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Message-ID: <159559214141.4006.8712776602481546473.tip-bot2@tip-bot2>
Date: Fri, 24 Jul 2020 12:02:21 -0000
From: "tip-bot2 for Ingo Molnar" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
Ingo Molnar <mingo@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Borislav Petkov <bp@...en8.de>,
Peter Zijlstra <peterz@...radead.org>, x86 <x86@...nel.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: [tip: core/headers] compiler.h: Move instrumentation_begin()/end() to
new <linux/instrumentation.h> header
The following commit has been merged into the core/headers branch of tip:
Commit-ID: d19e789f068b3d633cbac430764962f404198022
Gitweb: https://git.kernel.org/tip/d19e789f068b3d633cbac430764962f404198022
Author: Ingo Molnar <mingo@...nel.org>
AuthorDate: Fri, 24 Jul 2020 13:50:25 +02:00
Committer: Ingo Molnar <mingo@...nel.org>
CommitterDate: Fri, 24 Jul 2020 13:56:23 +02:00
compiler.h: Move instrumentation_begin()/end() to new <linux/instrumentation.h> header
Linus pointed out that compiler.h - which is a key header that gets included in every
single one of the 28,000+ kernel files during a kernel build - was bloated in:
655389666643: ("vmlinux.lds.h: Create section for protection against instrumentation")
Linus noted:
> I have pulled this, but do we really want to add this to a header file
> that is _so_ core that it gets included for basically every single
> file built?
>
> I don't even see those instrumentation_begin/end() things used
> anywhere right now.
>
> It seems excessive. That 53 lines is maybe not a lot, but it pushed
> that header file to over 12kB, and while it's mostly comments, it's
> extra IO and parsing basically for _every_ single file compiled in the
> kernel.
>
> For what appears to be absolutely zero upside right now, and I really
> don't see why this should be in such a core header file!
Move these primitives into a new header: <linux/instrumentation.h>, and include that
header in the headers that make use of it.
Unfortunately one of these headers is asm-generic/bug.h, which does get included
in a lot of places, similarly to compiler.h. So the de-bloating effect isn't as
good as we'd like it to be - but at least the interfaces are defined separately.
No change to functionality intended.
Reported-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Link: https://lore.kernel.org/r/20200604071921.GA1361070@gmail.com
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Peter Zijlstra <peterz@...radead.org>
---
arch/x86/include/asm/bug.h | 1 +-
include/asm-generic/bug.h | 1 +-
include/linux/compiler.h | 53 +-----------------------------
include/linux/context_tracking.h | 2 +-
include/linux/instrumentation.h | 57 +++++++++++++++++++++++++++++++-
5 files changed, 61 insertions(+), 53 deletions(-)
create mode 100644 include/linux/instrumentation.h
diff --git a/arch/x86/include/asm/bug.h b/arch/x86/include/asm/bug.h
index 0281895..297fa12 100644
--- a/arch/x86/include/asm/bug.h
+++ b/arch/x86/include/asm/bug.h
@@ -3,6 +3,7 @@
#define _ASM_X86_BUG_H
#include <linux/stringify.h>
+#include <linux/instrumentation.h>
/*
* Despite that some emulators terminate on UD2, we use it for WARN().
diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h
index c94e33a..18b0f4e 100644
--- a/include/asm-generic/bug.h
+++ b/include/asm-generic/bug.h
@@ -3,6 +3,7 @@
#define _ASM_GENERIC_BUG_H
#include <linux/compiler.h>
+#include <linux/instrumentation.h>
#define CUT_HERE "------------[ cut here ]------------\n"
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 204e768..681894b 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -120,65 +120,12 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
/* Annotate a C jump table to allow objtool to follow the code flow */
#define __annotate_jump_table __section(.rodata..c_jump_table)
-#ifdef CONFIG_DEBUG_ENTRY
-/* Begin/end of an instrumentation safe region */
-#define instrumentation_begin() ({ \
- asm volatile("%c0: nop\n\t" \
- ".pushsection .discard.instr_begin\n\t" \
- ".long %c0b - .\n\t" \
- ".popsection\n\t" : : "i" (__COUNTER__)); \
-})
-
-/*
- * Because instrumentation_{begin,end}() can nest, objtool validation considers
- * _begin() a +1 and _end() a -1 and computes a sum over the instructions.
- * When the value is greater than 0, we consider instrumentation allowed.
- *
- * There is a problem with code like:
- *
- * noinstr void foo()
- * {
- * instrumentation_begin();
- * ...
- * if (cond) {
- * instrumentation_begin();
- * ...
- * instrumentation_end();
- * }
- * bar();
- * instrumentation_end();
- * }
- *
- * If instrumentation_end() would be an empty label, like all the other
- * annotations, the inner _end(), which is at the end of a conditional block,
- * would land on the instruction after the block.
- *
- * If we then consider the sum of the !cond path, we'll see that the call to
- * bar() is with a 0-value, even though, we meant it to happen with a positive
- * value.
- *
- * To avoid this, have _end() be a NOP instruction, this ensures it will be
- * part of the condition block and does not escape.
- */
-#define instrumentation_end() ({ \
- asm volatile("%c0: nop\n\t" \
- ".pushsection .discard.instr_end\n\t" \
- ".long %c0b - .\n\t" \
- ".popsection\n\t" : : "i" (__COUNTER__)); \
-})
-#endif /* CONFIG_DEBUG_ENTRY */
-
#else
#define annotate_reachable()
#define annotate_unreachable()
#define __annotate_jump_table
#endif
-#ifndef instrumentation_begin
-#define instrumentation_begin() do { } while(0)
-#define instrumentation_end() do { } while(0)
-#endif
-
#ifndef ASM_UNREACHABLE
# define ASM_UNREACHABLE
#endif
diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
index 981b880..d53cd33 100644
--- a/include/linux/context_tracking.h
+++ b/include/linux/context_tracking.h
@@ -5,6 +5,8 @@
#include <linux/sched.h>
#include <linux/vtime.h>
#include <linux/context_tracking_state.h>
+#include <linux/instrumentation.h>
+
#include <asm/ptrace.h>
diff --git a/include/linux/instrumentation.h b/include/linux/instrumentation.h
new file mode 100644
index 0000000..93e2ad6
--- /dev/null
+++ b/include/linux/instrumentation.h
@@ -0,0 +1,57 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __LINUX_INSTRUMENTATION_H
+#define __LINUX_INSTRUMENTATION_H
+
+#if defined(CONFIG_DEBUG_ENTRY) && defined(CONFIG_STACK_VALIDATION)
+
+/* Begin/end of an instrumentation safe region */
+#define instrumentation_begin() ({ \
+ asm volatile("%c0: nop\n\t" \
+ ".pushsection .discard.instr_begin\n\t" \
+ ".long %c0b - .\n\t" \
+ ".popsection\n\t" : : "i" (__COUNTER__)); \
+})
+
+/*
+ * Because instrumentation_{begin,end}() can nest, objtool validation considers
+ * _begin() a +1 and _end() a -1 and computes a sum over the instructions.
+ * When the value is greater than 0, we consider instrumentation allowed.
+ *
+ * There is a problem with code like:
+ *
+ * noinstr void foo()
+ * {
+ * instrumentation_begin();
+ * ...
+ * if (cond) {
+ * instrumentation_begin();
+ * ...
+ * instrumentation_end();
+ * }
+ * bar();
+ * instrumentation_end();
+ * }
+ *
+ * If instrumentation_end() would be an empty label, like all the other
+ * annotations, the inner _end(), which is at the end of a conditional block,
+ * would land on the instruction after the block.
+ *
+ * If we then consider the sum of the !cond path, we'll see that the call to
+ * bar() is with a 0-value, even though, we meant it to happen with a positive
+ * value.
+ *
+ * To avoid this, have _end() be a NOP instruction, this ensures it will be
+ * part of the condition block and does not escape.
+ */
+#define instrumentation_end() ({ \
+ asm volatile("%c0: nop\n\t" \
+ ".pushsection .discard.instr_end\n\t" \
+ ".long %c0b - .\n\t" \
+ ".popsection\n\t" : : "i" (__COUNTER__)); \
+})
+#else
+# define instrumentation_begin() do { } while(0)
+# define instrumentation_end() do { } while(0)
+#endif
+
+#endif /* __LINUX_INSTRUMENTATION_H */
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