[PATCH] kernel: trace: do not generate undefsyms_base.c

[Paolo Bonzini]

The code to autogenerate undefsyms_base.c in the Makefile is larger
than the file itself.

Remove the "echo" indirection that creates the file, which keeps
the build system sane and makes it much easier to edit it if/when
new situations arrive.

Reported-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
 kernel/trace/.gitignore       |  1 -
 kernel/trace/Makefile         | 35 ++++-------------------------------
 kernel/trace/undefsyms_base.c | 28 ++++++++++++++++++++++++++++
 3 files changed, 32 insertions(+), 32 deletions(-)
 delete mode 100644 kernel/trace/.gitignore
 create mode 100644 kernel/trace/undefsyms_base.c

diff --git a/kernel/trace/.gitignore b/kernel/trace/.gitignore
deleted file mode 100644
index 6adbb09d6deb..000000000000
--- a/kernel/trace/.gitignore
+++ /dev/null
@@ -1 +0,0 @@
-/undefsyms_base.c
diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
index 4d4229e5eec4..1decdce8cbef 100644
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -133,41 +133,14 @@ obj-$(CONFIG_TRACE_REMOTE) += trace_remote.o
 obj-$(CONFIG_SIMPLE_RING_BUFFER) += simple_ring_buffer.o
 obj-$(CONFIG_TRACE_REMOTE_TEST) += remote_test.o
 
-#
 # simple_ring_buffer is used by the pKVM hypervisor which does not have access
 # to all kernel symbols. Fail the build if forbidden symbols are found.
-#
-# undefsyms_base generates a set of compiler and tooling-generated symbols that can
-# safely be ignored for simple_ring_buffer.
-#
-filechk_undefsyms_base = \
-	echo '$(pound)include <linux/atomic.h>'; \
-	echo '$(pound)include <linux/string.h>'; \
-	echo '$(pound)include <asm/page.h>'; \
-	echo 'static char page[PAGE_SIZE] __aligned(PAGE_SIZE);'; \
-	echo 'void undefsyms_base(void *p, int n);'; \
-	echo 'void undefsyms_base(void *p, int n) {'; \
-	echo '	char buffer[256] = { 0 };'; \
-	echo '	u32 u = 0;'; \
-	echo '	memset((char * volatile)page, 8, PAGE_SIZE);'; \
-	echo '	memset((char * volatile)buffer, 8, sizeof(buffer));'; \
-	echo '	memcpy((void * volatile)p, buffer, sizeof(buffer));'; \
-	echo '	cmpxchg((u32 * volatile)&u, 0, 8);'; \
-	echo '	WARN_ON(n == 0xdeadbeef);'; \
-	echo '}'
-
-$(obj)/undefsyms_base.c: FORCE
-	$(call filechk,undefsyms_base)
-
-clean-files += undefsyms_base.c
-
-$(obj)/undefsyms_base.o: $(obj)/undefsyms_base.c
 
+# Basic compiler and tooling-generated symbols that can safely be left
+# undefined. Ensure KASAN is enabled to avoid logic that may disable
+# FORTIFY_SOURCE when KASAN is not enabled. undefsyms_base.o does not
+# automatically get KASAN flags because it is not linked into vmlinux.
 targets += undefsyms_base.o
-
-# Ensure KASAN is enabled to avoid logic that may disable FORTIFY_SOURCE when
-# KASAN is not enabled. undefsyms_base.o does not automatically get KASAN flags
-# because it is not linked into vmlinux.
 KASAN_SANITIZE_undefsyms_base.o := y
 
 UNDEFINED_ALLOWLIST = __asan __gcov __kasan __kcsan __hwasan __sancov __sanitizer __tsan __ubsan __x86_indirect_thunk \
diff --git a/kernel/trace/undefsyms_base.c b/kernel/trace/undefsyms_base.c
new file mode 100644
index 000000000000..e65baf58e6ff
--- /dev/null
+++ b/kernel/trace/undefsyms_base.c
@@ -0,0 +1,28 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * simple_ring_buffer is used by the pKVM hypervisor which does not have access
+ * to all kernel symbols.  Whatever is undefined when compiling this file is
+ * compiler and tooling-generated symbols that can safely be ignored for
+ * simple_ring_buffer.
+ */
+
+#include <linux/atomic.h>
+#include <linux/string.h>
+#include <asm/page.h>
+
+void undefsyms_base(void *p, int n);
+
+static char page[PAGE_SIZE] __aligned(PAGE_SIZE);
+
+void undefsyms_base(void *p, int n)
+{
+	char buffer[256] = { 0 };
+
+	u32 u = 0;
+	memset((char * volatile)page, 8, PAGE_SIZE);
+	memset((char * volatile)buffer, 8, sizeof(buffer));
+	memcpy((void * volatile)p, buffer, sizeof(buffer));
+	cmpxchg((u32 * volatile)&u, 0, 8);
+	WARN_ON(n == 0xdeadbeef);
+}
-- 
2.53.0