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Merge branch 'x86-debug-for-linus' of git://git.kernel.org/pub/scm/li…
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…nux/kernel/git/tip/tip

Pull x86 debug updates from Ingo Molnar:
 "This contains the x86 oops code printing reorganization and cleanups
  from Borislav Betkov, with a particular focus in enhancing opcode
  dumping all around"

* 'x86-debug-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/dumpstack: Explain the reasoning for the prologue and buffer size
  x86/dumpstack: Save first regs set for the executive summary
  x86/dumpstack: Add a show_ip() function
  x86/fault: Dump user opcode bytes on fatal faults
  x86/dumpstack: Add loglevel argument to show_opcodes()
  x86/dumpstack: Improve opcodes dumping in the code section
  x86/dumpstack: Carve out code-dumping into a function
  x86/dumpstack: Unexport oops_begin()
  x86/dumpstack: Remove code_bytes
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Linus Torvalds committed Jun 5, 2018
2 parents 0afe832 + 4dba072 commit 8316385
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Showing 5 changed files with 80 additions and 86 deletions.
5 changes: 0 additions & 5 deletions Documentation/admin-guide/kernel-parameters.txt
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Expand Up @@ -587,11 +587,6 @@
Sets the size of memory pool for coherent, atomic dma
allocations, by default set to 256K.

code_bytes [X86] How many bytes of object code to print
in an oops report.
Range: 0 - 8192
Default: 64

com20020= [HW,NET] ARCnet - COM20020 chipset
Format:
<io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
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2 changes: 2 additions & 0 deletions arch/x86/include/asm/stacktrace.h
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Original file line number Diff line number Diff line change
Expand Up @@ -111,4 +111,6 @@ static inline unsigned long caller_frame_pointer(void)
return (unsigned long)frame;
}

void show_opcodes(u8 *rip, const char *loglvl);
void show_ip(struct pt_regs *regs, const char *loglvl);
#endif /* _ASM_X86_STACKTRACE_H */
144 changes: 70 additions & 74 deletions arch/x86/kernel/dumpstack.c
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Original file line number Diff line number Diff line change
Expand Up @@ -22,11 +22,14 @@
#include <asm/stacktrace.h>
#include <asm/unwind.h>

#define OPCODE_BUFSIZE 64

int panic_on_unrecovered_nmi;
int panic_on_io_nmi;
static unsigned int code_bytes = 64;
static int die_counter;

static struct pt_regs exec_summary_regs;

bool in_task_stack(unsigned long *stack, struct task_struct *task,
struct stack_info *info)
{
Expand Down Expand Up @@ -69,9 +72,62 @@ static void printk_stack_address(unsigned long address, int reliable,
printk("%s %s%pB\n", log_lvl, reliable ? "" : "? ", (void *)address);
}

/*
* There are a couple of reasons for the 2/3rd prologue, courtesy of Linus:
*
* In case where we don't have the exact kernel image (which, if we did, we can
* simply disassemble and navigate to the RIP), the purpose of the bigger
* prologue is to have more context and to be able to correlate the code from
* the different toolchains better.
*
* In addition, it helps in recreating the register allocation of the failing
* kernel and thus make sense of the register dump.
*
* What is more, the additional complication of a variable length insn arch like
* x86 warrants having longer byte sequence before rIP so that the disassembler
* can "sync" up properly and find instruction boundaries when decoding the
* opcode bytes.
*
* Thus, the 2/3rds prologue and 64 byte OPCODE_BUFSIZE is just a random
* guesstimate in attempt to achieve all of the above.
*/
void show_opcodes(u8 *rip, const char *loglvl)
{
unsigned int code_prologue = OPCODE_BUFSIZE * 2 / 3;
u8 opcodes[OPCODE_BUFSIZE];
u8 *ip;
int i;

printk("%sCode: ", loglvl);

ip = (u8 *)rip - code_prologue;
if (probe_kernel_read(opcodes, ip, OPCODE_BUFSIZE)) {
pr_cont("Bad RIP value.\n");
return;
}

for (i = 0; i < OPCODE_BUFSIZE; i++, ip++) {
if (ip == rip)
pr_cont("<%02x> ", opcodes[i]);
else
pr_cont("%02x ", opcodes[i]);
}
pr_cont("\n");
}

void show_ip(struct pt_regs *regs, const char *loglvl)
{
#ifdef CONFIG_X86_32
printk("%sEIP: %pS\n", loglvl, (void *)regs->ip);
#else
printk("%sRIP: %04x:%pS\n", loglvl, (int)regs->cs, (void *)regs->ip);
#endif
show_opcodes((u8 *)regs->ip, loglvl);
}

void show_iret_regs(struct pt_regs *regs)
{
printk(KERN_DEFAULT "RIP: %04x:%pS\n", (int)regs->cs, (void *)regs->ip);
show_ip(regs, KERN_DEFAULT);
printk(KERN_DEFAULT "RSP: %04x:%016lx EFLAGS: %08lx", (int)regs->ss,
regs->sp, regs->flags);
}
Expand Down Expand Up @@ -267,7 +323,6 @@ unsigned long oops_begin(void)
bust_spinlocks(1);
return flags;
}
EXPORT_SYMBOL_GPL(oops_begin);
NOKPROBE_SYMBOL(oops_begin);

void __noreturn rewind_stack_do_exit(int signr);
Expand All @@ -287,6 +342,9 @@ void oops_end(unsigned long flags, struct pt_regs *regs, int signr)
raw_local_irq_restore(flags);
oops_exit();

/* Executive summary in case the oops scrolled away */
__show_regs(&exec_summary_regs, true);

if (!signr)
return;
if (in_interrupt())
Expand All @@ -305,10 +363,10 @@ NOKPROBE_SYMBOL(oops_end);

int __die(const char *str, struct pt_regs *regs, long err)
{
#ifdef CONFIG_X86_32
unsigned short ss;
unsigned long sp;
#endif
/* Save the regs of the first oops for the executive summary later. */
if (!die_counter)
exec_summary_regs = *regs;

printk(KERN_DEFAULT
"%s: %04lx [#%d]%s%s%s%s%s\n", str, err & 0xffff, ++die_counter,
IS_ENABLED(CONFIG_PREEMPT) ? " PREEMPT" : "",
Expand All @@ -318,26 +376,13 @@ int __die(const char *str, struct pt_regs *regs, long err)
IS_ENABLED(CONFIG_PAGE_TABLE_ISOLATION) ?
(boot_cpu_has(X86_FEATURE_PTI) ? " PTI" : " NOPTI") : "");

show_regs(regs);
print_modules();

if (notify_die(DIE_OOPS, str, regs, err,
current->thread.trap_nr, SIGSEGV) == NOTIFY_STOP)
return 1;

print_modules();
show_regs(regs);
#ifdef CONFIG_X86_32
if (user_mode(regs)) {
sp = regs->sp;
ss = regs->ss;
} else {
sp = kernel_stack_pointer(regs);
savesegment(ss, ss);
}
printk(KERN_EMERG "EIP: %pS SS:ESP: %04x:%08lx\n",
(void *)regs->ip, ss, sp);
#else
/* Executive summary in case the oops scrolled away */
printk(KERN_ALERT "RIP: %pS RSP: %016lx\n", (void *)regs->ip, regs->sp);
#endif
return 0;
}
NOKPROBE_SYMBOL(__die);
Expand All @@ -356,30 +401,9 @@ void die(const char *str, struct pt_regs *regs, long err)
oops_end(flags, regs, sig);
}

static int __init code_bytes_setup(char *s)
{
ssize_t ret;
unsigned long val;

if (!s)
return -EINVAL;

ret = kstrtoul(s, 0, &val);
if (ret)
return ret;

code_bytes = val;
if (code_bytes > 8192)
code_bytes = 8192;

return 1;
}
__setup("code_bytes=", code_bytes_setup);

void show_regs(struct pt_regs *regs)
{
bool all = true;
int i;

show_regs_print_info(KERN_DEFAULT);

Expand All @@ -389,36 +413,8 @@ void show_regs(struct pt_regs *regs)
__show_regs(regs, all);

/*
* When in-kernel, we also print out the stack and code at the
* time of the fault..
* When in-kernel, we also print out the stack at the time of the fault..
*/
if (!user_mode(regs)) {
unsigned int code_prologue = code_bytes * 43 / 64;
unsigned int code_len = code_bytes;
unsigned char c;
u8 *ip;

if (!user_mode(regs))
show_trace_log_lvl(current, regs, NULL, KERN_DEFAULT);

printk(KERN_DEFAULT "Code: ");

ip = (u8 *)regs->ip - code_prologue;
if (ip < (u8 *)PAGE_OFFSET || probe_kernel_address(ip, c)) {
/* try starting at IP */
ip = (u8 *)regs->ip;
code_len = code_len - code_prologue + 1;
}
for (i = 0; i < code_len; i++, ip++) {
if (ip < (u8 *)PAGE_OFFSET ||
probe_kernel_address(ip, c)) {
pr_cont(" Bad RIP value.");
break;
}
if (ip == (u8 *)regs->ip)
pr_cont("<%02x> ", c);
else
pr_cont("%02x ", c);
}
}
pr_cont("\n");
}
8 changes: 3 additions & 5 deletions arch/x86/kernel/process_32.c
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Original file line number Diff line number Diff line change
Expand Up @@ -76,16 +76,14 @@ void __show_regs(struct pt_regs *regs, int all)
savesegment(gs, gs);
}

printk(KERN_DEFAULT "EIP: %pS\n", (void *)regs->ip);
printk(KERN_DEFAULT "EFLAGS: %08lx CPU: %d\n", regs->flags,
raw_smp_processor_id());
show_ip(regs, KERN_DEFAULT);

printk(KERN_DEFAULT "EAX: %08lx EBX: %08lx ECX: %08lx EDX: %08lx\n",
regs->ax, regs->bx, regs->cx, regs->dx);
printk(KERN_DEFAULT "ESI: %08lx EDI: %08lx EBP: %08lx ESP: %08lx\n",
regs->si, regs->di, regs->bp, sp);
printk(KERN_DEFAULT " DS: %04x ES: %04x FS: %04x GS: %04x SS: %04x\n",
(u16)regs->ds, (u16)regs->es, (u16)regs->fs, gs, ss);
printk(KERN_DEFAULT "DS: %04x ES: %04x FS: %04x GS: %04x SS: %04x EFLAGS: %08lx\n",
(u16)regs->ds, (u16)regs->es, (u16)regs->fs, gs, ss, regs->flags);

if (!all)
return;
Expand Down
7 changes: 5 additions & 2 deletions arch/x86/mm/fault.c
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Original file line number Diff line number Diff line change
Expand Up @@ -829,20 +829,23 @@ static inline void
show_signal_msg(struct pt_regs *regs, unsigned long error_code,
unsigned long address, struct task_struct *tsk)
{
const char *loglvl = task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG;

if (!unhandled_signal(tsk, SIGSEGV))
return;

if (!printk_ratelimit())
return;

printk("%s%s[%d]: segfault at %lx ip %px sp %px error %lx",
task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG,
tsk->comm, task_pid_nr(tsk), address,
loglvl, tsk->comm, task_pid_nr(tsk), address,
(void *)regs->ip, (void *)regs->sp, error_code);

print_vma_addr(KERN_CONT " in ", regs->ip);

printk(KERN_CONT "\n");

show_opcodes((u8 *)regs->ip, loglvl);
}

static void
Expand Down

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