On Mon, Jul 21, 2025 at 12:37:23PM -0400, John Baldwin wrote: > On 7/21/25 10:58, Mark Johnston wrote: > > The branch main has been updated by markj: > > > > URL: > > https://cgit.FreeBSD.org/src/commit/?id=cc21f6e53f43f0e4c082222460d90ea581f3e2d6 > > > > commit cc21f6e53f43f0e4c082222460d90ea581f3e2d6 > > Author: Mark Johnston <ma...@freebsd.org> > > AuthorDate: 2025-07-21 13:33:31 +0000 > > Commit: Mark Johnston <ma...@freebsd.org> > > CommitDate: 2025-07-21 14:57:58 +0000 > > > > amd64: Make a comment less confusing > > Also merge two printf()s. No functional change intended. > > Reviewed by: kib > > MFC after: 1 week > > Differential Revision: https://reviews.freebsd.org/D51452 > > --- > > sys/amd64/amd64/trap.c | 13 ++++++------- > > 1 file changed, 6 insertions(+), 7 deletions(-) > > > > diff --git a/sys/amd64/amd64/trap.c b/sys/amd64/amd64/trap.c > > index d9a5f7096a6e..f3469ed5e2bc 100644 > > --- a/sys/amd64/amd64/trap.c > > +++ b/sys/amd64/amd64/trap.c > > @@ -37,7 +37,6 @@ > > * SUCH DAMAGE. > > */ > > -#include <sys/cdefs.h> > > /* > > * AMD64 Trap and System call handling > > */ > > @@ -898,9 +897,9 @@ trap_diag(struct trapframe *frame, vm_offset_t eva) > > printf("\n\nFatal trap %d: %s while in %s mode\n", type, > > type < nitems(trap_msg) ? trap_msg[type] : UNKNOWN, > > TRAPF_USERMODE(frame) ? "user" : "kernel"); > > - /* two separate prints in case of a trap on an unmapped page */ > > - printf("cpuid = %d; ", PCPU_GET(cpuid)); > > - printf("apic id = %02x\n", PCPU_GET(apic_id)); > > + /* Print these separately in case pcpu accesses trap. */ > > + printf("cpuid = %d; apic id = %02x\n", PCPU_GET(cpuid), > > + PCPU_GET(apic_id)); > > if (type == T_PAGEFLT) { > > printf("fault virtual address = 0x%lx\n", eva); > > printf("fault code = %s %s %s%s%s, %s\n", > > @@ -1021,9 +1020,9 @@ dblfault_handler(struct trapframe *frame) > > frame->tf_cs, frame->tf_ss, frame->tf_ds, frame->tf_es, > > frame->tf_fs, frame->tf_gs, > > rdmsr(MSR_FSBASE), rdmsr(MSR_GSBASE), rdmsr(MSR_KGSBASE)); > > - /* two separate prints in case of a trap on an unmapped page */ > > - printf("cpuid = %d; ", PCPU_GET(cpuid)); > > - printf("apic id = %02x\n", PCPU_GET(apic_id)); > > + /* Print these separately in case pcpu accesses trap. */ > > + printf("cpuid = %d; apic id = %02x\n", PCPU_GET(cpuid), > > + PCPU_GET(apic_id)); > > panic("double fault"); > > Eh, if any of the accesses fault you don't get any of the printf,
Right, but I believe the comment is referring to the preceding printf, which doesn't print any PCPU fields. In what situation would PCPU_GET(apic_id) fault while PCPU_GET(cpuid) succeeds? (Yes, my commit message here should have been better.) > so once > you've merged these, the comment is wrong and should just be removed. > FWIW, pre-5.0 (maybe pre-4.0?) per-CPU data on i386 used a fixed virtual > address that was mapped to different backing pages on each CPU instead of > %gs which is why the comment was probably worded that way originally. > > (This meant, btw, that each CPU had its own set of top-level kernel page > table and that cpu_switch had to munge the kernel-half of the top-level > page table of a process, which precluded multiple threads in a process.) > > -- > John Baldwin >
