[x86-core2] "CPU ISA level is lower than required" issue with glibc 2.33

[Romain Naour]

Hello,

When testing glibc 2.33 with x86-core2 toolchain, the system doesn't boot due to
a kernel panic:

Run /sbin/init as init process
/lib/libc.so.6: CPU ISA level is lower than required
Kernel panic - not syncing: Attempted to kill init! exitcode=0x00007f00

This is due to a new isa level check added by this commit:
"x86: Support GNU_PROPERTY_X86_ISA_1_V[234] marker [BZ #26717]"

https://sourceware.org/git/?p=glibc.git;a=commit;h=ecce11aa0752735c4fd730da6e7c9e0b98e12fb8

Before the glibc version bump the Buildroot defconfig was working.

Here is the qemu command line used to boot the system:

qemu-system-i386 -M pc -cpu core2duo -kernel bzImage -drive
file=rootfs.ext2,if=virtio,format=raw -append 'rootwait root=/dev/vda
console=tty1 console=ttyS0' -net nic,model=virtio -net user -serial stdio

The boot succeed as soon as we use a newer microarchitecture like Broadwell,
Nehalem, SandyBridge, Skylake on the Qemu command line.

It seems l->l_x86_isa_1_needed and cpu_features->isa_1 [1] are not agree about
GNU_PROPERTY_X86_ISA_1_V2 when core2duo is used.

Indeed the gnu.propery report GNU_PROPERTY_X86_ISA_1_V2 in the libc binary:

$ readelf -n [...]/staging/lib/libc-2.33.so

Displaying notes found in: .note.gnu.property
  Owner                Data size 	Description
  GNU                  0x00000010	NT_GNU_PROPERTY_TYPE_0
      Properties: <procesor-specific type 0xc0008002 data: 03 00 00 00 >

This is because ISA_LEVEL is set with ISA_BASELINE and ISA_V2 [2]

But get_isa_level() doesn't use the same condition to detect
GNU_PROPERTY_X86_ISA_1_V2 [3]

If I remove the condition to define ISA_V2 with 0, the system boot.

$ readelf -n [...]/staging/lib/libc-2.33.so

Displaying notes found in: .note.gnu.property
  Owner                Data size 	Description
  GNU                  0x00000024	NT_GNU_PROPERTY_TYPE_0
      Properties: <procesor-specific type 0xc0008002 data: 01 00 00 00 >
	x86 feature used: x86, x87, XMM
	<procesor-specific type 0xc0010002 data: 03 00 00 00 >

Here is the cpuinfo reported at runtime under Qemu with a working system:

# cat /proc/cpuinfo
processor	: 0
vendor_id	: GenuineIntel
cpu family	: 6
model		: 15
model name	: Intel(R) Core(TM)2 Duo CPU     T7700  @ 2.40GHz
stepping	: 11
microcode	: 0x1
cpu MHz		: 1991.966
cache size	: 16384 KB
physical id	: 0
siblings	: 1
core id		: 0
cpu cores	: 1
apicid		: 0
initial apicid	: 0
fpu		: yes
fpu_exception	: yes
cpuid level	: 10
wp		: yes
flags		: fpu de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36
clflush acpi mmx fxsr sse sse2 syscall nx lm constant_tsc rep_good nopl cpuid
pni monitor ssse3 cx16 hypervisor lahf_lm pti
bugs		: cpu_meltdown spectre_v1 spectre_v2 spec_store_bypass l1tf mds swapgs
itlb_multihit
bogomips	: 3983.93
clflush size	: 64
cache_alignment	: 64
address sizes	: 40 bits physical, 48 bits virtual
power management:

The issue doesn't seems specific to core2 architecture.
Can you have a look?

[1]
https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/x86/dl-prop.h;h=56bd020b3c0c2a96bce47fc9ce4665063becd2d6;hb=ecce11aa0752735c4fd730da6e7c9e0b98e12fb8#l53

[2]
https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/x86/isa-level.c;h=aaf524cb56c99cb43044fef3cac5b54f8d7dff9f;hb=ecce11aa0752735c4fd730da6e7c9e0b98e12fb8#l64

[3]
https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/x86/get-isa-level.h;h=a86e1e8941cc8f65e83b47ead6872fc823db8e16;hb=ecce11aa0752735c4fd730da6e7c9e0b98e12fb8#l38

Best regards,
Romain