On Sat, Apr 2, 2016 at 11:39 AM, Borislav Petkov <b...@alien8.de> wrote: > On Sat, Apr 02, 2016 at 07:01:34AM -0700, Andy Lutomirski wrote: >> This removes a bunch of assembly and adds some C code instead. It >> changes the actual printouts on both 32-bit and 64-bit kernels, but >> they still seem okay. >> >> Signed-off-by: Andy Lutomirski <l...@kernel.org> >> --- >> arch/x86/include/asm/uaccess.h | 2 +- >> arch/x86/kernel/head_32.S | 49 >> +++++------------------------------------- >> arch/x86/kernel/head_64.S | 45 ++------------------------------------ >> arch/x86/mm/extable.c | 29 ++++++++++++++++++++----- >> 4 files changed, 32 insertions(+), 93 deletions(-) > > ... > >> @@ -99,21 +101,38 @@ int __init early_fixup_exception(struct pt_regs *regs, >> int trapnr) >> >> /* Ignore early NMIs. */ >> if (trapnr == X86_TRAP_NMI) >> - return 1; >> + return; >> + >> + if (early_recursion_flag > 2) >> + goto halt_loop; >> + >> + if (regs->cs != __KERNEL_CS) >> + goto fail; >> >> e = search_exception_tables(regs->ip); >> if (!e) >> - return 0; >> + goto fail; >> >> new_ip = ex_fixup_addr(e); >> handler = ex_fixup_handler(e); >> >> /* special handling not supported during early boot */ >> if (handler != ex_handler_default) >> - return 0; >> + goto fail; >> >> regs->ip = new_ip; >> - return 1; >> + return; >> + >> +fail: >> + early_printk("PANIC: early exception 0x%02x IP %lx:%lx error %lx cr2 >> 0x%lx\n", >> + (unsigned)trapnr, (unsigned long)regs->cs, regs->ip, >> + regs->orig_ax, read_cr2()); >> + >> + show_regs(regs); > > To make this even better, it could be something called early_show_regs() > or so and be a simplified version of __show_regs() on both bitness but > which calls early_printk(). > > This way you'll be able to get out stuff to the console as early as > possible. > > Btw, you don't need to dump rIP, CR2, etc in the PANIC message above > since you're going to early_show_regs() anyway.
Given that I this isn't really a regression with my patches (it probably never worked much better on 32-bit and the regs never would have shown at all on 64-bit), I propose a different approach: make printk work earlier. Something like: if (early) { early_printk(args); } or early_vprintk or whatever. If the cost of a branch mattered, this could be alternative-patched out later on, but that seems silly. I also bet that a more sensible fallback could be created in which printk would try to use an early console if there's no real console. --Andy _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel