This makes the special PE sections available again in our output EFI
images.
Since the compiler provides no way to mark a section as not allocated,
we use GNU assembler syntax to emit the sections instead. This ensures
the section data isn't emitted twice as load segments will only contain
allocating input sections.
The main reason we need to apply a whole lot of logic to the section
conversion logic is because PE sections have to be aligned to the page
size (although, currently not even EDK2 enforces this). The process of
achieving this with a linker script is fraught with errors, they are a
pain to set up correctly and suck in general. They are also not
supported by mold, which requires us to forcibly use bfd, which also
means that linker feature detection is easily at odds as meson has a
differnt idea of what linker is in use.
Instead of forcing a manual ELF segment layout with a linker script we
just let the linker do its thing. We then simply copy/concatenate the
sections while observing proper page boundaries.
Note that we could just copy the ELF load *segments* directly and
achieve the same result. Doing this manually allows us to strip sections
we don't need at runtime like the dynamic linking information (the
elf2efi conversion is effectively the dynamic loader).
Important sections like .sbat that we emit directly from code will
currently *not* be exposed as individual PE sections as they are
contained within the ELF segments. A future commit will fix this.
The PE header size calculation failed to take the PE magic and coff
header size into account, which will lead to header truncation if we are
writing only 5 sections.
CentOS 8 ships python 3.6 so let's try and stay compatible with that
since the only feature we're using that requires python 3.9 is the
streamlined type annotations which are trivial to convert back to
the older stuff to stay compatible with python 3.6.
At least shim will choke on an empty relocation section when loading the
binary. Note that the binary is still considered relocatable (just with
no base relocations to apply) as we do not set the
IMAGE_FILE_RELOCS_STRIPPED DLL characteristic.
This adds back sd-boot builds by using meson compile targets directly.
We can do this now, because userspace binaries use the special
dependency that allows us to easily separate flags, so that we don't
pass anything to EFI builds that shouldn't be passed.
Additionally, we pass a bunch of flags to hopefully disable/override any
distro provided flags that should not be used for EFI binaries.
Fixes: #12275
