194 lines
5.1 KiB
C
194 lines
5.1 KiB
C
/*
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* Dynamic function tracer architecture backend.
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*
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* Copyright IBM Corp. 2009
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*
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* Author(s): Heiko Carstens <heiko.carstens@de.ibm.com>,
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* Martin Schwidefsky <schwidefsky@de.ibm.com>
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*/
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#include <linux/hardirq.h>
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#include <linux/uaccess.h>
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#include <linux/ftrace.h>
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#include <linux/kernel.h>
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#include <linux/types.h>
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#include <linux/kprobes.h>
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#include <trace/syscall.h>
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#include <asm/asm-offsets.h>
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#ifdef CONFIG_DYNAMIC_FTRACE
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void ftrace_disable_code(void);
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void ftrace_enable_insn(void);
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#ifdef CONFIG_64BIT
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/*
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* The 64-bit mcount code looks like this:
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* stg %r14,8(%r15) # offset 0
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* > larl %r1,<&counter> # offset 6
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* > brasl %r14,_mcount # offset 12
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* lg %r14,8(%r15) # offset 18
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* Total length is 24 bytes. The middle two instructions of the mcount
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* block get overwritten by ftrace_make_nop / ftrace_make_call.
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* The 64-bit enabled ftrace code block looks like this:
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* stg %r14,8(%r15) # offset 0
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* > lg %r1,__LC_FTRACE_FUNC # offset 6
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* > lgr %r0,%r0 # offset 12
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* > basr %r14,%r1 # offset 16
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* lg %r14,8(%15) # offset 18
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* The return points of the mcount/ftrace function have the same offset 18.
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* The 64-bit disable ftrace code block looks like this:
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* stg %r14,8(%r15) # offset 0
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* > jg .+18 # offset 6
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* > lgr %r0,%r0 # offset 12
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* > basr %r14,%r1 # offset 16
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* lg %r14,8(%15) # offset 18
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* The jg instruction branches to offset 24 to skip as many instructions
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* as possible.
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*/
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asm(
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" .align 4\n"
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"ftrace_disable_code:\n"
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" jg 0f\n"
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" lgr %r0,%r0\n"
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" basr %r14,%r1\n"
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"0:\n"
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" .align 4\n"
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"ftrace_enable_insn:\n"
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" lg %r1,"__stringify(__LC_FTRACE_FUNC)"\n");
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#define FTRACE_INSN_SIZE 6
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#else /* CONFIG_64BIT */
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/*
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* The 31-bit mcount code looks like this:
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* st %r14,4(%r15) # offset 0
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* > bras %r1,0f # offset 4
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* > .long _mcount # offset 8
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* > .long <&counter> # offset 12
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* > 0: l %r14,0(%r1) # offset 16
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* > l %r1,4(%r1) # offset 20
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* basr %r14,%r14 # offset 24
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* l %r14,4(%r15) # offset 26
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* Total length is 30 bytes. The twenty bytes starting from offset 4
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* to offset 24 get overwritten by ftrace_make_nop / ftrace_make_call.
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* The 31-bit enabled ftrace code block looks like this:
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* st %r14,4(%r15) # offset 0
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* > l %r14,__LC_FTRACE_FUNC # offset 4
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* > j 0f # offset 8
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* > .fill 12,1,0x07 # offset 12
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* 0: basr %r14,%r14 # offset 24
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* l %r14,4(%r14) # offset 26
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* The return points of the mcount/ftrace function have the same offset 26.
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* The 31-bit disabled ftrace code block looks like this:
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* st %r14,4(%r15) # offset 0
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* > j .+26 # offset 4
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* > j 0f # offset 8
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* > .fill 12,1,0x07 # offset 12
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* 0: basr %r14,%r14 # offset 24
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* l %r14,4(%r14) # offset 26
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* The j instruction branches to offset 30 to skip as many instructions
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* as possible.
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*/
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asm(
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" .align 4\n"
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"ftrace_disable_code:\n"
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" j 1f\n"
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" j 0f\n"
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" .fill 12,1,0x07\n"
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"0: basr %r14,%r14\n"
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"1:\n"
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" .align 4\n"
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"ftrace_enable_insn:\n"
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" l %r14,"__stringify(__LC_FTRACE_FUNC)"\n");
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#define FTRACE_INSN_SIZE 4
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#endif /* CONFIG_64BIT */
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int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
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unsigned long addr)
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{
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if (probe_kernel_write((void *) rec->ip, ftrace_disable_code,
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MCOUNT_INSN_SIZE))
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return -EPERM;
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return 0;
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}
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int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
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{
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if (probe_kernel_write((void *) rec->ip, ftrace_enable_insn,
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FTRACE_INSN_SIZE))
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return -EPERM;
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return 0;
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}
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int ftrace_update_ftrace_func(ftrace_func_t func)
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{
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return 0;
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}
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int __init ftrace_dyn_arch_init(void *data)
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{
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*(unsigned long *) data = 0;
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return 0;
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}
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#endif /* CONFIG_DYNAMIC_FTRACE */
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#ifdef CONFIG_FUNCTION_GRAPH_TRACER
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/*
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* Hook the return address and push it in the stack of return addresses
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* in current thread info.
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*/
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unsigned long __kprobes prepare_ftrace_return(unsigned long parent,
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unsigned long ip)
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{
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struct ftrace_graph_ent trace;
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if (unlikely(atomic_read(¤t->tracing_graph_pause)))
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goto out;
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ip = (ip & PSW_ADDR_INSN) - MCOUNT_INSN_SIZE;
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if (ftrace_push_return_trace(parent, ip, &trace.depth, 0) == -EBUSY)
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goto out;
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trace.func = ip;
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/* Only trace if the calling function expects to. */
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if (!ftrace_graph_entry(&trace)) {
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current->curr_ret_stack--;
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goto out;
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}
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parent = (unsigned long) return_to_handler;
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out:
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return parent;
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}
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#ifdef CONFIG_DYNAMIC_FTRACE
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/*
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* Patch the kernel code at ftrace_graph_caller location. The instruction
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* there is branch relative and save to prepare_ftrace_return. To disable
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* the call to prepare_ftrace_return we patch the bras offset to point
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* directly after the instructions. To enable the call we calculate
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* the original offset to prepare_ftrace_return and put it back.
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*/
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int ftrace_enable_ftrace_graph_caller(void)
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{
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unsigned short offset;
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offset = ((void *) prepare_ftrace_return -
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(void *) ftrace_graph_caller) / 2;
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return probe_kernel_write(ftrace_graph_caller + 2,
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&offset, sizeof(offset));
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}
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int ftrace_disable_ftrace_graph_caller(void)
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{
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static unsigned short offset = 0x0002;
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return probe_kernel_write(ftrace_graph_caller + 2,
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&offset, sizeof(offset));
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}
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#endif /* CONFIG_DYNAMIC_FTRACE */
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#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
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