On Mon, Jan 05, 2026 at 12:52:14PM +0000, Daniel Thompson wrote:

Hi Marcos

On Sat, Dec 27, 2025 at 09:16:07AM -0300, Marcos Paulo de Souza wrote:

quoted

The parts 1 and 2 can be found here [1] and here[2].

The changes proposed in this part 3 are mostly to clarify the usage of
the interfaces for NBCON, and use the printk helpers more broadly.
Besides it, it also introduces a new way to register consoles
and drop thes the CON_ENABLED flag. It seems too much, but in reality
the changes are not complex, and as the title says, it's basically a
cleanup without changing the functional changes.

I ran this patchset through the kgdb test suite and I'm afraid it is
reporting functional changes.

Specifically the earlycon support for kdb has regressed (FWIW the
problem bisects down to the final patch in the series where CON_ENABLED
is removed).

Reproduction on x86-64 KVM outside of the test suite should be easy:

    make defconfig
    scripts/config \
        --enable DEBUG_INFO \
	--enable DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT \
	--enable DEBUG_FS \
	--enable KALLSYMS_ALL \
	--enable MAGIC_SYSRQ \
	--enable KGDB \
	--enable KGDB_TESTS \
	--enable KGDB_KDB \
	--enable KDB_KEYBOARD \
	--enable LKDTM \
	--enable SECURITY_LOCKDOWN_LSM
    make olddefconfig
    make -j$(nproc)
    qemu-system-x86_64 \
        -m 1G -smp 2 -nographic \
	-kernel arch/x86/boot/bzImage \
	-append "console=ttyS0,115200 kgdboc=ttyS0 earlycon=uart8250,io,0x3f8 kgdboc_earlycon kgdbwait"

Actually I realized there was a simpler reproduction (hinted at by the
missing "printk: legacy bootconsole [uart8250] enabled" in the regressed
case). It looks like the earlycon simply doesn't work and that means the
reproduction doesn't require anything related to kgdb at all. Simply:

    make defconfig
    make -j$(nproc)
    qemu-system-x86_64 -m 1G -smp 2 -nographic -kernel arch/x86/boot/bzImage \
        -append "earlycon=uart8250,io,0x3f8"

With the part 3 patchset applied I get no output from the earlycon
(without the patch set I get the early boot messages which, as expected,
stop when tty0 comes up).


Daniel.