Edit File: calling.h
/* x86 function call convention, 64-bit: ------------------------------------- arguments | callee-saved | extra caller-saved | return [callee-clobbered] | | [callee-clobbered] | --------------------------------------------------------------------------- rdi rsi rdx rcx r8-9 | rbx rbp [*] r12-15 | r10-11 | rax, rdx [**] ( rsp is obviously invariant across normal function calls. (gcc can 'merge' functions when it sees tail-call optimization possibilities) rflags is clobbered. Leftover arguments are passed over the stack frame.) [*] In the frame-pointers case rbp is fixed to the stack frame. [**] for struct return values wider than 64 bits the return convention is a bit more complex: up to 128 bits width we return small structures straight in rax, rdx. For structures larger than that (3 words or larger) the caller puts a pointer to an on-stack return struct [allocated in the caller's stack frame] into the first argument - i.e. into rdi. All other arguments shift up by one in this case. Fortunately this case is rare in the kernel. For 32-bit we have the following conventions - kernel is built with -mregparm=3 and -freg-struct-return: x86 function calling convention, 32-bit: ---------------------------------------- arguments | callee-saved | extra caller-saved | return [callee-clobbered] | | [callee-clobbered] | ------------------------------------------------------------------------- eax edx ecx | ebx edi esi ebp [*] | <none> | eax, edx [**] ( here too esp is obviously invariant across normal function calls. eflags is clobbered. Leftover arguments are passed over the stack frame. ) [*] In the frame-pointers case ebp is fixed to the stack frame. [**] We build with -freg-struct-return, which on 32-bit means similar semantics as on 64-bit: edx can be used for a second return value (i.e. covering integer and structure sizes up to 64 bits) - after that it gets more complex and more expensive: 3-word or larger struct returns get done in the caller's frame and the pointer to the return struct goes into regparm0, i.e. eax - the other arguments shift up and the function's register parameters degenerate to regparm=2 in essence. */ #include <asm/dwarf2.h> #include <asm/cpufeatures.h> #include <asm/nops.h> /* * 64-bit system call stack frame layout defines and helpers, * for assembly code: */ #define R15 0 #define R14 8 #define R13 16 #define R12 24 #define RBP 32 #define RBX 40 /* arguments: interrupts/non tracing syscalls only save up to here: */ #define R11 48 #define R10 56 #define R9 64 #define R8 72 #define RAX 80 #define RCX 88 #define RDX 96 #define RSI 104 #define RDI 112 #define ORIG_RAX 120 /* + error_code */ /* end of arguments */ /* cpu exception frame or undefined in case of fast syscall: */ #define RIP 128 #define CS 136 #define EFLAGS 144 #define RSP 152 #define SS 160 #define ARGOFFSET R11 #define SWFRAME ORIG_RAX .macro SAVE_ARGS addskip=0, save_rcx=1, save_r891011=1 subq $9*8+\addskip, %rsp CFI_ADJUST_CFA_OFFSET 9*8+\addskip movq_cfi rdi, 8*8 movq_cfi rsi, 7*8 movq_cfi rdx, 6*8 .if \save_rcx movq_cfi rcx, 5*8 .endif movq_cfi rax, 4*8 .if \save_r891011 movq_cfi r8, 3*8 movq_cfi r9, 2*8 movq_cfi r10, 1*8 movq_cfi r11, 0*8 .endif .endm #define ARG_SKIP (9*8) .macro RESTORE_ARGS rstor_rax=1, addskip=0, rstor_rcx=1, rstor_r11=1, \ rstor_r8910=1, rstor_rdx=1 .if \rstor_r11 movq_cfi_restore 0*8, r11 .endif .if \rstor_r8910 movq_cfi_restore 1*8, r10 movq_cfi_restore 2*8, r9 movq_cfi_restore 3*8, r8 .endif .if \rstor_rax movq_cfi_restore 4*8, rax .endif .if \rstor_rcx movq_cfi_restore 5*8, rcx .endif .if \rstor_rdx movq_cfi_restore 6*8, rdx .endif movq_cfi_restore 7*8, rsi movq_cfi_restore 8*8, rdi .if ARG_SKIP+\addskip > 0 addq $ARG_SKIP+\addskip, %rsp CFI_ADJUST_CFA_OFFSET -(ARG_SKIP+\addskip) .endif .endm .macro LOAD_ARGS offset, skiprax=0 movq \offset(%rsp), %r11 movq \offset+8(%rsp), %r10 movq \offset+16(%rsp), %r9 movq \offset+24(%rsp), %r8 movq \offset+40(%rsp), %rcx movq \offset+48(%rsp), %rdx movq \offset+56(%rsp), %rsi movq \offset+64(%rsp), %rdi .if \skiprax .else movq \offset+72(%rsp), %rax .endif .endm #define REST_SKIP (6*8) .macro SAVE_REST subq $REST_SKIP, %rsp CFI_ADJUST_CFA_OFFSET REST_SKIP movq_cfi rbx, 5*8 movq_cfi rbp, 4*8 movq_cfi r12, 3*8 movq_cfi r13, 2*8 movq_cfi r14, 1*8 movq_cfi r15, 0*8 .endm .macro RESTORE_REST movq_cfi_restore 0*8, r15 movq_cfi_restore 1*8, r14 movq_cfi_restore 2*8, r13 movq_cfi_restore 3*8, r12 movq_cfi_restore 4*8, rbp movq_cfi_restore 5*8, rbx addq $REST_SKIP, %rsp CFI_ADJUST_CFA_OFFSET -(REST_SKIP) .endm .macro SAVE_ALL SAVE_ARGS SAVE_REST .endm .macro RESTORE_ALL addskip=0 RESTORE_REST RESTORE_ARGS 1, \addskip .endm .macro icebp .byte 0xf1 .endm /* * Must be called IMMEDIATELY after a branch to prevent speculation * past the bounds of the syscall table. Uses the carry flag from the * most recent CMP instruction to set the scratch reg to -1 if the * syscall was in bounds and 0 if it was out of bounds. So RAX -- * which holds the syscall number -- is cleared to zero in the * speculative out-of-bounds case. */ .macro ARRAY_INDEX_NOSPEC_SYSCALL clobber_reg sbb \clobber_reg, \clobber_reg and \clobber_reg, %rax /* prevent a data "leak" */ xorq \clobber_reg, \clobber_reg .endm .macro UNWIND_END_OF_STACK 417: .pushsection __unwind_end_of_stack, "a" .quad 417b .popsection .endm .macro UNWIND_UNSAFE_STACK 417: .pushsection __unwind_unsafe_stack, "a" .quad 417b .popsection .endm /* * Mitigate Spectre v1 for conditional swapgs code paths. * * FENCE_SWAPGS_USER_ENTRY is used in the user entry swapgs code path, to * prevent a speculative swapgs when coming from kernel space. * * FENCE_SWAPGS_KERNEL_ENTRY is used in the kernel entry non-swapgs code path, * to prevent the swapgs from getting speculatively skipped when coming from * user space. * * RHEL7 uses gs-indexed per-cpu variables for dynamic PTI enabling/disabling. * So that on/off state of PTI doesn't matter in determining if fencing should * be used or not. We have to properly fence swapgs before the invocation * of the PTI macros. * * RHEL7 also doesn't have the ALTERNATIVE asm macro. So we have to open-code * it. The lfence instruction is 3 bytes long. */ .macro _FENCE_SWAPGS feature 661: ASM_NOP3; 662: .pushsection .altinstr_replacement, "ax" 663: lfence; 664: .popsection .pushsection .altinstructions, "a" altinstruction_entry 661b, 663b, \feature, 662b-661b, 664b-663b .popsection .endm .macro FENCE_SWAPGS_USER_ENTRY _FENCE_SWAPGS X86_FEATURE_FENCE_SWAPGS_USER .endm .macro FENCE_SWAPGS_KERNEL_ENTRY _FENCE_SWAPGS X86_FEATURE_FENCE_SWAPGS_KERNEL .endm