[PATCH] coredump, vmcore: Set p_align to 4 for PT_NOTE

[Fangrui Song]

Tools like readelf/llvm-readelf use p_align to parse a PT_NOTE program
header as an array of 4-byte entries or 8-byte entries. Currently, there
are workarounds[1] in place for Linux to treat p_align==0 as 4. However,
it would be more appropriate to set the correct alignment so that tools
do not have to rely on guesswork. FreeBSD coredumps set p_align to 4 as
well.

[1]: https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=82ed9683ec099d8205dc499ac84febc975235af6
[2]: https://reviews.llvm.org/D150022
---
 fs/binfmt_elf.c       | 2 +-
 fs/binfmt_elf_fdpic.c | 2 +-
 fs/proc/vmcore.c      | 4 ++--
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 1033fbdfdbec..44b4c42ab8e8 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -1517,7 +1517,7 @@ static void fill_elf_note_phdr(struct elf_phdr *phdr, int sz, loff_t offset)
 	phdr->p_filesz = sz;
 	phdr->p_memsz = 0;
 	phdr->p_flags = 0;
-	phdr->p_align = 0;
+	phdr->p_align = 4;
 }
 
 static void fill_note(struct memelfnote *note, const char *name, int type,
diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c
index 05a1471d5283..d76ad3d4f676 100644
--- a/fs/binfmt_elf_fdpic.c
+++ b/fs/binfmt_elf_fdpic.c
@@ -1269,7 +1269,7 @@ static inline void fill_elf_note_phdr(struct elf_phdr *phdr, int sz, loff_t offs
 	phdr->p_filesz = sz;
 	phdr->p_memsz = 0;
 	phdr->p_flags = 0;
-	phdr->p_align = 0;
+	phdr->p_align = 4;
 	return;
 }
 
diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
index 03f5963914a1..cb80a7703d58 100644
--- a/fs/proc/vmcore.c
+++ b/fs/proc/vmcore.c
@@ -877,7 +877,7 @@ static int __init merge_note_headers_elf64(char *elfptr, size_t *elfsz,
 	phdr.p_offset  = roundup(note_off, PAGE_SIZE);
 	phdr.p_vaddr   = phdr.p_paddr = 0;
 	phdr.p_filesz  = phdr.p_memsz = phdr_sz;
-	phdr.p_align   = 0;
+	phdr.p_align   = 4;
 
 	/* Add merged PT_NOTE program header*/
 	tmp = elfptr + sizeof(Elf64_Ehdr);
@@ -1068,7 +1068,7 @@ static int __init merge_note_headers_elf32(char *elfptr, size_t *elfsz,
 	phdr.p_offset  = roundup(note_off, PAGE_SIZE);
 	phdr.p_vaddr   = phdr.p_paddr = 0;
 	phdr.p_filesz  = phdr.p_memsz = phdr_sz;
-	phdr.p_align   = 0;
+	phdr.p_align   = 4;
 
 	/* Add merged PT_NOTE program header*/
 	tmp = elfptr + sizeof(Elf32_Ehdr);
-- 
2.40.1.606.ga4b1b128d6-goog