Hi, Ralf
I have sent the [RFC 2/2] patch in another patchset [Add C version of
recordmcount for MIPS], and this [RFC 1/2] is also needed to discard
the old assumption on the module address space, so, could you please
apply it directly? or, should I resend it?
You can get it here:
[RFC,1/2] MIPS: tracing/ftrace: Replace in_module() with a generic
in_kernel_space()
http://patchwork.linux-mips.org/patch/1730/
And before applying it, you need to apply this mini patch at first,
otherwise, there will be conflict.
MIPS: tracing/ftrace: Speedup a little for function graph tracer
http://patchwork.linux-mips.org/patch/1728/
Regards,
Wu zhangjin
On Sat, Oct 23, 2010 at 4:58 AM, Wu Zhangjin <wuzhangjin@gmail.com> wrote:
> From: Wu Zhangjin <wuzhangjin@gmail.com>
>
> The module space may be the same as the kernel space sometimes(with
> related kernel config and gcc options), but the current in_module()
> assume they are always different, so, it should be fixed.
>
> As we know, for the limitation of the fixed 32bit long instruction of
> MIPS, the "jal target" can only jump to an address whose offset from the
> jal instruction is smaller than 2^28=256M, which means if the address is
> in kernel space(the kernel image should be always smaller than 256M), no
> long call is needed to jump from the address to _mcount, and further, if
> the module use the same space as kernel space, the situation for module
> will be the same as the kernel. but currently for MIPS, in most of the
> situations, module has different space(0xc0000000) from the kernel
> space(0x80000000) and the offset is bigger than 256M, a register is
> needed to load the address of _mcount and another instruction "jal
> <register>" is needed to jump from an address to _mcount.
>
> The above can be explained as:
>
> if (in_kernel_space(addr)) {
> jal _mcount;
> } else {
> load the address of _mcount to a register
> jalr <register>
> }
>
> As we can see, the above explanation covers all of the situations well
> and reflect the reality, so, we decide to add a new in_kernel_space()
> instead of the old in_module().
>
> Based on core_kernel_text() from kernel/extable.c, in_kernel_space() is
> easily to be added. Because all of the functions in the init sections is
> anotated with notrace, so, differ from core_kernel_text(),
> in_kernel_space() doesn't care about init section.
>
> With this new in_kernel_space(), the ftrace_make_{nop,call} can be
> explained as following.
>
> ftrace_make_call() ftrace_make_nop()
>
> if (in_kernel_space(addr)) {
> jal _mcount; (jal ftrace_caller) <--> nop
> } else {
> load the address of _mcount to a register <--> b label
> jalr <register>
> label:
> }
>
> Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>
> ---
> arch/mips/kernel/ftrace.c | 66 ++++++++++++++++++++++++--------------------
> 1 files changed, 36 insertions(+), 30 deletions(-)
>
> diff --git a/arch/mips/kernel/ftrace.c b/arch/mips/kernel/ftrace.c
> index 65f1949..6ff5a54 100644
> --- a/arch/mips/kernel/ftrace.c
> +++ b/arch/mips/kernel/ftrace.c
> @@ -17,21 +17,7 @@
> #include <asm/cacheflush.h>
> #include <asm/uasm.h>
>
> -/*
> - * If the Instruction Pointer is in module space (0xc0000000), return true;
> - * otherwise, it is in kernel space (0x80000000), return false.
> - *
> - * FIXME: This will not work when the kernel space and module space are the
> - * same. If they are the same, we need to modify scripts/recordmcount.pl,
> - * ftrace_make_nop/call() and the other related parts to ensure the
> - * enabling/disabling of the calling site to _mcount is right for both kernel
> - * and module.
> - */
> -
> -static inline int in_module(unsigned long ip)
> -{
> - return ip & 0x40000000;
> -}
> +#include <asm-generic/sections.h>
>
> #ifdef CONFIG_DYNAMIC_FTRACE
>
> @@ -69,6 +55,20 @@ static inline void ftrace_dyn_arch_init_insns(void)
> #endif
> }
>
> +/*
> + * Check if the address is in kernel space
> + *
> + * Clone core_kernel_text() from kernel/extable.c, but don't call
> + * init_kernel_text() for Ftrace don't trace functions in init sections.
> + */
> +static inline int in_kernel_space(unsigned long ip)
> +{
> + if (ip >= (unsigned long)_stext &&
> + ip <= (unsigned long)_etext)
> + return 1;
> + return 0;
> +}
> +
> static int ftrace_modify_code(unsigned long ip, unsigned int new_code)
> {
> int faulted;
> @@ -91,10 +91,16 @@ int ftrace_make_nop(struct module *mod,
> unsigned long ip = rec->ip;
>
> /*
> - * We have compiled module with -mlong-calls, but compiled the kernel
> - * without it, we need to cope with them respectively.
> + * If ip is in kernel space, long call is not needed, otherwise, it is
> + * needed.
> */
> - if (in_module(ip)) {
> + if (in_kernel_space(ip)) {
> + /*
> + * move at, ra
> + * jal _mcount --> nop
> + */
> + new = INSN_NOP;
> + } else {
> #if defined(KBUILD_MCOUNT_RA_ADDRESS) && defined(CONFIG_32BIT)
> /*
> * lui v1, hi_16bit_of_mcount --> b 1f (0x10000005)
> @@ -117,12 +123,6 @@ int ftrace_make_nop(struct module *mod,
> */
> new = INSN_B_1F_4;
> #endif
> - } else {
> - /*
> - * move at, ra
> - * jal _mcount --> nop
> - */
> - new = INSN_NOP;
> }
> return ftrace_modify_code(ip, new);
> }
> @@ -132,8 +132,12 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned
> long addr)
> unsigned int new;
> unsigned long ip = rec->ip;
>
> - /* ip, module: 0xc0000000, kernel: 0x80000000 */
> - new = in_module(ip) ? insn_lui_v1_hi16_mcount :
> insn_jal_ftrace_caller;
> + /*
> + * If ip is in kernel space, long call is not needed, otherwise, it is
> + * needed.
> + */
> + new = in_kernel_space(ip) ? insn_jal_ftrace_caller :
> + insn_lui_v1_hi16_mcount;
>
> return ftrace_modify_code(ip, new);
> }
> @@ -200,11 +204,13 @@ unsigned long ftrace_get_parent_addr(unsigned long
> self_addr,
> int faulted;
>
> /*
> - * For module, move the ip from calling site of mcount after the
> - * instruction "lui v1, hi_16bit_of_mcount"(offset is 24), but for
> - * kernel, move after the instruction "move ra, at"(offset is 16)
> + * If self_addr is in kernel space, long call is not needed, only need
> + * to move ip after the instruction "move ra, at"(offset is 16),
> + * otherwise, long call is needed, need to move ip from calling site
> of
> + * mcount after the instruction "lui v1, hi_16bit_of_mcount"(offset is
> + * 24).
> */
> - ip = self_addr - (in_module(self_addr) ? 24 : 16);
> + ip = self_addr - (in_kernel_space(self_addr) ? 16 : 24);
>
> /*
> * search the text until finding the non-store instruction or "s{d,w}
> --
> 1.7.1
>
>
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