Commit cfce092d authored by Mark Rutland's avatar Mark Rutland Committed by Will Deacon
Browse files

ftrace: arm64: remove static ftrace 

The build test robot pointer out that there's a build failure when:

  CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS=y
  CONFIG_DYNAMIC_FTRACE_WITH_ARGS=n

... due to some mismatched ifdeffery, some of which checks
CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS, and some of which checks
CONFIG_DYNAMIC_FTRACE_WITH_ARGS, leading to some missing definitions expected
by the core code when CONFIG_DYNAMIC_FTRACE=n and consequently
CONFIG_DYNAMIC_FTRACE_WITH_ARGS=n.

There's really not much point in supporting CONFIG_DYNAMIC_FTRACE=n (AKA
static ftrace). All supported toolchains allow us to implement
DYNAMIC_FTRACE, distributions all prefer DYNAMIC_FTRACE, and both
powerpc and s390 removed support for static ftrace in commits:

  0c0c5230 ("powerpc: Only support DYNAMIC_FTRACE not static")
  5d6a0163 ("s390/ftrace: enforce DYNAMIC_FTRACE if FUNCTION_TRACER is selected")

... and according to Steven, static ftrace is only supported on x86 to
allow testing that the core code still functions in this configuration.

Given that, let's simplify matters by removing arm64's support for
static ftrace. This avoids the problem originally reported, and leaves
us with less code to maintain.

Fixes: 26299b3f ("ftrace: arm64: move from REGS to ARGS")
Link: https://lore.kernel.org/r/202211212249.livTPi3Y-lkp@intel.com


Suggested-by: default avatarSteven Rostedt <rostedt@goodmis.org>
Signed-off-by: default avatarMark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20221122163624.1225912-1-mark.rutland@arm.com


Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent 26299b3f

arch/arm64/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -117,6 +117,7 @@ config ARM64 
	select CPU_PM if (SUSPEND || CPU_IDLE)

	select CRC32

	select DCACHE_WORD_ACCESS

	select DYNAMIC_FTRACE if FUNCTION_TRACER

	select DMA_DIRECT_REMAP

	select EDAC_SUPPORT

	select FRAME_POINTER

arch/arm64/kernel/entry-ftrace.S

+0 −39
Original line number Diff line number Diff line
@@ -170,44 +170,6 @@ SYM_CODE_END(ftrace_caller) 
	add	\reg, \reg, #8

	.endm



#ifndef CONFIG_DYNAMIC_FTRACE

/*

 * void _mcount(unsigned long return_address)

 * @return_address: return address to instrumented function

 *

 * This function makes calls, if enabled, to:

 *     - tracer function to probe instrumented function's entry,

 *     - ftrace_graph_caller to set up an exit hook

 */

SYM_FUNC_START(_mcount)

	mcount_enter



	ldr_l	x2, ftrace_trace_function

	adr	x0, ftrace_stub

	cmp	x0, x2			// if (ftrace_trace_function

	b.eq	skip_ftrace_call	//     != ftrace_stub) {



	mcount_get_pc	x0		//       function's pc

	mcount_get_lr	x1		//       function's lr (= parent's pc)

	blr	x2			//   (*ftrace_trace_function)(pc, lr);



skip_ftrace_call:			// }

#ifdef CONFIG_FUNCTION_GRAPH_TRACER

	ldr_l	x2, ftrace_graph_return

	cmp	x0, x2			//   if ((ftrace_graph_return

	b.ne	ftrace_graph_caller	//        != ftrace_stub)



	ldr_l	x2, ftrace_graph_entry	//     || (ftrace_graph_entry

	adr_l	x0, ftrace_graph_entry_stub //     != ftrace_graph_entry_stub))

	cmp	x0, x2

	b.ne	ftrace_graph_caller	//     ftrace_graph_caller();

#endif /* CONFIG_FUNCTION_GRAPH_TRACER */

	mcount_exit

SYM_FUNC_END(_mcount)

EXPORT_SYMBOL(_mcount)

NOKPROBE(_mcount)



#else /* CONFIG_DYNAMIC_FTRACE */

/*

 * _mcount() is used to build the kernel with -pg option, but all the branch

 * instructions to _mcount() are replaced to NOP initially at kernel start up,
@@ -247,7 +209,6 @@ SYM_INNER_LABEL(ftrace_graph_call, SYM_L_GLOBAL) // ftrace_graph_caller(); 


	mcount_exit

SYM_FUNC_END(ftrace_caller)

#endif /* CONFIG_DYNAMIC_FTRACE */



#ifdef CONFIG_FUNCTION_GRAPH_TRACER

/*

arch/arm64/kernel/ftrace.c

+0 −5
Original line number Diff line number Diff line
@@ -60,7 +60,6 @@ int ftrace_regs_query_register_offset(const char *name) 
}

#endif



#ifdef CONFIG_DYNAMIC_FTRACE

/*

 * Replace a single instruction, which may be a branch or NOP.

 * If @validate == true, a replaced instruction is checked against 'old'.
@@ -268,7 +267,6 @@ void arch_ftrace_update_code(int command) 
	command |= FTRACE_MAY_SLEEP;

	ftrace_modify_all_code(command);

}

#endif /* CONFIG_DYNAMIC_FTRACE */



#ifdef CONFIG_FUNCTION_GRAPH_TRACER

/*
@@ -299,8 +297,6 @@ void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent, 
	}

}



#ifdef CONFIG_DYNAMIC_FTRACE



#ifdef CONFIG_DYNAMIC_FTRACE_WITH_ARGS

void ftrace_graph_func(unsigned long ip, unsigned long parent_ip,

		       struct ftrace_ops *op, struct ftrace_regs *fregs)
@@ -338,5 +334,4 @@ int ftrace_disable_ftrace_graph_caller(void) 
	return ftrace_modify_graph_caller(false);

}

#endif /* CONFIG_DYNAMIC_FTRACE_WITH_ARGS */

#endif /* CONFIG_DYNAMIC_FTRACE */

#endif /* CONFIG_FUNCTION_GRAPH_TRACER */