Messages in this thread | | | Date | Sun, 5 Apr 2020 18:08:59 -0700 | From | Fangrui Song <> | Subject | Re: [RESEND][PATCH v3 09/17] x86/static_call: Add out-of-line static call implementation |
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On 2020-03-24, Peter Zijlstra wrote: >Add the x86 out-of-line static call implementation. For each key, a >permanent trampoline is created which is the destination for all static >calls for the given key. The trampoline has a direct jump which gets >patched by static_call_update() when the destination function changes. > >Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> >[peterz: fixed trampoline, rewrote patching code] >Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> >--- > arch/x86/Kconfig | 1 + > arch/x86/include/asm/static_call.h | 22 ++++++++++++++++++++++ > arch/x86/kernel/Makefile | 1 + > arch/x86/kernel/static_call.c | 31 +++++++++++++++++++++++++++++++ > 4 files changed, 55 insertions(+) > create mode 100644 arch/x86/include/asm/static_call.h > create mode 100644 arch/x86/kernel/static_call.c > >--- a/arch/x86/Kconfig >+++ b/arch/x86/Kconfig >@@ -205,6 +205,7 @@ config X86 > select HAVE_FUNCTION_ARG_ACCESS_API > select HAVE_STACKPROTECTOR if CC_HAS_SANE_STACKPROTECTOR > select HAVE_STACK_VALIDATION if X86_64 >+ select HAVE_STATIC_CALL > select HAVE_RSEQ > select HAVE_SYSCALL_TRACEPOINTS > select HAVE_UNSTABLE_SCHED_CLOCK >--- /dev/null >+++ b/arch/x86/include/asm/static_call.h >@@ -0,0 +1,22 @@ >+/* SPDX-License-Identifier: GPL-2.0 */ >+#ifndef _ASM_STATIC_CALL_H >+#define _ASM_STATIC_CALL_H >+ >+#include <asm/text-patching.h> >+ >+/* >+ * For CONFIG_HAVE_STATIC_CALL, this is a permanent trampoline which >+ * does a direct jump to the function. The direct jump gets patched by >+ * static_call_update(). >+ */ >+#define ARCH_DEFINE_STATIC_CALL_TRAMP(name, func) \ >+ asm(".pushsection .text, \"ax\" \n" \ >+ ".align 4 \n" \ >+ ".globl " STATIC_CALL_TRAMP_STR(name) " \n" \ >+ STATIC_CALL_TRAMP_STR(name) ": \n" \ >+ " jmp.d32 " #func " \n" \ >+ ".type " STATIC_CALL_TRAMP_STR(name) ", @function \n" \ >+ ".size " STATIC_CALL_TRAMP_STR(name) ", . - " STATIC_CALL_TRAMP_STR(name) " \n" \ >+ ".popsection \n") >+ >+#endif /* _ASM_STATIC_CALL_H */
Hi Peter,
Coming here from https://github.com/ClangBuiltLinux/linux/issues/974
jmp.d32 is not recognized by clang integrated assembler. The syntax appears to be very rarely used. According to Debian Code Search, u-boot is the only project using this syntax.
In March 2017, gas added the pseudo prefix {disp32} https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=86fa6981e7487e2c2df4337aa75ed2d93c32eaf2 which generalizes jmp.d32 ({disp32} jmp foo)
I wonder whether the instruction jmp.d32 can be replaced with the trick in arch/x86/include/asm/jump_label.h for clang portability.
% grep -A2 'jmp.d32' arch/x86/include/asm/jump_label.h /* Equivalent to "jmp.d32 \target" */ .byte 0xe9 .long \target - .Lstatic_jump_after_\@ ...
+ clang-built-linux@googlegroups.com
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