[PATCHv2 4/9] bfd/riscv: prepare to handle bare metal core dump creation

[Luis Machado]

On 1/20/21 5:23 PM, Andrew Burgess wrote:
> When creating a core file GDB will call the function
> elfcore_write_prstatus to write out the general purpose registers
> along with the pid/tid for the thread.
> 
> However, for a bare metal RISC-V tool chain the prstatus*_t types are
> not defined so the elfcore_write_prstatus function will return NULL,
> preventing core file creation.
> 
> This commit provides the `elf_backend_write_core_note' hook and uses
> the provided function to write out the ptstatus information.

ptstatus -> prstatus?

> 
> In order to keep changes in the non bare metal tools to a minimum, the
> provided backend function will itself return NULL when the prstatus*_t
> types are available, the consequence of this is that the generic code
> in elfcore_write_prstatus will be used just as before.  But, when
> prstatus*_t is not available, the new backend function will write out
> the prstatus information using predefined offsets.
> 
> This new functionality will be used by a later GDB commit that will
> add bare metal core dumps for RISC-V.
> 
> bfd/ChangeLog:
> 
> 	* elfnn-riscv.c (riscv_write_core_note): New function.
> 	(elf_backend_write_core_note): Define.
> ---
>   bfd/ChangeLog     |  6 ++++
>   bfd/elfnn-riscv.c | 72 +++++++++++++++++++++++++++++++++++++++++++++++
>   2 files changed, 78 insertions(+)
> 
> diff --git a/bfd/elfnn-riscv.c b/bfd/elfnn-riscv.c
> index b2ec6a29fbf..70a683b45a3 100644
> --- a/bfd/elfnn-riscv.c
> +++ b/bfd/elfnn-riscv.c
> @@ -4886,6 +4886,77 @@ _bfd_riscv_relax_section (bfd *abfd, asection *sec,
>   # define PRPSINFO_OFFSET_PR_PSARGS	56
>   #endif
>   
> +/* Write PRSTATUS and PRPSINFO note into core file.  This will be called
> +   before the generic code in elf.c.  By checking the compiler defines we
> +   only perform any action here if the generic code would otherwise not be
> +   able to help us.  The intention is that bare metal core dumps (where the
> +   prstatus_t and/or prpsinfo_t might not be available) will use this code,
> +   while non bare metal tools will use the generic elf code.  */
> +
> +static char *
> +riscv_write_core_note (bfd *abfd ATTRIBUTE_UNUSED,
> +                       char *buf ATTRIBUTE_UNUSED,
> +                       int *bufsiz ATTRIBUTE_UNUSED,
> +                       int note_type ATTRIBUTE_UNUSED, ...)
> +{
> +  switch (note_type)
> +    {
> +    default:
> +      return NULL;
> +
> +#if !defined (HAVE_PRPSINFO_T)
> +    case NT_PRPSINFO:
> +      {
> +	char data[PRPSINFO_SIZE] ATTRIBUTE_NONSTRING;
> +	va_list ap;
> +
> +	va_start (ap, note_type);
> +	memset (data, 0, sizeof (data));
> +	strncpy (data + PRPSINFO_OFFSET_PR_FNAME, va_arg (ap, const char *), 16);
> +#if GCC_VERSION == 8000 || GCC_VERSION == 8001
> +	DIAGNOSTIC_PUSH;
> +	/* GCC 8.0 and 8.1 warn about 80 equals destination size with
> +	   -Wstringop-truncation:
> +	   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85643
> +	 */
> +	DIAGNOSTIC_IGNORE_STRINGOP_TRUNCATION;
> +#endif
> +	strncpy (data + PRPSINFO_OFFSET_PR_PSARGS, va_arg (ap, const char *), 80);
> +#if GCC_VERSION == 8000 || GCC_VERSION == 8001
> +	DIAGNOSTIC_POP;
> +#endif
> +	va_end (ap);
> +	return elfcore_write_note (abfd, buf, bufsiz,
> +				   "CORE", note_type, data, sizeof (data));
> +      }
> +#endif /* !HAVE_PRPSINFO_T */
> +
> +#if !defined (HAVE_PRSTATUS_T)
> +    case NT_PRSTATUS:
> +      {
> +        char data[PRSTATUS_SIZE];
> +        va_list ap;
> +        long pid;
> +        int cursig;
> +        const void *greg;
> +
> +        va_start (ap, note_type);
> +        memset (data, 0, sizeof(data));
> +        pid = va_arg (ap, long);
> +        bfd_put_32 (abfd, pid, data + PRSTATUS_OFFSET_PR_PID);
> +        cursig = va_arg (ap, int);
> +        bfd_put_16 (abfd, cursig, data + PRSTATUS_OFFSET_PR_CURSIG);
> +        greg = va_arg (ap, const void *);
> +        memcpy (data + PRSTATUS_OFFSET_PR_REG, greg,
> +                PRSTATUS_SIZE - PRSTATUS_OFFSET_PR_REG - ARCH_SIZE / 8);
> +        va_end (ap);
> +        return elfcore_write_note (abfd, buf, bufsiz,
> +                                   "CORE", note_type, data, sizeof (data));
> +      }
> +#endif /* !HAVE_PRSTATUS_T */
> +    }
> +}
> +
>   /* Support for core dump NOTE sections.  */
>   
>   static bfd_boolean
> @@ -5000,6 +5071,7 @@ riscv_elf_obj_attrs_arg_type (int tag)
>   #define elf_backend_grok_prstatus		riscv_elf_grok_prstatus
>   #define elf_backend_grok_psinfo			riscv_elf_grok_psinfo
>   #define elf_backend_object_p			riscv_elf_object_p
> +#define elf_backend_write_core_note		riscv_write_core_note
>   #define elf_info_to_howto_rel			NULL
>   #define elf_info_to_howto			riscv_info_to_howto_rela
>   #define bfd_elfNN_bfd_relax_section		_bfd_riscv_relax_section
>