https://sourceware.org/ml/libc-alpha/2014-04/msg00006.html 2014-04-01 Will Newton [BZ #16629] * sysdeps/unix/sysv/linux/aarch64/setcontext.S (__setcontext): Re-implement to restore registers in user code and avoid rt_sigreturn system call. --- sysdeps/unix/sysv/linux/aarch64/setcontext.S | 147 +++++++++++++++++---------- 2 files changed, 95 insertions(+), 58 deletions(-) Index: eglibc-2.19/ports/sysdeps/unix/sysv/linux/aarch64/setcontext.S =================================================================== --- eglibc-2.19.orig/ports/sysdeps/unix/sysv/linux/aarch64/setcontext.S 2150-05-09 09:36:21.925789000 +0000 +++ eglibc-2.19/ports/sysdeps/unix/sysv/linux/aarch64/setcontext.S 2150-05-09 09:36:48.235789000 +0000 @@ -22,68 +22,105 @@ #include "ucontext_i.h" #include "ucontext-internal.h" -/* int setcontext (const ucontext_t *ucp) */ +/* int __setcontext (const ucontext_t *ucp) - .text - -ENTRY(__setcontext) - - /* Create a signal frame on the stack: - - fp - lr - ... - sp-> rt_sigframe - */ - - stp x29, x30, [sp, -16]! - cfi_adjust_cfa_offset (16) - cfi_rel_offset (x29, 0) - cfi_rel_offset (x30, 8) - - mov x29, sp - cfi_def_cfa_register (x29) - - /* Allocate space for the sigcontext. */ - mov w3, #((RT_SIGFRAME_SIZE + SP_ALIGN_SIZE) & SP_ALIGN_MASK) - sub sp, sp, x3 + Restores the machine context in UCP and thereby resumes execution + in that context. - /* Compute the base address of the ucontext structure. */ - add x1, sp, #RT_SIGFRAME_UCONTEXT + This implementation is intended to be used for *synchronous* context + switches only. Therefore, it does not have to restore anything + other than the PRESERVED state. */ - /* Only ucontext is required in the frame, *copy* it in. */ - -#if UCONTEXT_SIZE % 16 -#error The implementation of setcontext.S assumes sizeof(ucontext_t) % 16 == 0 -#endif - - mov x2, #UCONTEXT_SIZE / 16 -0: - ldp x3, x4, [x0], #16 - stp x3, x4, [x1], #16 - sub x2, x2, 1 - cbnz x2, 0b + .text - /* rt_sigreturn () -- no arguments, sp points to struct rt_sigframe. */ - mov x8, SYS_ify (rt_sigreturn) +ENTRY (__setcontext) + /* Save a copy of UCP. */ + mov x9, x0 + + /* Set the signal mask with + rt_sigprocmask (SIG_SETMASK, mask, NULL, _NSIG/8). */ + mov x0, #SIG_SETMASK + add x1, x9, #UCONTEXT_SIGMASK + mov x2, #0 + mov x3, #_NSIG8 + mov x8, SYS_ify (rt_sigprocmask) svc 0 - - /* Ooops we failed. Recover the stack */ - - mov sp, x29 - cfi_def_cfa_register (sp) - - ldp x29, x30, [sp], 16 - cfi_adjust_cfa_offset (16) - cfi_restore (x29) - cfi_restore (x30) - b C_SYMBOL_NAME(__syscall_error) - + cbz x0, 1f + b C_SYMBOL_NAME (__syscall_error) +1: + /* Restore the general purpose registers. */ + mov x0, x9 + cfi_def_cfa (x0, 0) + cfi_offset (x18, oX0 + 18 * SZREG) + cfi_offset (x19, oX0 + 19 * SZREG) + cfi_offset (x20, oX0 + 20 * SZREG) + cfi_offset (x21, oX0 + 21 * SZREG) + cfi_offset (x22, oX0 + 22 * SZREG) + cfi_offset (x23, oX0 + 23 * SZREG) + cfi_offset (x24, oX0 + 24 * SZREG) + cfi_offset (x25, oX0 + 25 * SZREG) + cfi_offset (x26, oX0 + 26 * SZREG) + cfi_offset (x27, oX0 + 27 * SZREG) + cfi_offset (x28, oX0 + 28 * SZREG) + cfi_offset (x29, oX0 + 29 * SZREG) + cfi_offset (x30, oX0 + 30 * SZREG) + + cfi_offset ( d8, oV0 + 8 * SZVREG) + cfi_offset ( d9, oV0 + 9 * SZVREG) + cfi_offset (d10, oV0 + 10 * SZVREG) + cfi_offset (d11, oV0 + 11 * SZVREG) + cfi_offset (d12, oV0 + 12 * SZVREG) + cfi_offset (d13, oV0 + 13 * SZVREG) + cfi_offset (d14, oV0 + 14 * SZVREG) + cfi_offset (d15, oV0 + 15 * SZVREG) + ldp x18, x19, [x0, oX0 + 18 * SZREG] + ldp x20, x21, [x0, oX0 + 20 * SZREG] + ldp x22, x23, [x0, oX0 + 22 * SZREG] + ldp x24, x25, [x0, oX0 + 24 * SZREG] + ldp x26, x27, [x0, oX0 + 26 * SZREG] + ldp x28, x29, [x0, oX0 + 28 * SZREG] + ldr x30, [x0, oX0 + 30 * SZREG] + ldr x2, [x0, oSP] + mov sp, x2 + + /* Check for FP SIMD context. */ + add x2, x0, #oEXTENSION + + mov w3, #(FPSIMD_MAGIC & 0xffff) + movk w3, #(FPSIMD_MAGIC >> 16), lsl #16 + ldr w1, [x2, #oHEAD + oMAGIC] + cmp w1, w3 + b.ne 2f + + /* Restore the FP SIMD context. */ + add x3, x2, #oV0 + 8 * SZVREG + ldp d8, d9, [x3], #2 * SZVREG + ldp d10, d11, [x3], #2 * SZVREG + ldp d12, d13, [x3], #2 * SZVREG + ldp d14, d15, [x3], #2 * SZVREG + + add x3, x2, oFPSR + + ldr w4, [x3] + msr fpsr, x4 + + ldr w4, [x3, oFPCR - oFPSR] + msr fpcr, x4 + +2: + ldr x16, [x0, oPC] + /* Restore arg registers. */ + ldp x2, x3, [x0, oX0 + 2 * SZREG] + ldp x4, x5, [x0, oX0 + 4 * SZREG] + ldp x6, x7, [x0, oX0 + 6 * SZREG] + ldp x0, x1, [x0, oX0 + 0 * SZREG] + /* Jump to the new pc value. */ + br x16 PSEUDO_END (__setcontext) weak_alias (__setcontext, setcontext) -ENTRY(__startcontext) +ENTRY (__startcontext) mov x0, x19 cbnz x0, __setcontext -1: b HIDDEN_JUMPTARGET(_exit) -END(__startcontext) +1: b HIDDEN_JUMPTARGET (_exit) +END (__startcontext) -- 1.8.1.4