Re: [PATCH] [AArch64] Support AArch64 MTE memory tag dumps in core files

[Luis Machado <luis.machado@arm.com>]

Alan,

Does this updated version look OK to you?

On 5/3/22 12:33, Luis Machado via Binutils wrote:
> v3:
> 
> - Update the segment name from PT_ARM_MEMTAG_MTE to PT_AARCH64_MEMTAG_MTE
>    and change its value to PT_LOPROC + 0x2, as PT_LOPROC + 0x1 was taken.
> 
> v2:
> 
> - Drop arch-specific fields from the generic section data structure.
> - Use the rawsize field of the section structure to store the original
>    memory range of the memory-tagged area.
> - Implement the bfd_elf_modify_headers for aarch64, to adjust the values
>    for the memory tag segment according to the Linux Kernel's format.
> 
> --
> 
> The Linux kernel can dump memory tag segments to a core file, one segment
> per mapped range. The format and documentation can be found in the Linux
> kernel tree [1].
> 
> The following patch adjusts bfd and binutils so they can handle this new
> segment type and display it accordingly. It also adds code required so GDB
> can properly read/dump core file data containing memory tags.
> 
> Upon reading, each segment that contains memory tags gets mapped to a
> section named "memtag". These sections will be used by GDB to lookup the tag
> data. There can be multiple such sections with the same name, and they are not
> numbered to simplify GDB's handling and lookup.
> 
> There is another patch for GDB that enables both reading
> and dumping of memory tag segments.
> 
> Tested on aarch64-linux Ubuntu 20.04.
> 
> [1] Documentation/arm64/memory-tagging-extension.rst (Core Dump Support)
> ---
>   bfd/elfnn-aarch64.c   | 89 +++++++++++++++++++++++++++++++++++++++++++
>   binutils/readelf.c    |  1 +
>   include/elf/aarch64.h |  3 ++
>   3 files changed, 93 insertions(+)
> 
> diff --git a/bfd/elfnn-aarch64.c b/bfd/elfnn-aarch64.c
> index 4926bab9cf2..3eee97b7ada 100644
> --- a/bfd/elfnn-aarch64.c
> +++ b/bfd/elfnn-aarch64.c
> @@ -8158,6 +8158,89 @@ elfNN_aarch64_section_from_shdr (bfd *abfd,
>     return true;
>   }
>   
> +/* Process any AArch64-specific program segment types.  */
> +
> +static bool
> +elfNN_aarch64_section_from_phdr (bfd *abfd ATTRIBUTE_UNUSED,
> +				 Elf_Internal_Phdr *hdr,
> +				 int hdr_index ATTRIBUTE_UNUSED,
> +				 const char *name ATTRIBUTE_UNUSED)
> +{
> +  /* Right now we only handle the PT_AARCH64_MEMTAG_MTE segment type.  */
> +  if (hdr == NULL || hdr->p_type != PT_AARCH64_MEMTAG_MTE)
> +    return false;
> +
> +  if (hdr->p_filesz > 0)
> +    {
> +      /* Sections created from memory tag p_type's are always named
> +	 "memtag".  This makes it easier for tools (for example, GDB)
> +	 to find them.  */
> +      asection *newsect = bfd_make_section_anyway (abfd, "memtag");
> +
> +      if (newsect == NULL)
> +	return false;
> +
> +      unsigned int opb = bfd_octets_per_byte (abfd, NULL);
> +
> +      /* p_vaddr holds the original start address of the tagged memory
> +	 range.  */
> +      newsect->vma = hdr->p_vaddr / opb;
> +
> +      /* p_filesz holds the storage size of the packed tags.  */
> +      newsect->size = hdr->p_filesz;
> +      newsect->filepos = hdr->p_offset;
> +
> +      /* p_memsz holds the size of the memory range that contains tags.  The
> +	 section's rawsize field is reused for this purpose.  */
> +      newsect->rawsize = hdr->p_memsz;
> +
> +      /* Make sure the section's flags has SEC_HAS_CONTENTS set, otherwise
> +	 BFD will return all zeroes when attempting to get contents from this
> +	 section.  */
> +      newsect->flags |= SEC_HAS_CONTENTS;
> +    }
> +
> +  return true;
> +}
> +
> +/* Implements the bfd_elf_modify_headers hook for aarch64.  */
> +
> +static bool
> +elfNN_aarch64_modify_headers (bfd *abfd,
> +			      struct bfd_link_info *info)
> +{
> +  struct elf_segment_map *m;
> +  unsigned int segment_count = 0;
> +  Elf_Internal_Phdr *p;
> +
> +  for (m = elf_seg_map (abfd); m != NULL; m = m->next, segment_count++)
> +    {
> +      /* We are only interested in the memory tag segment that will be dumped
> +	 to a core file.  If we have no memory tags or this isn't a core file we
> +	 are dealing with, just skip this segment.  */
> +      if (m->p_type != PT_AARCH64_MEMTAG_MTE
> +	  || bfd_get_format (abfd) != bfd_core)
> +	continue;
> +
> +      /* For memory tag segments in core files, the size of the file contents
> +	 is smaller than the size of the memory range.  Adjust the memory size
> +	 accordingly.  The real memory size is held in the section's rawsize
> +	 field.  */
> +      if (m->count > 0)
> +	{
> +	  p = elf_tdata (abfd)->phdr;
> +	  p += m->idx;
> +	  p->p_memsz = m->sections[0]->rawsize;
> +	  p->p_flags = 0;
> +	  p->p_paddr = 0;
> +	  p->p_align = 0;
> +	}
> +    }
> +
> +  /* Give the generic code a chance to handle the headers.  */
> +  return _bfd_elf_modify_headers (abfd, info);
> +}
> +
>   /* A structure used to record a list of sections, independently
>      of the next and prev fields in the asection structure.  */
>   typedef struct section_list
> @@ -10059,6 +10142,12 @@ const struct elf_size_info elfNN_aarch64_size_info =
>   #define elf_backend_section_from_shdr		\
>     elfNN_aarch64_section_from_shdr
>   
> +#define elf_backend_section_from_phdr		\
> +  elfNN_aarch64_section_from_phdr
> +
> +#define elf_backend_modify_headers		\
> +  elfNN_aarch64_modify_headers
> +
>   #define elf_backend_size_dynamic_sections	\
>     elfNN_aarch64_size_dynamic_sections
>   
> diff --git a/binutils/readelf.c b/binutils/readelf.c
> index d45e0920788..ea20479daef 100644
> --- a/binutils/readelf.c
> +++ b/binutils/readelf.c
> @@ -4499,6 +4499,7 @@ get_aarch64_segment_type (unsigned long type)
>     switch (type)
>       {
>       case PT_AARCH64_ARCHEXT:  return "AARCH64_ARCHEXT";
> +    case PT_AARCH64_MEMTAG_MTE:	return "AARCH64_MEMTAG_MTE";
>       default:                  return NULL;
>       }
>   }
> diff --git a/include/elf/aarch64.h b/include/elf/aarch64.h
> index 703a62baeca..e368ff2dffe 100644
> --- a/include/elf/aarch64.h
> +++ b/include/elf/aarch64.h
> @@ -27,6 +27,9 @@
>   /* Processor specific program header types.  */
>   #define PT_AARCH64_ARCHEXT	(PT_LOPROC + 0)
>   
> +/* MTE memory tag segment type.  */
> +#define PT_AARCH64_MEMTAG_MTE     (PT_LOPROC + 0x2)
> +
>   /* Additional section types.  */
>   #define SHT_AARCH64_ATTRIBUTES	0x70000003  /* Section holds attributes.  */
>