Hi Ralf,When ftrace is used, unwind_stack() is unable to retrieve the frame infoand call-trace doesn't work. Please find the bug fix patch when HAVE_FUNCTION_TRACER is enable.Please comment.From 89004f88a1f8399be7a856b43b475f06c3d5bb30 Mon Sep 17 00:00:00 2001From: Akhilesh Kumar <akhilesh.lxr@xxxxxxxxx>Date: Fri, 4 May 2012 18:52:46 +0530Subject: [PATCH 1/1] Patch fix the backtrcae problem using unwind_stack())When ftrace is used, unwind_stack() is unable to retrieve the frame infoand call-trace doesn't work.test module----------------static struct timer_list backtrace_timer;static void backtrace_test_timer(unsigned long data){printk("Testing a backtrace from irq context.\n");printk("The following trace is a kernel self test and not abug!\n");dump_stack();}static int backtrace_regression_test(void){printk("====[ backtrace testing ]===========\n");printk("Testing a backtrace from process context.\n");printk("The following trace is a kernel self test and not abug!\n");dump_stack();init_timer(&backtrace_timer);backtrace_timer.function = backtrace_test_timer;mod_timer(&backtrace_timer, jiffies + 10);msleep(10);printk("====[ end of backtrace testing ]====\n");return 0;}static void exitf(void){}module_init(backtrace_regression_test);module_exit(exitf);MODULE_LICENSE("GPL");---------------------------------------------------------------------out put when HAVE_FUNCTION_TRACER is disable====[ backtrace testing ]===========Testing a backtrace from process context.The following trace is a kernel self test and not a bug!Testing a backtrace.The following trace is a kernel self test and not a bug!Call Trace:[<80295134>] dump_stack+0x8/0x34[<c0946060>] backtrace_regression_test+0x60/0x94 [sisc_backtrcae][<800004f0>] do_one_initcall+0xf0/0x1d0[<80060954>] sys_init_module+0x19c8/0x1c60[<8000a418>] stack_done+0x20/0x40output befor patch when HAVE_FUNCTION_TRACER is enable---------------------------------------------------------------------VDLinux#> insmod sisc_backtrcae.ko====[ backtrace testing ]===========Testing a backtrace from process context.The following trace is a kernel self test and not a bug!Testing a backtrace.The following trace is a kernel self test and not a bug!Call Trace:[<802e5164>] dump_stack+0x1c/0x50[<802e5164>] dump_stack+0x1c/0x50====[ end of backtrace testing ]====------------------------------------------------------above shows the wrong back trcaeoutput after patch when HAVE_FUNCTION_TRACER is enable----------------------------------------------------------------------====[ backtrace testing ]===========Testing a backtrace from process context.The following trace is a kernel self test and not a bug!Testing a backtrace.The following trace is a kernel self test and not a bug!Call Trace:[<802eb1a4>] dump_stack+0x20/0x54[<c003405c>] backtrace_test_timer+0x5c/0x74 [sisc_backtrcae][<c00340dc>] init_module+0x68/0xa0 [sisc_backtrcae][<80000508>] do_one_initcall+0x108/0x1f0[<8006d4c4>] sys_init_module+0x1a10/0x1c74[<8000b038>] stack_done+0x20/0x40------------------------------------------------------------------get_frame_info() is used to fetch the frame information from thefunction.However,1. this function just considers the first stack adjustment for framesize.2. On finding the save_lr instruction, it returns.It doesn't handle the ftrace condition.If Dynamic Frace "CONFIG_DYNAMIC_FTRACE" is enabled, the instrumentation code is:- jal <ftrace_caller>- addiu sp,sp,-8Thus, the current Frame Size of function is increased by 8 for Ftrace.Signed-off-by: Akhilesh Kumar <akhilesh.lxr@xxxxxxxxx>Signed-off-by: Himanshu Maithani <hmaithani@xxxxxxxxx>---arch/mips/kernel/process.c | 67 ++++++++++++++++++++++++++++++++++++++++++++1 files changed, 67 insertions(+), 0 deletions(-)diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.cindex 7955409..df72738 100644--- a/arch/mips/kernel/process.c+++ b/arch/mips/kernel/process.c@@ -290,12 +290,45 @@ static inline int is_sp_move_ins(union mips_instruction *ip)return 0;}+#ifdef CONFIG_DYNAMIC_FTRACE+/*+ * To create the jal <> instruction from mcount.+ * taken from:+ * - arch/mips/kernel/ftrace.c+ */+#define ADDR_MASK 0x03ffffff /* op_code|addr : 31...26|25 ....0 */+#define JAL 0x0c000000 /* jump & link: ip --> ra, jump to target */+#define INSN_JAL(addr) \+ ((unsigned int)(JAL | (((addr) >> 2) & ADDR_MASK)))++/*+ * We assume jal <mcount>/<ftrace_caller> to be present in+ * first JAL_MAX_OFFSET instructions.+ * Increment this, if its otherwise+ */+#define JAL_MAX_OFFSET 16U+#define MCOUNT_STACK_INST 0x27bdfff8 /* addiu sp,sp,-8 */++/*+ * If Dynamic Ftrace is enabled, ftrace_caller is the trace function.+ * Otherwise its - mcount+ */+extern void ftrace_caller(void);+#endif /* CONFIG_DYNAMIC_FTRACE */+static int get_frame_info(struct mips_frame_info *info){union mips_instruction *ip = info->func;unsigned max_insns = info->func_size / sizeof(union mips_instruction);unsigned i;+#ifdef CONFIG_DYNAMIC_FTRACE+ unsigned max_prolog_inst = max_insns;+ int jal_found = 0;+ /* instruction corresponding to jal <_mcount>/<ftrace_caller> */+ int jal_mcount = 0;+#endif+info->pc_offset = -1;info->frame_size = 0;@@ -306,6 +339,28 @@ static int get_frame_info(struct mips_frame_info *info)max_insns = 128U; /* unknown function size */max_insns = min(128U, max_insns);+#ifdef CONFIG_DYNAMIC_FTRACE+ max_prolog_inst = min(JAL_MAX_OFFSET, max_prolog_inst);+ jal_mcount = INSN_JAL((unsigned)&ftrace_caller);++ for (i = 0; i < max_prolog_inst; i++, ip++) {+ if ((*(int *)ip == jal_mcount) ||+ /*+ * for dyn ftrace, the code initially has 0.+ * so we check whether the next instruction is+ * addiu sp,sp,-8+ */+ (!(*(int *)ip) &&+ (*(int *)(ip + 1) == MCOUNT_STACK_INST))+ ) {+ jal_found = 1;+ break;+ }+ }+ /* restore the ip to start of function */+ ip = info->func;+#endif+for (i = 0; i < max_insns; i++, ip++) {if (is_jal_jalr_jr_ins(ip))@@ -321,6 +376,18 @@ static int get_frame_info(struct mips_frame_info *info)break;}}+#ifdef CONFIG_DYNAMIC_FTRACE+ /*+ * to offset the effect of:+ * addiu sp,sp,-8+ */+ if (jal_found) {+ if (info->frame_size)+ info->frame_size += 8;+ if (info->pc_offset >= 0)+ info->pc_offset += 8 / sizeof(long);+ }+#endifif (info->frame_size && info->pc_offset >= 0) /* nested */return 0;if (info->pc_offset < 0) /* leaf */--1.7.8.4
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0001-Patch-fix-the-backtrcae-problem-using-unwind_stack.patch
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