop-portal-kde-
  • All .cpp.o files relative paths are relative to xdg-desktop-portal-kde-
  • All .a files relative paths are relative to xdg-desktop-portal-kde-
This classification is very important to keep in mind because a couple of operations hereafter depends on this directory tree structure.

If we give a closer look at the above command line, we can decompose it in three consecutive parts:

  • Part A => spans from -O3 to -lpthread this is the various options that governs the GCC's behavior
  • Part B => spans from src/CMakeFiles/xdg-desktop-portal-kde.dir/xdg-desktop-portal-kde_autogen/mocs_compilation.cpp.o to src/CMakeFiles/xdg-desktop-portal-kde.dir/fdo_application_interface.cpp.o src/CMakeFiles/xdg-desktop-portal-kde.dir/xdg-desktop-portal-kde_autogen/EWIEGA46WW/qrc_resources.cpp.o this big list is all of the object files previouly produced by GCC (we are at the final compilation stage... optimize and link with all other needed objects files and librairies)
  • Part C => spans from -o bin/xdg-desktop-portal-kde to /usr/lib64/libQt5Core.so.5.15.8 which is the list of the libraries/shared object files GCC will link against with.

Notice the presence of a relative path in the middle of part C which is lib/libKirigamiFilepicker.a. This file is produced by some previous building steps of the package kde-plasma/xdg-desktop-portal-kde itself, it will be taken care of a bit later.

Minimize responsible objects

The failure is in lto1 which by its nature is considering multiple objects. To narrow down the failure, the full command being passed must be considered.

Let's focus on part B (the big list of .cpp.o files) of the GCC command-line. The goal is to transform all of those relative paths of this list to their absolute path counterparts. Do you remember the directory structure we have talked about in the previous section herebefore? All of those .cpp.o files are residing under xdg-desktop-portal-kde-, thus we must prepend their path with that latter one. As xdg-desktop-portal-kde- resides itself under /var/tmp/portage/kde-plasma/xdg-desktop-portal-kde-, the full path to prepend with is: /var/tmp/portage/kde-plasma/xdg-desktop-portal-kde-

Now, create a file (here named full_objects_list) which contains the whole list of those .cpp.o files (do not reformat it! just copy/paste the whole list as is). The result should be like:

FILE 'full_objects_list'

We will transform full_objects_list to not only convert relative paths to absolute paths but also put one item of the list per line. Here is tr comes at the rescue (don't forget the final slash in the sed directive!):

root #cat full_objects_list | tr ' ' '\n' | sed -e "s:^:/var/tmp/portage/kde-plasma/xdg-desktop-portal-kde-" > full_objects_list_fixed

The file full_objects_list_fixed should look like this (one file per line):

FILE 'full_objects_list'

Now create a copy of the full_objects_list_fixed and name it bad (the original contents will be needed later) :

root #cp full_objects_list_fixed bad

The crunchy part is to use cvise-delta (Package dev-util/cvise) to reduce the contents of the list stored in the file bad to the bare minimum. The only missing piece of that puzzle is to write a small shell-script (here named check.sh) that will be used by cvise-delta and this where the "part A" and the "part B" (respectively the set of options controlling the compiler's behaviour and the set of libraries to link with) we have talked about in the previous section appears in the landscape.

While "part A" can be kept as is (after all we want the very same options set to reproduce the crash), however, "part B" needs to be changed a little bit. So this:

-o bin/xdg-desktop-portal-kde /usr/lib64/libKF5Declarative.so.5.105.0 /usr/lib64/libKF5Notifications.so.5.105.0 /usr/lib64/libKF5WaylandClient.so.5.105.0 /var/tmp/portage/kde-plasma/xdg-desktop-portal-kde- /usr/lib64/libwayland-client.so /usr/lib64/libQt5QuickWidgets.so.5.15.8 /usr/lib64/libKF5Package.so.5.105.0 /usr/lib64/libKF5KIOFileWidgets.so.5.105.0 /usr/lib64/libKF5KIOWidgets.so.5.105.0 /usr/lib64/libKF5KIOGui.so.5.105.0 /usr/lib64/libKF5WindowSystem.so.5.105.0 /usr/lib64/libX11.so /usr/lib64/libKF5JobWidgets.so.5.105.0 /usr/lib64/libKF5Completion.so.5.105.0 /usr/lib64/libKF5Bookmarks.so.5.105.0 /usr/lib64/libKF5XmlGui.so.5.105.0 /usr/lib64/libKF5GlobalAccel.so.5.105.0 /usr/lib64/libKF5IconThemes.so.5.105.0 /usr/lib64/libQt5PrintSupport.so.5.15.8 /usr/lib64/libKF5ItemViews.so.5.105.0 /usr/lib64/libKF5ConfigWidgets.so.5.105.0 /usr/lib64/libKF5GuiAddons.so.5.105.0 /usr/lib64/libQt5WaylandClient.so.5.15.8 /usr/lib64/libKF5WidgetsAddons.so.5.105.0 /usr/lib64/libKF5ConfigGui.so.5.105.0 /usr/lib64/libKF5Codecs.so.5.105.0 /usr/lib64/libKF5Auth.so.5.105.0 /usr/lib64/libQt5Widgets.so.5.15.8 /usr/lib64/libKF5Solid.so.5.105.0 /usr/lib64/libQt5Quick.so.5.15.8 /usr/lib64/libQt5QmlModels.so.5.15.8 /usr/lib64/libQt5Qml.so.5.15.8 /usr/lib64/libKF5KIOCore.so.5.105.0 /usr/lib64/libKF5Service.so.5.105.0 /usr/lib64/libKF5ConfigCore.so.5.105.0 /usr/lib64/libKF5I18n.so.5.105.0 /usr/lib64/libQt5Concurrent.so.5.15.8 /usr/lib64/libQt5Network.so.5.15.8 /usr/lib64/libQt5Xml.so.5.15.8 /usr/lib64/libKF5AuthCore.so.5.105.0 /usr/lib64/libKF5CoreAddons.so.5.105.0 /usr/lib64/libQt5DBus.so.5.15.8 /usr/lib64/libQt5XkbCommonSupport.a /usr/lib64//libQt5Gui.so /usr/lib64//libQt5Core.so /usr/lib64/libxkbcommon.so /usr/lib64/libGL.so /usr/lib64/libQt5Gui.so.5.15.8 /usr/lib64/libQt5Core.so.5.15.8

Becomes that:

@bad -o /dev/null /usr/lib64/libKF5Declarative.so.5.105.0 /usr/lib64/libKF5Notifications.so.5.105.0 /usr/lib64/libKF5WaylandClient.so.5.105.0 lib/libKirigamiFilepicker.a /usr/lib64/libwayland-client.so /usr/lib64/libQt5QuickWidgets.so.5.15.8 /usr/lib64/libKF5Package.so.5.105.0 /usr/lib64/libKF5KIOFileWidgets.so.5.105.0 /usr/lib64/libKF5KIOWidgets.so.5.105.0 /usr/lib64/libKF5KIOGui.so.5.105.0 /usr/lib64/libKF5WindowSystem.so.5.105.0 /usr/lib64/libX11.so /usr/lib64/libKF5JobWidgets.so.5.105.0 /usr/lib64/libKF5Completion.so.5.105.0 /usr/lib64/libKF5Bookmarks.so.5.105.0 /usr/lib64/libKF5XmlGui.so.5.105.0 /usr/lib64/libKF5GlobalAccel.so.5.105.0 /usr/lib64/libKF5IconThemes.so.5.105.0 /usr/lib64/libQt5PrintSupport.so.5.15.8 /usr/lib64/libKF5ItemViews.so.5.105.0 /usr/lib64/libKF5ConfigWidgets.so.5.105.0 /usr/lib64/libKF5GuiAddons.so.5.105.0 /usr/lib64/libQt5WaylandClient.so.5.15.8 /usr/lib64/libKF5WidgetsAddons.so.5.105.0 /usr/lib64/libKF5ConfigGui.so.5.105.0 /usr/lib64/libKF5Codecs.so.5.105.0 /usr/lib64/libKF5Auth.so.5.105.0 /usr/lib64/libQt5Widgets.so.5.15.8 /usr/lib64/libKF5Solid.so.5.105.0 /usr/lib64/libQt5Quick.so.5.15.8 /usr/lib64/libQt5QmlModels.so.5.15.8 /usr/lib64/libQt5Qml.so.5.15.8 /usr/lib64/libKF5KIOCore.so.5.105.0 /usr/lib64/libKF5Service.so.5.105.0 /usr/lib64/libKF5ConfigCore.so.5.105.0 /usr/lib64/libKF5I18n.so.5.105.0 /usr/lib64/libQt5Concurrent.so.5.15.8 /usr/lib64/libQt5Network.so.5.15.8 /usr/lib64/libQt5Xml.so.5.15.8 /usr/lib64/libKF5AuthCore.so.5.105.0 /usr/lib64/libKF5CoreAddons.so.5.105.0 /usr/lib64/libQt5DBus.so.5.15.8 /usr/lib64/libQt5XkbCommonSupport.a /usr/lib64//libQt5Gui.so /usr/lib64//libQt5Core.so /usr/lib64/libxkbcommon.so /usr/lib64/libGL.so /usr/lib64/libQt5Gui.so.5.15.8 /usr/lib64/libQt5Core.so.5.15.8 2>&1 | grep -q "internal compiler error"

The three brought-in changes are:

  • Replacing the original -o bin/xdg-desktop-portal-kde by @bad -o /dev/null to make GCC consider the object list stored in the file bad (rather than the original full-fledged list) and make GCC output the result to /dev/null.
  • Substituting the relative path of libKirigamiFilepicker.a for its absolute one counterpart (this is an archive produced by the package itself, not something external)
  • Appending 2>&1 | grep -q "internal compiler error" at the very end

Putting all pieces together, the test script check.sh is this one:

FILE check.sh
# Reproduces the ICE by calling g++ on object files (within @bad)
if [[ -z "${files[@]}" ]] ; then
        exit 1

/usr/bin/x86_64-pc-linux-gnu-g++ -O3 -pipe -march=native -fomit-frame-pointer -fopt-info-vec -fcf-protection=return -flto=auto -ffat-lto-objects -fno-operator-names -fno-exceptions -Wall -Wextra -Wcast-align -Wchar-subscripts -Wformat-security -Wno-long-long -Wpointer-arith -Wundef -Wnon-virtual-dtor -Woverloaded-virtual -Werror=return-type -Werror=init-self -Wvla -Wdate-time -Wsuggest-override -Wlogical-op -fdiagnostics-color=always -Wl,--enable-new-dtags -flto=auto -pthread @bad -o /dev/null /usr/lib64/libKF5Declarative.so.5.105.0  /usr/lib64/libKF5Notifications.so.5.105.0  /usr/lib64/libKF5WaylandClient.so.5.105.0 /var/tmp/portage/kde-plasma/xdg-desktop-portal-kde-  /usr/lib64/libwayland-client.so  /usr/lib64/libQt5QuickWidgets.so.5.15.8  /usr/lib64/libKF5Package.so.5.105.0  /usr/lib64/libKF5KIOFileWidgets.so.5.105.0  /usr/lib64/libKF5KIOWidgets.so.5.105.0  /usr/lib64/libKF5KIOGui.so.5.105.0  /usr/lib64/libKF5WindowSystem.so.5.105.0  /usr/lib64/libX11.so  /usr/lib64/libKF5JobWidgets.so.5.105.0  /usr/lib64/libKF5Completion.so.5.105.0  /usr/lib64/libKF5Bookmarks.so.5.105.0  /usr/lib64/libKF5XmlGui.so.5.105.0  /usr/lib64/libKF5GlobalAccel.so.5.105.0  /usr/lib64/libKF5IconThemes.so.5.105.0  /usr/lib64/libQt5PrintSupport.so.5.15.8  /usr/lib64/libKF5ItemViews.so.5.105.0  /usr/lib64/libKF5ConfigWidgets.so.5.105.0  /usr/lib64/libKF5GuiAddons.so.5.105.0  /usr/lib64/libQt5WaylandClient.so.5.15.8  /usr/lib64/libKF5WidgetsAddons.so.5.105.0  /usr/lib64/libKF5ConfigGui.so.5.105.0  /usr/lib64/libKF5Codecs.so.5.105.0  /usr/lib64/libKF5Auth.so.5.105.0  /usr/lib64/libQt5Widgets.so.5.15.8  /usr/lib64/libKF5Solid.so.5.105.0  /usr/lib64/libQt5Quick.so.5.15.8  /usr/lib64/libQt5QmlModels.so.5.15.8  /usr/lib64/libQt5Qml.so.5.15.8  /usr/lib64/libKF5KIOCore.so.5.105.0  /usr/lib64/libKF5Service.so.5.105.0  /usr/lib64/libKF5ConfigCore.so.5.105.0  /usr/lib64/libKF5I18n.so.5.105.0  /usr/lib64/libQt5Concurrent.so.5.15.8  /usr/lib64/libQt5Network.so.5.15.8  /usr/lib64/libQt5Xml.so.5.15.8  /usr/lib64/libKF5AuthCore.so.5.105.0  /usr/lib64/libKF5CoreAddons.so.5.105.0  /usr/lib64/libQt5DBus.so.5.15.8  /usr/lib64/libQt5XkbCommonSupport.a  /usr/lib64//libQt5Gui.so  /usr/lib64//libQt5Core.so  /usr/lib64/libxkbcommon.so  /usr/lib64/libGL.so  /usr/lib64/libQt5Gui.so.5.15.8  /usr/lib64/libQt5Core.so.5.15.8 2>&1 | grep -q 'internal compiler error'

Now unleash the power of cvise-delta:

root #chmod +x check.sh
root #cvise-delta ./check.sh bad
00:00:01 INFO ===< 20595 >===
00:00:01 INFO running 16 interestingness tests in parallel
00:00:01 INFO ===< LinesPass::None >===
00:00:02 INFO ===< LinesPass::None >===
00:00:02 INFO cache hit for /var/tmp/portage/kde-plasma/xdg-desktop-portal-kde-
00:00:02 INFO ===< LinesPass::None >===
00:00:02 INFO cache hit for /var/tmp/portage/kde-plasma/xdg-desktop-portal-kde-
00:00:02 INFO ===< LinesPass::None >===
00:00:02 INFO cache hit for /var/tmp/portage/kde-plasma/xdg-desktop-portal-kde-
00:00:02 INFO ===< LinesPass::None >===
00:00:02 INFO cache hit for /var/tmp/portage/kde-plasma/xdg-desktop-portal-kde-
00:00:02 INFO ===< LinesPass::None >===
00:00:02 INFO cache hit for /var/tmp/portage/kde-plasma/xdg-desktop-portal-kde-
00:00:02 INFO ===< LinesPass::None >===
00:00:02 INFO cache hit for /var/tmp/portage/kde-plasma/xdg-desktop-portal-kde-
00:00:02 INFO ===< LinesPass::None >===
00:00:02 INFO cache hit for /var/tmp/portage/kde-plasma/xdg-desktop-portal-kde-
00:00:02 INFO Termination check: size was 166; now 166
00:00:02 INFO ===================== done ====================
===< PASS statistics >===
  pass name                                              time (s) time (%)   worked   failed  total executed
  LinesPass::None                                            0.34    12.15        0        0               1

Runtime: 3 seconds
Reduced test-cases:

--- /var/tmp/portage/kde-plasma/xdg-desktop-portal-kde- ---

Now the file bad should contain only a small number of problematic object files:

root #cat bad

Manually invoke the g++ command as it is in check.sh from the command-line with that reduced subset should trigger a compiler crash :)

root #/usr/bin/x86_64-pc-linux-gnu-g++ -O3 -pipe -march=native -fomit-frame-pointer -fopt-info-vec -fcf-protection=return -flto=auto -ffat-lto-objects -fno-operator-names -fno-exceptions -Wall -Wextra -Wcast-align -Wchar-subscripts -Wformat-security -Wno-long-long -Wpointer-arith -Wundef -Wnon-virtual-dtor -Woverloaded-virtual -Werror=return-type -Werror=init-self -Wvla -Wdate-time -Wsuggest-override -Wlogical-op -fdiagnostics-color=always -Wl,--enable-new-dtags -flto=auto -pthread @bad -o /dev/null /usr/lib64/libKF5Declarative.so.5.105.0 /usr/lib64/libKF5Notifications.so.5.105.0 /usr/lib64/libKF5WaylandClient.so.5.105.0 /var/tmp/portage/kde-plasma/xdg-desktop-portal-kde- /usr/lib64/libwayland-client.so /usr/lib64/libQt5QuickWidgets.so.5.15.8 /usr/lib64/libKF5Package.so.5.105.0 /usr/lib64/libKF5KIOFileWidgets.so.5.105.0 /usr/lib64/libKF5KIOWidgets.so.5.105.0 /usr/lib64/libKF5KIOGui.so.5.105.0 /usr/lib64/libKF5WindowSystem.so.5.105.0 /usr/lib64/libX11.so /usr/lib64/libKF5JobWidgets.so.5.105.0 /usr/lib64/libKF5Completion.so.5.105.0 /usr/lib64/libKF5Bookmarks.so.5.105.0 /usr/lib64/libKF5XmlGui.so.5.105.0 /usr/lib64/libKF5GlobalAccel.so.5.105.0 /usr/lib64/libKF5IconThemes.so.5.105.0 /usr/lib64/libQt5PrintSupport.so.5.15.8 /usr/lib64/libKF5ItemViews.so.5.105.0 /usr/lib64/libKF5ConfigWidgets.so.5.105.0 /usr/lib64/libKF5GuiAddons.so.5.105.0 /usr/lib64/libQt5WaylandClient.so.5.15.8 /usr/lib64/libKF5WidgetsAddons.so.5.105.0 /usr/lib64/libKF5ConfigGui.so.5.105.0 /usr/lib64/libKF5Codecs.so.5.105.0 /usr/lib64/libKF5Auth.so.5.105.0 /usr/lib64/libQt5Widgets.so.5.15.8 /usr/lib64/libKF5Solid.so.5.105.0 /usr/lib64/libQt5Quick.so.5.15.8 /usr/lib64/libQt5QmlModels.so.5.15.8 /usr/lib64/libQt5Qml.so.5.15.8 /usr/lib64/libKF5KIOCore.so.5.105.0 /usr/lib64/libKF5Service.so.5.105.0 /usr/lib64/libKF5ConfigCore.so.5.105.0 /usr/lib64/libKF5I18n.so.5.105.0 /usr/lib64/libQt5Concurrent.so.5.15.8 /usr/lib64/libQt5Network.so.5.15.8 /usr/lib64/libQt5Xml.so.5.15.8 /usr/lib64/libKF5AuthCore.so.5.105.0 /usr/lib64/libKF5CoreAddons.so.5.105.0 /usr/lib64/libQt5DBus.so.5.15.8 /usr/lib64/libQt5XkbCommonSupport.a /usr/lib64//libQt5Gui.so /usr/lib64//libQt5Core.so /usr/lib64/libxkbcommon.so /usr/lib64/libGL.so /usr/lib64/libQt5Gui.so.5.15.8 /usr/lib64/libQt5Core.so.5.15.8

The point being: the same failure now occurs with far fewer arguments because cvise-delta reduced the list down to those responsible.

Now we only need to keep aside:

  • The files xdgshortcut.cpp.o and libKirigamiFilepicker.a
  • the gcc++ command-line to use

Perfect! We have a lean work basis. Next step: debug the compiler.

Debugging the compiler

it is highly suggested to rebuild GCC and glibc with debugging symbols. See the first section for detailed instruction on how to do this.

Invoke GDB by passing the whole problematic command-line after --args:

root #gdb --quiet --args /usr/bin/x86_64-pc-linux-gnu-g++ -O3 -pipe -march=native -fomit-frame-pointer -fopt-info-vec -fcf-protection=return -flto=auto -ffat-lto-objects -fno-operator-names -fno-exceptions -Wall -Wextra -Wcast-align -Wchar-subscripts -Wformat-security -Wno-long-long -Wpointer-arith -Wundef -Wnon-virtual-dtor -Woverloaded-virtual -Werror=return-type -Werror=init-self -Wvla -Wdate-time -Wsuggest-override -Wlogical-op -fdiagnostics-color=always -Wl,--enable-new-dtags -flto=auto -pthread @bad -o /dev/null /usr/lib64/libKF5Declarative.so.5.105.0 /usr/lib64/libKF5Notifications.so.5.105.0 /usr/lib64/libKF5WaylandClient.so.5.105.0 /var/tmp/portage/kde-plasma/xdg-desktop-portal-kde- /usr/lib64/libwayland-client.so /usr/lib64/libQt5QuickWidgets.so.5.15.8 /usr/lib64/libKF5Package.so.5.105.0 /usr/lib64/libKF5KIOFileWidgets.so.5.105.0 /usr/lib64/libKF5KIOWidgets.so.5.105.0 /usr/lib64/libKF5KIOGui.so.5.105.0 /usr/lib64/libKF5WindowSystem.so.5.105.0 /usr/lib64/libX11.so /usr/lib64/libKF5JobWidgets.so.5.105.0 /usr/lib64/libKF5Completion.so.5.105.0 /usr/lib64/libKF5Bookmarks.so.5.105.0 /usr/lib64/libKF5XmlGui.so.5.105.0 /usr/lib64/libKF5GlobalAccel.so.5.105.0 /usr/lib64/libKF5IconThemes.so.5.105.0 /usr/lib64/libQt5PrintSupport.so.5.15.8 /usr/lib64/libKF5ItemViews.so.5.105.0 /usr/lib64/libKF5ConfigWidgets.so.5.105.0 /usr/lib64/libKF5GuiAddons.so.5.105.0 /usr/lib64/libQt5WaylandClient.so.5.15.8 /usr/lib64/libKF5WidgetsAddons.so.5.105.0 /usr/lib64/libKF5ConfigGui.so.5.105.0 /usr/lib64/libKF5Codecs.so.5.105.0 /usr/lib64/libKF5Auth.so.5.105.0 /usr/lib64/libQt5Widgets.so.5.15.8 /usr/lib64/libKF5Solid.so.5.105.0 /usr/lib64/libQt5Quick.so.5.15.8 /usr/lib64/libQt5QmlModels.so.5.15.8 /usr/lib64/libQt5Qml.so.5.15.8 /usr/lib64/libKF5KIOCore.so.5.105.0 /usr/lib64/libKF5Service.so.5.105.0 /usr/lib64/libKF5ConfigCore.so.5.105.0 /usr/lib64/libKF5I18n.so.5.105.0 /usr/lib64/libQt5Concurrent.so.5.15.8 /usr/lib64/libQt5Network.so.5.15.8 /usr/lib64/libQt5Xml.so.5.15.8 /usr/lib64/libKF5AuthCore.so.5.105.0 /usr/lib64/libKF5CoreAddons.so.5.105.0 /usr/lib64/libQt5DBus.so.5.15.8 /usr/lib64/libQt5XkbCommonSupport.a /usr/lib64//libQt5Gui.so /usr/lib64//libQt5Core.so /usr/lib64/libxkbcommon.so /usr/lib64/libGL.so /usr/lib64/libQt5Gui.so.5.15.8 /usr/lib64/libQt5Core.so.5.15.8
Reading symbols from /usr/bin/x86_64-pc-linux-gnu-g++...
Reading symbols from /usr/lib/debug//usr/x86_64-pc-linux-gnu/gcc-bin/13/x86_64-pc-linux-gnu-g++.debug...

Set the variable follow-fork-mode to child (set follow-fork-mode child).

To be continued

See also

* Bisecting_with_live_ebuilds#GCC_example * Bugzilla/Bug_report_guide — explains how to report bugs on the Gentoo Bugzilla * Bugzilla/Guide — covers the recommended method of reporting bugs for Gentoo.

External resources

* Reducing an LTO Linux kernel bug with cvise * Bug with an example of needing timeouts and such in cvise script