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 /* -*- Mode: C; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */

 /* This Source Code Form is subject to the terms of the Mozilla Public

  * License, v. 2.0. If a copy of the MPL was not distributed with this

  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

 /* Platform specific code to invoke XPCOM methods on native objects */

 #include "xptcprivate.h"

 #include "mozilla/Compiler.h"

 #if !defined(__arm__) && !(defined(LINUX) || defined(ANDROID))

 #error "This code is for Linux ARM only. Check that it works on your system, too.\nBeware that this code is highly compiler dependent."

 #endif

 #if MOZ_IS_GCC

 #if MOZ_GCC_VERSION_AT_LEAST(4, 5, 0) \

     && defined(__ARM_EABI__) && !defined(__ARM_PCS_VFP) && !defined(__ARM_PCS)

 #error "Can't identify floating point calling conventions.\nPlease ensure that your toolchain defines __ARM_PCS or __ARM_PCS_VFP."

 #endif

 #endif

 #ifndef __ARM_PCS_VFP

 /* This function copies a 64-bits word from dw to the given pointer in

  * a buffer delimited by start and end, possibly wrapping around the

  * buffer boundaries, and/or properly aligning the data at 64-bits word

  * boundaries (for EABI).

  * start and end are both assumed to be 64-bits aligned.

  * Returns a pointer to the second 32-bits word copied (to accomodate

  * the invoke_copy_to_stack loop).

  */

 static uint32_t *

 copy_double_word(uint32_t *start, uint32_t *current, uint32_t *end, uint64_t *dw)

 {

 #ifdef __ARM_EABI__

     /* Aligning the pointer for EABI */

     current = (uint32_t *)(((uint32_t)current + 7) & ~7);

     /* Wrap when reaching the end of the buffer */

     if (current == end) current = start;

 #else

     /* On non-EABI, 64-bits values are not aligned and when we reach the end

      * of the buffer, we need to write half of the data at the end, and the

      * other half at the beginning. */

     if (current == end - 1) {

         *current = ((uint32_t*)dw)[0];

         *start = ((uint32_t*)dw)[1];

         return start;

     }

 #endif

     *((uint64_t*) current) = *dw;

     return current + 1;

 }

 /* See stack_space comment in NS_InvokeByIndex to see why this needs not to

  * be static on DEBUG builds. */

 #ifndef DEBUG

 static

 #endif

 void

 invoke_copy_to_stack(uint32_t* stk, uint32_t *end,

                      uint32_t paramCount, nsXPTCVariant* s)

 {

     /* The stack buffer is 64-bits aligned. The end argument points to its end.

      * The caller is assumed to create a stack buffer of at least four 32-bits

      * words.

      * We use the last three 32-bit words to store the values for r1, r2 and r3

      * for the method call, i.e. the first words for arguments passing.

      */

     uint32_t *d = end - 3;

     for(uint32_t i = 0; i < paramCount; i++, d++, s++)

     {

         /* Wrap when reaching the end of the stack buffer */

         if (d == end) d = stk;

         NS_ASSERTION(d >= stk && d < end,

             "invoke_copy_to_stack is copying outside its given buffer");

         if(s->IsPtrData())

         {

             *((void**)d) = s->ptr;

             continue;

         }

         // According to the ARM EABI, integral types that are smaller than a word

         // are to be sign/zero-extended to a full word and treated as 4-byte values.

         switch(s->type)

         {

         case nsXPTType::T_I8     : *((int32_t*) d) = s->val.i8;          break;

         case nsXPTType::T_I16    : *((int32_t*) d) = s->val.i16;         break;

         case nsXPTType::T_I32    : *((int32_t*) d) = s->val.i32;         break;

         case nsXPTType::T_I64    :

             d = copy_double_word(stk, d, end, (uint64_t *)&s->val.i64);

             break;

         case nsXPTType::T_U8     : *((uint32_t*)d) = s->val.u8;          break;

         case nsXPTType::T_U16    : *((uint32_t*)d) = s->val.u16;         break;

         case nsXPTType::T_U32    : *((uint32_t*)d) = s->val.u32;         break;

         case nsXPTType::T_U64    :

             d = copy_double_word(stk, d, end, (uint64_t *)&s->val.u64);

             break;

         case nsXPTType::T_FLOAT  : *((float*)   d) = s->val.f;           break;

         case nsXPTType::T_DOUBLE :

             d = copy_double_word(stk, d, end, (uint64_t *)&s->val.d);

             break;

         case nsXPTType::T_BOOL   : *((int32_t*) d) = s->val.b;           break;

         case nsXPTType::T_CHAR   : *((int32_t*) d) = s->val.c;           break;

         case nsXPTType::T_WCHAR  : *((int32_t*) d) = s->val.wc;          break;

         default:

             // all the others are plain pointer types

             *((void**)d) = s->val.p;

             break;

         }

     }

 }

 typedef nsresult (*vtable_func)(nsISupports *, uint32_t, uint32_t, uint32_t);

 EXPORT_XPCOM_API(nsresult)

 NS_InvokeByIndex(nsISupports* that, uint32_t methodIndex,

                    uint32_t paramCount, nsXPTCVariant* params)

 {

 /* This is to call a given method of class that.

  * The parameters are in params, the number is in paramCount.

  * The routine will issue calls to count the number of words

  * required for argument passing and to copy the arguments to

  * the stack.

  * ACPS passes the first 3 params in r1-r3 (with exceptions for 64-bits

  * arguments), and the remaining goes onto the stack.

  * We allocate a buffer on the stack for a "worst case" estimate of how much

  * stack might be needed for EABI, i.e. twice the number of parameters.

  * The end of this buffer will be used to store r1 to r3, so that the start

  * of the stack is the remaining parameters.

  * The magic here is to call the method with "that" and three 32-bits

  * arguments corresponding to r1-r3, so that the compiler generates the

  * proper function call. The stack will also contain the remaining arguments.

  *

  * !!! IMPORTANT !!!

  * This routine makes assumptions about the vtable layout of the c++ compiler. It's implemented

  * for arm-linux GNU g++ >= 2.8.1 (including egcs and gcc-2.95.[1-3])!

  *

  */

   vtable_func *vtable, func;

   int base_size = (paramCount > 1) ? paramCount : 2;

 /* !!! IMPORTANT !!!

  * On DEBUG builds, the NS_ASSERTION used in invoke_copy_to_stack needs to use

  * the stack to pass the 5th argument to NS_DebugBreak. When invoke_copy_to_stack

  * is inlined, this can result, depending on the compiler and flags, in the

  * stack pointer not pointing at stack_space when the method is called at the

  * end of this function. More generally, any function call requiring stack

  * allocation of arguments is unsafe to be inlined in this function.

  */

   uint32_t *stack_space = (uint32_t *) __builtin_alloca(base_size * 8);

   invoke_copy_to_stack(stack_space, &stack_space[base_size * 2],

                        paramCount, params);

   vtable = *reinterpret_cast<vtable_func **>(that);

   func = vtable[methodIndex];

   return func(that, stack_space[base_size * 2 - 3],

                     stack_space[base_size * 2 - 2],

                     stack_space[base_size * 2 - 1]);

 }    

 #else /* __ARM_PCS_VFP */

 /* "Procedure Call Standard for the ARM Architecture" document, sections

  * "5.5 Parameter Passing" and "6.1.2 Procedure Calling" contain all the

  * needed information.

  *

  * http://infocenter.arm.com/help/topic/com.arm.doc.ihi0042d/IHI0042D_aapcs.pdf

  */

 #if defined(__thumb__) && !defined(__thumb2__)

 #error "Thumb1 is not supported"

 #endif

 #ifndef __ARMEL__

 #error "Only little endian compatibility was tested"

 #endif

 /*

  * Allocation of integer function arguments initially to registers r1-r3

  * and then to stack. Handling of 'this' argument which goes to r0 registers

  * is handled separately and does not belong to these two inline functions.

  *

  * The doubleword arguments are allocated to even:odd

  * register pairs or get aligned at 8-byte boundary on stack. The "holes"

  * which may appear as a result of this realignment remain unused.

  *

  * 'ireg_args'  - pointer to the current position in the buffer,

  *                corresponding to the register arguments

  * 'stack_args' - pointer to the current position in the buffer,

  *                corresponding to the arguments on stack

  * 'end'        - pointer to the end of the registers argument

  *                buffer (it is guaranteed to be 8-bytes aligned)

  */

 static inline void copy_word(uint32_t* &ireg_args,

                              uint32_t* &stack_args,

                              uint32_t* end,

                              uint32_t  data)

 {

   if (ireg_args < end) {

     *ireg_args = data;

     ireg_args++;

   } else {

     *stack_args = data;

     stack_args++;

   }

 }

 static inline void copy_dword(uint32_t* &ireg_args,

                               uint32_t* &stack_args,

                               uint32_t* end,

                               uint64_t  data)

 {

   if (ireg_args + 1 < end) {

     if ((uint32_t)ireg_args & 4) {

       ireg_args++;

     }

     *(uint64_t *)ireg_args = data;

     ireg_args += 2;

   } else {

     if ((uint32_t)stack_args & 4) {

       stack_args++;

     }

     *(uint64_t *)stack_args = data;

     stack_args += 2;

   }

 }

 /*

  * Allocation of floating point arguments to VFP registers (s0-s15, d0-d7).

  *

  * Unlike integer registers allocation, "back-filling" needs to be

  * supported. For example, the third floating point argument in the

  * following function is going to be allocated to s1 register, back-filling

  * the "hole":

  *    void f(float s0, double d1, float s1)

  *

  * Refer to the "Procedure Call Standard for the ARM Architecture" document

  * for more details.

  *

  * 'vfp_s_args' - pointer to the current position in the buffer with

  *                the next unallocated single precision register

  * 'vfp_d_args' - pointer to the current position in the buffer with

  *                the next unallocated double precision register,

  *                it has the same value as 'vfp_s_args' when back-filling

  *                is not used

  * 'end'        - pointer to the end of the vfp registers argument

  *                buffer (it is guaranteed to be 8-bytes aligned)

  *

  * Mozilla bugtracker has a test program attached which be used for

  * experimenting with VFP registers allocation code and testing its

  * correctness:

  * https://bugzilla.mozilla.org/show_bug.cgi?id=601914#c19

  */

 static inline bool copy_vfp_single(float* &vfp_s_args, double* &vfp_d_args,

                                    float* end, float data)

 {

   if (vfp_s_args >= end)

     return false;

   *vfp_s_args = data;

   vfp_s_args++;

   if (vfp_s_args < (float *)vfp_d_args) {

     // It was the case of back-filling, now the next free single precision

     // register should overlap with the next free double precision register

     vfp_s_args = (float *)vfp_d_args;

   } else if (vfp_s_args > (float *)vfp_d_args) {

     // also update the pointer to the next free double precision register

     vfp_d_args++;

   }

   return true;

 }

 static inline bool copy_vfp_double(float* &vfp_s_args, double* &vfp_d_args,

                                    float* end, double data)

 {

   if (vfp_d_args >= (double *)end) {

     // The back-filling continues only so long as no VFP CPRC has been

     // allocated to a slot on the stack. Basically no VFP registers can

     // be allocated after this point.

     vfp_s_args = end;

     return false;

   }

   if (vfp_s_args == (float *)vfp_d_args) {

     // also update the pointer to the next free single precision register

     vfp_s_args += 2;

   }

   *vfp_d_args = data;

   vfp_d_args++;

   return true;

 }

 static void

 invoke_copy_to_stack(uint32_t* stk, uint32_t *end,

                      uint32_t paramCount, nsXPTCVariant* s)

 {

   uint32_t *ireg_args  = end - 3;

   float    *vfp_s_args = (float *)end;

   double   *vfp_d_args = (double *)end;

   float    *vfp_end    = vfp_s_args + 16;

   for (uint32_t i = 0; i < paramCount; i++, s++) {

     if (s->IsPtrData()) {

       copy_word(ireg_args, stk, end, (uint32_t)s->ptr);

       continue;

     }

     // According to the ARM EABI, integral types that are smaller than a word

     // are to be sign/zero-extended to a full word and treated as 4-byte values

     switch (s->type)

     {

       case nsXPTType::T_FLOAT:

         if (!copy_vfp_single(vfp_s_args, vfp_d_args, vfp_end, s->val.f)) {

           copy_word(end, stk, end, reinterpret_cast<uint32_t&>(s->val.f));

         }

         break;

       case nsXPTType::T_DOUBLE:

         if (!copy_vfp_double(vfp_s_args, vfp_d_args, vfp_end, s->val.d)) {

           copy_dword(end, stk, end, reinterpret_cast<uint64_t&>(s->val.d));

         }

         break;

       case nsXPTType::T_I8:  copy_word(ireg_args, stk, end, s->val.i8);   break;

       case nsXPTType::T_I16: copy_word(ireg_args, stk, end, s->val.i16);  break;

       case nsXPTType::T_I32: copy_word(ireg_args, stk, end, s->val.i32);  break;

       case nsXPTType::T_I64: copy_dword(ireg_args, stk, end, s->val.i64); break;

       case nsXPTType::T_U8:  copy_word(ireg_args, stk, end, s->val.u8);   break;

       case nsXPTType::T_U16: copy_word(ireg_args, stk, end, s->val.u16);  break;

       case nsXPTType::T_U32: copy_word(ireg_args, stk, end, s->val.u32);  break;

       case nsXPTType::T_U64: copy_dword(ireg_args, stk, end, s->val.u64); break;

       case nsXPTType::T_BOOL: copy_word(ireg_args, stk, end, s->val.b);   break;

       case nsXPTType::T_CHAR: copy_word(ireg_args, stk, end, s->val.c);   break;

       case nsXPTType::T_WCHAR: copy_word(ireg_args, stk, end, s->val.wc); break;

       default:

         // all the others are plain pointer types

         copy_word(ireg_args, stk, end, reinterpret_cast<uint32_t>(s->val.p));

         break;

     }

   }

 }

 typedef uint32_t (*vtable_func)(nsISupports *, uint32_t, uint32_t, uint32_t);

 EXPORT_XPCOM_API(nsresult)

 NS_InvokeByIndex(nsISupports* that, uint32_t methodIndex,

                    uint32_t paramCount, nsXPTCVariant* params)

 {

   vtable_func *vtable = *reinterpret_cast<vtable_func **>(that);

   vtable_func func = vtable[methodIndex];

   // 'register uint32_t result asm("r0")' could be used here, but it does not

   //  seem to be reliable in all cases: http://gcc.gnu.org/PR46164

   nsresult result;

   asm (

     "mov    r3, sp\n"

     "mov    %[stack_space_size], %[param_count_plus_2], lsl #3\n"

     "tst    r3, #4\n" /* check stack alignment */

     "add    %[stack_space_size], #(4 * 16)\n" /* space for VFP registers */

     "mov    r3, %[params]\n"

     "it     ne\n"

     "addne  %[stack_space_size], %[stack_space_size], #4\n"

     "sub    r0, sp, %[stack_space_size]\n" /* allocate space on stack */

     "sub    r2, %[param_count_plus_2], #2\n"

     "mov    sp, r0\n"

     "add    r1, r0, %[param_count_plus_2], lsl #3\n"

     "blx    %[invoke_copy_to_stack]\n"

     "add    ip, sp, %[param_count_plus_2], lsl #3\n"

     "mov    r0, %[that]\n"

     "ldmdb  ip, {r1, r2, r3}\n"

     "vldm   ip, {d0, d1, d2, d3, d4, d5, d6, d7}\n"

     "blx    %[func]\n"

     "add    sp, sp, %[stack_space_size]\n" /* cleanup stack */

     "mov    %[stack_space_size], r0\n" /* it's actually 'result' variable */

     : [stack_space_size]     "=&r" (result)

     : [func]                 "r"   (func),

       [that]                 "r"   (that),

       [params]               "r"   (params),

       [param_count_plus_2]   "r"   (paramCount + 2),

       [invoke_copy_to_stack] "r"   (invoke_copy_to_stack)

     : "cc", "memory",

       // Mark all the scratch registers as clobbered because they may be

       // modified by the functions, called from this inline assembly block

       "r0", "r1", "r2", "r3", "ip", "lr",

       "d0",  "d1",  "d2",  "d3",  "d4",  "d5",  "d6",  "d7",

       // Also unconditionally mark d16-d31 registers as clobbered even though

       // they actually don't exist in vfpv2 and vfpv3-d16 variants. There is

       // no way to identify VFP variant using preprocessor at the momemnt

       // (see http://gcc.gnu.org/PR46128 for more details), but fortunately

       // current versions of gcc do not seem to complain about these registers

       // even when this code is compiled with '-mfpu=vfpv3-d16' option.

       // If gcc becomes more strict in the future and/or provides a way to

       // identify VFP variant, the following d16-d31 registers list needs

       // to be wrapped into some #ifdef

       "d16", "d17", "d18", "d19", "d20", "d21", "d22", "d23",

       "d24", "d25", "d26", "d27", "d28", "d29", "d30", "d31"

   );

   return result;

 }

 #endif