From: Menglong Dong menglong8.dong@gmail.com
[ Upstream commit 35561bab768977c9e05f1f1a9bc00134c85f3e28 ]
The include/generated/asm-offsets.h is generated in Kbuild during compiling from arch/SRCARCH/kernel/asm-offsets.c. When we want to generate another similar offset header file, circular dependency can happen.
For example, we want to generate a offset file include/generated/test.h, which is included in include/sched/sched.h. If we generate asm-offsets.h first, it will fail, as include/sched/sched.h is included in asm-offsets.c and include/generated/test.h doesn't exist; If we generate test.h first, it can't success neither, as include/generated/asm-offsets.h is included by it.
In x86_64, the macro COMPILE_OFFSETS is used to avoid such circular dependency. We can generate asm-offsets.h first, and if the COMPILE_OFFSETS is defined, we don't include the "generated/test.h".
And we define the macro COMPILE_OFFSETS for all the asm-offsets.c for this purpose.
Signed-off-by: Menglong Dong dongml2@chinatelecom.cn Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Signed-off-by: Sasha Levin sashal@kernel.org ---
LLM Generated explanations, may be completely bogus:
Based on my thorough investigation, I can now provide a comprehensive analysis of this commit.
## **Backport Analysis: COMPILE_OFFSETS Commit**
**Backport Status: YES** (with important conditions)
### Summary
This commit adds `#define COMPILE_OFFSETS` to all architecture-specific asm-offsets.c files. It is a **preparatory infrastructure patch** that enables the generation of additional offset header files while avoiding circular dependency issues during the kernel build process.
### Critical Context
This commit (upstream: 35561bab76897) is **inseparable** from its companion commit: - **378b7708194ff**: "sched: Make migrate_{en,dis}able() inline"
These two commits form a **mandatory pair** where: 1. The COMPILE_OFFSETS commit prepares the build infrastructure 2. The migrate_enable/disable commit actually uses this infrastructure to generate `include/generated/rq-offsets.h`
### Why This Should Be Backported
1. **Already being backported**: The companion commit (378b7708194ff) is already tagged for stable backport (as commit d0e888caa43cc shows `[ Upstream commit 378b7708194fff77c9020392067329931c3fcc04 ]`)
2. **Build dependency**: Without this COMPILE_OFFSETS commit, the migrate_enable/disable backport will **fail to build** due to circular dependency: - `asm-offsets.c` includes `<linux/sched.h>` - `<linux/sched.h>` will include `<generated/rq-offsets.h>` - But `rq-offsets.h` doesn't exist yet when generating `asm- offsets.h` - The COMPILE_OFFSETS macro allows conditional inclusion to break this cycle
3. **Performance improvement for BPF**: The complete patch series improves BPF FENTRY performance from ~113M/s to ~150M/s (27-32% improvement) by inlining migrate_enable/disable functions
4. **Low risk**: This commit only adds a simple `#define` to each asm- offsets.c file with no functional changes to any existing code paths
### Code Changes Analysis
The changes are identical across all 23 architectures: - **alpha, arc, arm, arm64, csky, hexagon, loongarch, m68k, microblaze, mips, nios2, openrisc, parisc, powerpc, riscv, s390, sh, sparc, um, xtensa**
Each file receives: ```c +#define COMPILE_OFFSETS ```
This macro is used in header files (specifically `include/linux/sched.h`) to conditionally guard includes: ```c #ifndef COMPILE_OFFSETS #include <generated/rq-offsets.h> #endif ```
### Dependencies
- **Must be backported together with**: commit 378b7708194ff - **Order matters**: COMPILE_OFFSETS must be applied first (or in same merge) - **No standalone value**: This commit has no effect without the follow- up changes
### Risk Assessment
- **Risk Level**: Low - **Regression Potential**: Minimal - only adds a preprocessor definition - **Testing**: Should build-test on all architectures - **Compatibility**: X86_64 already had this pattern since 2011 (commit b82fef82d567)
### References
- Upstream commits: 35561bab76897 (this one) → 378b7708194ff (migrate inline) - Author: Menglong Dong dongml2@chinatelecom.cn - Maintainer: Peter Zijlstra (Intel) peterz@infradead.org - Subsystem: Scheduler / Build infrastructure
**Conclusion**: This is a mandatory prerequisite patch that must be backported alongside its companion commit to avoid build breakage. The stable maintainers should ensure both patches are applied together in the correct order.
arch/alpha/kernel/asm-offsets.c | 1 + arch/arc/kernel/asm-offsets.c | 1 + arch/arm/kernel/asm-offsets.c | 2 ++ arch/arm64/kernel/asm-offsets.c | 1 + arch/csky/kernel/asm-offsets.c | 1 + arch/hexagon/kernel/asm-offsets.c | 1 + arch/loongarch/kernel/asm-offsets.c | 2 ++ arch/m68k/kernel/asm-offsets.c | 1 + arch/microblaze/kernel/asm-offsets.c | 1 + arch/mips/kernel/asm-offsets.c | 2 ++ arch/nios2/kernel/asm-offsets.c | 1 + arch/openrisc/kernel/asm-offsets.c | 1 + arch/parisc/kernel/asm-offsets.c | 1 + arch/powerpc/kernel/asm-offsets.c | 1 + arch/riscv/kernel/asm-offsets.c | 1 + arch/s390/kernel/asm-offsets.c | 1 + arch/sh/kernel/asm-offsets.c | 1 + arch/sparc/kernel/asm-offsets.c | 1 + arch/um/kernel/asm-offsets.c | 2 ++ arch/xtensa/kernel/asm-offsets.c | 1 + 20 files changed, 24 insertions(+)
diff --git a/arch/alpha/kernel/asm-offsets.c b/arch/alpha/kernel/asm-offsets.c index e9dad60b147f3..1ebb058904992 100644 --- a/arch/alpha/kernel/asm-offsets.c +++ b/arch/alpha/kernel/asm-offsets.c @@ -4,6 +4,7 @@ * This code generates raw asm output which is post-processed to extract * and format the required data. */ +#define COMPILE_OFFSETS
#include <linux/types.h> #include <linux/stddef.h> diff --git a/arch/arc/kernel/asm-offsets.c b/arch/arc/kernel/asm-offsets.c index f77deb7991757..2978da85fcb65 100644 --- a/arch/arc/kernel/asm-offsets.c +++ b/arch/arc/kernel/asm-offsets.c @@ -2,6 +2,7 @@ /* * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com) */ +#define COMPILE_OFFSETS
#include <linux/sched.h> #include <linux/mm.h> diff --git a/arch/arm/kernel/asm-offsets.c b/arch/arm/kernel/asm-offsets.c index 123f4a8ef4466..2101938d27fcb 100644 --- a/arch/arm/kernel/asm-offsets.c +++ b/arch/arm/kernel/asm-offsets.c @@ -7,6 +7,8 @@ * This code generates raw asm output which is post-processed to extract * and format the required data. */ +#define COMPILE_OFFSETS + #include <linux/compiler.h> #include <linux/sched.h> #include <linux/mm.h> diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c index 30d4bbe68661f..b6367ff3a49ca 100644 --- a/arch/arm64/kernel/asm-offsets.c +++ b/arch/arm64/kernel/asm-offsets.c @@ -6,6 +6,7 @@ * 2001-2002 Keith Owens * Copyright (C) 2012 ARM Ltd. */ +#define COMPILE_OFFSETS
#include <linux/arm_sdei.h> #include <linux/sched.h> diff --git a/arch/csky/kernel/asm-offsets.c b/arch/csky/kernel/asm-offsets.c index d1e9035794733..5525c8e7e1d9e 100644 --- a/arch/csky/kernel/asm-offsets.c +++ b/arch/csky/kernel/asm-offsets.c @@ -1,5 +1,6 @@ // SPDX-License-Identifier: GPL-2.0 // Copyright (C) 2018 Hangzhou C-SKY Microsystems co.,ltd. +#define COMPILE_OFFSETS
#include <linux/sched.h> #include <linux/kernel_stat.h> diff --git a/arch/hexagon/kernel/asm-offsets.c b/arch/hexagon/kernel/asm-offsets.c index 03a7063f94561..50eea9fa6f137 100644 --- a/arch/hexagon/kernel/asm-offsets.c +++ b/arch/hexagon/kernel/asm-offsets.c @@ -8,6 +8,7 @@ * * Copyright (c) 2010-2012, The Linux Foundation. All rights reserved. */ +#define COMPILE_OFFSETS
#include <linux/compat.h> #include <linux/types.h> diff --git a/arch/loongarch/kernel/asm-offsets.c b/arch/loongarch/kernel/asm-offsets.c index db1e4bb26b6a0..3017c71576009 100644 --- a/arch/loongarch/kernel/asm-offsets.c +++ b/arch/loongarch/kernel/asm-offsets.c @@ -4,6 +4,8 @@ * * Copyright (C) 2020-2022 Loongson Technology Corporation Limited */ +#define COMPILE_OFFSETS + #include <linux/types.h> #include <linux/sched.h> #include <linux/mm.h> diff --git a/arch/m68k/kernel/asm-offsets.c b/arch/m68k/kernel/asm-offsets.c index 906d732305374..67a1990f9d748 100644 --- a/arch/m68k/kernel/asm-offsets.c +++ b/arch/m68k/kernel/asm-offsets.c @@ -9,6 +9,7 @@ * #defines from the assembly-language output. */
+#define COMPILE_OFFSETS #define ASM_OFFSETS_C
#include <linux/stddef.h> diff --git a/arch/microblaze/kernel/asm-offsets.c b/arch/microblaze/kernel/asm-offsets.c index 104c3ac5f30c8..b4b67d58e7f6a 100644 --- a/arch/microblaze/kernel/asm-offsets.c +++ b/arch/microblaze/kernel/asm-offsets.c @@ -7,6 +7,7 @@ * License. See the file "COPYING" in the main directory of this archive * for more details. */ +#define COMPILE_OFFSETS
#include <linux/init.h> #include <linux/stddef.h> diff --git a/arch/mips/kernel/asm-offsets.c b/arch/mips/kernel/asm-offsets.c index 1e29efcba46e5..5debd9a3854a9 100644 --- a/arch/mips/kernel/asm-offsets.c +++ b/arch/mips/kernel/asm-offsets.c @@ -9,6 +9,8 @@ * Kevin Kissell, kevink@mips.com and Carsten Langgaard, carstenl@mips.com * Copyright (C) 2000 MIPS Technologies, Inc. */ +#define COMPILE_OFFSETS + #include <linux/compat.h> #include <linux/types.h> #include <linux/sched.h> diff --git a/arch/nios2/kernel/asm-offsets.c b/arch/nios2/kernel/asm-offsets.c index e3d9b7b6fb48a..88190b503ce5d 100644 --- a/arch/nios2/kernel/asm-offsets.c +++ b/arch/nios2/kernel/asm-offsets.c @@ -2,6 +2,7 @@ /* * Copyright (C) 2011 Tobias Klauser tklauser@distanz.ch */ +#define COMPILE_OFFSETS
#include <linux/stddef.h> #include <linux/sched.h> diff --git a/arch/openrisc/kernel/asm-offsets.c b/arch/openrisc/kernel/asm-offsets.c index 710651d5aaae1..3cc826f2216b1 100644 --- a/arch/openrisc/kernel/asm-offsets.c +++ b/arch/openrisc/kernel/asm-offsets.c @@ -18,6 +18,7 @@ * compile this file to assembler, and then extract the * #defines from the assembly-language output. */ +#define COMPILE_OFFSETS
#include <linux/signal.h> #include <linux/sched.h> diff --git a/arch/parisc/kernel/asm-offsets.c b/arch/parisc/kernel/asm-offsets.c index 757816a7bd4b2..9abfe65492c65 100644 --- a/arch/parisc/kernel/asm-offsets.c +++ b/arch/parisc/kernel/asm-offsets.c @@ -13,6 +13,7 @@ * Copyright (C) 2002 Randolph Chung <tausq with parisc-linux.org> * Copyright (C) 2003 James Bottomley <jejb at parisc-linux.org> */ +#define COMPILE_OFFSETS
#include <linux/types.h> #include <linux/sched.h> diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c index b3048f6d3822c..a4bc80b30410a 100644 --- a/arch/powerpc/kernel/asm-offsets.c +++ b/arch/powerpc/kernel/asm-offsets.c @@ -8,6 +8,7 @@ * compile this file to assembler, and then extract the * #defines from the assembly-language output. */ +#define COMPILE_OFFSETS
#include <linux/compat.h> #include <linux/signal.h> diff --git a/arch/riscv/kernel/asm-offsets.c b/arch/riscv/kernel/asm-offsets.c index 6e8c0d6feae9e..7d42d3b8a32a7 100644 --- a/arch/riscv/kernel/asm-offsets.c +++ b/arch/riscv/kernel/asm-offsets.c @@ -3,6 +3,7 @@ * Copyright (C) 2012 Regents of the University of California * Copyright (C) 2017 SiFive */ +#define COMPILE_OFFSETS
#include <linux/kbuild.h> #include <linux/mm.h> diff --git a/arch/s390/kernel/asm-offsets.c b/arch/s390/kernel/asm-offsets.c index 95ecad9c7d7d2..a8915663e917f 100644 --- a/arch/s390/kernel/asm-offsets.c +++ b/arch/s390/kernel/asm-offsets.c @@ -4,6 +4,7 @@ * This code generates raw asm output which is post-processed to extract * and format the required data. */ +#define COMPILE_OFFSETS
#include <linux/kbuild.h> #include <linux/sched.h> diff --git a/arch/sh/kernel/asm-offsets.c b/arch/sh/kernel/asm-offsets.c index a0322e8328456..429b6a7631468 100644 --- a/arch/sh/kernel/asm-offsets.c +++ b/arch/sh/kernel/asm-offsets.c @@ -8,6 +8,7 @@ * compile this file to assembler, and then extract the * #defines from the assembly-language output. */ +#define COMPILE_OFFSETS
#include <linux/stddef.h> #include <linux/types.h> diff --git a/arch/sparc/kernel/asm-offsets.c b/arch/sparc/kernel/asm-offsets.c index 3d9b9855dce91..6e660bde48dd8 100644 --- a/arch/sparc/kernel/asm-offsets.c +++ b/arch/sparc/kernel/asm-offsets.c @@ -10,6 +10,7 @@ * * On sparc, thread_info data is static and TI_XXX offsets are computed by hand. */ +#define COMPILE_OFFSETS
#include <linux/sched.h> #include <linux/mm_types.h> diff --git a/arch/um/kernel/asm-offsets.c b/arch/um/kernel/asm-offsets.c index 1fb12235ab9c8..a69873aa697f4 100644 --- a/arch/um/kernel/asm-offsets.c +++ b/arch/um/kernel/asm-offsets.c @@ -1 +1,3 @@ +#define COMPILE_OFFSETS + #include <sysdep/kernel-offsets.h> diff --git a/arch/xtensa/kernel/asm-offsets.c b/arch/xtensa/kernel/asm-offsets.c index da38de20ae598..cfbced95e944a 100644 --- a/arch/xtensa/kernel/asm-offsets.c +++ b/arch/xtensa/kernel/asm-offsets.c @@ -11,6 +11,7 @@ * * Chris Zankel chris@zankel.net */ +#define COMPILE_OFFSETS
#include <asm/processor.h> #include <asm/coprocessor.h>