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k_current_get(): make it a "const" function

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This function always returns the same value for a given thread.
Add the const attribute to it so the compiler won't call it over and
over needlessly each time _current is referenced, making for far more
efficient code.

The __attribute_const__ symbol is used to mimic the Linux equivalent.
We want to make it clear that this is distinct from the const keyword.

Fix the test_x86_cpu_scrubs_regs where the compiler wasn't told that a
bunch of registers are being clobbered as highlighted by this change.

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>
This commit is contained in:
Nicolas Pitre 2021-04-09 00:40:41 -04:00 • committed by Anas Nashif
commit 0dc7b9ee46
4 changed files with 22 additions and 15 deletions
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1
doc/conf.py
View file

@ -180,6 +180,7 @@ cpp_id_attributes = [
"__used",
"__unused",
"__weak",
"__attribute_const__",
"__DEPRECATED_MACRO",
"FUNC_NORETURN",
"__subsystem",

2
include/kernel.h
View file

@ -528,7 +528,7 @@ __syscall void k_wakeup(k_tid_t thread);
* @return ID of current thread.
*
*/
__syscall k_tid_t k_current_get(void);
__syscall k_tid_t k_current_get(void) __attribute_const__;
/**
* @brief Abort a thread.

3
include/toolchain/gcc.h
View file

@ -190,6 +190,9 @@ do { \
#ifndef __deprecated
#define __deprecated __attribute__((deprecated))
#endif
#ifndef __attribute_const__
#define __attribute_const__ __attribute__((__const__))
#endif
#define ARG_UNUSED(x) (void)(x)
#define likely(x) __builtin_expect((bool)!!(x), true)

31
tests/arch/x86/cpu_scrubs_regs/src/main.c
View file

@ -27,23 +27,26 @@ void z_impl_test_cpu_write_reg(void)
#if CONFIG_X86
#ifndef CONFIG_X86_64
__asm__ volatile (
"movl $0xDEADBEEF, %eax;\n\t"
"movl $0xDEADBEEF, %ebx;\n\t"
"movl $0xDEADBEEF, %ecx;\n\t"
"movl $0xDEADBEEF, %edx;\n\t"
"movl $0xDEADBEEF, %edi;\n\t"
"movl $0xDEADBEEF, %%eax;\n\t"
"movl $0xDEADBEEF, %%ebx;\n\t"
"movl $0xDEADBEEF, %%ecx;\n\t"
"movl $0xDEADBEEF, %%edx;\n\t"
"movl $0xDEADBEEF, %%edi;\n\t"
: : : "eax", "ebx", "ecx", "edx", "edi"
);
#else
__asm__ volatile (
"movq $0xDEADBEEF, %rax;\n\t"
"movq $0xDEADBEEF, %rcx;\n\t"
"movq $0xDEADBEEF, %rdx;\n\t"
"movq $0xDEADBEEF, %rsi;\n\t"
"movq $0xDEADBEEF, %rdi;\n\t"
"movq $0xDEADBEEF, %r8;\n\t"
"movq $0xDEADBEEF, %r9;\n\t"
"movq $0xDEADBEEF, %r10;\n\t"
"movq $0xDEADBEEF, %r11;\n\t"
"movq $0xDEADBEEF, %%rax;\n\t"
"movq $0xDEADBEEF, %%rcx;\n\t"
"movq $0xDEADBEEF, %%rdx;\n\t"
"movq $0xDEADBEEF, %%rsi;\n\t"
"movq $0xDEADBEEF, %%rdi;\n\t"
"movq $0xDEADBEEF, %%r8;\n\t"
"movq $0xDEADBEEF, %%r9;\n\t"
"movq $0xDEADBEEF, %%r10;\n\t"
"movq $0xDEADBEEF, %%r11;\n\t"
: : : "rax", "rcx", "rdx", "rsi", "rdi",
"r8", "r9", "r10", "r11"
);
#endif
#endif