x86/kexec: Debugging support: Dump registers on exception

The actual serial output function is a no-op for now.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>

diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index 5bf3eec2821bfa45a1e318dca221b917e7f92976..2cc35ca11c3e9c221b32d7fb9c506b35eda696f1 100644 (file)
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -379,6 +379,69 @@ SYM_CODE_START_LOCAL_NOALIGN(swap_pages)
        int3
 SYM_CODE_END(swap_pages)
 
+/*
+ * Generic 'print character' routine (as yet unimplemented)
+ *  - %al: Character to be printed (may clobber %rax)
+ *  - %rdx: MMIO address or port.
+ */
+SYM_CODE_START_LOCAL_NOALIGN(pr_char)
+       UNWIND_HINT_FUNC
+       ANNOTATE_NOENDBR
+       ANNOTATE_UNRET_SAFE
+       ret
+SYM_CODE_END(pr_char)
+
+/*
+ * Load pr_char function pointer into %rsi and load %rdx with whatever
+ * that function wants to see there (typically port/MMIO address).
+ */
+.macro pr_setup
+       /* No output; pr_char just returns */
+       leaq    pr_char(%rip), %rsi
+.endm
+
+/* Print the nybble in %bl, clobber %rax */
+SYM_CODE_START_LOCAL_NOALIGN(pr_nybble)
+       UNWIND_HINT_FUNC
+       movb    %bl, %al
+       nop
+       andb    $0x0f, %al
+       addb    $0x30, %al
+       cmpb    $0x3a, %al
+       jb      1f
+       addb    $('a' - '0' - 10), %al
+       ANNOTATE_RETPOLINE_SAFE
+1:     jmp     *%rsi
+SYM_CODE_END(pr_nybble)
+
+SYM_CODE_START_LOCAL_NOALIGN(pr_qword)
+       UNWIND_HINT_FUNC
+       movq    $16, %rcx
+1:     rolq    $4, %rbx
+       call    pr_nybble
+       loop    1b
+       movb    $'\n', %al
+       ANNOTATE_RETPOLINE_SAFE
+       jmp     *%rsi
+SYM_CODE_END(pr_qword)
+
+.macro print_reg a, b, c, d, r
+       movb    $\a, %al
+       ANNOTATE_RETPOLINE_SAFE
+       call    *%rsi
+       movb    $\b, %al
+       ANNOTATE_RETPOLINE_SAFE
+       call    *%rsi
+       movb    $\c, %al
+       ANNOTATE_RETPOLINE_SAFE
+       call    *%rsi
+       movb    $\d, %al
+       ANNOTATE_RETPOLINE_SAFE
+       call    *%rsi
+       movq    \r, %rbx
+       call    pr_qword
+.endm
+
 SYM_CODE_START_NOALIGN(kexec_debug_exc_vectors)
        /* Each of these is 6 bytes. */
 .macro vec_err exc
@@ -419,11 +482,43 @@ SYM_CODE_END(kexec_debug_exc_vectors)
 
 SYM_CODE_START_LOCAL_NOALIGN(exc_handler)
        pushq   %rax
+       pushq   %rbx
+       pushq   %rcx
        pushq   %rdx
-       movw    $0x3f8, %dx
-       movb    $'A', %al
-       outb    %al, %dx
+       pushq   %rsi
+
+       /* Set up %rdx/%rsi for debug output */
+       pr_setup
+
+       /* rip and exception info */
+       print_reg 'E', 'x', 'c', ':', 0x28(%rsp)
+       print_reg 'E', 'r', 'r', ':', 0x30(%rsp)
+       print_reg 'r', 'i', 'p', ':', 0x38(%rsp)
+       print_reg 'r', 's', 'p', ':', 0x50(%rsp)
+
+       /* We spilled these to the stack */
+       print_reg 'r', 'a', 'x', ':', 0x20(%rsp)
+       print_reg 'r', 'b', 'x', ':', 0x18(%rsp)
+       print_reg 'r', 'c', 'x', ':', 0x10(%rsp)
+       print_reg 'r', 'd', 'x', ':', 0x08(%rsp)
+
+       /* Other registers */
+       print_reg 'r', 's', 'i', ':', (%rsp)
+       print_reg 'r', 'd', 'i', ':', %rdi
+       print_reg 'r', '8', ' ', ':', %r8
+       print_reg 'r', '9', ' ', ':', %r9
+       print_reg 'r', '1', '0', ':', %r10
+       print_reg 'r', '1', '1', ':', %r11
+       print_reg 'r', '1', '2', ':', %r12
+       print_reg 'r', '1', '3', ':', %r13
+       print_reg 'r', '1', '4', ':', %r14
+       print_reg 'r', '1', '5', ':', %r15
+       print_reg 'c', 'r', '2', ':', %cr2
+
+       popq    %rsi
        popq    %rdx
+       popq    %rcx
+       popq    %rbx
        popq    %rax
 
        /* Only return from int3 */