arm64: ftrace: Add dynamic ftrace support
This patch allows "dynamic ftrace" if CONFIG_DYNAMIC_FTRACE is enabled. Here we can turn on and off tracing dynamically per-function base. On arm64, this is done by patching single branch instruction to _mcount() inserted by gcc -pg option. The branch is replaced to NOP initially at kernel start up, and later on, NOP to branch to ftrace_caller() when enabled or branch to NOP when disabled. Please note that ftrace_caller() is a counterpart of _mcount() in case of 'static' ftrace. More details on architecture specific requirements are described in Documentation/trace/ftrace-design.txt. Acked-by: Will Deacon <will.deacon@arm.com> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org> Signed-off-by: Will Deacon <will.deacon@arm.com>
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@ -36,6 +36,7 @@ config ARM64
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select HAVE_DMA_API_DEBUG
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select HAVE_DMA_ATTRS
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select HAVE_DMA_CONTIGUOUS
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select HAVE_DYNAMIC_FTRACE
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select HAVE_EFFICIENT_UNALIGNED_ACCESS
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select HAVE_FTRACE_MCOUNT_RECORD
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select HAVE_FUNCTION_TRACER
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@ -18,6 +18,21 @@
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#ifndef __ASSEMBLY__
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extern void _mcount(unsigned long);
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struct dyn_arch_ftrace {
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/* No extra data needed for arm64 */
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};
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extern unsigned long ftrace_graph_call;
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static inline unsigned long ftrace_call_adjust(unsigned long addr)
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{
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/*
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* addr is the address of the mcount call instruction.
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* recordmcount does the necessary offset calculation.
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*/
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return addr;
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}
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#endif /* __ASSEMBLY__ */
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#endif /* __ASM_FTRACE_H */
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@ -86,6 +86,7 @@
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add \reg, \reg, #8
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.endm
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#ifndef CONFIG_DYNAMIC_FTRACE
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/*
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* void _mcount(unsigned long return_address)
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* @return_address: return address to instrumented function
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@ -134,6 +135,48 @@ skip_ftrace_call:
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#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
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ENDPROC(_mcount)
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#else /* CONFIG_DYNAMIC_FTRACE */
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/*
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* _mcount() is used to build the kernel with -pg option, but all the branch
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* instructions to _mcount() are replaced to NOP initially at kernel start up,
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* and later on, NOP to branch to ftrace_caller() when enabled or branch to
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* NOP when disabled per-function base.
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*/
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ENTRY(_mcount)
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ret
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ENDPROC(_mcount)
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/*
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* void ftrace_caller(unsigned long return_address)
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* @return_address: return address to instrumented function
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*
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* This function is a counterpart of _mcount() in 'static' ftrace, and
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* makes calls to:
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* - tracer function to probe instrumented function's entry,
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* - ftrace_graph_caller to set up an exit hook
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*/
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ENTRY(ftrace_caller)
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mcount_enter
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mcount_get_pc0 x0 // function's pc
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mcount_get_lr x1 // function's lr
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.global ftrace_call
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ftrace_call: // tracer(pc, lr);
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nop // This will be replaced with "bl xxx"
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// where xxx can be any kind of tracer.
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#ifdef CONFIG_FUNCTION_GRAPH_TRACER
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.global ftrace_graph_call
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ftrace_graph_call: // ftrace_graph_caller();
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nop // If enabled, this will be replaced
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// "b ftrace_graph_caller"
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#endif
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mcount_exit
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ENDPROC(ftrace_caller)
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#endif /* CONFIG_DYNAMIC_FTRACE */
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ENTRY(ftrace_stub)
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ret
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ENDPROC(ftrace_stub)
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@ -17,6 +17,87 @@
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#include <asm/ftrace.h>
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#include <asm/insn.h>
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#ifdef CONFIG_DYNAMIC_FTRACE
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/*
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* Replace a single instruction, which may be a branch or NOP.
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* If @validate == true, a replaced instruction is checked against 'old'.
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*/
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static int ftrace_modify_code(unsigned long pc, u32 old, u32 new,
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bool validate)
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{
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u32 replaced;
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/*
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* Note:
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* Due to modules and __init, code can disappear and change,
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* we need to protect against faulting as well as code changing.
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* We do this by aarch64_insn_*() which use the probe_kernel_*().
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*
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* No lock is held here because all the modifications are run
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* through stop_machine().
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*/
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if (validate) {
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if (aarch64_insn_read((void *)pc, &replaced))
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return -EFAULT;
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if (replaced != old)
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return -EINVAL;
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}
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if (aarch64_insn_patch_text_nosync((void *)pc, new))
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return -EPERM;
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return 0;
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}
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/*
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* Replace tracer function in ftrace_caller()
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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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unsigned long pc;
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u32 new;
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pc = (unsigned long)&ftrace_call;
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new = aarch64_insn_gen_branch_imm(pc, (unsigned long)func, true);
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return ftrace_modify_code(pc, 0, new, false);
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}
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/*
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* Turn on the call to ftrace_caller() in instrumented function
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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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unsigned long pc = rec->ip;
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u32 old, new;
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old = aarch64_insn_gen_nop();
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new = aarch64_insn_gen_branch_imm(pc, addr, true);
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return ftrace_modify_code(pc, old, new, true);
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}
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/*
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* Turn off the call to ftrace_caller() in instrumented function
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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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unsigned long pc = rec->ip;
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u32 old, new;
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old = aarch64_insn_gen_branch_imm(pc, addr, true);
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new = aarch64_insn_gen_nop();
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return ftrace_modify_code(pc, old, new, true);
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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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#endif /* CONFIG_DYNAMIC_FTRACE */
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#ifdef CONFIG_FUNCTION_GRAPH_TRACER
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/*
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* function_graph tracer expects ftrace_return_to_handler() to be called
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@ -61,4 +142,35 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
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return;
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}
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}
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#ifdef CONFIG_DYNAMIC_FTRACE
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/*
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* Turn on/off the call to ftrace_graph_caller() in ftrace_caller()
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* depending on @enable.
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*/
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static int ftrace_modify_graph_caller(bool enable)
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{
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unsigned long pc = (unsigned long)&ftrace_graph_call;
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u32 branch, nop;
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branch = aarch64_insn_gen_branch_imm(pc,
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(unsigned long)ftrace_graph_caller, false);
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nop = aarch64_insn_gen_nop();
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if (enable)
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return ftrace_modify_code(pc, nop, branch, true);
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else
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return ftrace_modify_code(pc, branch, nop, true);
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}
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int ftrace_enable_ftrace_graph_caller(void)
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{
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return ftrace_modify_graph_caller(true);
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}
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int ftrace_disable_ftrace_graph_caller(void)
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{
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return ftrace_modify_graph_caller(false);
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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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