本身可以通过关闭C++异常支持，rtti支持来减少代码段的大小，使用如下的命令行参数：-fno-exceptions -fno-unwind-tables -fno-asynchronous-unwind-tables
但是有时候却并不能彻底关闭，比如说unity引擎开发的ios游戏，il2cpp后的C++代码与其它代码混在一起，il2cpp的代码是需要异常支持的。此时我们可以考虑将自己的C++代码加上noexcept关键字，这样也可以减少代码段。
但是有一些情况下，加noexcept并不能减少代码段，还可能会增加，看起来在这种情况下，“省略帧指针优化”将不起作用（这个优化的命令行为：omit-frame-pointer）
举个例子：
1 // 2 // Encodes input (uint32) into output (uint8). 3 // Assumes len is a multiple of 4. 4 // 5 __attribute__((__noinline__)) 6 __attribute__((visibility("default"))) 7 void __appMD5Encode_common(uint8* output, const uint32* input, int len) 8 { 9 int i, j; 10 11 for (i = 0, j = 0; j < len; i++, j += 4) { 12 output[j] = (uint8)(input[i] & 0xff); 13 output[j + 1] = (uint8)((input[i] >> 8) & 0xff); 14 output[j + 2] = (uint8)((input[i] >> 16) & 0xff); 15 output[j + 3] = (uint8)((input[i] >> 24) & 0xff); 16 } 17 } 18 19 __attribute__((__noinline__)) 20 __attribute__((visibility("default"))) 21 void __appMD5Encode_noexcept(uint8* output, const uint32* input, int len) noexcept 22 { 23 int i, j; 24 25 for (i = 0, j = 0; j < len; i++, j += 4) { 26 output[j] = (uint8)(input[i] & 0xff); 27 output[j + 1] = (uint8)((input[i] >> 8) & 0xff); 28 output[j + 2] = (uint8)((input[i] >> 16) & 0xff); 29 output[j + 3] = (uint8)((input[i] >> 24) & 0xff); 30 } 31 } 32 33 typedef void (*func_type)(uint8*, const uint32*, int); 34 35 void* g_commonFuncPtr = (void*) & __appMD5Encode_common; 36 void* g_noexceptFuncPtr = (void*)&__appMD5Encode_noexcept; 37 38 39 __attribute__((visibility("default"))) void appMD5Encode_noexcept_call_common(uint8* output, const uint32* input, int len) noexcept 40 { 41 __appMD5Encode_common(output, input, len); 42 } 43 44 __attribute__((visibility("default"))) void appMD5Encode_noexcept_call_noexcept(uint8* output, const uint32* input, int len) noexcept 45 { 46 __appMD5Encode_noexcept(output, input, len); 47 } 48 49 __attribute__((visibility("default"))) void appMD5Encode_noexcept_call_common_pointer(uint8* output, const uint32* input, int len) noexcept 50 { 51 ((void (*)(uint8*, const uint32*, int))g_commonFuncPtr)(output, input, len); 52 } 53 54 __attribute__((visibility("default"))) void appMD5Encode_noexcept_call_noexcept_pointer(uint8* output, const uint32* input, int len) noexcept 55 { 56 ((void (*)(uint8*, const uint32*, int))g_noexceptFuncPtr)(output, input, len); 57 } 58 59 __attribute__((visibility("default"))) void appMD5Encode_noexcept_call_common_pointer_extra_noexcept(uint8* output, const uint32* input, int len) noexcept 60 { 61 ((void (*)(uint8*, const uint32*, int) noexcept )g_commonFuncPtr)(output, input, len); 62 } 63 64 __attribute__((visibility("default"))) void appMD5Encode_noexcept_call_noexcept_pointer_extra_noexcept(uint8* output, const uint32* input, int len) noexcept 65 { 66 ((void (*)(uint8*, const uint32*, int) noexcept)g_noexceptFuncPtr)(output, input, len); 67 } 68 69 __attribute__((visibility("default"))) void appMD5Encode_common_call_common(uint8* output, const uint32* input, int len) 70 { 71 __appMD5Encode_common(output, input, len); 72 } 73 74 75 __attribute__((visibility("default"))) void appMD5Encode_common_call_noexcept(uint8* output, const uint32* input, int len) 76 { 77 __appMD5Encode_noexcept(output, input, len); 78 } 79 80 __attribute__((visibility("default"))) void appMD5Encode_common_call_common_pointer(uint8* output, const uint32* input, int len) 81 { 82 ((void (*)(uint8*, const uint32*, int))g_commonFuncPtr)(output, input, len); 83 } 84 85 __attribute__((visibility("default"))) void appMD5Encode_common_call_noexcept_pointer(uint8* output, const uint32* input, int len) 86 { 87 ((void (*)(uint8*, const uint32*, int))g_noexceptFuncPtr)(output, input, len); 88 } 89 90 __attribute__((visibility("default"))) void appMD5Encode_common_call_common_pointer_extra_noexcept(uint8* output, const uint32* input, int len) 91 { 92 ((void (*)(uint8*, const uint32*, int) noexcept)g_commonFuncPtr)(output, input, len); 93 } 94 95 __attribute__((visibility("default"))) void appMD5Encode_common_call_noexcept_pointer_extra_noexcept(uint8* output, const uint32* input, int len) 96 { 97 ((void (*)(uint8*, const uint32*, int) noexcept )g_noexceptFuncPtr)(output, input, len); 98 }
观察汇编可以发现端倪：
.text:000000000000F10C ; =============== S U B R O U T I N E ======================================= .text:000000000000F10C .text:000000000000F10C .text:000000000000F10C ; __int64 __fastcall __appMD5Encode_common(unsigned __int8 *, const unsigned int *, int) .text:000000000000F10C EXPORT _Z21__appMD5Encode_commonPhPKji .text:000000000000F10C _Z21__appMD5Encode_commonPhPKji ; CODE XREF: __appMD5Encode_common(uchar *,uint const*,int)+C↑j .text:000000000000F10C ; appMD5Encode_noexcept_call_common_pointer_extra_noexcept(uchar *,uint const*,int)+C↓j ... .text:000000000000F10C ; __unwind { .text:000000000000F10C SUBS W8, W2, #1 .text:000000000000F110 B.LT locret_F150 .text:000000000000F114 LSR W8, W8, #2 .text:000000000000F118 ADD W8, W8, #1 .text:000000000000F11C ADD X9, X0, #3 .text:000000000000F120 .text:000000000000F120 loc_F120 ; CODE XREF: __appMD5Encode_common(uchar *,uint const*,int)+40↓j .text:000000000000F120 LDR W10, [X1] .text:000000000000F124 SUBS X8, X8, #1 .text:000000000000F128 STURB W10, [X9,#-3] .text:000000000000F12C LDR W10, [X1] .text:000000000000F130 LSR W10, W10, #8 .text:000000000000F134 STURB W10, [X9,#-2] .text:000000000000F138 LDRH W10, [X1,#2] .text:000000000000F13C STURB W10, [X9,#-1] .text:000000000000F140 LDRB W10, [X1,#3] .text:000000000000F144 ADD X1, X1, #4 .text:000000000000F148 STRB W10, [X9],#4 .text:000000000000F14C B.NE loc_F120 .text:000000000000F150 .text:000000000000F150 locret_F150 ; CODE XREF: __appMD5Encode_common(uchar *,uint const*,int)+4↑j .text:000000000000F150 RET .text:000000000000F150 ; } // starts at F10C .text:000000000000F150 ; End of function __appMD5Encode_common(uchar *,uint const*,int) .text:000000000000F150 .text:000000000000F154 .text:000000000000F154 ; =============== S U B R O U T I N E ======================================= .text:000000000000F154 .text:000000000000F154 .text:000000000000F154 ; __int64 __fastcall __appMD5Encode_noexcept(unsigned __int8 *, const unsigned int *, int) .text:000000000000F154 EXPORT _Z23__appMD5Encode_noexceptPhPKji .text:000000000000F154 _Z23__appMD5Encode_noexceptPhPKji ; CODE XREF: __appMD5Encode_noexcept(uchar *,uint const*,int)+C↑j .text:000000000000F154 ; appMD5Encode_noexcept_call_noexcept_pointer_extra_noexcept(uchar *,uint const*,int)+C↓j ... .text:000000000000F154 ; __unwind { .text:000000000000F154 SUBS W8, W2, #1 .text:000000000000F158 B.LT locret_F198 .text:000000000000F15C LSR W8, W8, #2 .text:000000000000F160 ADD W8, W8, #1 .text:000000000000F164 ADD X9, X0, #3 .text:000000000000F168 .text:000000000000F168 loc_F168 ; CODE XREF: __appMD5Encode_noexcept(uchar *,uint const*,int)+40↓j .text:000000000000F168 LDR W10, [X1] .text:000000000000F16C SUBS X8, X8, #1 .text:000000000000F170 STURB W10, [X9,#-3] .text:000000000000F174 LDR W10, [X1] .text:000000000000F178 LSR W10, W10, #8 .text:000000000000F17C STURB W10, [X9,#-2] .text:000000000000F180 LDRH W10, [X1,#2] .text:000000000000F184 STURB W10, [X9,#-1] .text:000000000000F188 LDRB W10, [X1,#3] .text:000000000000F18C ADD X1, X1, #4 .text:000000000000F190 STRB W10, [X9],#4 .text:000000000000F194 B.NE loc_F168 .text:000000000000F198 .text:000000000000F198 locret_F198 ; CODE XREF: __appMD5Encode_noexcept(uchar *,uint const*,int)+4↑j .text:000000000000F198 RET .text:000000000000F198 ; } // starts at F154 .text:000000000000F198 ; End of function __appMD5Encode_noexcept(uchar *,uint const*,int) .text:000000000000F198 .text:000000000000F19C .text:000000000000F19C ; =============== S U B R O U T I N E ======================================= .text:000000000000F19C .text:000000000000F19C .text:000000000000F19C ; __int64 __fastcall appMD5Encode_noexcept_call_common(unsigned __int8 *, const unsigned int *, int) .text:000000000000F19C EXPORT _Z33appMD5Encode_noexcept_call_commonPhPKji .text:000000000000F19C _Z33appMD5Encode_noexcept_call_commonPhPKji .text:000000000000F19C ; DATA XREF: LOAD:0000000000003310↑o .text:000000000000F19C ; __unwind { .text:000000000000F19C B ._Z21__appMD5Encode_commonPhPKji ; __appMD5Encode_common(uchar *,uint const*,int) .text:000000000000F19C ; } // starts at F19C .text:000000000000F19C ; End of function appMD5Encode_noexcept_call_common(uchar *,uint const*,int) .text:000000000000F19C .text:000000000000F1A0 .text:000000000000F1A0 ; =============== S U B R O U T I N E ======================================= .text:000000000000F1A0 .text:000000000000F1A0 .text:000000000000F1A0 ; __int64 __fastcall appMD5Encode_noexcept_call_noexcept(unsigned __int8 *, const unsigned int *, int) .text:000000000000F1A0 EXPORT _Z35appMD5Encode_noexcept_call_noexceptPhPKji .text:000000000000F1A0 _Z35appMD5Encode_noexcept_call_noexceptPhPKji .text:000000000000F1A0 ; DATA XREF: LOAD:0000000000002650↑o .text:000000000000F1A0 ; __unwind { .text:000000000000F1A0 B ._Z23__appMD5Encode_noexceptPhPKji ; __appMD5Encode_noexcept(uchar *,uint const*,int) .text:000000000000F1A0 ; } // starts at F1A0 .text:000000000000F1A0 ; End of function appMD5Encode_noexcept_call_noexcept(uchar *,uint const*,int) .text:000000000000F1A0 .text:000000000000F1A4 .text:000000000000F1A4 ; =============== S U B R O U T I N E ======================================= .text:000000000000F1A4 .text:000000000000F1A4 .text:000000000000F1A4 ; __int64 __fastcall appMD5Encode_noexcept_call_common_pointer(unsigned __int8 *, const unsigned int *, int) .text:000000000000F1A4 EXPORT _Z41appMD5Encode_noexcept_call_common_pointerPhPKji .text:000000000000F1A4 _Z41appMD5Encode_noexcept_call_common_pointerPhPKji .text:000000000000F1A4 ; DATA XREF: LOAD:0000000000002F98↑o .text:000000000000F1A4 .text:000000000000F1A4 var_10 = -0x10 .text:000000000000F1A4 .text:000000000000F1A4 ; __unwind { // __gxx_personality_v0 .text:000000000000F1A4 STR X30, [SP,#var_10]! .text:000000000000F1A8 ADRP X8, #g_commonFuncPtr_ptr@PAGE .text:000000000000F1AC LDR X8, [X8,#g_commonFuncPtr_ptr@PAGEOFF] .text:000000000000F1B0 LDR X8, [X8] ; __appMD5Encode_common(uchar *,uint const*,int) .text:000000000000F1B4 ; try { .text:000000000000F1B4 BLR X8 .text:000000000000F1B4 ; } // starts at F1B4 .text:000000000000F1B8 LDR X30, [SP+0x10+var_10],#0x10 .text:000000000000F1BC RET .text:000000000000F1C0 ; --------------------------------------------------------------------------- .text:000000000000F1C0 ; catch(...) // owned by F1B4 .text:000000000000F1C0 BL __clang_call_terminate .text:000000000000F1C0 ; } // starts at F1A4 .text:000000000000F1C0 ; End of function appMD5Encode_noexcept_call_common_pointer(uchar *,uint const*,int) .text:000000000000F1C0 .text:000000000000F1C4 .text:000000000000F1C4 ; =============== S U B R O U T I N E ======================================= .text:000000000000F1C4 .text:000000000000F1C4 .text:000000000000F1C4 ; __int64 __fastcall appMD5Encode_noexcept_call_noexcept_pointer(unsigned __int8 *, const unsigned int *, int) .text:000000000000F1C4 EXPORT _Z43appMD5Encode_noexcept_call_noexcept_pointerPhPKji .text:000000000000F1C4 _Z43appMD5Encode_noexcept_call_noexcept_pointerPhPKji .text:000000000000F1C4 ; DATA XREF: LOAD:0000000000003C40↑o .text:000000000000F1C4 .text:000000000000F1C4 var_10 = -0x10 .text:000000000000F1C4 .text:000000000000F1C4 ; __unwind { // __gxx_personality_v0 .text:000000000000F1C4 STR X30, [SP,#var_10]! .text:000000000000F1C8 ADRP X8, #g_noexceptFuncPtr_ptr@PAGE .text:000000000000F1CC LDR X8, [X8,#g_noexceptFuncPtr_ptr@PAGEOFF] .text:000000000000F1D0 LDR X8, [X8] ; __appMD5Encode_noexcept(uchar *,uint const*,int) .text:000000000000F1D4 ; try { .text:000000000000F1D4 BLR X8 .text:000000000000F1D4 ; } // starts at F1D4 .text:000000000000F1D8 LDR X30, [SP+0x10+var_10],#0x10 .text:000000000000F1DC RET .text:000000000000F1E0 ; --------------------------------------------------------------------------- .text:000000000000F1E0 ; catch(...) // owned by F1D4 .text:000000000000F1E0 BL __clang_call_terminate .text:000000000000F1E0 ; } // starts at F1C4 .text:000000000000F1E0 ; End of function appMD5Encode_noexcept_call_noexcept_pointer(uchar *,uint const*,int) .text:000000000000F1E0 .text:000000000000F1E4 .text:000000000000F1E4 ; =============== S U B R O U T I N E ======================================= .text:000000000000F1E4 .text:000000000000F1E4 .text:000000000000F1E4 ; __int64 __fastcall appMD5Encode_noexcept_call_common_pointer_extra_noexcept(unsigned __int8 *, const unsigned int *, int) .text:000000000000F1E4 EXPORT _Z56appMD5Encode_noexcept_call_common_pointer_extra_noexceptPhPKji .text:000000000000F1E4 _Z56appMD5Encode_noexcept_call_common_pointer_extra_noexceptPhPKji .text:000000000000F1E4 ; DATA XREF: LOAD:0000000000002AA0↑o .text:000000000000F1E4 ; __unwind { .text:000000000000F1E4 ADRP X8, #g_commonFuncPtr_ptr@PAGE .text:000000000000F1E8 LDR X8, [X8,#g_commonFuncPtr_ptr@PAGEOFF] .text:000000000000F1EC LDR X3, [X8] ; __appMD5Encode_common(uchar *,uint const*,int) .text:000000000000F1F0 BR X3 ; __appMD5Encode_common(uchar *,uint const*,int) .text:000000000000F1F0 ; } // starts at F1E4 .text:000000000000F1F0 ; End of function appMD5Encode_noexcept_call_common_pointer_extra_noexcept(uchar *,uint const*,int) .text:000000000000F1F0 .text:000000000000F1F4 .text:000000000000F1F4 ; =============== S U B R O U T I N E ======================================= .text:000000000000F1F4 .text:000000000000F1F4 .text:000000000000F1F4 ; __int64 __fastcall appMD5Encode_noexcept_call_noexcept_pointer_extra_noexcept(unsigned __int8 *, const unsigned int *, int) .text:000000000000F1F4 EXPORT _Z58appMD5Encode_noexcept_call_noexcept_pointer_extra_noexceptPhPKji .text:000000000000F1F4 _Z58appMD5Encode_noexcept_call_noexcept_pointer_extra_noexceptPhPKji .text:000000000000F1F4 ; DATA XREF: LOAD:00000000000024D0↑o .text:000000000000F1F4 ; __unwind { .text:000000000000F1F4 ADRP X8, #g_noexceptFuncPtr_ptr@PAGE .text:000000000000F1F8 LDR X8, [X8,#g_noexceptFuncPtr_ptr@PAGEOFF] .text:000000000000F1FC LDR X3, [X8] ; __appMD5Encode_noexcept(uchar *,uint const*,int) .text:000000000000F200 BR X3 ; __appMD5Encode_noexcept(uchar *,uint const*,int) .text:000000000000F200 ; } // starts at F1F4 .text:000000000000F200 ; End of function appMD5Encode_noexcept_call_noexcept_pointer_extra_noexcept(uchar *,uint const*,int) .text:000000000000F200 .text:000000000000F204 .text:000000000000F204 ; =============== S U B R O U T I N E ======================================= .text:000000000000F204 .text:000000000000F204 .text:000000000000F204 ; __int64 __fastcall appMD5Encode_common_call_common(unsigned __int8 *, const unsigned int *, int) .text:000000000000F204 EXPORT _Z31appMD5Encode_common_call_commonPhPKji .text:000000000000F204 _Z31appMD5Encode_common_call_commonPhPKji .text:000000000000F204 ; DATA XREF: LOAD:0000000000002EA8↑o .text:000000000000F204 ; __unwind { .text:000000000000F204 B ._Z21__appMD5Encode_commonPhPKji ; __appMD5Encode_common(uchar *,uint const*,int) .text:000000000000F204 ; } // starts at F204 .text:000000000000F204 ; End of function appMD5Encode_common_call_common(uchar *,uint const*,int) .text:000000000000F204 .text:000000000000F208 .text:000000000000F208 ; =============== S U B R O U T I N E ======================================= .text:000000000000F208 .text:000000000000F208 .text:000000000000F208 ; __int64 __fastcall appMD5Encode_common_call_noexcept(unsigned __int8 *, const unsigned int *, int) .text:000000000000F208 EXPORT _Z33appMD5Encode_common_call_noexceptPhPKji .text:000000000000F208 _Z33appMD5Encode_common_call_noexceptPhPKji .text:000000000000F208 ; DATA XREF: LOAD:0000000000002320↑o .text:000000000000F208 ; __unwind { .text:000000000000F208 B ._Z23__appMD5Encode_noexceptPhPKji ; __appMD5Encode_noexcept(uchar *,uint const*,int) .text:000000000000F208 ; } // starts at F208 .text:000000000000F208 ; End of function appMD5Encode_common_call_noexcept(uchar *,uint const*,int) .text:000000000000F208 .text:000000000000F20C .text:000000000000F20C ; =============== S U B R O U T I N E ======================================= .text:000000000000F20C .text:000000000000F20C .text:000000000000F20C ; __int64 __fastcall appMD5Encode_common_call_common_pointer(unsigned __int8 *, const unsigned int *, int) .text:000000000000F20C EXPORT _Z39appMD5Encode_common_call_common_pointerPhPKji .text:000000000000F20C _Z39appMD5Encode_common_call_common_pointerPhPKji .text:000000000000F20C ; DATA XREF: LOAD:0000000000002230↑o .text:000000000000F20C ; __unwind { .text:000000000000F20C ADRP X8, #g_commonFuncPtr_ptr@PAGE .text:000000000000F210 LDR X8, [X8,#g_commonFuncPtr_ptr@PAGEOFF] .text:000000000000F214 LDR X3, [X8] ; __appMD5Encode_common(uchar *,uint const*,int) .text:000000000000F218 BR X3 ; __appMD5Encode_common(uchar *,uint const*,int) .text:000000000000F218 ; } // starts at F20C .text:000000000000F218 ; End of function appMD5Encode_common_call_common_pointer(uchar *,uint const*,int) .text:000000000000F218 .text:000000000000F21C .text:000000000000F21C ; =============== S U B R O U T I N E ======================================= .text:000000000000F21C .text:000000000000F21C .text:000000000000F21C ; __int64 __fastcall appMD5Encode_common_call_noexcept_pointer(unsigned __int8 *, const unsigned int *, int) .text:000000000000F21C EXPORT _Z41appMD5Encode_common_call_noexcept_pointerPhPKji .text:000000000000F21C _Z41appMD5Encode_common_call_noexcept_pointerPhPKji .text:000000000000F21C ; DATA XREF: LOAD:0000000000002D10↑o .text:000000000000F21C ; __unwind { .text:000000000000F21C ADRP X8, #g_noexceptFuncPtr_ptr@PAGE .text:000000000000F220 LDR X8, [X8,#g_noexceptFuncPtr_ptr@PAGEOFF] .text:000000000000F224 LDR X3, [X8] ; __appMD5Encode_noexcept(uchar *,uint const*,int) .text:000000000000F228 BR X3 ; __appMD5Encode_noexcept(uchar *,uint const*,int) .text:000000000000F228 ; } // starts at F21C .text:000000000000F228 ; End of function appMD5Encode_common_call_noexcept_pointer(uchar *,uint const*,int) .text:000000000000F228 .text:000000000000F22C .text:000000000000F22C ; =============== S U B R O U T I N E ======================================= .text:000000000000F22C .text:000000000000F22C .text:000000000000F22C ; __int64 __fastcall appMD5Encode_common_call_common_pointer_extra_noexcept(unsigned __int8 *, const unsigned int *, int) .text:000000000000F22C EXPORT _Z54appMD5Encode_common_call_common_pointer_extra_noexceptPhPKji .text:000000000000F22C _Z54appMD5Encode_common_call_common_pointer_extra_noexceptPhPKji .text:000000000000F22C ; DATA XREF: LOAD:0000000000002620↑o .text:000000000000F22C ; __unwind { .text:000000000000F22C ADRP X8, #g_commonFuncPtr_ptr@PAGE .text:000000000000F230 LDR X8, [X8,#g_commonFuncPtr_ptr@PAGEOFF] .text:000000000000F234 LDR X3, [X8] ; __appMD5Encode_common(uchar *,uint const*,int) .text:000000000000F238 BR X3 ; __appMD5Encode_common(uchar *,uint const*,int) .text:000000000000F238 ; } // starts at F22C .text:000000000000F238 ; End of function appMD5Encode_common_call_common_pointer_extra_noexcept(uchar *,uint const*,int) .text:000000000000F238 .text:000000000000F23C .text:000000000000F23C ; =============== S U B R O U T I N E ======================================= .text:000000000000F23C .text:000000000000F23C .text:000000000000F23C ; __int64 __fastcall appMD5Encode_common_call_noexcept_pointer_extra_noexcept(unsigned __int8 *, const unsigned int *, int) .text:000000000000F23C EXPORT _Z56appMD5Encode_common_call_noexcept_pointer_extra_noexceptPhPKji .text:000000000000F23C _Z56appMD5Encode_common_call_noexcept_pointer_extra_noexceptPhPKji .text:000000000000F23C ; DATA XREF: LOAD:0000000000001EB8↑o .text:000000000000F23C ; __unwind { .text:000000000000F23C ADRP X8, #g_noexceptFuncPtr_ptr@PAGE .text:000000000000F240 LDR X8, [X8,#g_noexceptFuncPtr_ptr@PAGEOFF] .text:000000000000F244 LDR X3, [X8] ; __appMD5Encode_noexcept(uchar *,uint const*,int) .text:000000000000F248 BR X3 ; __appMD5Encode_noexcept(uchar *,uint const*,int) .text:000000000000F248 ; } // starts at F23C .text:000000000000F248 ; End of function appMD5Encode_common_call_noexcept_pointer_extra_noexcept(uchar *,uint const*,int) .text:000000000000F248
当使用noexcept的函数调用普通函数时并没有什么问题，如果在noexcept的函数中调用普通的函数指针，那么编译器会安插一些额外的指令来确保noexcept函数中抛出异常时执行terminate操作。所以，此时需要将函数指针也标记成noexcept，那么它将按照常规的方式来调用目标函数指针了。
((void (*)(uint8*, const uint32*, int) noexcept)g_noexceptFuncPtr)(output, input, len);
如上所示。