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Diffstat (limited to 'common-user/host/mips/safe-syscall.inc.S')
| -rw-r--r-- | common-user/host/mips/safe-syscall.inc.S | 149 |
1 files changed, 149 insertions, 0 deletions
diff --git a/common-user/host/mips/safe-syscall.inc.S b/common-user/host/mips/safe-syscall.inc.S new file mode 100644 index 0000000000..6a44614970 --- /dev/null +++ b/common-user/host/mips/safe-syscall.inc.S @@ -0,0 +1,149 @@ +/* + * safe-syscall.inc.S : host-specific assembly fragment + * to handle signals occurring at the same time as system calls. + * This is intended to be included by common-user/safe-syscall.S + * + * Written by Richard Henderson <richard.henderson@linaro.org> + * Copyright (C) 2021 Linaro, Inc. + * + * This work is licensed under the terms of the GNU GPL, version 2 or later. + * See the COPYING file in the top-level directory. + */ + +#include "sys/regdef.h" +#include "sys/asm.h" + + .text + .set nomips16 + .set reorder + + .global safe_syscall_start + .global safe_syscall_end + .type safe_syscall_start, @function + .type safe_syscall_end, @function + + /* + * This is the entry point for making a system call. The calling + * convention here is that of a C varargs function with the + * first argument an 'int *' to the signal_pending flag, the + * second one the system call number (as a 'long'), and all further + * arguments being syscall arguments (also 'long'). + */ + +#if _MIPS_SIM == _ABIO32 +/* 8 * 4 = 32 for outgoing parameters; 1 * 4 for s0 save; 1 * 4 for align. */ +#define FRAME 40 +#define OFS_S0 32 +#else +/* 1 * 8 for s0 save; 1 * 8 for align. */ +#define FRAME 16 +#define OFS_S0 0 +#endif + + +NESTED(safe_syscall_base, FRAME, ra) + .cfi_startproc + PTR_ADDIU sp, sp, -FRAME + .cfi_adjust_cfa_offset FRAME + REG_S s0, OFS_S0(sp) + .cfi_rel_offset s0, OFS_S0 +#if _MIPS_SIM == _ABIO32 + /* + * The syscall calling convention is nearly the same as C: + * we enter with a0 == &signal_pending + * a1 == syscall number + * a2, a3, stack == syscall arguments + * and return the result in a0 + * and the syscall instruction needs + * v0 == syscall number + * a0 ... a3, stack == syscall arguments + * and returns the result in v0 + * Shuffle everything around appropriately. + */ + move s0, a0 /* signal_pending pointer */ + move v0, a1 /* syscall number */ + move a0, a2 /* syscall arguments */ + move a1, a3 + lw a2, FRAME+16(sp) + lw a3, FRAME+20(sp) + lw t4, FRAME+24(sp) + lw t5, FRAME+28(sp) + lw t6, FRAME+32(sp) + lw t7, FRAME+40(sp) + sw t4, 16(sp) + sw t5, 20(sp) + sw t6, 24(sp) + sw t7, 28(sp) +#else + /* + * The syscall calling convention is nearly the same as C: + * we enter with a0 == &signal_pending + * a1 == syscall number + * a2 ... a7 == syscall arguments + * and return the result in a0 + * and the syscall instruction needs + * v0 == syscall number + * a0 ... a5 == syscall arguments + * and returns the result in v0 + * Shuffle everything around appropriately. + */ + move s0, a0 /* signal_pending pointer */ + move v0, a1 /* syscall number */ + move a0, a2 /* syscall arguments */ + move a1, a3 + move a2, a4 + move a3, a5 + move a4, a6 + move a5, a7 +#endif + + /* + * This next sequence of code works in conjunction with the + * rewind_if_safe_syscall_function(). If a signal is taken + * and the interrupted PC is anywhere between 'safe_syscall_start' + * and 'safe_syscall_end' then we rewind it to 'safe_syscall_start'. + * The code sequence must therefore be able to cope with this, and + * the syscall instruction must be the final one in the sequence. + */ +safe_syscall_start: + /* If signal_pending is non-zero, don't do the call */ + lw t1, 0(s0) + bnez t1, 2f + syscall +safe_syscall_end: + + /* code path for having successfully executed the syscall */ + REG_L s0, OFS_S0(sp) + PTR_ADDIU sp, sp, FRAME + .cfi_remember_state + .cfi_adjust_cfa_offset -FRAME + .cfi_restore s0 + bnez a3, 1f + jr ra + .cfi_restore_state + + /* code path when we didn't execute the syscall */ +2: REG_L s0, OFS_S0(sp) + PTR_ADDIU sp, sp, FRAME + .cfi_adjust_cfa_offset -FRAME + .cfi_restore s0 + li v0, QEMU_ERESTARTSYS + + /* code path setting errno */ + /* + * We didn't setup GP on entry, optimistic of the syscall success. + * We must do so now to load the address of the helper, as required + * by the ABI, into t9. + * + * Note that SETUP_GPX and SETUP_GPX64 are themselves conditional, + * so we can simply let the one that's not empty succeed. + */ +1: USE_ALT_CP(t0) + SETUP_GPX(t1) + SETUP_GPX64(t0, t1) + move a0, v0 + PTR_LA t9, safe_syscall_set_errno_tail + jr t9 + + .cfi_endproc +END(safe_syscall_base) |