It turns out that the notes section for corefiles (or really any elf
file with multiple notes) is set up in such a way for LLVM formatted
output that the JSON equivalent only has the last note since the notes
are held in a dictionary with every key being Note. This pr alters the
layout for the notes to a list of dictionaries to sidestep this issue
for JSON output. Prior to this pr a note section in the output looked
like (for LLVM output):
```
Notes [
NoteSection {
Name: <?>
Offset: 0x2148
Size: 0x1F864
Note {
Owner: CORE
Data size: 0x150
Type: NT_PRSTATUS (prstatus structure)
Description data (
0000: 06000000 00000000 00000000 06000000 |................|
...
)
}
Note {
Owner: CORE
Data size: 0x88
Type: NT_PRPSINFO (prpsinfo structure)
Description data (
0000: 02440000 00000000 04054040 00000000 |.D........@@....|
....
```
But is now:
```
NoteSections [
NoteSection {
Name: <?>
Offset: 0x2148
Size: 0x1F864
Notes [
{
Owner: CORE
Data size: 0x150
Type: NT_PRSTATUS (prstatus structure)
Description data (
0000: 06000000 00000000 00000000 06000000 |................|
...
)
}
{
Owner: CORE
Data size: 0x88
Type: NT_PRPSINFO (prpsinfo structure)
Description data (
0000: 02440000 00000000 04054040 00000000 |.D........@@....|
...
```
The generic ABI says:
> Padding is present, if necessary, to ensure 8 or 4-byte alignment for the next note entry (depending on whether the file is a 64-bit or 32-bit object). Such padding is not included in descsz.
Our parsing code currently aligns n_namesz. Fix the bug by aligning the start
offset of the descriptor instead. This issue has been benign because the primary
uses of sh_addralign=8 notes are `.note.gnu.property`, where
`sizeof(Elf_Nhdr) + sizeof("GNU") = 16` (already aligned by 8).
In practice, many 64-bit systems incorrectly use sh_addralign=4 notes.
We can use sh_addralign (= p_align) to decide the descriptor padding.
Treat an alignment of 0 and 1 as 4. This approach matches modern GNU readelf
(since 2018).
We have a few tests incorrectly using sh_addralign=0. We may make our behavior
stricter after fixing these tests.
Linux kernel dumped core files use `p_align=0` notes, so we need to support the
case for compatibility.
Reviewed By: jhenderson
Differential Revision: https://reviews.llvm.org/D150022
This changes the output of `llvm-readelf -n` from:
```
Displaying notes found at file offset 0x<...> with length 0x<...>:
```
to:
```
Displaying notes found in: .note.foo
```
And similarly, adds a `Name:` field to the `llvm-readobj -n` output for notes.
This change not only increases GNU compatibility, it also makes it much easier to read notes. Note that we still fall back to printing the file offset/length in cases where we don't have a section name, such as when printing notes in program headers or printing notes in a partially stripped file (GNU readelf does the same).
Fixes llvm.org/PR41339.
Reviewed By: MaskRay
Differential Revision: https://reviews.llvm.org/D75647
This creates the next subfolders in the test directory:
"COFF", "ELF", "MachO", "wasm".
I've also removed platform specific prefixes, like "coff-*".
One unused binary was removed as well: `Inputs/relocs.obj.elf-mips`
Differential revision: https://reviews.llvm.org/D71203
