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x86/kexec: Debugging support: Dump registers on exception

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

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20250314173226.3062535-3-dwmw2@infradead.org
This commit is contained in:
David Woodhouse 2025-03-14 17:27:34 +00:00 committed by Ingo Molnar
parent 8df505af7f
commit 3d66af75b0
1 changed files with 115 additions and 6 deletions
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121
arch/x86/kernel/relocate_kernel_64.S
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@ -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
@ -422,17 +485,63 @@ SYM_CODE_START_LOCAL_NOALIGN(exc_handler)
VALIDATE_UNRET_END
pushq %rax
pushq %rbx
pushq %rcx
pushq %rdx
movw $0x3f8, %dx
movb $'A', %al
outb %al, %dx
popq %rdx
popq %rax
pushq %rsi
/* Stack frame */
#define EXC_SS 0x58 /* Architectural... */
#define EXC_RSP 0x50
#define EXC_EFLAGS 0x48
#define EXC_CS 0x40
#define EXC_RIP 0x38
#define EXC_ERRORCODE 0x30 /* Either architectural or zero pushed by handler */
#define EXC_EXCEPTION 0x28 /* Pushed by handler entry point */
#define EXC_RAX 0x20 /* Pushed just above in exc_handler */
#define EXC_RBX 0x18
#define EXC_RCX 0x10
#define EXC_RDX 0x08
#define EXC_RSI 0x00
/* Set up %rdx/%rsi for debug output */
pr_setup
/* rip and exception info */
print_reg 'E', 'x', 'c', ':', EXC_EXCEPTION(%rsp)
print_reg 'E', 'r', 'r', ':', EXC_ERRORCODE(%rsp)
print_reg 'r', 'i', 'p', ':', EXC_RIP(%rsp)
print_reg 'r', 's', 'p', ':', EXC_RSP(%rsp)
/* We spilled these to the stack */
print_reg 'r', 'a', 'x', ':', EXC_RAX(%rsp)
print_reg 'r', 'b', 'x', ':', EXC_RBX(%rsp)
print_reg 'r', 'c', 'x', ':', EXC_RCX(%rsp)
print_reg 'r', 'd', 'x', ':', EXC_RDX(%rsp)
print_reg 'r', 's', 'i', ':', EXC_RSI(%rsp)
/* Other registers untouched */
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
/* Only return from INT3 */
cmpq $3, (%rsp)
cmpq $3, EXC_EXCEPTION(%rsp)
jne .Ldie
popq %rsi
popq %rdx
popq %rcx
popq %rbx
popq %rax
addq $16, %rsp
iretq