Commit dce0e7d5 authored by Petri Gynther's avatar Petri Gynther Committed by Ralf Baechle
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MIPS: ftrace: Fix dynamic tracing of kernel modules 



Dynamic tracing of kernel modules is broken on 32-bit MIPS. When modules
are loaded, the kernel crashes when dynamic tracing is enabled with:
 cd /sys/kernel/debug/tracing
 echo > set_ftrace_filter
 echo function > current_tracer

1) arch/mips/kernel/ftrace.c
When the kernel boots, or when a module is initialized, ftrace_make_nop()
modifies every _mcount call site to eliminate the ftrace overhead.
However, when ftrace is later enabled for a call site, ftrace_make_call()
does not currently restore the _mcount call correctly for module call sites.
Added ftrace_modify_code_2r() and modified ftrace_make_call() to fix this.

2) arch/mips/kernel/mcount.S
_mcount assembly routine is supposed to have the caller's _mcount call site
address in register a0. However, a0 is currently not calculated correctly for
module call sites. a0 should be (ra - 20) or (ra - 24), depending on whether
the kernel was built with KBUILD_MCOUNT_RA_ADDRESS or not.

This fix has been tested on Broadcom BMIPS5000 processor. Dynamic tracing
now works for both built-in functions and module functions.

Signed-off-by: default avatarPetri Gynther <pgynther@google.com>
Cc: linux-mips@linux-mips.org
Cc: rostedt@goodmis.org
Cc: alcooperx@gmail.com
Cc: cminyard@mvista.com
Patchwork: https://patchwork.linux-mips.org/patch/7476/


Signed-off-by: default avatarRalf Baechle <ralf@linux-mips.org>
parent b1442d39

arch/mips/kernel/ftrace.c

+47 −9
Original line number Diff line number Diff line
@@ -63,7 +63,7 @@ static inline int in_kernel_space(unsigned long ip) 
	((unsigned int)(JAL | (((addr) >> 2) & ADDR_MASK)))



static unsigned int insn_jal_ftrace_caller __read_mostly;

static unsigned int insn_lui_v1_hi16_mcount __read_mostly;

static unsigned int insn_la_mcount[2] __read_mostly;

static unsigned int insn_j_ftrace_graph_caller __maybe_unused __read_mostly;



static inline void ftrace_dyn_arch_init_insns(void)
@@ -71,10 +71,10 @@ static inline void ftrace_dyn_arch_init_insns(void) 
	u32 *buf;

	unsigned int v1;



	/* lui v1, hi16_mcount */

	/* la v1, _mcount */

	v1 = 3;

	buf = (u32 *)&insn_lui_v1_hi16_mcount;

	UASM_i_LA_mostly(&buf, v1, MCOUNT_ADDR);

	buf = (u32 *)&insn_la_mcount[0];

	UASM_i_LA(&buf, v1, MCOUNT_ADDR);



	/* jal (ftrace_caller + 8), jump over the first two instruction */

	buf = (u32 *)&insn_jal_ftrace_caller;
@@ -111,14 +111,47 @@ static int ftrace_modify_code_2(unsigned long ip, unsigned int new_code1, 
				unsigned int new_code2)

{

	int faulted;

	mm_segment_t old_fs;



	safe_store_code(new_code1, ip, faulted);

	if (unlikely(faulted))

		return -EFAULT;

	safe_store_code(new_code2, ip + 4, faulted);



	ip += 4;

	safe_store_code(new_code2, ip, faulted);

	if (unlikely(faulted))

		return -EFAULT;



	ip -= 4;

	old_fs = get_fs();

	set_fs(get_ds());

	flush_icache_range(ip, ip + 8);

	set_fs(old_fs);



	return 0;

}



static int ftrace_modify_code_2r(unsigned long ip, unsigned int new_code1,

				 unsigned int new_code2)

{

	int faulted;

	mm_segment_t old_fs;



	ip += 4;

	safe_store_code(new_code2, ip, faulted);

	if (unlikely(faulted))

		return -EFAULT;



	ip -= 4;

	safe_store_code(new_code1, ip, faulted);

	if (unlikely(faulted))

		return -EFAULT;



	old_fs = get_fs();

	set_fs(get_ds());

	flush_icache_range(ip, ip + 8);

	set_fs(old_fs);



	return 0;

}

#endif
@@ -130,13 +163,14 @@ static int ftrace_modify_code_2(unsigned long ip, unsigned int new_code1, 
 *

 * move at, ra

 * jal _mcount		--> nop

 *  sub sp, sp, 8	--> nop  (CONFIG_32BIT)

 *

 * 2. For modules:

 *

 * 2.1 For KBUILD_MCOUNT_RA_ADDRESS and CONFIG_32BIT

 *

 * lui v1, hi_16bit_of_mcount	     --> b 1f (0x10000005)

 * addiu v1, v1, low_16bit_of_mcount

 * addiu v1, v1, low_16bit_of_mcount --> nop  (CONFIG_32BIT)

 * move at, ra

 * move $12, ra_address

 * jalr v1
@@ -145,7 +179,7 @@ static int ftrace_modify_code_2(unsigned long ip, unsigned int new_code1, 
 * 2.2 For the Other situations

 *

 * lui v1, hi_16bit_of_mcount	     --> b 1f (0x10000004)

 * addiu v1, v1, low_16bit_of_mcount

 * addiu v1, v1, low_16bit_of_mcount --> nop  (CONFIG_32BIT)

 * move at, ra

 * jalr v1

 *  nop | move $12, ra_address | sub sp, sp, 8
@@ -184,10 +218,14 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) 
	unsigned int new;

	unsigned long ip = rec->ip;



	new = in_kernel_space(ip) ? insn_jal_ftrace_caller :

		insn_lui_v1_hi16_mcount;

	new = in_kernel_space(ip) ? insn_jal_ftrace_caller : insn_la_mcount[0];



#ifdef CONFIG_64BIT

	return ftrace_modify_code(ip, new);

#else

	return ftrace_modify_code_2r(ip, new, in_kernel_space(ip) ?

						INSN_NOP : insn_la_mcount[1]);

#endif

}



#define FTRACE_CALL_IP ((unsigned long)(&ftrace_call))

arch/mips/kernel/mcount.S

+13 −0
Original line number Diff line number Diff line
@@ -84,6 +84,19 @@ _mcount: 
#endif



	PTR_SUBU a0, ra, 8	/* arg1: self address */

	PTR_LA   t1, _stext

	sltu     t2, a0, t1	/* t2 = (a0 < _stext) */

	PTR_LA   t1, _etext

	sltu     t3, t1, a0	/* t3 = (a0 > _etext) */

	or       t1, t2, t3

	beqz     t1, ftrace_call

	 nop

#if defined(KBUILD_MCOUNT_RA_ADDRESS) && defined(CONFIG_32BIT)

	PTR_SUBU a0, a0, 16	/* arg1: adjust to module's recorded callsite */

#else

	PTR_SUBU a0, a0, 12

#endif



	.globl ftrace_call

ftrace_call:

	nop	/* a placeholder for the call to a real tracing function */

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