[ARM/FDPIC,v2,2/4] linux-user: ARM-FDPIC: Identify ARM FDPIC binaries

Define an ARM-specific version of elf_is_fdpic:
FDPIC ELF objects are identified with e_ident[EI_OSABI] ==
ELFOSABI_ARM_FDPIC.

Co-Authored-By: Mickaël Guêné <mickael.guene@st.com>
Signed-off-by: Christophe Lyon <christophe.lyon@st.com>

On 23 April 2018 at 08:51, Christophe Lyon <christophe.lyon@st.com> wrote:
> Define an ARM-specific version of elf_is_fdpic:
> FDPIC ELF objects are identified with e_ident[EI_OSABI] ==
> ELFOSABI_ARM_FDPIC.
>
> Co-Authored-By: Mickaël Guêné <mickael.guene@st.com>
> Signed-off-by: Christophe Lyon <christophe.lyon@st.com>
>
> diff --git a/include/elf.h b/include/elf.h
> index c0dc9bb..934dbbd 100644
> --- a/include/elf.h
> +++ b/include/elf.h
> @@ -1483,6 +1483,7 @@ typedef struct elf64_shdr {
>  #define ELFOSABI_TRU64          10      /* Compaq TRU64 UNIX.  */
>  #define ELFOSABI_MODESTO        11      /* Novell Modesto.  */
>  #define ELFOSABI_OPENBSD        12      /* OpenBSD.  */
> +#define ELFOSABI_ARM_FDPIC      65      /* ARM FDPIC */
>  #define ELFOSABI_ARM            97      /* ARM */
>  #define ELFOSABI_STANDALONE     255     /* Standalone (embedded) application */
>
> diff --git a/linux-user/elfload.c b/linux-user/elfload.c
> index bbe93b0..76d7718 100644
> --- a/linux-user/elfload.c
> +++ b/linux-user/elfload.c
> @@ -1681,11 +1681,18 @@ static void zero_bss(abi_ulong elf_bss, abi_ulong last_bss, int prot)
>      }
>  }
>
> +#ifdef TARGET_ARM
> +static int elf_is_fdpic(struct elfhdr *exec)
> +{
> +    return exec->e_ident[EI_OSABI] == ELFOSABI_ARM_FDPIC;
> +}
> +#else
>  /* Default implementation, always false.  */
>  static int elf_is_fdpic(struct elfhdr *exec)
>  {
>      return 0;
>  }
> +#endif

I have a strong dislike for per-target ifdef ladders. Can we instead
put the target's implementation of elf_is_fdpic() into
linux-user/$ARCH/target_elf.h
and also have that header do
#define TARGET_HAS_ELF_FDPIC

and then in the generic code we can protect the default elf_is_fdpic()
with #ifndef TARGET_HAS_ELF_FDPIC.

thanks
-- PMM

On 23/04/2018 14:17, Peter Maydell wrote:
> On 23 April 2018 at 08:51, Christophe Lyon <christophe.lyon@st.com> wrote:
>> Define an ARM-specific version of elf_is_fdpic:
>> FDPIC ELF objects are identified with e_ident[EI_OSABI] ==
>> ELFOSABI_ARM_FDPIC.
>>
>> Co-Authored-By: Mickaël Guêné <mickael.guene@st.com>
>> Signed-off-by: Christophe Lyon <christophe.lyon@st.com>
>>
>> diff --git a/include/elf.h b/include/elf.h
>> index c0dc9bb..934dbbd 100644
>> --- a/include/elf.h
>> +++ b/include/elf.h
>> @@ -1483,6 +1483,7 @@ typedef struct elf64_shdr {
>>   #define ELFOSABI_TRU64          10      /* Compaq TRU64 UNIX.  */
>>   #define ELFOSABI_MODESTO        11      /* Novell Modesto.  */
>>   #define ELFOSABI_OPENBSD        12      /* OpenBSD.  */
>> +#define ELFOSABI_ARM_FDPIC      65      /* ARM FDPIC */
>>   #define ELFOSABI_ARM            97      /* ARM */
>>   #define ELFOSABI_STANDALONE     255     /* Standalone (embedded) application */
>>
>> diff --git a/linux-user/elfload.c b/linux-user/elfload.c
>> index bbe93b0..76d7718 100644
>> --- a/linux-user/elfload.c
>> +++ b/linux-user/elfload.c
>> @@ -1681,11 +1681,18 @@ static void zero_bss(abi_ulong elf_bss, abi_ulong last_bss, int prot)
>>       }
>>   }
>>
>> +#ifdef TARGET_ARM
>> +static int elf_is_fdpic(struct elfhdr *exec)
>> +{
>> +    return exec->e_ident[EI_OSABI] == ELFOSABI_ARM_FDPIC;
>> +}
>> +#else
>>   /* Default implementation, always false.  */
>>   static int elf_is_fdpic(struct elfhdr *exec)
>>   {
>>       return 0;
>>   }
>> +#endif
> 
> I have a strong dislike for per-target ifdef ladders. Can we instead
> put the target's implementation of elf_is_fdpic() into
> linux-user/$ARCH/target_elf.h
> and also have that header do
> #define TARGET_HAS_ELF_FDPIC
> 
> and then in the generic code we can protect the default elf_is_fdpic()
> with #ifndef TARGET_HAS_ELF_FDPIC.
> 

How invasive could that be?
Your proposal is appealing, but target_elf.h is only included by linux-user/main.c, which does not define elfhdr etc...
All that knowledge is in linux-user/elfload.c, which controls what include/elf.h defines.

Should I re-engineer that?

Thanks,

Christophe


> thanks
> -- PMM
> .
>

On 23 April 2018 at 13:53, Christophe Lyon <christophe.lyon@st.com> wrote:
> On 23/04/2018 14:17, Peter Maydell wrote:
>> I have a strong dislike for per-target ifdef ladders. Can we instead
>> put the target's implementation of elf_is_fdpic() into
>> linux-user/$ARCH/target_elf.h
>> and also have that header do
>> #define TARGET_HAS_ELF_FDPIC
>>
>> and then in the generic code we can protect the default elf_is_fdpic()
>> with #ifndef TARGET_HAS_ELF_FDPIC.
>>
>
> How invasive could that be?
> Your proposal is appealing, but target_elf.h is only included by
> linux-user/main.c, which does not define elfhdr etc...
> All that knowledge is in linux-user/elfload.c, which controls what
> include/elf.h defines.

Hmm, I see what you mean. We can't even put the function inside the
existing per-target ifdef ladder, because that comes before the
include of elf.h halfway down elfload.c.

That's a bit of a mess, but it's a mess we shouldn't try to
clean up as part of this patchset, so

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>

thanks
-- PMM