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91ff28ae6d050e0ca01ac13eb8ba31d744cf672f
clang is generating very inefficient code for native_save_fl() which is
used for local_irq_save() in critical spots.
Allowing the "pop %0" to use memory:
1) forces the compiler to add annoying stack canaries when
CONFIG_STACKPROTECTOR_STRONG=y in many places.
2) Almost always is followed by an immediate "move memory,register"
One good example is _raw_spin_lock_irqsave, with 8 extra instructions
ffffffff82067a30 <_raw_spin_lock_irqsave>:
ffffffff82067a30: ...
ffffffff82067a39: 53 push %rbx
// Three instructions to ajust the stack, read the per-cpu canary
// and copy it to 8(%rsp)
ffffffff82067a3a: 48 83 ec 10 sub $0x10,%rsp
ffffffff82067a3e: 65 48 8b 05 da 15 45 02 mov %gs:0x24515da(%rip),%rax # <__stack_chk_guard>
ffffffff82067a46: 48 89 44 24 08 mov %rax,0x8(%rsp)
ffffffff82067a4b: 9c pushf
// instead of pop %rbx, compiler uses 2 instructions.
ffffffff82067a4c: 8f 04 24 pop (%rsp)
ffffffff82067a4f: 48 8b 1c 24 mov (%rsp),%rbx
ffffffff82067a53: fa cli
ffffffff82067a54: b9 01 00 00 00 mov $0x1,%ecx
ffffffff82067a59: 31 c0 xor %eax,%eax
ffffffff82067a5b: f0 0f b1 0f lock cmpxchg %ecx,(%rdi)
ffffffff82067a5f: 75 1d jne ffffffff82067a7e <_raw_spin_lock_irqsave+0x4e>
// three instructions to check the stack canary
ffffffff82067a61: 65 48 8b 05 b7 15 45 02 mov %gs:0x24515b7(%rip),%rax # <__stack_chk_guard>
ffffffff82067a69: 48 3b 44 24 08 cmp 0x8(%rsp),%rax
ffffffff82067a6e: 75 17 jne ffffffff82067a87
...
// One extra instruction to adjust the stack.
ffffffff82067a73: 48 83 c4 10 add $0x10,%rsp
...
// One more instruction in case the stack was mangled.
ffffffff82067a87: e8 a4 35 ff ff call ffffffff8205b030 <__stack_chk_fail>
This patch changes nothing for gcc, but for clang saves ~20000 bytes of text
even though more functions are inlined.
$ size vmlinux.gcc.before vmlinux.gcc.after vmlinux.clang.before vmlinux.clang.after
text data bss dec hex filename
45565821 25005462 4704800 75276083 47c9f33 vmlinux.gcc.before
45565821 25005462 4704800 75276083 47c9f33 vmlinux.gcc.after
45121072 24638617 5533040 75292729 47ce039 vmlinux.clang.before
45093887 24638633 5536808 75269328 47c84d0 vmlinux.clang.after
$ scripts/bloat-o-meter -t vmlinux.clang.before vmlinux.clang.after
add/remove: 1/2 grow/shrink: 21/533 up/down: 2250/-22112 (-19862)
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
…
Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. Quick Start ----------- * Report a bug: See Documentation/admin-guide/reporting-issues.rst * Get the latest kernel: https://kernel.org * Build the kernel: See Documentation/admin-guide/quickly-build-trimmed-linux.rst * Join the community: https://lore.kernel.org/ Essential Documentation ----------------------- All users should be familiar with: * Building requirements: Documentation/process/changes.rst * Code of Conduct: Documentation/process/code-of-conduct.rst * License: See COPYING Documentation can be built with make htmldocs or viewed online at: https://www.kernel.org/doc/html/latest/ Who Are You? ============ Find your role below: * New Kernel Developer - Getting started with kernel development * Academic Researcher - Studying kernel internals and architecture * Security Expert - Hardening and vulnerability analysis * Backport/Maintenance Engineer - Maintaining stable kernels * System Administrator - Configuring and troubleshooting * Maintainer - Leading subsystems and reviewing patches * Hardware Vendor - Writing drivers for new hardware * Distribution Maintainer - Packaging kernels for distros For Specific Users ================== New Kernel Developer -------------------- Welcome! Start your kernel development journey here: * Getting Started: Documentation/process/development-process.rst * Your First Patch: Documentation/process/submitting-patches.rst * Coding Style: Documentation/process/coding-style.rst * Build System: Documentation/kbuild/index.rst * Development Tools: Documentation/dev-tools/index.rst * Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst * Core APIs: Documentation/core-api/index.rst Academic Researcher ------------------- Explore the kernel's architecture and internals: * Researcher Guidelines: Documentation/process/researcher-guidelines.rst * Memory Management: Documentation/mm/index.rst * Scheduler: Documentation/scheduler/index.rst * Networking Stack: Documentation/networking/index.rst * Filesystems: Documentation/filesystems/index.rst * RCU (Read-Copy Update): Documentation/RCU/index.rst * Locking Primitives: Documentation/locking/index.rst * Power Management: Documentation/power/index.rst Security Expert --------------- Security documentation and hardening guides: * Security Documentation: Documentation/security/index.rst * LSM Development: Documentation/security/lsm-development.rst * Self Protection: Documentation/security/self-protection.rst * Reporting Vulnerabilities: Documentation/process/security-bugs.rst * CVE Procedures: Documentation/process/cve.rst * Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst * Security Features: Documentation/userspace-api/seccomp_filter.rst Backport/Maintenance Engineer ----------------------------- Maintain and stabilize kernel versions: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * Backporting Guide: Documentation/process/backporting.rst * Applying Patches: Documentation/process/applying-patches.rst * Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git for Maintainers: Documentation/maintainer/configure-git.rst System Administrator -------------------- Configure, tune, and troubleshoot Linux systems: * Admin Guide: Documentation/admin-guide/index.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst * Tracing/Debugging: Documentation/trace/index.rst * Performance Security: Documentation/admin-guide/perf-security.rst * Hardware Monitoring: Documentation/hwmon/index.rst Maintainer ---------- Lead kernel subsystems and manage contributions: * Maintainer Handbook: Documentation/maintainer/index.rst * Pull Requests: Documentation/maintainer/pull-requests.rst * Managing Patches: Documentation/maintainer/modifying-patches.rst * Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst * Development Process: Documentation/process/maintainer-handbooks.rst * Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git Configuration: Documentation/maintainer/configure-git.rst Hardware Vendor --------------- Write drivers and support new hardware: * Driver API Guide: Documentation/driver-api/index.rst * Driver Model: Documentation/driver-api/driver-model/driver.rst * Device Drivers: Documentation/driver-api/infrastructure.rst * Bus Types: Documentation/driver-api/driver-model/bus.rst * Device Tree Bindings: Documentation/devicetree/bindings/ * Power Management: Documentation/driver-api/pm/index.rst * DMA API: Documentation/core-api/dma-api.rst Distribution Maintainer ----------------------- Package and distribute the kernel: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * ABI Documentation: Documentation/ABI/README * Kernel Configuration: Documentation/kbuild/kconfig.rst * Module Signing: Documentation/admin-guide/module-signing.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst Communication and Support ========================= * Mailing Lists: https://lore.kernel.org/ * IRC: #kernelnewbies on irc.oftc.net * Bugzilla: https://bugzilla.kernel.org/ * MAINTAINERS file: Lists subsystem maintainers and mailing lists * Email Clients: Documentation/process/email-clients.rst
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