Re: [RFC 02/13] i387-tdep: Add function to read XSAVE layout from NT_X86_CPUID

[Simon Marchi <simon.marchi@polymtl.ca>]

On 2023-10-09 14:36, John Baldwin wrote:
> This can be used by x86 arches to determine the XSAVE layout instead
> of guessing based on the XCR0 mask and XSAVE register note size.

Just some nits below:

> +typedef std::unordered_map<cpuid_key, cpuid_values> cpuid_map;

For new stuff I would suggest:

  using cpuid_map = std::unordered_map<cpuid_key, cpuid_values>;

> +
> +static cpuid_map
> +i387_parse_cpuid_from_core (bfd *bfd)
> +{
> +  asection *section = bfd_get_section_by_name (bfd, ".reg-x86-cpuid");
> +  if (section == nullptr)
> +    return {};
> +
> +  size_t size = bfd_section_size (section);
> +  if (size == 0 || (size % (6 * 4)) != 0)

That 4 could be `sizeof (uint32_t)`.  And `6 * 4` appears below again,
it could a constexpr value with a name like entry_size.

> +    return {};
> +
> +  char contents[size];
> +  if (!bfd_get_section_contents (bfd, section, contents, 0, size))
> +    {
> +      warning (_("Couldn't read `.reg-x86-cpuid' section in core file."));
> +      return {};
> +    }
> +
> +  cpuid_map map;
> +  size_t index = 0;
> +  while (index < size)
> +    {
> +      uint32_t leaf = bfd_get_32 (bfd, contents + index);
> +      uint32_t count = bfd_get_32 (bfd, contents + index + 4);
> +      uint32_t eax = bfd_get_32 (bfd, contents + index + 8);
> +      uint32_t ebx = bfd_get_32 (bfd, contents + index + 12);
> +      uint32_t ecx = bfd_get_32 (bfd, contents + index + 16);
> +      uint32_t edx = bfd_get_32 (bfd, contents + index + 20);
> +
> +      if (map.count (cpuid_key (leaf, count)) != 0)
> +	{
> +	  warning (_("Duplicate cpuid leaf %#x,%#x"), leaf, count);
> +	  return {};
> +	}
> +      map.emplace (cpuid_key (leaf, count),
> +		   cpuid_values (eax, ebx, ecx, edx));

This could be slightly more optimal using map::try_emplace (to avoid
having two map lookups).

Simon