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: Petri Gynther <pgynther@xxxxxxxxxx>
---
arch/mips/kernel/ftrace.c | 56 +++++++++++++++++++++++++++++++++++++++--------
arch/mips/kernel/mcount.S | 13 +++++++++++
2 files changed, 60 insertions(+), 9 deletions(-)
diff --git a/arch/mips/kernel/ftrace.c b/arch/mips/kernel/ftrace.c
index 60e7e5e..2a72208 100644
--- a/arch/mips/kernel/ftrace.c
+++ b/arch/mips/kernel/ftrace.c
@@ -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))
diff --git a/arch/mips/kernel/mcount.S b/arch/mips/kernel/mcount.S
index 539b629..26ceb3c 100644
--- a/arch/mips/kernel/mcount.S
+++ b/arch/mips/kernel/mcount.S
@@ -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 */
--
2.0.0.526.g5318336
