Re: [PATCH] ftrace: recordmcount: avoid STT_FUNC symbols as baseon ARM

From: Steven Rostedt
Date: Tue May 17 2011 - 12:10:35 EST


On Wed, 2011-05-11 at 22:53 +0530, Rabin Vincent wrote:
> While find_secsym_ndx often finds the unamed local STT_SECTION, if a
> section has only one function in it, the ARM toolchain generates the
> STT_FUNC symbol before the STT_SECTION, and recordmcount finds this
> instead.
>
> This is problematic on ARM because in ARM ELFs, "if a [STT_FUNC] symbol
> addresses a Thumb instruction, its value is the address of the
> instruction with bit zero set (in a relocatable object, the section
> offset with bit zero set)". This leads to incorrect mcount addresses
> being recorded.
>
> Fix this by not using STT_FUNC symbols as the base on ARM.

Hi Russell,

Can you give me an Acked-by on this patch?

Thanks,

-- Steve

>
> Signed-off-by: Rabin Vincent <rabin@xxxxxx>
> ---
> scripts/recordmcount.h | 8 ++++++++
> 1 files changed, 8 insertions(+), 0 deletions(-)
>
> diff --git a/scripts/recordmcount.h b/scripts/recordmcount.h
> index baf187b..0e2944a 100644
> --- a/scripts/recordmcount.h
> +++ b/scripts/recordmcount.h
> @@ -39,6 +39,7 @@
> #undef ELF_R_INFO
> #undef Elf_r_info
> #undef ELF_ST_BIND
> +#undef ELF_ST_TYPE
> #undef fn_ELF_R_SYM
> #undef fn_ELF_R_INFO
> #undef uint_t
> @@ -68,6 +69,7 @@
> # define ELF_R_INFO ELF64_R_INFO
> # define Elf_r_info Elf64_r_info
> # define ELF_ST_BIND ELF64_ST_BIND
> +# define ELF_ST_TYPE ELF64_ST_TYPE
> # define fn_ELF_R_SYM fn_ELF64_R_SYM
> # define fn_ELF_R_INFO fn_ELF64_R_INFO
> # define uint_t uint64_t
> @@ -96,6 +98,7 @@
> # define ELF_R_INFO ELF32_R_INFO
> # define Elf_r_info Elf32_r_info
> # define ELF_ST_BIND ELF32_ST_BIND
> +# define ELF_ST_TYPE ELF32_ST_TYPE
> # define fn_ELF_R_SYM fn_ELF32_R_SYM
> # define fn_ELF_R_INFO fn_ELF32_R_INFO
> # define uint_t uint32_t
> @@ -333,6 +336,11 @@ static unsigned find_secsym_ndx(unsigned const txtndx,
> if (txtndx == w2(symp->st_shndx)
> /* avoid STB_WEAK */
> && (STB_LOCAL == st_bind || STB_GLOBAL == st_bind)) {
> + /* function symbols on ARM have quirks, avoid them */
> + if (w2(ehdr->e_machine) == EM_ARM
> + && ELF_ST_TYPE(symp->st_info) == STT_FUNC)
> + continue;
> +
> *recvalp = _w(symp->st_value);
> return symp - sym0;
> }


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