54eea9957f
For slowpath syscalls, we initialize regs->ax to -ENOSYS and stick the syscall number into regs->orig_ax prior to any possible tracing and syscall execution. This is user-visible ABI used by ptrace syscall emulation and seccomp. For fastpath syscalls, there's no good reason not to do the same thing. It's even slightly simpler than what we're currently doing. It probably has no measureable performance impact. It should have no user-visible effect. The purpose of this patch is to prepare for two-phase syscall tracing, in which the first phase might modify the saved RAX without leaving the fast path. This change is just subtle enough that I'm keeping it separate. Signed-off-by: Andy Lutomirski <luto@amacapital.net> Link: http://lkml.kernel.org/r/01218b493f12ae2f98034b78c9ae085e38e94350.1409954077.git.luto@amacapital.net Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
249 lines
6 KiB
C
249 lines
6 KiB
C
/*
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x86 function call convention, 64-bit:
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-------------------------------------
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arguments | callee-saved | extra caller-saved | return
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[callee-clobbered] | | [callee-clobbered] |
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---------------------------------------------------------------------------
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rdi rsi rdx rcx r8-9 | rbx rbp [*] r12-15 | r10-11 | rax, rdx [**]
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( rsp is obviously invariant across normal function calls. (gcc can 'merge'
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functions when it sees tail-call optimization possibilities) rflags is
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clobbered. Leftover arguments are passed over the stack frame.)
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[*] In the frame-pointers case rbp is fixed to the stack frame.
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[**] for struct return values wider than 64 bits the return convention is a
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bit more complex: up to 128 bits width we return small structures
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straight in rax, rdx. For structures larger than that (3 words or
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larger) the caller puts a pointer to an on-stack return struct
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[allocated in the caller's stack frame] into the first argument - i.e.
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into rdi. All other arguments shift up by one in this case.
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Fortunately this case is rare in the kernel.
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For 32-bit we have the following conventions - kernel is built with
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-mregparm=3 and -freg-struct-return:
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x86 function calling convention, 32-bit:
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----------------------------------------
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arguments | callee-saved | extra caller-saved | return
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[callee-clobbered] | | [callee-clobbered] |
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-------------------------------------------------------------------------
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eax edx ecx | ebx edi esi ebp [*] | <none> | eax, edx [**]
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( here too esp is obviously invariant across normal function calls. eflags
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is clobbered. Leftover arguments are passed over the stack frame. )
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[*] In the frame-pointers case ebp is fixed to the stack frame.
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[**] We build with -freg-struct-return, which on 32-bit means similar
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semantics as on 64-bit: edx can be used for a second return value
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(i.e. covering integer and structure sizes up to 64 bits) - after that
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it gets more complex and more expensive: 3-word or larger struct returns
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get done in the caller's frame and the pointer to the return struct goes
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into regparm0, i.e. eax - the other arguments shift up and the
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function's register parameters degenerate to regparm=2 in essence.
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*/
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#include <asm/dwarf2.h>
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#ifdef CONFIG_X86_64
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/*
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* 64-bit system call stack frame layout defines and helpers,
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* for assembly code:
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*/
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#define R15 0
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#define R14 8
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#define R13 16
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#define R12 24
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#define RBP 32
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#define RBX 40
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/* arguments: interrupts/non tracing syscalls only save up to here: */
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#define R11 48
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#define R10 56
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#define R9 64
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#define R8 72
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#define RAX 80
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#define RCX 88
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#define RDX 96
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#define RSI 104
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#define RDI 112
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#define ORIG_RAX 120 /* + error_code */
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/* end of arguments */
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/* cpu exception frame or undefined in case of fast syscall: */
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#define RIP 128
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#define CS 136
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#define EFLAGS 144
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#define RSP 152
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#define SS 160
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#define ARGOFFSET R11
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#define SWFRAME ORIG_RAX
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.macro SAVE_ARGS addskip=0, save_rcx=1, save_r891011=1, rax_enosys=0
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subq $9*8+\addskip, %rsp
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CFI_ADJUST_CFA_OFFSET 9*8+\addskip
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movq_cfi rdi, 8*8
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movq_cfi rsi, 7*8
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movq_cfi rdx, 6*8
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.if \save_rcx
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movq_cfi rcx, 5*8
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.endif
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.if \rax_enosys
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movq $-ENOSYS, 4*8(%rsp)
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.else
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movq_cfi rax, 4*8
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.endif
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.if \save_r891011
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movq_cfi r8, 3*8
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movq_cfi r9, 2*8
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movq_cfi r10, 1*8
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movq_cfi r11, 0*8
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.endif
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.endm
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#define ARG_SKIP (9*8)
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.macro RESTORE_ARGS rstor_rax=1, addskip=0, rstor_rcx=1, rstor_r11=1, \
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rstor_r8910=1, rstor_rdx=1
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.if \rstor_r11
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movq_cfi_restore 0*8, r11
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.endif
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.if \rstor_r8910
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movq_cfi_restore 1*8, r10
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movq_cfi_restore 2*8, r9
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movq_cfi_restore 3*8, r8
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.endif
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.if \rstor_rax
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movq_cfi_restore 4*8, rax
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.endif
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.if \rstor_rcx
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movq_cfi_restore 5*8, rcx
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.endif
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.if \rstor_rdx
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movq_cfi_restore 6*8, rdx
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.endif
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movq_cfi_restore 7*8, rsi
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movq_cfi_restore 8*8, rdi
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.if ARG_SKIP+\addskip > 0
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addq $ARG_SKIP+\addskip, %rsp
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CFI_ADJUST_CFA_OFFSET -(ARG_SKIP+\addskip)
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.endif
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.endm
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.macro LOAD_ARGS offset, skiprax=0
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movq \offset(%rsp), %r11
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movq \offset+8(%rsp), %r10
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movq \offset+16(%rsp), %r9
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movq \offset+24(%rsp), %r8
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movq \offset+40(%rsp), %rcx
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movq \offset+48(%rsp), %rdx
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movq \offset+56(%rsp), %rsi
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movq \offset+64(%rsp), %rdi
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.if \skiprax
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.else
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movq \offset+72(%rsp), %rax
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.endif
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.endm
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#define REST_SKIP (6*8)
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.macro SAVE_REST
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subq $REST_SKIP, %rsp
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CFI_ADJUST_CFA_OFFSET REST_SKIP
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movq_cfi rbx, 5*8
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movq_cfi rbp, 4*8
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movq_cfi r12, 3*8
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movq_cfi r13, 2*8
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movq_cfi r14, 1*8
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movq_cfi r15, 0*8
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.endm
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.macro RESTORE_REST
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movq_cfi_restore 0*8, r15
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movq_cfi_restore 1*8, r14
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movq_cfi_restore 2*8, r13
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movq_cfi_restore 3*8, r12
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movq_cfi_restore 4*8, rbp
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movq_cfi_restore 5*8, rbx
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addq $REST_SKIP, %rsp
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CFI_ADJUST_CFA_OFFSET -(REST_SKIP)
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.endm
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.macro SAVE_ALL
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SAVE_ARGS
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SAVE_REST
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.endm
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.macro RESTORE_ALL addskip=0
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RESTORE_REST
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RESTORE_ARGS 1, \addskip
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.endm
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.macro icebp
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.byte 0xf1
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.endm
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#else /* CONFIG_X86_64 */
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/*
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* For 32bit only simplified versions of SAVE_ALL/RESTORE_ALL. These
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* are different from the entry_32.S versions in not changing the segment
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* registers. So only suitable for in kernel use, not when transitioning
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* from or to user space. The resulting stack frame is not a standard
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* pt_regs frame. The main use case is calling C code from assembler
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* when all the registers need to be preserved.
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*/
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.macro SAVE_ALL
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pushl_cfi %eax
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CFI_REL_OFFSET eax, 0
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pushl_cfi %ebp
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CFI_REL_OFFSET ebp, 0
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pushl_cfi %edi
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CFI_REL_OFFSET edi, 0
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pushl_cfi %esi
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CFI_REL_OFFSET esi, 0
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pushl_cfi %edx
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CFI_REL_OFFSET edx, 0
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pushl_cfi %ecx
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CFI_REL_OFFSET ecx, 0
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pushl_cfi %ebx
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CFI_REL_OFFSET ebx, 0
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.endm
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.macro RESTORE_ALL
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popl_cfi %ebx
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CFI_RESTORE ebx
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popl_cfi %ecx
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CFI_RESTORE ecx
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popl_cfi %edx
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CFI_RESTORE edx
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popl_cfi %esi
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CFI_RESTORE esi
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popl_cfi %edi
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CFI_RESTORE edi
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popl_cfi %ebp
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CFI_RESTORE ebp
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popl_cfi %eax
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CFI_RESTORE eax
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.endm
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#endif /* CONFIG_X86_64 */
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