kpatch/0020-support-remove-static-variables-using-KPATCH_IGNORE_.patch

From a81f64c1eae14f2b0da8168ca60b3d9beb0a9fb0 Mon Sep 17 00:00:00 2001
From: Zhipeng Xie <xiezhipeng1@huawei.com>
Date: Wed, 30 Dec 2020 21:13:10 -0500
Subject: [PATCH 20/24] support remove static variables using
 KPATCH_IGNORE_STATIC

Static variables will be removed due to compiler optimization.
And some static variables can be treated as new variables, such as
static variables in print limit macros. So add KPATCH_IGNORE_STATIC
to tell kpatch to treat the static variables as new variables.

Signed-off-by: Zhipeng Xie <xiezhipeng1@huawei.com>
---
 kmod/patch/kpatch-macros.h        |  4 +++
 kpatch-build/create-diff-object.c | 45 ++++++++++++++++++++++++++++++-
 2 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/kmod/patch/kpatch-macros.h b/kmod/patch/kpatch-macros.h
index caaadbc..ee455d2 100644
--- a/kmod/patch/kpatch-macros.h
+++ b/kmod/patch/kpatch-macros.h
@@ -12,6 +12,10 @@
 # define __kpatch_section(section) __section(#section)
 #endif
 
+#define KPATCH_IGNORE_STATIC(_static) \
+	char *__UNIQUE_ID(kpatch_ignore_static_) __section(.kpatch.ignore.statics) = _static;
+
+
 /*
  * KPATCH_IGNORE_SECTION macro
  *
diff --git a/kpatch-build/create-diff-object.c b/kpatch-build/create-diff-object.c
index 0bef022..f83000b 100644
--- a/kpatch-build/create-diff-object.c
+++ b/kpatch-build/create-diff-object.c
@@ -1345,6 +1345,40 @@ static struct rela *kpatch_find_static_twin_ref(struct section *rela_sec, struct
 	return NULL;
 }
 
+static int kpatch_mark_ignored_statics(struct kpatch_elf *kelf, struct symbol *sym)
+{
+	struct section *sec, *strsec;
+	struct rela *rela;
+	char *name;
+
+	sec = find_section_by_name(&kelf->sections, ".kpatch.ignore.statics");
+	if (!sec)
+		return 0;
+
+	list_for_each_entry(rela, &sec->rela->relas, list) {
+		strsec = rela->sym->sec;
+		strsec->status = CHANGED;
+		/*
+		 * Include the string section here.  This is because the
+		 * KPATCH_IGNORE_STATIC() macro is passed a literal string
+		 * by the patch author, resulting in a change to the string
+		 * section.  If we don't include it, then we will potentially
+		 * get a "changed section not included" error in
+		 * kpatch_verify_patchability() if no other function based change
+		 * also changes the string section.  We could try to exclude each
+		 * literal string added to the section by KPATCH_IGNORE_STATIC()
+		 * from the section data comparison, but this is a simpler way.
+		 */
+		strsec->include = 1;
+		strsec->secsym->include = 1;
+		name = strsec->data->d_buf + rela->addend;
+		if (!strncmp(name, sym->name, strlen(name)))
+			return 1;
+	}
+
+	return 0;
+}
+
 /*
  * gcc renames static local variables by appending a period and a number.  For
  * example, __foo could be renamed to __foo.31452.  Unfortunately this number
@@ -1425,6 +1459,11 @@ static void kpatch_correlate_static_local_variables(struct kpatch_elf *orig,
 			if (sym->twin)
 				continue;
 
+			if (kpatch_mark_ignored_statics(patched, sym)) {
+				log_normal("KPATCH_IGNORE_STATIC:ignore static variable %s\n", sym->name);
+				continue;
+			}
+
 			bundled = sym == sym->sec->sym;
 			if (bundled && sym->sec == sec->base) {
 				/*
@@ -1482,6 +1521,11 @@ static void kpatch_correlate_static_local_variables(struct kpatch_elf *orig,
 			if (!kpatch_is_normal_static_local(sym))
 				continue;
 
+			if (kpatch_mark_ignored_statics(patched, sym)) {
+				log_normal("KPATCH_IGNORE_STATIC:ignore static variable %s\n", sym->name);
+				continue;
+			}
+
 			if (!sec->twin && sec->base->sym) {
 				struct symbol *parent = NULL;
 
@@ -1525,7 +1569,6 @@ static void kpatch_correlate_static_local_variables(struct kpatch_elf *orig,
 			log_normal("WARNING: unable to correlate static local variable %s used by %s, assuming variable is new\n",
 				   sym->name,
 				   kpatch_section_function_name(sec));
-			return;
 		}
 	}
 }
-- 
2.23.0