Re: [PATCH 5/5] IA64 dynamic ftrace support

Shaohua Li
2008-12-31T09:11:25Z

On Tue, 2008-12-23 at 14:08 +0800, Shaohua Li wrote:
> IA64 dynamic ftrace support. The main tricky thing here is to support module.
> In a module, each routine's mcount call will call a PLT stub, which
> will call kernel mcount. We can't simply make the mcount call call into
> kernel mcount, as kernel and mocule have different gp and the
> instruction just supports 25bit offset. So I introduced a new PLT stub,
> which will call into kernel ftrace_caller. When module loading, all
> mcount call will be converted to nop. When the nop is converted to call,
> we make the call to the new PLT stub instead of old mcount PLT stub.
This is the new implementation for dyn-ftrace. Previous 4 patches are
still required and can be applied to latest kernel too. Just replace the
5 patch with this one. This new patch should address Steven's concern.

IA64 dynamic ftrace support.
The original _mcount stub for each function is like:
alloc r40=ar.pfs,12,8,0
mov r43=r0;;
mov r42°
mov r41=r1
nop.i 0x0
br.call.sptk.many b0 = _mcount;;

The patch convert it to below for nop:
[MII] nop.m 0x0
mov r3=ip
nop.i 0x0
[MLX] nop.m 0x0
nop.x 0x0;;
This isn't completely nop, as there is one instuction 'mov r3=ip', but
it should be light and harmless for code follow it.

And below is for call
[MII] nop.m 0x0
mov r3=ip
nop.i 0x0
[MLX] nop.m 0x0
brl.many .;;
In this way, only one instruction is changed to convert code between nop
and call. This should meet dyn-ftrace's requirement.
But this requires CPU support brl instruction, so dyn-ftrace isn't
supported for old Itanium system. Assume there are quite few such old
system running.

Signed-off-by: Shaohua Li <shaohua.li@intel.com>
---
arch/ia64/Kconfig | 2
arch/ia64/include/asm/ftrace.h | 13 ++
arch/ia64/kernel/Makefile | 5
arch/ia64/kernel/entry.S | 52 +++++++++
arch/ia64/kernel/ftrace.c | 235 +++++++++++++++++++++++++++++++++++++++++
scripts/recordmcount.pl | 7 +
6 files changed, 314 insertions(+)

Index: linux/arch/ia64/Kconfig
=================================--- linux.orig/arch/ia64/Kconfig 2008-12-31 10:30:26.000000000 +0800
+++ linux/arch/ia64/Kconfig 2008-12-31 16:55:05.000000000 +0800
@@ -21,6 +21,8 @@ config IA64
select HAVE_OPROFILE
select HAVE_KPROBES
select HAVE_KRETPROBES
+ select HAVE_FTRACE_MCOUNT_RECORD
+ select HAVE_DYNAMIC_FTRACE if (!ITANIUM)
select HAVE_FUNCTION_TRACER
select HAVE_DMA_ATTRS
select HAVE_KVM
Index: linux/arch/ia64/kernel/Makefile
=================================--- linux.orig/arch/ia64/kernel/Makefile 2008-12-31 10:30:26.000000000 +0800
+++ linux/arch/ia64/kernel/Makefile 2008-12-31 10:30:41.000000000 +0800
@@ -2,6 +2,10 @@
# Makefile for the linux kernel.
#

+ifdef CONFIG_DYNAMIC_FTRACE
+CFLAGS_REMOVE_ftrace.o = -pg
+endif
+
extra-y := head.o init_task.o vmlinux.lds

obj-y := acpi.o entry.o efi.o efi_stub.o gate-data.o fsys.o ia64_ksyms.o irq.o irq_ia64.o \
@@ -28,6 +32,7 @@ obj-$(CONFIG_IA64_CYCLONE) += cyclone.o
obj-$(CONFIG_CPU_FREQ) += cpufreq/
obj-$(CONFIG_IA64_MCA_RECOVERY) += mca_recovery.o
obj-$(CONFIG_KPROBES) += kprobes.o jprobes.o
+obj-$(CONFIG_DYNAMIC_FTRACE) += ftrace.o
obj-$(CONFIG_KEXEC) += machine_kexec.o relocate_kernel.o crash.o
obj-$(CONFIG_CRASH_DUMP) += crash_dump.o
obj-$(CONFIG_IA64_UNCACHED_ALLOCATOR) += uncached.o
Index: linux/arch/ia64/kernel/ftrace.c
=================================--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ linux/arch/ia64/kernel/ftrace.c 2008-12-31 16:58:56.000000000 +0800
@@ -0,0 +1,235 @@
+/*
+ * Dynamic function tracing support.
+ *
+ * Copyright (C) 2008 Shaohua Li <shaohua.li@intel.com>
+ *
+ * For licencing details, see COPYING.
+ *
+ * Defines low-level handling of mcount calls when the kernel
+ * is compiled with the -pg flag. When using dynamic ftrace, the
+ * mcount call-sites get patched lazily with NOP till they are
+ * enabled. All code mutation routines here take effect atomically.
+ */
+
+#include <linux/uaccess.h>
+#include <linux/ftrace.h>
+
+#include <asm/cacheflush.h>
+#include <asm/patch.h>
+
+/* In IA64, each function will be added below two bundles with -pg option */
+static unsigned char __attribute__((aligned(8)))
+ftrace_orig_code[MCOUNT_INSN_SIZE] = {
+ 0x02, 0x40, 0x31, 0x10, 0x80, 0x05, /* alloc r40=ar.pfs,12,8,0 */
+ 0xb0, 0x02, 0x00, 0x00, 0x42, 0x40, /* mov r43=r0;; */
+ 0x05, 0x00, 0xc4, 0x00, /* mov r42° */
+ 0x11, 0x48, 0x01, 0x02, 0x00, 0x21, /* mov r41=r1 */
+ 0x00, 0x00, 0x00, 0x02, 0x00, 0x00, /* nop.i 0x0 */
+ 0x08, 0x00, 0x00, 0x50 /* br.call.sptk.many b0 = _mcount;; */
+};
+
+struct ftrace_orig_insn {
+ u64 dummy1, dummy2, dummy3;
+ u64 dummy4:64-41+13;
+ u64 imm20:20;
+ u64 dummy5:3;
+ u64 sign:1;
+ u64 dummy6:4;
+};
+
+/* mcount stub will be converted below for nop */
+static unsigned char ftrace_nop_code[MCOUNT_INSN_SIZE] = {
+ 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, /* [MII] nop.m 0x0 */
+ 0x30, 0x00, 0x00, 0x60, 0x00, 0x00, /* mov r3=ip */
+ 0x00, 0x00, 0x04, 0x00, /* nop.i 0x0 */
+ 0x05, 0x00, 0x00, 0x00, 0x01, 0x00, /* [MLX] nop.m 0x0 */
+ 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, /* nop.x 0x0;; */
+ 0x00, 0x00, 0x04, 0x00
+};
+
+static unsigned char *ftrace_nop_replace(void)
+{
+ return ftrace_nop_code;
+}
+
+/*
+ * mcount stub will be converted below for call
+ * Note: Just the last instruction is changed against nop
+ * */
+static unsigned char __attribute__((aligned(8)))
+ftrace_call_code[MCOUNT_INSN_SIZE] = {
+ 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, /* [MII] nop.m 0x0 */
+ 0x30, 0x00, 0x00, 0x60, 0x00, 0x00, /* mov r3=ip */
+ 0x00, 0x00, 0x04, 0x00, /* nop.i 0x0 */
+ 0x05, 0x00, 0x00, 0x00, 0x01, 0x00, /* [MLX] nop.m 0x0 */
+ 0xff, 0xff, 0xff, 0xff, 0x7f, 0x00, /* brl.many .;;*/
+ 0xf8, 0xff, 0xff, 0xc8
+};
+
+struct ftrace_call_insn {
+ u64 dummy1, dummy2;
+ u64 dummy3:48;
+ u64 imm39_l:16;
+ u64 imm39_h:23;
+ u64 dummy4:13;
+ u64 imm20:20;
+ u64 dummy5:3;
+ u64 i:1;
+ u64 dummy6:4;
+};
+
+static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
+{
+ struct ftrace_call_insn *code = (void *)ftrace_call_code;
+ unsigned long offset = addr - (ip + 0x10);
+
+ code->imm39_l = offset >> 24;
+ code->imm39_h = offset >> 40;
+ code->imm20 = offset >> 4;
+ code->i = offset >> 63;
+ return ftrace_call_code;
+}
+
+static int
+ftrace_modify_code(unsigned long ip, unsigned char *old_code,
+ unsigned char *new_code, int do_check)
+{
+ unsigned char replaced[MCOUNT_INSN_SIZE];
+
+ /*
+ * Note: Due to modules and __init, 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.
+ *
+ * No real locking needed, this code is run through
+ * kstop_machine, or before SMP starts.
+ */
+
+ if (!do_check)
+ goto skip_check;
+
+ /* read the text we want to modify */
+ if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
+ return -EFAULT;
+
+ /* Make sure it is what we expect it to be */
+ if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
+ return -EINVAL;
+
+skip_check:
+ /* replace the text with the new text */
+ if (probe_kernel_write(((void *)ip), new_code, MCOUNT_INSN_SIZE))
+ return -EPERM;
+ flush_icache_range(ip, ip + MCOUNT_INSN_SIZE);
+
+ return 0;
+}
+
+static int ftrace_make_nop_check(struct dyn_ftrace *rec, unsigned long addr)
+{
+ unsigned char __attribute__((aligned(8))) replaced[MCOUNT_INSN_SIZE];
+ unsigned long ip = rec->ip;
+
+ if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
+ return -EFAULT;
+ if (rec->flags & FTRACE_FL_CONVERTED) {
+ struct ftrace_call_insn *call_insn, *tmp_call;
+
+ call_insn = (void *)ftrace_call_code;
+ tmp_call = (void *)replaced;
+ call_insn->imm39_l = tmp_call->imm39_l;
+ call_insn->imm39_h = tmp_call->imm39_h;
+ call_insn->imm20 = tmp_call->imm20;
+ call_insn->i = tmp_call->i;
+ if (memcmp(replaced, ftrace_call_code, MCOUNT_INSN_SIZE) != 0)
+ return -EINVAL;
+ return 0;
+ } else {
+ struct ftrace_orig_insn *call_insn, *tmp_call;
+
+ call_insn = (void *)ftrace_orig_code;
+ tmp_call = (void *)replaced;
+ call_insn->sign = tmp_call->sign;
+ call_insn->imm20 = tmp_call->imm20;
+ if (memcmp(replaced, ftrace_orig_code, MCOUNT_INSN_SIZE) != 0)
+ return -EINVAL;
+ return 0;
+ }
+}
+
+int ftrace_make_nop(struct module *mod,
+ struct dyn_ftrace *rec, unsigned long addr)
+{
+ int ret;
+ char *new;
+
+ ret = ftrace_make_nop_check(rec, addr);
+ if (ret)
+ return ret;
+ new = ftrace_nop_replace();
+ return ftrace_modify_code(rec->ip, NULL, new, 0);
+}
+
+int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
+{
+ unsigned long ip = rec->ip;
+ unsigned char *old, *new;
+
+ old= ftrace_nop_replace();
+ new = ftrace_call_replace(ip, addr);
+ return ftrace_modify_code(ip, old, new, 1);
+}
+
+struct ftrace_caller_code {
+ u64 dummy1:46;
+ u64 imm41_18:64-46;
+ u64 imm41_23:41-(64-46);
+ u64 dummy2:13;
+ u64 imm7b:7;
+ u64 dummy3:1;
+ u64 ic:1;
+ u64 imm5c:5;
+ u64 imm9d:9;
+ u64 i:1;
+ u64 dummy4:4;
+};
+
+/* in IA64, _mcount can't directly call ftrace_stub. Only jump is ok */
+int ftrace_update_ftrace_func(ftrace_func_t func)
+{
+ unsigned long ip;
+ unsigned long addr = ((struct fnptr *)ftrace_call)->ip;
+ struct ftrace_caller_code *code = (void *)addr;
+
+ if (func = ftrace_stub)
+ return 0;
+ ip = ((struct fnptr *)func)->ip;
+
+ code->i = ip >> 63;
+ code->imm9d = ip >> 7;
+ code->imm5c = ip >> 16;
+ code->ic = ip >> 21;
+ code->imm7b = ip & 0x7f;
+ code->imm41_18 = ip >> 22;
+ code->imm41_23 = ip >> 40;
+
+ flush_icache_range(addr, addr + 16);
+ return 0;
+}
+
+extern void ftrace_patch_gp(void);
+
+/* run from kstop_machine */
+int __init ftrace_dyn_arch_init(void *data)
+{
+ unsigned long ip = ((struct fnptr *)ftrace_patch_gp)->ip;
+ unsigned long gp = ((struct fnptr *)ftrace_dyn_arch_init)->gp;
+
+ ia64_patch_imm64(ip + 2, gp);
+ flush_icache_range(ip, ip + 16);
+
+ *(unsigned long *)data = 0;
+
+ return 0;
+}
Index: linux/scripts/recordmcount.pl
=================================--- linux.orig/scripts/recordmcount.pl 2008-12-31 10:30:26.000000000 +0800
+++ linux/scripts/recordmcount.pl 2008-12-31 10:30:41.000000000 +0800
@@ -206,6 +206,13 @@ if ($arch eq "x86_64") {
$alignment = 2;
$section_type = '%progbits';

+} elsif ($arch eq "ia64") {
+ $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s_mcount\$";
+ $type = "data8";
+
+ if ($is_module eq "0") {
+ $cc .= " -mconstant-gp";
+ }
} else {
die "Arch $arch is not supported with CONFIG_FTRACE_MCOUNT_RECORD";
}
Index: linux/arch/ia64/include/asm/ftrace.h
=================================--- linux.orig/arch/ia64/include/asm/ftrace.h 2008-12-31 10:30:26.000000000 +0800
+++ linux/arch/ia64/include/asm/ftrace.h 2008-12-31 10:30:41.000000000 +0800
@@ -8,6 +8,19 @@
extern void _mcount(unsigned long pfs, unsigned long r1, unsigned long b0, unsigned long r0);
#define mcount _mcount

+#include <asm/kprobes.h>
+/* In IA64, MCOUNT_ADDR is set in link time, so it's not a constant at compile time */
+#define MCOUNT_ADDR (((struct fnptr *)mcount)->ip)
+#define FTRACE_ADDR (((struct fnptr *)ftrace_caller)->ip)
+
+static inline unsigned long ftrace_call_adjust(unsigned long addr)
+{
+ /* second bundle, insn 2 */
+ return addr - 0x12;
+}
+
+struct dyn_arch_ftrace {
+};
#endif

#endif /* CONFIG_FUNCTION_TRACER */
Index: linux/arch/ia64/kernel/entry.S
=================================--- linux.orig/arch/ia64/kernel/entry.S 2008-12-31 10:30:26.000000000 +0800
+++ linux/arch/ia64/kernel/entry.S 2008-12-31 15:26:21.000000000 +0800
@@ -1406,6 +1406,57 @@ GLOBAL_ENTRY(unw_init_running)
END(unw_init_running)

#ifdef CONFIG_FUNCTION_TRACER
+#ifdef CONFIG_DYNAMIC_FTRACE
+GLOBAL_ENTRY(_mcount)
+ br ftrace_stub
+END(_mcount)
+
+.here:
+ br.ret.sptk.many b0
+
+GLOBAL_ENTRY(ftrace_caller)
+ alloc out0 = ar.pfs, 8, 0, 4, 0
+ mov out3 = r0
+ ;;
+ mov out2 = b0
+ add r3 = 0x20, r3
+ mov out1 = r1;
+ br.call.sptk.many b0 = ftrace_patch_gp
+ //this might be called from module, so we must patch gp
+.global ftrace_patch_gp;
+ftrace_patch_gp:
+ movl gp=0
+ mov b0 = r3
+ ;;
+.global ftrace_call;
+ftrace_call:
+{
+ .mlx
+ nop.m 0x0
+ movl r3 = .here;;
+}
+ alloc loc0 = ar.pfs, 4, 4, 2, 0
+ ;;
+ mov loc1 = b0
+ mov out0 = b0
+ mov loc2 = r8
+ mov loc3 = r15
+ ;;
+ adds out0 = -MCOUNT_INSN_SIZE, out0
+ mov out1 = in2
+ mov b6 = r3
+
+ br.call.sptk.many b0 = b6
+ ;;
+ mov ar.pfs = loc0
+ mov b0 = loc1
+ mov r8 = loc2
+ mov r15 = loc3
+ br ftrace_stub
+ ;;
+END(ftrace_caller)
+
+#else
GLOBAL_ENTRY(_mcount)
movl r2 = ftrace_stub
movl r3 = ftrace_trace_function;;
@@ -1435,6 +1486,7 @@ GLOBAL_ENTRY(_mcount)
br ftrace_stub
;;
END(_mcount)
+#endif

GLOBAL_ENTRY(ftrace_stub)
mov r3 = b0