ftrace/x86: Have arch x86_64 use breakpoints instead of stop machine
This method changes x86 to add a breakpoint to the mcount locations instead of calling stop machine. Now that iret can be handled by NMIs, we perform the following to update code: 1) Add a breakpoint to all locations that will be modified 2) Sync all cores 3) Update all locations to be either a nop or call (except breakpoint op) 4) Sync all cores 5) Remove the breakpoint with the new code. 6) Sync all cores [ Added updates that Masami suggested: Use unlikely(modifying_ftrace_code) in int3 trap to keep kprobes efficient. Don't use NOTIFY_* in ftrace handler in int3 as it is not a notifier. ] Cc: H. Peter Anvin <hpa@zytor.com> Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>hifive-unleashed-5.1
Steven Rostedt
Steven Rostedt
parent
438ced1720
commit
08d636b6d4
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@ -34,6 +34,7 @@
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#ifndef __ASSEMBLY__
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extern void mcount(void);
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extern int modifying_ftrace_code;
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static inline unsigned long ftrace_call_adjust(unsigned long addr)
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{
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@ -50,6 +51,8 @@ struct dyn_arch_ftrace {
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/* No extra data needed for x86 */
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};
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int ftrace_int3_handler(struct pt_regs *regs);
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#endif /* CONFIG_DYNAMIC_FTRACE */
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#endif /* __ASSEMBLY__ */
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#endif /* CONFIG_FUNCTION_TRACER */
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@ -20,6 +20,7 @@
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#include <linux/init.h>
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#include <linux/list.h>
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#include <linux/module.h>
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#include <linux/kprobes.h>
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#include <trace/syscall.h>
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@ -334,6 +335,347 @@ int ftrace_update_ftrace_func(ftrace_func_t func)
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return ret;
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}
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int modifying_ftrace_code __read_mostly;
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/*
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* A breakpoint was added to the code address we are about to
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* modify, and this is the handle that will just skip over it.
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* We are either changing a nop into a trace call, or a trace
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* call to a nop. While the change is taking place, we treat
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* it just like it was a nop.
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*/
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int ftrace_int3_handler(struct pt_regs *regs)
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{
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if (WARN_ON_ONCE(!regs))
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return 0;
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if (!ftrace_location(regs->ip - 1))
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return 0;
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regs->ip += MCOUNT_INSN_SIZE - 1;
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return 1;
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}
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static int ftrace_write(unsigned long ip, const char *val, int size)
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{
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/*
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* On x86_64, kernel text mappings are mapped read-only with
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* CONFIG_DEBUG_RODATA. So we use the kernel identity mapping instead
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* of the kernel text mapping to modify the kernel text.
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*
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* For 32bit kernels, these mappings are same and we can use
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* kernel identity mapping to modify code.
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*/
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if (within(ip, (unsigned long)_text, (unsigned long)_etext))
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ip = (unsigned long)__va(__pa(ip));
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return probe_kernel_write((void *)ip, val, size);
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}
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static int add_break(unsigned long ip, const char *old)
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{
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unsigned char replaced[MCOUNT_INSN_SIZE];
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unsigned char brk = BREAKPOINT_INSTRUCTION;
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if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
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return -EFAULT;
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/* Make sure it is what we expect it to be */
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if (memcmp(replaced, old, MCOUNT_INSN_SIZE) != 0)
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return -EINVAL;
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if (ftrace_write(ip, &brk, 1))
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return -EPERM;
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return 0;
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}
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static int add_brk_on_call(struct dyn_ftrace *rec, unsigned long addr)
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{
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unsigned const char *old;
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unsigned long ip = rec->ip;
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old = ftrace_call_replace(ip, addr);
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return add_break(rec->ip, old);
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}
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static int add_brk_on_nop(struct dyn_ftrace *rec)
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{
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unsigned const char *old;
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old = ftrace_nop_replace();
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return add_break(rec->ip, old);
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}
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static int add_breakpoints(struct dyn_ftrace *rec, int enable)
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{
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unsigned long ftrace_addr;
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int ret;
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ret = ftrace_test_record(rec, enable);
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ftrace_addr = (unsigned long)FTRACE_ADDR;
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switch (ret) {
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case FTRACE_UPDATE_IGNORE:
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return 0;
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case FTRACE_UPDATE_MAKE_CALL:
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/* converting nop to call */
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return add_brk_on_nop(rec);
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case FTRACE_UPDATE_MAKE_NOP:
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/* converting a call to a nop */
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return add_brk_on_call(rec, ftrace_addr);
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}
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return 0;
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}
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/*
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* On error, we need to remove breakpoints. This needs to
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* be done caefully. If the address does not currently have a
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* breakpoint, we know we are done. Otherwise, we look at the
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* remaining 4 bytes of the instruction. If it matches a nop
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* we replace the breakpoint with the nop. Otherwise we replace
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* it with the call instruction.
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*/
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static int remove_breakpoint(struct dyn_ftrace *rec)
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{
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unsigned char ins[MCOUNT_INSN_SIZE];
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unsigned char brk = BREAKPOINT_INSTRUCTION;
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const unsigned char *nop;
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unsigned long ftrace_addr;
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unsigned long ip = rec->ip;
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/* If we fail the read, just give up */
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if (probe_kernel_read(ins, (void *)ip, MCOUNT_INSN_SIZE))
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return -EFAULT;
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/* If this does not have a breakpoint, we are done */
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if (ins[0] != brk)
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return -1;
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nop = ftrace_nop_replace();
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/*
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* If the last 4 bytes of the instruction do not match
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* a nop, then we assume that this is a call to ftrace_addr.
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*/
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if (memcmp(&ins[1], &nop[1], MCOUNT_INSN_SIZE - 1) != 0) {
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/*
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* For extra paranoidism, we check if the breakpoint is on
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* a call that would actually jump to the ftrace_addr.
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* If not, don't touch the breakpoint, we make just create
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* a disaster.
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*/
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ftrace_addr = (unsigned long)FTRACE_ADDR;
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nop = ftrace_call_replace(ip, ftrace_addr);
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if (memcmp(&ins[1], &nop[1], MCOUNT_INSN_SIZE - 1) != 0)
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return -EINVAL;
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}
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return probe_kernel_write((void *)ip, &nop[0], 1);
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}
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static int add_update_code(unsigned long ip, unsigned const char *new)
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{
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/* skip breakpoint */
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ip++;
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new++;
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if (ftrace_write(ip, new, MCOUNT_INSN_SIZE - 1))
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return -EPERM;
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return 0;
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}
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static int add_update_call(struct dyn_ftrace *rec, unsigned long addr)
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{
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unsigned long ip = rec->ip;
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unsigned const char *new;
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new = ftrace_call_replace(ip, addr);
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return add_update_code(ip, new);
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}
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static int add_update_nop(struct dyn_ftrace *rec)
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{
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unsigned long ip = rec->ip;
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unsigned const char *new;
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new = ftrace_nop_replace();
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return add_update_code(ip, new);
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}
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static int add_update(struct dyn_ftrace *rec, int enable)
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{
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unsigned long ftrace_addr;
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int ret;
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ret = ftrace_test_record(rec, enable);
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ftrace_addr = (unsigned long)FTRACE_ADDR;
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switch (ret) {
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case FTRACE_UPDATE_IGNORE:
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return 0;
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case FTRACE_UPDATE_MAKE_CALL:
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/* converting nop to call */
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return add_update_call(rec, ftrace_addr);
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case FTRACE_UPDATE_MAKE_NOP:
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/* converting a call to a nop */
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return add_update_nop(rec);
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}
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return 0;
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}
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static int finish_update_call(struct dyn_ftrace *rec, unsigned long addr)
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{
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unsigned long ip = rec->ip;
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unsigned const char *new;
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new = ftrace_call_replace(ip, addr);
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if (ftrace_write(ip, new, 1))
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return -EPERM;
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return 0;
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}
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static int finish_update_nop(struct dyn_ftrace *rec)
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{
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unsigned long ip = rec->ip;
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unsigned const char *new;
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new = ftrace_nop_replace();
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if (ftrace_write(ip, new, 1))
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return -EPERM;
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return 0;
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}
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static int finish_update(struct dyn_ftrace *rec, int enable)
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{
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unsigned long ftrace_addr;
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int ret;
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ret = ftrace_update_record(rec, enable);
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ftrace_addr = (unsigned long)FTRACE_ADDR;
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switch (ret) {
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case FTRACE_UPDATE_IGNORE:
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return 0;
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case FTRACE_UPDATE_MAKE_CALL:
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/* converting nop to call */
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return finish_update_call(rec, ftrace_addr);
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case FTRACE_UPDATE_MAKE_NOP:
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/* converting a call to a nop */
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return finish_update_nop(rec);
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}
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return 0;
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}
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static void do_sync_core(void *data)
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{
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sync_core();
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}
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static void run_sync(void)
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{
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int enable_irqs = irqs_disabled();
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/* We may be called with interrupts disbled (on bootup). */
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if (enable_irqs)
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local_irq_enable();
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on_each_cpu(do_sync_core, NULL, 1);
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if (enable_irqs)
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local_irq_disable();
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}
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static void ftrace_replace_code(int enable)
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{
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struct ftrace_rec_iter *iter;
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struct dyn_ftrace *rec;
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const char *report = "adding breakpoints";
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int count = 0;
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int ret;
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for_ftrace_rec_iter(iter) {
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rec = ftrace_rec_iter_record(iter);
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ret = add_breakpoints(rec, enable);
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if (ret)
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goto remove_breakpoints;
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count++;
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}
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run_sync();
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report = "updating code";
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for_ftrace_rec_iter(iter) {
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rec = ftrace_rec_iter_record(iter);
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ret = add_update(rec, enable);
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if (ret)
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goto remove_breakpoints;
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}
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run_sync();
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report = "removing breakpoints";
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for_ftrace_rec_iter(iter) {
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rec = ftrace_rec_iter_record(iter);
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ret = finish_update(rec, enable);
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if (ret)
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goto remove_breakpoints;
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}
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run_sync();
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return;
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remove_breakpoints:
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ftrace_bug(ret, rec ? rec->ip : 0);
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printk(KERN_WARNING "Failed on %s (%d):\n", report, count);
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for_ftrace_rec_iter(iter) {
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rec = ftrace_rec_iter_record(iter);
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remove_breakpoint(rec);
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}
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}
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void arch_ftrace_update_code(int command)
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{
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modifying_ftrace_code++;
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if (command & FTRACE_UPDATE_CALLS)
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ftrace_replace_code(1);
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else if (command & FTRACE_DISABLE_CALLS)
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ftrace_replace_code(0);
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if (command & FTRACE_UPDATE_TRACE_FUNC)
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ftrace_update_ftrace_func(ftrace_trace_function);
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if (command & FTRACE_START_FUNC_RET)
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ftrace_enable_ftrace_graph_caller();
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else if (command & FTRACE_STOP_FUNC_RET)
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ftrace_disable_ftrace_graph_caller();
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modifying_ftrace_code--;
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}
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int __init ftrace_dyn_arch_init(void *data)
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{
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/* The return code is retured via data */
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@ -50,6 +50,7 @@
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#include <asm/processor.h>
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#include <asm/debugreg.h>
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#include <linux/atomic.h>
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#include <asm/ftrace.h>
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#include <asm/traps.h>
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#include <asm/desc.h>
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#include <asm/i387.h>
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@ -303,8 +304,13 @@ gp_in_kernel:
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}
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/* May run on IST stack. */
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dotraplinkage void __kprobes do_int3(struct pt_regs *regs, long error_code)
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dotraplinkage void __kprobes notrace do_int3(struct pt_regs *regs, long error_code)
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{
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#ifdef CONFIG_DYNAMIC_FTRACE
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/* ftrace must be first, everything else may cause a recursive crash */
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if (unlikely(modifying_ftrace_code) && ftrace_int3_handler(regs))
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return;
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#endif
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#ifdef CONFIG_KGDB_LOW_LEVEL_TRAP
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if (kgdb_ll_trap(DIE_INT3, "int3", regs, error_code, X86_TRAP_BP,
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SIGTRAP) == NOTIFY_STOP)
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@ -286,6 +286,12 @@ struct ftrace_rec_iter *ftrace_rec_iter_start(void);
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struct ftrace_rec_iter *ftrace_rec_iter_next(struct ftrace_rec_iter *iter);
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struct dyn_ftrace *ftrace_rec_iter_record(struct ftrace_rec_iter *iter);
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#define for_ftrace_rec_iter(iter) \
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for (iter = ftrace_rec_iter_start(); \
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iter; \
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iter = ftrace_rec_iter_next(iter))
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int ftrace_update_record(struct dyn_ftrace *rec, int enable);
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int ftrace_test_record(struct dyn_ftrace *rec, int enable);
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void ftrace_run_stop_machine(int command);
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