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build/elf: don't require the same alignment for all load segments (#659)
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philipc authored Apr 1, 2024
1 parent d65bc75 commit 0e59bfc
Showing 1 changed file with 16 additions and 7 deletions.
23 changes: 16 additions & 7 deletions src/build/elf.rs
Original file line number Diff line number Diff line change
Expand Up @@ -28,6 +28,13 @@ pub struct Builder<'data> {
/// Use to set the file class when writing the ELF file.
pub is_64: bool,
/// The alignment of [`elf::PT_LOAD`] segments.
///
/// This is an informational field and is not used when writing the ELF file.
/// It can optionally be used when calling [`Segments::add_load_segment`].
///
/// It is determined heuristically when reading the ELF file. Currently,
/// if all load segments have the same alignment, that alignment is used,
/// otherwise it is set to 1.
pub load_align: u64,
/// The file header.
pub header: Header,
Expand Down Expand Up @@ -64,7 +71,7 @@ impl<'data> Builder<'data> {
Self {
endian,
is_64,
load_align: 0,
load_align: 1,
header: Header::default(),
segments: Segments::new(),
sections: Sections::new(),
Expand Down Expand Up @@ -145,10 +152,11 @@ impl<'data> Builder<'data> {
for segment in segments {
if segment.p_type(endian) == elf::PT_LOAD {
let p_align = segment.p_align(endian).into();
if builder.load_align != 0 && builder.load_align != p_align {
return Err(Error::new("Unsupported alignments for PT_LOAD segments"));
if builder.load_align == 0 {
builder.load_align = p_align;
} else if builder.load_align != p_align {
builder.load_align = 1;
}
builder.load_align = p_align;
}

let id = builder.segments.next_id();
Expand All @@ -167,9 +175,8 @@ impl<'data> Builder<'data> {
marker: PhantomData,
});
}
if !builder.segments.is_empty() && builder.load_align == 0 {
// There should be at least one PT_LOAD segment.
return Err(Error::new("Unsupported segments without a PT_LOAD segment"));
if builder.load_align == 0 {
builder.load_align = 1;
}

for (index, section) in sections.iter().enumerate().skip(1) {
Expand Down Expand Up @@ -2365,6 +2372,8 @@ impl<'data> Segments<'data> {
/// Add a new `PT_LOAD` segment to the table.
///
/// The file offset and address will be derived from the current maximum for any segment.
/// The address will be chosen so that `p_paddr % align == p_offset % align`.
/// You may wish to use [`Builder::load_align`] for the alignment.
pub fn add_load_segment(&mut self, flags: u32, align: u64) -> &mut Segment<'data> {
let mut max_offset = 0;
let mut max_addr = 0;
Expand Down

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