kpatch/0026-support-remove-static-variables-using-KPATCH_IGNORE_.patch

From 0e08aa99583573953367d5c1ec21901325c7faee Mon Sep 17 00:00:00 2001
From: Zhipeng Xie <xiezhipeng1@huawei.com>
Date: Wed, 30 Dec 2020 21:13:10 -0500
Subject: [PATCH] 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        |  3 +++
 kpatch-build/create-diff-object.c | 45 ++++++++++++++++++++++++++++++-
 2 files changed, 47 insertions(+), 1 deletion(-)

diff --git a/kmod/patch/kpatch-macros.h b/kmod/patch/kpatch-macros.h
index a60a267..9a30d68 100644
--- a/kmod/patch/kpatch-macros.h
+++ b/kmod/patch/kpatch-macros.h
@@ -5,6 +5,9 @@
 #include <linux/jiffies.h>
 #include <linux/version.h>
 
+#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 a2a9cab..211ea72 100644
--- a/kpatch-build/create-diff-object.c
+++ b/kpatch-build/create-diff-object.c
@@ -1151,6 +1151,40 @@ static int kpatch_is_normal_static_local(struct symbol *sym)
 	return 1;
 }
 
+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
@@ -1230,6 +1264,11 @@ static void kpatch_correlate_static_local_variables(struct kpatch_elf *base,
 			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) {
 				/*
@@ -1286,6 +1325,11 @@ static void kpatch_correlate_static_local_variables(struct kpatch_elf *base,
 			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 (!sym->twin || !sec->twin)
 				DIFF_FATAL("reference to static local variable %s in %s was removed",
 					   sym->name,
@@ -1329,7 +1373,6 @@ static void kpatch_correlate_static_local_variables(struct kpatch_elf *base,
 			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;
 		}
 	}
 }
-- 
2.18.1