Haiku x86_64 built with GCC 7.3 KDLs on startup

[waddlesplash]

e.g. ​https://keybase.pub/kallisti5/Screenshots/gpe.png

kallisti5 says this happens on QEMU-KVM but not QEMU (without KVM.)

If you want to build your own GCC 7.3 Haiku:

• get GCC 7.3 buildtools from ​https://github.com/waddlesplash/buildtools (master)
• get x86_64 HaikuPorts package listing, which is attached to this ticket

[waddlesplash]

should have sha256sum 79ad0dd02282cf4d06aeb3f0df7a91a053ca23c1bf676535c625f8992ef348bd

[waddlesplash]

Linux kernel makefile has these:

# clang sets -fmerge-all-constants by default as optimization, but this
# is non-conforming behavior for C and in fact breaks the kernel, so we
# need to disable it here generally.
KBUILD_CFLAGS	+= $(call cc-option,-fno-merge-all-constants)

# for gcc -fno-merge-all-constants disables everything, but it is fine
# to have actual conforming behavior enabled.
KBUILD_CFLAGS	+= $(call cc-option,-fmerge-constants)

# Make sure -fstack-check isn't enabled (like gentoo apparently did)
KBUILD_CFLAGS  += $(call cc-option,-fno-stack-check,)

Related?

[waddlesplash]

Actually looking at ​https://gcc.gnu.org/gcc-6/porting_to.html it might be the lifetime-dse one, based on ​https://bugzilla.redhat.com/show_bug.cgi?id=1316999 and other comments about C++ code.

[waddlesplash]

The panic only occurs with {{-O2}}; with {{-O1}} there is no panic.

[waddlesplash]

The culprit pass is rtl-stv1. If you disable it using -fdisable-rtl-stv1 on the whole kernel, the KDL goes away.

[waddlesplash]

Minimum patch/workaround:

diff --git a/src/system/kernel/Jamfile b/src/system/kernel/Jamfile
index 7964320883..10f61bd224 100644
--- a/src/system/kernel/Jamfile
+++ b/src/system/kernel/Jamfile
@@ -75,6 +75,10 @@ KernelMergeObject kernel_core.o :
        : $(TARGET_KERNEL_PIC_CCFLAGS)
 ;
 
+if $(HAIKU_GCC_VERSION_$(HAIKU_ARCH)[1]) >= 7 {
+       ObjectC++Flags commpage.o signal.o thread.o : -fdisable-rtl-stv1 ;
+}
+
 # Generate the header defining macros for C++ structure sizes.
 local kernelC++StructSizesHeader = [ FGristFiles kernel_c++_struct_sizes.h ] ;
 TARGET_HDRS_$(TARGET_PACKAGING_ARCH) on $(kernelC++StructSizesHeader)

I've tried a few permutations of those by themselves, but as far as I can tell, you need all 3 in order for the KDL to be fixed.

[waddlesplash]

And the proposed comment for that if:

	# With the rtl-stv1 pass on these files, the kernel panics towards the end
	# of the boot process with a "General Protection Exception", see
	# https://dev.haiku-os.org/ticket/14160. The pass itself vectorizes
	# a significant number of otherwise-scalar operations, which may be why
	# disabling it fixes the problem.
	#
	# At time of writing, GCC does not seem to have a way to disable
	# vectorization as a result of optimization without disabling
	# FPU usage altogether, which of course is not what we want and
	# breaks when using libstdc++'s headers anyway.

[waddlesplash]

Added in hrev51968.

[korli]

Please attach kdl screenshot to the bug tracker.

It would be nice to point to the documentation reference for the GCC flag.

[kallisti5]

Running tests... gcc7 builds seem ok so far.

[korli]

KDL screenshot

[waddlesplash]

Fixed (for now at least) by that commit.

[waddlesplash]

Actual fix pushed in hrev52020.