Re: [PATCH 3/5]explictly ignore a file in recordmcount.pl

[Steven Rostedt <srostedt@redhat.com>]

On Tue, 2008-12-23 at 14:08 +0800, Shaohua Li wrote:
> In IA64, a function pointer isn't a 'unsigned long' but a
> 'struct {unsigned long ip, unsigned long gp}'. MCOUNT_ADDR is determined
> at link time not compile time, so explictly ignore kernel/trace/ftrace.o
> in recordmcount.pl.
> 
> Signed-off-by: Shaohua Li <shaohua.li@intel.com>
> ---
>  kernel/trace/ftrace.c   |   10 +---------
>  scripts/recordmcount.pl |    5 +++++
>  2 files changed, 6 insertions(+), 9 deletions(-)
> 
> Index: linux/kernel/trace/ftrace.c
> =================================> --- linux.orig/kernel/trace/ftrace.c	2008-12-23 13:11:28.000000000 +0800
> +++ linux/kernel/trace/ftrace.c	2008-12-23 13:24:59.000000000 +0800
> @@ -263,14 +263,6 @@ static void ftrace_update_pid_func(void)
>  # error Dynamic ftrace depends on MCOUNT_RECORD
>  #endif
>  
> -/*
> - * Since MCOUNT_ADDR may point to mcount itself, we do not want
> - * to get it confused by reading a reference in the code as we
> - * are parsing on objcopy output of text. Use a variable for
> - * it instead.
> - */
> -static unsigned long mcount_addr = MCOUNT_ADDR;
> -
>  enum {
>  	FTRACE_ENABLE_CALLS		= (1 << 0),
>  	FTRACE_DISABLE_CALLS		= (1 << 1),
> @@ -575,7 +567,7 @@ ftrace_code_disable(struct module *mod, 
>  
>  	ip = rec->ip;
>  
> -	ret = ftrace_make_nop(mod, rec, mcount_addr);
> +	ret = ftrace_make_nop(mod, rec, MCOUNT_ADDR);

This change will make dynamic ftrace fail on other archs (ppc and x86).
Please read the comment you deleted. By using MCOUNT_ADDR directly in
the code, you will create a reference to mcount in a text section that
will confuse recordmcount.pl. It will think this reference is a call to
mcount and when it tries to modify it, it will fail because the code is
not a call.

-- Steve



>  	if (ret) {
>  		ftrace_bug(ret, ip);
>  		rec->flags |= FTRACE_FL_FAILED;
> Index: linux/scripts/recordmcount.pl
> =================================> --- linux.orig/scripts/recordmcount.pl	2008-12-23 13:24:38.000000000 +0800
> +++ linux/scripts/recordmcount.pl	2008-12-23 13:24:59.000000000 +0800
> @@ -109,6 +109,11 @@ if ($#ARGV < 7) {
>  my ($arch, $bits, $objdump, $objcopy, $cc,
>      $ld, $nm, $rm, $mv, $is_module, $inputfile) = @ARGV;
>  
> +# This file refers to mcount and shouldn't be ftraced, so lets' ignore it
> +if ($inputfile eq "kernel/trace/ftrace.o") {
> +    exit(0);
> +}
> +
>  # Acceptable sections to record.
>  my %text_sections = (
>       ".text" => 1,
> 
>