While the generic ABI requires notes to be 8-byte aligned in ELF64, many
vendor-specific notes (from Linux, NetBSD, Solaris, etc) use 4-byte
In a PT_NOTE segment, if 4-byte aligned notes are followed by an 8-byte
aligned note, the possible 4-byte padding may make consumers fail to
parse the 8-byte aligned note. See PR41000 for the recent report about
(Note, for NT_GNU_PROPERTY_TYPE_0, the consumers should probably migrate
to PT_GNU_PROPERTY, but the alignment issue affects other notes as well.)
To fix the issue, this patches disallows notes with different alignments
from being placed in the same PT_NOTE. If compilers emit 4-byte aligned
notes before 8-byte aligned notes, we'll create at most 2 segments.
We don't have to check whether sh_size is a multiple of sh_addralign.
It is unrealistic and it shouldn't cause parsing issues anyway (the
output is not different from the case with the sh_size aligned up).
An alternative approach is to create a PT_NOTE for each SHT_NOTE, but
we'll have to incur the sizeof(Elf64_Phdr) = 56 overhead every time a
new note section is introduced.