[9/9] create-diff-object: account for special section changes

Commit Message

Roger Pau Monné April 29, 2024, 2:56 p.m. UTC

When deciding whether there's content to generate a payload also take into
account whether special sections have changed.  Initially account for changes
to alternative related section to cause the generation of a livepatch.

Note that accounting for hook sections is already done by
kpatch_include_hook_elements() when deciding whether there's changed content in
the object file.  .bugframe sections are also not accounted for since any
section in a bugframe section will be accompanied by a change in the function
the bugframe references (the placement of the BUG_INSTR will change in the
caller function).

Signed-off-by: Roger Pau Monné <[e-mail]>
---
 create-diff-object.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

Patch

diff --git a/create-diff-object.c b/create-diff-object.c
index 8bfb6bf92a1b..957631097b8a 100644
--- a/create-diff-object.c
+++ b/create-diff-object.c
@@ -1663,6 +1663,28 @@  static int kpatch_include_hook_elements(struct kpatch_elf *kelf)
 	return num_new_functions;
 }
 
+static unsigned int include_special_sections(const struct kpatch_elf *kelf)
+{
+	const struct section *sec;
+	unsigned int nr = 0;
+
+	/*
+	 * Only account for changes in alternatives and exception table related
+	 * sections.  Hooks are already taken care of separately, and changes
+	 * in bug_frame sections always go along with changes in the caller
+	 * functions.
+	 */
+	list_for_each_entry(sec, &kelf->sections, list)
+		if (sec->status != SAME &&
+		    (!strcmp(sec->name, ".altinstructions") ||
+		     !strcmp(sec->name, ".altinstr_replacement") ||
+		     !strcmp(sec->name, ".ex_table") ||
+		     !strcmp(sec->name, ".fixup")))
+			nr++;
+
+	return nr;
+}
+
 static int kpatch_include_new_globals(struct kpatch_elf *kelf)
 {
 	struct symbol *sym;
@@ -2469,6 +2491,8 @@  int main(int argc, char *argv[])
 	kpatch_include_debug_sections(kelf_patched);
 	log_debug("Include hook elements\n");
 	num_changed += kpatch_include_hook_elements(kelf_patched);
+	log_debug("Include special sections\n");
+	num_changed += include_special_sections(kelf_patched);
 	log_debug("num_changed = %d\n", num_changed);
 	log_debug("Include new globals\n");
 	new_globals_exist = kpatch_include_new_globals(kelf_patched);