tools/include/nolibc/arch-arm.h

Source file repositories/reference/linux-study-clean/tools/include/nolibc/arch-arm.h

File Facts

System
Linux kernel
Corpus path
tools/include/nolibc/arch-arm.h
Extension
.h
Size
10906 bytes
Lines
210
Domain
Support Tooling And Documentation
Bucket
tools
Inferred role
Support Tooling And Documentation: implementation source
Status
source implementation candidate

Why This File Exists

Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

Dependency Surface

Detected Declarations

Annotated Snippet

#ifndef _NOLIBC_ARCH_ARM_H
#define _NOLIBC_ARCH_ARM_H

#include <linux/unistd.h>

#include "compiler.h"
#include "crt.h"
#include "std.h"

/* Syscalls for ARM in ARM or Thumb modes :
 *   - registers are 32-bit
 *   - stack is 8-byte aligned
 *     ( http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.faqs/ka4127.html)
 *   - syscall number is passed in r7
 *   - arguments are in r0, r1, r2, r3, r4, r5
 *   - the system call is performed by calling svc #0
 *   - syscall return comes in r0.
 *   - only lr is clobbered.
 *   - the arguments are cast to long and assigned into the target registers
 *     which are then simply passed as registers to the asm code, so that we
 *     don't have to experience issues with register constraints.
 *   - the syscall number is always specified last in order to allow to force
 *     some registers before (gcc refuses a %-register at the last position).
 *   - in thumb mode without -fomit-frame-pointer, r7 is also used to store the
 *     frame pointer, and we cannot directly assign it as a register variable,
 *     nor can we clobber it. Instead we assign the r6 register and swap it
 *     with r7 before calling svc, and r6 is marked as clobbered.
 *     We're just using any regular register which we assign to r7 after saving
 *     it.
 *
 * Also, ARM supports the old_select syscall if newselect is not available
 */
#define __ARCH_WANT_SYS_OLD_SELECT

#if (defined(__THUMBEB__) || defined(__THUMBEL__)) && \
    !defined(NOLIBC_OMIT_FRAME_POINTER)
/* swap r6,r7 needed in Thumb mode since we can't use nor clobber r7 */
#define _NOLIBC_SYSCALL_REG         "r6"
#define _NOLIBC_THUMB_SET_R7        "eor r7, r6\neor r6, r7\neor r7, r6\n"
#define _NOLIBC_THUMB_RESTORE_R7    "mov r7, r6\n"

#else  /* we're in ARM mode */
/* in Arm mode we can directly use r7 */
#define _NOLIBC_SYSCALL_REG         "r7"
#define _NOLIBC_THUMB_SET_R7        ""
#define _NOLIBC_THUMB_RESTORE_R7    ""

#endif /* end THUMB */

#define __nolibc_syscall0(num)                                                \
({                                                                            \
	register long _num  __asm__(_NOLIBC_SYSCALL_REG) = (num);             \
	register long _arg1 __asm__ ("r0");                                   \
									      \
	__asm__ volatile (                                                    \
		_NOLIBC_THUMB_SET_R7                                          \
		"svc #0\n"                                                    \
		_NOLIBC_THUMB_RESTORE_R7                                      \
		: "=r"(_arg1), "=r"(_num)                                     \
		: "r"(_arg1),                                                 \
		  "r"(_num)                                                   \
		: "memory", "cc", "lr"                                        \
	);                                                                    \
	_arg1;                                                                \
})

#define __nolibc_syscall1(num, arg1)                                          \
({                                                                            \
	register long _num  __asm__(_NOLIBC_SYSCALL_REG) = (num);             \
	register long _arg1 __asm__ ("r0") = (long)(arg1);                    \
									      \
	__asm__ volatile (                                                    \
		_NOLIBC_THUMB_SET_R7                                          \
		"svc #0\n"                                                    \
		_NOLIBC_THUMB_RESTORE_R7                                      \
		: "=r"(_arg1), "=r" (_num)                                    \
		: "r"(_arg1),                                                 \
		  "r"(_num)                                                   \
		: "memory", "cc", "lr"                                        \
	);                                                                    \
	_arg1;                                                                \
})

#define __nolibc_syscall2(num, arg1, arg2)                                    \
({                                                                            \
	register long _num  __asm__(_NOLIBC_SYSCALL_REG) = (num);             \
	register long _arg1 __asm__ ("r0") = (long)(arg1);                    \
	register long _arg2 __asm__ ("r1") = (long)(arg2);                    \
									      \
	__asm__ volatile (                                                    \

Annotation

Implementation Notes