[S390] cleanup ftrace backend functions

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

4 files changed, 135 insertions, 171 deletions

diff --git a/arch/s390/include/asm/ftrace.h b/arch/s390/include/asm/ftrace.h
index 96c14a9102b8..3c29be4836ed 100644
--- a/arch/s390/include/asm/ftrace.h
+++ b/arch/s390/include/asm/ftrace.h
@@ -4,20 +4,17 @@
 #ifndef __ASSEMBLY__
 
 extern void _mcount(void);
-extern unsigned long ftrace_dyn_func;
 
 struct dyn_arch_ftrace { };
 
 #define MCOUNT_ADDR ((long)_mcount)
 
 #ifdef CONFIG_64BIT
-#define MCOUNT_OFFSET_RET 18
-#define MCOUNT_INSN_SIZE  24
-#define MCOUNT_OFFSET     14
-#else
-#define MCOUNT_OFFSET_RET 26
-#define MCOUNT_INSN_SIZE  30
+#define MCOUNT_INSN_SIZE  12
 #define MCOUNT_OFFSET      8
+#else
+#define MCOUNT_INSN_SIZE  20
+#define MCOUNT_OFFSET      4
 #endif
 
 static inline unsigned long ftrace_call_adjust(unsigned long addr)
diff --git a/arch/s390/kernel/ftrace.c b/arch/s390/kernel/ftrace.c
index 6a83d0581317..78bdf0e5dff7 100644
--- a/arch/s390/kernel/ftrace.c
+++ b/arch/s390/kernel/ftrace.c
@@ -4,7 +4,7 @@
  * Copyright IBM Corp. 2009
  *
  *   Author(s): Heiko Carstens <heiko.carstens@de.ibm.com>,
- *
+ *              Martin Schwidefsky <schwidefsky@de.ibm.com>
  */
 
 #include <linux/hardirq.h>
@@ -12,176 +12,144 @@
 #include <linux/ftrace.h>
 #include <linux/kernel.h>
 #include <linux/types.h>
+#include <linux/kprobes.h>
 #include <trace/syscall.h>
 #include <asm/asm-offsets.h>
 
+#ifdef CONFIG_64BIT
+#define MCOUNT_OFFSET_RET 12
+#else
+#define MCOUNT_OFFSET_RET 22
+#endif
+
 #ifdef CONFIG_DYNAMIC_FTRACE
 
 void ftrace_disable_code(void);
-void ftrace_disable_return(void);
-void ftrace_call_code(void);
-void ftrace_nop_code(void);
-
-#define FTRACE_INSN_SIZE 4
+void ftrace_enable_insn(void);
 
 #ifdef CONFIG_64BIT
-
+/*
+ * The 64-bit mcount code looks like this:
+ *      stg     %r14,8(%r15)            # offset 0
+ * >    larl    %r1,<&counter>          # offset 6
+ * >    brasl   %r14,_mcount            # offset 12
+ *      lg      %r14,8(%r15)            # offset 18
+ * Total length is 24 bytes. The middle two instructions of the mcount
+ * block get overwritten by ftrace_make_nop / ftrace_make_call.
+ * The 64-bit enabled ftrace code block looks like this:
+ *      stg     %r14,8(%r15)            # offset 0
+ * >    lg      %r1,__LC_FTRACE_FUNC    # offset 6
+ * >    lgr     %r0,%r0                 # offset 12
+ * >    basr    %r14,%r1                # offset 16
+ *      lg      %r14,8(%15)             # offset 18
+ * The return points of the mcount/ftrace function have the same offset 18.
+ * The 64-bit disable ftrace code block looks like this:
+ *      stg     %r14,8(%r15)            # offset 0
+ * >    jg      .+18                    # offset 6
+ * >    lgr     %r0,%r0                 # offset 12
+ * >    basr    %r14,%r1                # offset 16
+ *      lg      %r14,8(%15)             # offset 18
+ * The jg instruction branches to offset 24 to skip as many instructions
+ * as possible.
+ */
 asm(
         "       .align  4\n"
         "ftrace_disable_code:\n"
-        "       j       0f\n"
-        "       .word   0x0024\n"
-        "       lg      %r1,"__stringify(__LC_FTRACE_FUNC)"\n"
-        "       basr    %r14,%r1\n"
-        "ftrace_disable_return:\n"
-        "       lg      %r14,8(15)\n"
+        "       jg      0f\n"
         "       lgr     %r0,%r0\n"
-        "0:\n");
-
-asm(
+        "       basr    %r14,%r1\n"
+        "0:\n"
         "       .align  4\n"
-        "ftrace_nop_code:\n"
-        "       j       .+"__stringify(MCOUNT_INSN_SIZE)"\n");
+        "ftrace_enable_insn:\n"
+        "       lg      %r1,"__stringify(__LC_FTRACE_FUNC)"\n");
 
-asm(
-        "       .align  4\n"
-        "ftrace_call_code:\n"
-        "       stg     %r14,8(%r15)\n");
+#define FTRACE_INSN_SIZE        6
 
 #else /* CONFIG_64BIT */
-
+/*
+ * The 31-bit mcount code looks like this:
+ *      st      %r14,4(%r15)            # offset 0
+ * >    bras    %r1,0f                  # offset 4
+ * >    .long   _mcount                 # offset 8
+ * >    .long   <&counter>              # offset 12
+ * > 0: l       %r14,0(%r1)             # offset 16
+ * >    l       %r1,4(%r1)              # offset 20
+ *      basr    %r14,%r14               # offset 24
+ *      l       %r14,4(%r15)            # offset 26
+ * Total length is 30 bytes. The twenty bytes starting from offset 4
+ * to offset 24 get overwritten by ftrace_make_nop / ftrace_make_call.
+ * The 31-bit enabled ftrace code block looks like this:
+ *      st      %r14,4(%r15)            # offset 0
+ * >    l       %r14,__LC_FTRACE_FUNC   # offset 4
+ * >    j       0f                      # offset 8
+ * >    .fill   12,1,0x07               # offset 12
+ *   0: basr    %r14,%r14               # offset 24
+ *      l       %r14,4(%r14)            # offset 26
+ * The return points of the mcount/ftrace function have the same offset 26.
+ * The 31-bit disabled ftrace code block looks like this:
+ *      st      %r14,4(%r15)            # offset 0
+ * >    j       .+26                    # offset 4
+ * >    j       0f                      # offset 8
+ * >    .fill   12,1,0x07               # offset 12
+ *   0: basr    %r14,%r14               # offset 24
+ *      l       %r14,4(%r14)            # offset 26
+ * The j instruction branches to offset 30 to skip as many instructions
+ * as possible.
+ */
 asm(
         "       .align  4\n"
         "ftrace_disable_code:\n"
+        "       j       1f\n"
         "       j       0f\n"
-        "       l       %r1,"__stringify(__LC_FTRACE_FUNC)"\n"
-        "       basr    %r14,%r1\n"
-        "ftrace_disable_return:\n"
-        "       l       %r14,4(%r15)\n"
-        "       j       0f\n"
-        "       bcr     0,%r7\n"
-        "       bcr     0,%r7\n"
-        "       bcr     0,%r7\n"
-        "       bcr     0,%r7\n"
-        "       bcr     0,%r7\n"
-        "       bcr     0,%r7\n"
-        "0:\n");
-
-asm(
+        "       .fill   12,1,0x07\n"
+        "0:     basr    %r14,%r14\n"
+        "1:\n"
         "       .align  4\n"
-        "ftrace_nop_code:\n"
-        "       j       .+"__stringify(MCOUNT_INSN_SIZE)"\n");
+        "ftrace_enable_insn:\n"
+        "       l       %r14,"__stringify(__LC_FTRACE_FUNC)"\n");
 
-asm(
-        "       .align  4\n"
-        "ftrace_call_code:\n"
-        "       st      %r14,4(%r15)\n");
+#define FTRACE_INSN_SIZE        4
 
 #endif /* CONFIG_64BIT */
 
-static int ftrace_modify_code(unsigned long ip,
-                              void *old_code, int old_size,
-                              void *new_code, int new_size)
-{
-        unsigned char replaced[MCOUNT_INSN_SIZE];
-
-        /*
-         * Note: Due to modules code can disappear and change.
-         *  We need to protect against faulting as well as code
-         *  changing. We do this by using the probe_kernel_*
-         *  functions.
-         *  This however is just a simple sanity check.
-         */
-        if (probe_kernel_read(replaced, (void *)ip, old_size))
-                return -EFAULT;
-        if (memcmp(replaced, old_code, old_size) != 0)
-                return -EINVAL;
-        if (probe_kernel_write((void *)ip, new_code, new_size))
-                return -EPERM;
-        return 0;
-}
-
-static int ftrace_make_initial_nop(struct module *mod, struct dyn_ftrace *rec,
-                                   unsigned long addr)
-{
-        return ftrace_modify_code(rec->ip,
-                                  ftrace_call_code, FTRACE_INSN_SIZE,
-                                  ftrace_disable_code, MCOUNT_INSN_SIZE);
-}
 
 int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
                     unsigned long addr)
 {
-        if (addr == MCOUNT_ADDR)
-                return ftrace_make_initial_nop(mod, rec, addr);
-        return ftrace_modify_code(rec->ip,
-                                  ftrace_call_code, FTRACE_INSN_SIZE,
-                                  ftrace_nop_code, FTRACE_INSN_SIZE);
+        if (probe_kernel_write((void *) rec->ip, ftrace_disable_code,
+                               MCOUNT_INSN_SIZE))
+                return -EPERM;
+        return 0;
 }
 
 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 {
-        return ftrace_modify_code(rec->ip,
-                                  ftrace_nop_code, FTRACE_INSN_SIZE,
-                                  ftrace_call_code, FTRACE_INSN_SIZE);
+        if (probe_kernel_write((void *) rec->ip, ftrace_enable_insn,
+                               FTRACE_INSN_SIZE))
+                return -EPERM;
+        return 0;
 }
 
 int ftrace_update_ftrace_func(ftrace_func_t func)
 {
-        ftrace_dyn_func = (unsigned long)func;
         return 0;
 }
 
 int __init ftrace_dyn_arch_init(void *data)
 {
-        *(unsigned long *)data = 0;
+        *(unsigned long *) data = 0;
         return 0;
 }
 
 #endif /* CONFIG_DYNAMIC_FTRACE */
 
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
-#ifdef CONFIG_DYNAMIC_FTRACE
-/*
- * Patch the kernel code at ftrace_graph_caller location:
- * The instruction there is branch relative on condition. The condition mask
- * is either all ones (always branch aka disable ftrace_graph_caller) or all
- * zeroes (nop aka enable ftrace_graph_caller).
- * Instruction format for brc is a7m4xxxx where m is the condition mask.
- */
-int ftrace_enable_ftrace_graph_caller(void)
-{
-        unsigned short opcode = 0xa704;
-
-        return probe_kernel_write(ftrace_graph_caller, &opcode, sizeof(opcode));
-}
-
-int ftrace_disable_ftrace_graph_caller(void)
-{
-        unsigned short opcode = 0xa7f4;
-
-        return probe_kernel_write(ftrace_graph_caller, &opcode, sizeof(opcode));
-}
-
-static inline unsigned long ftrace_mcount_call_adjust(unsigned long addr)
-{
-        return addr - (ftrace_disable_return - ftrace_disable_code);
-}
-
-#else /* CONFIG_DYNAMIC_FTRACE */
-
-static inline unsigned long ftrace_mcount_call_adjust(unsigned long addr)
-{
-        return addr - MCOUNT_OFFSET_RET;
-}
-
-#endif /* CONFIG_DYNAMIC_FTRACE */
-
 /*
  * Hook the return address and push it in the stack of return addresses
  * in current thread info.
  */
-unsigned long prepare_ftrace_return(unsigned long ip, unsigned long parent)
+unsigned long __kprobes prepare_ftrace_return(unsigned long parent,
+                                              unsigned long ip)
 {
         struct ftrace_graph_ent trace;
 
@@ -189,14 +157,42 @@ unsigned long prepare_ftrace_return(unsigned long ip, unsigned long parent)
                 goto out;
         if (ftrace_push_return_trace(parent, ip, &trace.depth, 0) == -EBUSY)
                 goto out;
-        trace.func = ftrace_mcount_call_adjust(ip) & PSW_ADDR_INSN;
+        trace.func = (ip & PSW_ADDR_INSN) - MCOUNT_OFFSET_RET;
         /* Only trace if the calling function expects to. */
         if (!ftrace_graph_entry(&trace)) {
                 current->curr_ret_stack--;
                 goto out;
         }
-        parent = (unsigned long)return_to_handler;
+        parent = (unsigned long) return_to_handler;
 out:
         return parent;
 }
+
+#ifdef CONFIG_DYNAMIC_FTRACE
+/*
+ * Patch the kernel code at ftrace_graph_caller location. The instruction
+ * there is branch relative and save to prepare_ftrace_return. To disable
+ * the call to prepare_ftrace_return we patch the bras offset to point
+ * directly after the instructions. To enable the call we calculate
+ * the original offset to prepare_ftrace_return and put it back.
+ */
+int ftrace_enable_ftrace_graph_caller(void)
+{
+        unsigned short offset;
+
+        offset = ((void *) prepare_ftrace_return -
+                  (void *) ftrace_graph_caller) / 2;
+        return probe_kernel_write(ftrace_graph_caller + 2,
+                                  &offset, sizeof(offset));
+}
+
+int ftrace_disable_ftrace_graph_caller(void)
+{
+        static unsigned short offset = 0x0002;
+
+        return probe_kernel_write(ftrace_graph_caller + 2,
+                                  &offset, sizeof(offset));
+}
+
+#endif /* CONFIG_DYNAMIC_FTRACE */
 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
diff --git a/arch/s390/kernel/mcount.S b/arch/s390/kernel/mcount.S
index 4a6e1a575f9e..1e6a55795628 100644
--- a/arch/s390/kernel/mcount.S
+++ b/arch/s390/kernel/mcount.S
@@ -18,22 +18,12 @@ _mcount:
 #ifdef CONFIG_DYNAMIC_FTRACE
         br      %r14
 
-        .data
-        .globl  ftrace_dyn_func
-ftrace_dyn_func:
-        .long   ftrace_stub
-        .previous
-
         .globl ftrace_caller
 ftrace_caller:
 #endif
         stm     %r2,%r5,16(%r15)
         bras    %r1,2f
-#ifdef CONFIG_DYNAMIC_FTRACE
-0:      .long   ftrace_dyn_func
-#else
 0:      .long   ftrace_trace_function
-#endif
 1:      .long   function_trace_stop
 2:      l       %r2,1b-0b(%r1)
         icm     %r2,0xf,0(%r2)
@@ -49,21 +39,15 @@ ftrace_caller:
         l       %r14,0(%r14)
         basr    %r14,%r14
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
-#ifdef CONFIG_DYNAMIC_FTRACE
+        l       %r2,100(%r15)
+        l       %r3,152(%r15)
         .globl  ftrace_graph_caller
 ftrace_graph_caller:
-        # This unconditional branch gets runtime patched. Change only if
-        # you know what you are doing. See ftrace_enable_graph_caller().
-        j       1f
-#endif
-        bras    %r1,0f
-        .long   prepare_ftrace_return
-0:      l       %r2,152(%r15)
-        l       %r4,0(%r1)
-        l       %r3,100(%r15)
-        basr    %r14,%r4
-        st      %r2,100(%r15)
-1:
+# The bras instruction gets runtime patched to call prepare_ftrace_return.
+# See ftrace_enable_ftrace_graph_caller. The patched instruction is:
+#       bras    %r14,prepare_ftrace_return
+        bras    %r14,0f
+0:      st      %r2,100(%r15)
 #endif
         ahi     %r15,96
         l       %r14,56(%r15)
diff --git a/arch/s390/kernel/mcount64.S b/arch/s390/kernel/mcount64.S
index b2bae06ad6c7..e73667286ac0 100644
--- a/arch/s390/kernel/mcount64.S
+++ b/arch/s390/kernel/mcount64.S
@@ -18,12 +18,6 @@ _mcount:
 #ifdef CONFIG_DYNAMIC_FTRACE
         br      %r14
 
-        .data
-        .globl  ftrace_dyn_func
-ftrace_dyn_func:
-        .quad   ftrace_stub
-        .previous
-
         .globl ftrace_caller
 ftrace_caller:
 #endif
@@ -37,26 +31,19 @@ ftrace_caller:
         stg     %r1,__SF_BACKCHAIN(%r15)
         lgr     %r2,%r14
         lg      %r3,168(%r15)
-#ifdef CONFIG_DYNAMIC_FTRACE
-        larl    %r14,ftrace_dyn_func
-#else
         larl    %r14,ftrace_trace_function
-#endif
         lg      %r14,0(%r14)
         basr    %r14,%r14
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
-#ifdef CONFIG_DYNAMIC_FTRACE
+        lg      %r2,168(%r15)
+        lg      %r3,272(%r15)
         .globl  ftrace_graph_caller
 ftrace_graph_caller:
-        # This unconditional branch gets runtime patched. Change only if
-        # you know what you are doing. See ftrace_enable_graph_caller().
-        j       0f
-#endif
-        lg      %r2,272(%r15)
-        lg      %r3,168(%r15)
-        brasl   %r14,prepare_ftrace_return
-        stg     %r2,168(%r15)
-0:
+# The bras instruction gets runtime patched to call prepare_ftrace_return.
+# See ftrace_enable_ftrace_graph_caller. The patched instruction is:
+#       bras    %r14,prepare_ftrace_return
+        bras    %r14,0f
+0:      stg     %r2,168(%r15)
 #endif
         aghi    %r15,160
         lmg     %r2,%r5,32(%r15)