2 * Compatibility mode system call entry point for x86-64.
4 * Copyright 2000-2002 Andi Kleen, SuSE Labs.
7 #include <asm/asm-offsets.h>
8 #include <asm/current.h>
10 #include <asm/ia32_unistd.h>
11 #include <asm/thread_info.h>
12 #include <asm/segment.h>
13 #include <asm/irqflags.h>
16 #include <asm/pgtable_types.h>
17 #include <asm/kaiser.h>
18 #include <linux/linkage.h>
19 #include <linux/err.h>
21 .section .entry.text, "ax"
24 * 32-bit SYSENTER entry.
26 * 32-bit system calls through the vDSO's __kernel_vsyscall enter here
27 * on 64-bit kernels running on Intel CPUs.
29 * The SYSENTER instruction, in principle, should *only* occur in the
30 * vDSO. In practice, a small number of Android devices were shipped
31 * with a copy of Bionic that inlined a SYSENTER instruction. This
32 * never happened in any of Google's Bionic versions -- it only happened
33 * in a narrow range of Intel-provided versions.
35 * SYSENTER loads SS, RSP, CS, and RIP from previously programmed MSRs.
36 * IF and VM in RFLAGS are cleared (IOW: interrupts are off).
37 * SYSENTER does not save anything on the stack,
38 * and does not save old RIP (!!!), RSP, or RFLAGS.
41 * eax system call number
50 ENTRY(entry_SYSENTER_compat)
51 /* Interrupts are off on entry. */
53 SWITCH_KERNEL_CR3_NO_STACK
54 movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
57 * User tracing code (ptrace or signal handlers) might assume that
58 * the saved RAX contains a 32-bit number when we're invoking a 32-bit
59 * syscall. Just in case the high bits are nonzero, zero-extend
60 * the syscall number. (This could almost certainly be deleted
61 * with no ill effects.)
65 /* Construct struct pt_regs on stack */
66 pushq $__USER32_DS /* pt_regs->ss */
67 pushq %rbp /* pt_regs->sp (stashed in bp) */
70 * Push flags. This is nasty. First, interrupts are currently
71 * off, but we need pt_regs->flags to have IF set. Second, even
72 * if TF was set when SYSENTER started, it's clear by now. We fix
73 * that later using TIF_SINGLESTEP.
75 pushfq /* pt_regs->flags (except IF = 0) */
76 orl $X86_EFLAGS_IF, (%rsp) /* Fix saved flags */
77 pushq $__USER32_CS /* pt_regs->cs */
78 pushq $0 /* pt_regs->ip = 0 (placeholder) */
79 pushq %rax /* pt_regs->orig_ax */
80 pushq %rdi /* pt_regs->di */
81 pushq %rsi /* pt_regs->si */
82 pushq %rdx /* pt_regs->dx */
83 pushq %rcx /* pt_regs->cx */
84 pushq $-ENOSYS /* pt_regs->ax */
85 pushq $0 /* pt_regs->r8 = 0 */
86 xorq %r8, %r8 /* nospec r8 */
87 pushq $0 /* pt_regs->r9 = 0 */
88 xorq %r9, %r9 /* nospec r9 */
89 pushq $0 /* pt_regs->r10 = 0 */
90 xorq %r10, %r10 /* nospec r10 */
91 pushq $0 /* pt_regs->r11 = 0 */
92 xorq %r11, %r11 /* nospec r11 */
93 pushq %rbx /* pt_regs->rbx */
94 xorl %ebx, %ebx /* nospec rbx */
95 pushq %rbp /* pt_regs->rbp (will be overwritten) */
96 xorl %ebp, %ebp /* nospec rbp */
97 pushq $0 /* pt_regs->r12 = 0 */
98 xorq %r12, %r12 /* nospec r12 */
99 pushq $0 /* pt_regs->r13 = 0 */
100 xorq %r13, %r13 /* nospec r13 */
101 pushq $0 /* pt_regs->r14 = 0 */
102 xorq %r14, %r14 /* nospec r14 */
103 pushq $0 /* pt_regs->r15 = 0 */
104 xorq %r15, %r15 /* nospec r15 */
108 * SYSENTER doesn't filter flags, so we need to clear NT and AC
109 * ourselves. To save a few cycles, we can check whether
110 * either was set instead of doing an unconditional popfq.
111 * This needs to happen before enabling interrupts so that
112 * we don't get preempted with NT set.
114 * If TF is set, we will single-step all the way to here -- do_debug
115 * will ignore all the traps. (Yes, this is slow, but so is
116 * single-stepping in general. This allows us to avoid having
117 * a more complicated code to handle the case where a user program
118 * forces us to single-step through the SYSENTER entry code.)
120 * NB.: .Lsysenter_fix_flags is a label with the code under it moved
121 * out-of-line as an optimization: NT is unlikely to be set in the
122 * majority of the cases and instead of polluting the I$ unnecessarily,
123 * we're keeping that code behind a branch which will predict as
124 * not-taken and therefore its instructions won't be fetched.
126 testl $X86_EFLAGS_NT|X86_EFLAGS_AC|X86_EFLAGS_TF, EFLAGS(%rsp)
127 jnz .Lsysenter_fix_flags
128 .Lsysenter_flags_fixed:
131 * User mode is traced as though IRQs are on, and SYSENTER
137 call do_fast_syscall_32
138 /* XEN PV guests always use IRET path */
139 ALTERNATIVE "testl %eax, %eax; jz .Lsyscall_32_done", \
140 "jmp .Lsyscall_32_done", X86_FEATURE_XENPV
141 jmp sysret32_from_system_call
143 .Lsysenter_fix_flags:
144 pushq $X86_EFLAGS_FIXED
146 jmp .Lsysenter_flags_fixed
147 GLOBAL(__end_entry_SYSENTER_compat)
148 ENDPROC(entry_SYSENTER_compat)
151 * 32-bit SYSCALL entry.
153 * 32-bit system calls through the vDSO's __kernel_vsyscall enter here
154 * on 64-bit kernels running on AMD CPUs.
156 * The SYSCALL instruction, in principle, should *only* occur in the
157 * vDSO. In practice, it appears that this really is the case.
160 * - The calling convention for SYSCALL has changed several times without
163 * - Prior to the in-kernel X86_BUG_SYSRET_SS_ATTRS fixup, anything
164 * user task that did SYSCALL without immediately reloading SS
165 * would randomly crash.
167 * - Most programmers do not directly target AMD CPUs, and the 32-bit
168 * SYSCALL instruction does not exist on Intel CPUs. Even on AMD
169 * CPUs, Linux disables the SYSCALL instruction on 32-bit kernels
170 * because the SYSCALL instruction in legacy/native 32-bit mode (as
171 * opposed to compat mode) is sufficiently poorly designed as to be
172 * essentially unusable.
174 * 32-bit SYSCALL saves RIP to RCX, clears RFLAGS.RF, then saves
175 * RFLAGS to R11, then loads new SS, CS, and RIP from previously
176 * programmed MSRs. RFLAGS gets masked by a value from another MSR
177 * (so CLD and CLAC are not needed). SYSCALL does not save anything on
178 * the stack and does not change RSP.
180 * Note: RFLAGS saving+masking-with-MSR happens only in Long mode
181 * (in legacy 32-bit mode, IF, RF and VM bits are cleared and that's it).
182 * Don't get confused: RFLAGS saving+masking depends on Long Mode Active bit
183 * (EFER.LMA=1), NOT on bitness of userspace where SYSCALL executes
184 * or target CS descriptor's L bit (SYSCALL does not read segment descriptors).
187 * eax system call number
190 * ebp arg2 (note: not saved in the stack frame, should not be touched)
197 ENTRY(entry_SYSCALL_compat)
198 /* Interrupts are off on entry. */
200 SWITCH_KERNEL_CR3_NO_STACK
202 /* Stash user ESP and switch to the kernel stack. */
204 movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
206 /* Zero-extending 32-bit regs, do not remove */
209 /* Construct struct pt_regs on stack */
210 pushq $__USER32_DS /* pt_regs->ss */
211 pushq %r8 /* pt_regs->sp */
212 pushq %r11 /* pt_regs->flags */
213 pushq $__USER32_CS /* pt_regs->cs */
214 pushq %rcx /* pt_regs->ip */
215 pushq %rax /* pt_regs->orig_ax */
216 pushq %rdi /* pt_regs->di */
217 pushq %rsi /* pt_regs->si */
218 pushq %rdx /* pt_regs->dx */
219 pushq %rbp /* pt_regs->cx (stashed in bp) */
220 pushq $-ENOSYS /* pt_regs->ax */
221 pushq $0 /* pt_regs->r8 = 0 */
222 xorq %r8, %r8 /* nospec r8 */
223 pushq $0 /* pt_regs->r9 = 0 */
224 xorq %r9, %r9 /* nospec r9 */
225 pushq $0 /* pt_regs->r10 = 0 */
226 xorq %r10, %r10 /* nospec r10 */
227 pushq $0 /* pt_regs->r11 = 0 */
228 xorq %r11, %r11 /* nospec r11 */
229 pushq %rbx /* pt_regs->rbx */
230 xorl %ebx, %ebx /* nospec rbx */
231 pushq %rbp /* pt_regs->rbp (will be overwritten) */
232 xorl %ebp, %ebp /* nospec rbp */
233 pushq $0 /* pt_regs->r12 = 0 */
234 xorq %r12, %r12 /* nospec r12 */
235 pushq $0 /* pt_regs->r13 = 0 */
236 xorq %r13, %r13 /* nospec r13 */
237 pushq $0 /* pt_regs->r14 = 0 */
238 xorq %r14, %r14 /* nospec r14 */
239 pushq $0 /* pt_regs->r15 = 0 */
240 xorq %r15, %r15 /* nospec r15 */
243 * User mode is traced as though IRQs are on, and SYSENTER
249 call do_fast_syscall_32
250 /* XEN PV guests always use IRET path */
251 ALTERNATIVE "testl %eax, %eax; jz .Lsyscall_32_done", \
252 "jmp .Lsyscall_32_done", X86_FEATURE_XENPV
254 /* Opportunistic SYSRET */
255 sysret32_from_system_call:
256 TRACE_IRQS_ON /* User mode traces as IRQs on. */
257 movq RBX(%rsp), %rbx /* pt_regs->rbx */
258 movq RBP(%rsp), %rbp /* pt_regs->rbp */
259 movq EFLAGS(%rsp), %r11 /* pt_regs->flags (in r11) */
260 movq RIP(%rsp), %rcx /* pt_regs->ip (in rcx) */
261 addq $RAX, %rsp /* Skip r8-r15 */
262 popq %rax /* pt_regs->rax */
263 popq %rdx /* Skip pt_regs->cx */
264 popq %rdx /* pt_regs->dx */
265 popq %rsi /* pt_regs->si */
266 popq %rdi /* pt_regs->di */
269 * USERGS_SYSRET32 does:
270 * GSBASE = user's GS base
276 * ECX will not match pt_regs->cx, but we're returning to a vDSO
277 * trampoline that will fix up RCX, so this is okay.
279 * R12-R15 are callee-saved, so they contain whatever was in them
280 * when the system call started, which is already known to user
281 * code. We zero R8-R10 to avoid info leaks.
287 movq RSP-ORIG_RAX(%rsp), %rsp
290 END(entry_SYSCALL_compat)
293 * 32-bit legacy system call entry.
295 * 32-bit x86 Linux system calls traditionally used the INT $0x80
296 * instruction. INT $0x80 lands here.
298 * This entry point can be used by 32-bit and 64-bit programs to perform
299 * 32-bit system calls. Instances of INT $0x80 can be found inline in
300 * various programs and libraries. It is also used by the vDSO's
301 * __kernel_vsyscall fallback for hardware that doesn't support a faster
302 * entry method. Restarted 32-bit system calls also fall back to INT
303 * $0x80 regardless of what instruction was originally used to do the
306 * This is considered a slow path. It is not used by most libc
307 * implementations on modern hardware except during process startup.
310 * eax system call number
318 ENTRY(entry_INT80_compat)
320 * Interrupts are off on entry.
322 PARAVIRT_ADJUST_EXCEPTION_FRAME
323 ASM_CLAC /* Do this early to minimize exposure */
325 SWITCH_KERNEL_CR3_NO_STACK
327 * User tracing code (ptrace or signal handlers) might assume that
328 * the saved RAX contains a 32-bit number when we're invoking a 32-bit
329 * syscall. Just in case the high bits are nonzero, zero-extend
330 * the syscall number. (This could almost certainly be deleted
331 * with no ill effects.)
335 /* Construct struct pt_regs on stack (iret frame is already on stack) */
336 pushq %rax /* pt_regs->orig_ax */
337 pushq %rdi /* pt_regs->di */
338 pushq %rsi /* pt_regs->si */
339 pushq %rdx /* pt_regs->dx */
340 pushq %rcx /* pt_regs->cx */
341 pushq $-ENOSYS /* pt_regs->ax */
342 pushq $0 /* pt_regs->r8 = 0 */
343 xorq %r8, %r8 /* nospec r8 */
344 pushq $0 /* pt_regs->r9 = 0 */
345 xorq %r9, %r9 /* nospec r9 */
346 pushq $0 /* pt_regs->r10 = 0 */
347 xorq %r10, %r10 /* nospec r10 */
348 pushq $0 /* pt_regs->r11 = 0 */
349 xorq %r11, %r11 /* nospec r11 */
350 pushq %rbx /* pt_regs->rbx */
351 xorl %ebx, %ebx /* nospec rbx */
352 pushq %rbp /* pt_regs->rbp */
353 xorl %ebp, %ebp /* nospec rbp */
354 pushq %r12 /* pt_regs->r12 */
355 xorq %r12, %r12 /* nospec r12 */
356 pushq %r13 /* pt_regs->r13 */
357 xorq %r13, %r13 /* nospec r13 */
358 pushq %r14 /* pt_regs->r14 */
359 xorq %r14, %r14 /* nospec r14 */
360 pushq %r15 /* pt_regs->r15 */
361 xorq %r15, %r15 /* nospec r15 */
365 * User mode is traced as though IRQs are on, and the interrupt
366 * gate turned them off.
371 call do_int80_syscall_32
374 /* Go back to user mode. */
378 jmp restore_regs_and_iret
379 END(entry_INT80_compat)
384 * The 32-bit clone ABI is: clone(..., int tls_val, int *child_tidptr).
385 * The 64-bit clone ABI is: clone(..., int *child_tidptr, int tls_val).
387 * The native 64-bit kernel's sys_clone() implements the latter,
388 * so we need to swap arguments here before calling it: