GNU-gABI: Alignment of .note.ABI-tag and .note.gnu.build-id sections

["H.J. Lu" <hjl.tools@gmail.com>]

According to gABI, each note entry should be aligned to 4 bytes in 32-bit
objects or 8 bytes in 64-bit objects.  But Linux has been using 4 byte 
alignment for .note.ABI-tag note and .note.gnu.build-id note in 64-bit
objects.  We can't change their alignment to 8 bytes.  Since all notes i
n one PT_LOAD segment must have the same alignment which equals to p_align.
Note parser can use p_align of PT_LOAD segment for note alignment, instead
of assuming alignment based on ELF file class.

Here is a patch to Linux Extensions to gABI.  I also regenerated PDF
file at

https://github.com/hjl-tools/linux-abi/wiki/Linux-Extensions-to-gABI

H.J.
---
Document difference in alignment of .note.ABI-tag and .note.gnu.build-id
sections from gABI.
---
 object-files.tex | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/object-files.tex b/object-files.tex
index 64ce243..5b7b414 100644
--- a/object-files.tex
+++ b/object-files.tex
@@ -518,6 +518,18 @@ identify OS and version targeted.  It can be merged with other
    signifies a 2.2.5 kernel.
 \end{description}
 
+\subsection{Alignment of Note Sections}
+
+All entries in a \texttt{PT_LOAD} segment have the same alignment which
+equals to the {\tt p_align} field in program header.
+
+According to gABI, each note entry should be aligned to 4 bytes in
+32-bit objects or 8 bytes in 64-bit objects.  But \code{.note.ABI-tag}
+section (see Section~\ref{sec_abi_tag}) and \code{.note.gnu.build-id}
+section (see Section~\ref{sec_build_id}) are aligned to 4 bytes in
+both 32-bit and 64-bit objects.  Note parser should use {\tt p_align}
+for note alignment, instead of assuming alignment based on ELF file class.
+
 \section{Symbol Table}
 
 \begin{table}[H]
-- 
2.14.3