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0cccdda8d1
We can simply patch the mask field within the branch relative on condition instruction at the beginning of the ftrace_graph_caller code block. This makes the logic even simpler and we get rid of the displacement calculation. Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
162 lines
4.5 KiB
C
162 lines
4.5 KiB
C
/*
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* Dynamic function tracer architecture backend.
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*
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* Copyright IBM Corp. 2009,2014
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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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#include "entry.h"
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void mcount_replace_code(void);
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void ftrace_disable_code(void);
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void ftrace_enable_insn(void);
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/*
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* The 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 complete mcount block initially gets replaced
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* by ftrace_make_nop. Subsequent calls to ftrace_make_call / ftrace_make_nop
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* only patch the jg/lg instruction within the block.
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* Note: we do not patch the first instruction to an unconditional branch,
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* since that would break kprobes/jprobes. It is easier to leave the larl
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* instruction in and only modify the second instruction.
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* The enabled ftrace code block looks like this:
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* larl %r0,.+24 # offset 0
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* > lg %r1,__LC_FTRACE_FUNC # offset 6
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* br %r1 # offset 12
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* brcl 0,0 # offset 14
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* brc 0,0 # offset 20
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* The ftrace function gets called with a non-standard C function call ABI
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* where r0 contains the return address. It is also expected that the called
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* function only clobbers r0 and r1, but restores r2-r15.
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* The return point of the ftrace function has offset 24, so execution
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* continues behind the mcount block.
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* larl %r0,.+24 # offset 0
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* > jg .+18 # offset 6
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* br %r1 # offset 12
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* brcl 0,0 # offset 14
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* brc 0,0 # offset 20
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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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"mcount_replace_code:\n"
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" larl %r0,0f\n"
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"ftrace_disable_code:\n"
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" jg 0f\n"
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" br %r1\n"
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" brcl 0,0\n"
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" brc 0,0\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 MCOUNT_BLOCK_SIZE 24
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#define MCOUNT_INSN_OFFSET 6
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#define FTRACE_INSN_SIZE 6
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int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
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unsigned long addr)
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{
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return 0;
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}
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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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/* Initial replacement of the whole mcount block */
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if (addr == MCOUNT_ADDR) {
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if (probe_kernel_write((void *) rec->ip - MCOUNT_INSN_OFFSET,
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mcount_replace_code,
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MCOUNT_BLOCK_SIZE))
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return -EPERM;
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return 0;
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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)
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{
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return 0;
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}
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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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trace.func = ip;
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trace.depth = current->curr_ret_stack + 1;
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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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goto out;
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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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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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/*
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* Patch the kernel code at ftrace_graph_caller location. The instruction
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* there is branch relative on condition. To enable the ftrace graph code
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* block, we simply patch the mask field of the instruction to zero and
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* turn the instruction into a nop.
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* To disable the ftrace graph code the mask field will be patched to
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* all ones, which turns the instruction into an unconditional branch.
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*/
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int ftrace_enable_ftrace_graph_caller(void)
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{
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u8 op = 0x04; /* set mask field to zero */
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return probe_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op));
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}
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int ftrace_disable_ftrace_graph_caller(void)
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{
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u8 op = 0xf4; /* set mask field to all ones */
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return probe_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op));
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}
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#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
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