powerpc/ppc32: ftrace, dynamic ftrace to handle modules

Impact: add ability to trace modules on 32 bit PowerPC

This patch performs the necessary trampoline calls to handle
modules with dynamic ftrace on 32 bit PowerPC.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>

3 files changed, 109 insertions, 7 deletions

diff --git a/arch/powerpc/include/asm/module.h b/arch/powerpc/include/asm/module.h
index 340bc699b620..08454880a2c0 100644
--- a/arch/powerpc/include/asm/module.h
+++ b/arch/powerpc/include/asm/module.h
@@ -39,11 +39,14 @@ struct mod_arch_specific {
         unsigned long tramp;
 #endif
 
-#else
+#else /* powerpc64 */
         /* Indices of PLT sections within module. */
         unsigned int core_plt_section;
         unsigned int init_plt_section;
+#ifdef CONFIG_DYNAMIC_FTRACE
+        unsigned long tramp;
 #endif
+#endif /* powerpc64 */
 
         /* List of BUG addresses, source line numbers and filenames */
         struct list_head bug_list;
diff --git a/arch/powerpc/kernel/ftrace.c b/arch/powerpc/kernel/ftrace.c
index 1aec559bdfcb..3271cd698e4c 100644
--- a/arch/powerpc/kernel/ftrace.c
+++ b/arch/powerpc/kernel/ftrace.c
@@ -274,7 +274,63 @@ static int
 __ftrace_make_nop(struct module *mod,
                   struct dyn_ftrace *rec, unsigned long addr)
 {
-        /* Ignore modules for PPC32 (for now) */
+        unsigned char replaced[MCOUNT_INSN_SIZE];
+        unsigned int *op = (unsigned *)&replaced;
+        unsigned char jmp[8];
+        unsigned int *ptr = (unsigned int *)&jmp;
+        unsigned long ip = rec->ip;
+        unsigned long tramp;
+        int offset;
+
+        if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
+                return -EFAULT;
+
+        /* Make sure that that this is still a 24bit jump */
+        if (!is_bl_op(*op)) {
+                printk(KERN_ERR "Not expected bl: opcode is %x\n", *op);
+                return -EINVAL;
+        }
+
+        /* lets find where the pointer goes */
+        tramp = find_bl_target(ip, *op);
+
+        /*
+         * On PPC32 the trampoline looks like:
+         * lis r11,sym@ha
+         * addi r11,r11,sym@l
+         * mtctr r11
+         * bctr
+         */
+
+        DEBUGP("ip:%lx jumps to %lx", ip, tramp);
+
+        /* Find where the trampoline jumps to */
+        if (probe_kernel_read(jmp, (void *)tramp, 8)) {
+                printk(KERN_ERR "Failed to read %lx\n", tramp);
+                return -EFAULT;
+        }
+
+        DEBUGP(" %08x %08x ", ptr[0], ptr[1]);
+
+        tramp = (ptr[1] & 0xffff) |
+                ((ptr[0] & 0xffff) << 16);
+        if (tramp & 0x8000)
+                tramp -= 0x10000;
+
+        DEBUGP(" %x ", tramp);
+
+        if (tramp != addr) {
+                printk(KERN_ERR
+                       "Trampoline location %08lx does not match addr\n",
+                       tramp);
+                return -EINVAL;
+        }
+
+        op[0] = PPC_NOP_INSTR;
+
+        if (probe_kernel_write((void *)ip, replaced, MCOUNT_INSN_SIZE))
+                return -EPERM;
+
         return 0;
 }
 #endif /* PPC64 */
@@ -297,7 +353,6 @@ int ftrace_make_nop(struct module *mod,
                 return ftrace_modify_code(ip, old, new);
         }
 
-#ifdef CONFIG_PPC64
         /*
          * Out of range jumps are called from modules.
          * We should either already have a pointer to the module
@@ -320,7 +375,6 @@ int ftrace_make_nop(struct module *mod,
                 /* nothing to do if mod == rec->arch.mod */
         } else
                 mod = rec->arch.mod;
-#endif /* CONFIG_PPC64 */
 
         return __ftrace_make_nop(mod, rec, addr);
 
@@ -380,7 +434,44 @@ __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 static int
 __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 {
-        /* PPC32 ignores modules for now */
+        unsigned char replaced[MCOUNT_INSN_SIZE];
+        unsigned int *op = (unsigned *)&replaced;
+        unsigned long ip = rec->ip;
+        unsigned long offset;
+
+        /* read where this goes */
+        if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
+                return -EFAULT;
+
+        /* It should be pointing to a nop */
+        if (op[0] != PPC_NOP_INSTR) {
+                printk(KERN_ERR "Expected NOP but have %x\n", op[0]);
+                return -EINVAL;
+        }
+
+        /* If we never set up a trampoline to ftrace_caller, then bail */
+        if (!rec->arch.mod->arch.tramp) {
+                printk(KERN_ERR "No ftrace trampoline\n");
+                return -EINVAL;
+        }
+
+        /* now calculate a jump to the ftrace caller trampoline */
+        offset = rec->arch.mod->arch.tramp - ip;
+
+        if (test_offset(offset)) {
+                printk(KERN_ERR "REL24 %li out of range!\n",
+                       (long int)offset);
+                return -EINVAL;
+        }
+
+        /* Set to "bl addr" */
+        op[0] = branch_offset(offset);
+
+        DEBUGP("write to %lx\n", rec->ip);
+
+        if (probe_kernel_write((void *)ip, replaced, MCOUNT_INSN_SIZE))
+                return -EPERM;
+
         return 0;
 }
 #endif /* CONFIG_PPC64 */
@@ -402,7 +493,6 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
                 return ftrace_modify_code(ip, old, new);
         }
 
-#ifdef CONFIG_PPC64
         /*
          * Out of range jumps are called from modules.
          * Being that we are converting from nop, it had better
@@ -412,7 +502,6 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
                 printk(KERN_ERR "No module loaded\n");
                 return -EINVAL;
         }
-#endif
 
         return __ftrace_make_call(rec, addr);
 }
diff --git a/arch/powerpc/kernel/module_32.c b/arch/powerpc/kernel/module_32.c
index 2df91a03462a..f832773fc28e 100644
--- a/arch/powerpc/kernel/module_32.c
+++ b/arch/powerpc/kernel/module_32.c
@@ -22,6 +22,7 @@
 #include <linux/fs.h>
 #include <linux/string.h>
 #include <linux/kernel.h>
+#include <linux/ftrace.h>
 #include <linux/cache.h>
 #include <linux/bug.h>
 #include <linux/sort.h>
@@ -53,6 +54,9 @@ static unsigned int count_relocs(const Elf32_Rela *rela, unsigned int num)
                         r_addend = rela[i].r_addend;
                 }
 
+#ifdef CONFIG_DYNAMIC_FTRACE
+        _count_relocs++;        /* add one for ftrace_caller */
+#endif
         return _count_relocs;
 }
 
@@ -306,5 +310,11 @@ int apply_relocate_add(Elf32_Shdr *sechdrs,
                         return -ENOEXEC;
                 }
         }
+#ifdef CONFIG_DYNAMIC_FTRACE
+        module->arch.tramp =
+                do_plt_call(module->module_core,
+                            (unsigned long)ftrace_caller,
+                            sechdrs, module);
+#endif
         return 0;
 }