在Habr撰写这篇纯技术文章的过程中，Habr设法成为了WHO的一个当地办事处，现在我什至感到羞耻地出版了该文章……但人们对IT人员尚未逃离的希望充满了希望，她将找到她的读者。或不？
标准C库和C本身一直令我赞叹不已，尽管它具有极简主义，但它仍然震撼了最初的那些人的精神。 红眼 骇客。第一个正式标准（ANSI C，也称为C89，又称为 ANS X3.159-1989，后来，C90和IEC 9899：1990）的草案定义了145个功能和宏，其中约有25个是变体（由于缺少用重载语言表示），而26纯粹是数学上的。在第二版中，K＆R引用了114个函数（加上数学函数），并将其余函数视为奇异函数。在草案C11中，已经有348个函数，但是数学中有一百多个函数，而“过载”则有90多个。现在让我们看一下Boost，那里只有160个库。 hur我...
在这一百零五种函数中，总有：信号处理，变化函数（25年后才达到解释PHP的水平，而在曾经蓬勃发展的Delphi中，它们仍然缺失）和大约50个字符串函数，如printf（）（mmm ... JavaScript），strftime（）（...）和scanf（）（是常规的廉价替代品）。
一直都有setjmp（） / longjmp（），它允许您实现其他语言中熟悉的异常机制，而不会超出可移植C的范围。这里是关于它们的讨论-Quake World，堆栈，寄存器，汇编器和其他物料，cherry是一个奇怪的统计数据（破坏者：Visual Studio并不是恒定的，因为三月的野兔，并且投入 saneex.c了一半的时间）。
隐藏文字¹ .
² , . 270 , 80 — . , . K&R — , .
³ , ANSI ISO , . .
⁴ , «» TinyURL, URL , і . , -. urlex.org.
目录：
, — setjmp()/longjmp(), setjmp.h, «SJLJ» ( , ). C89 , -, , ( — , — ).
, , , zzeng. , , , ¹, , ,
¹ CException — 60 , , , ANSI C, finally , .
, — , , , , , « ». (, , - «» , errno . — , .)
, :
- , - , ( , — ,
if (error) return -1;) - - — , ,
. , .
setjmp()/longjmp()
, longjmp() — goto, setjmp() —
, , , , setjmp.h ^W ? , setjmp() , (, , ). ,
, , setjmp() — fork() POSIX . , *nix’ API WinAPI, — , . — « , ?»… .
, , — , () . — ( Intel’ — ), — ( Intel’ — -, ). :
void sub(int s) {
char buf[256];
sub(2);
}
int main(int m) {
sub(1);
}
— tcc (Tiny C Compiler) - . . tcc . sub() ( Intel, ):
sub esp, 100h ;
mov eax, 2 ;
push eax
call sub_401000 ; sub()
add esp, 4 ; (= cdecl)
:
— ( Intel… , ). ESP (RSP x86_64). setjmp() ESP/RSP, , jmp_buf, . longjmp() ( ) — , , setjmp(), (). , «undo» (, ).
setjmp() jmp FEF8h (FDF0h .. — ) , :
void sub(int s) {
char buf[256];
jmp_buf jmp;
setjmp(jmp);
sub(2);
}
, , ™:
- — , , ! — , , , setjmp() , longjmp() , setjmp()
, -, clobbering
. :
#include <stdlib.h>
#include <stdio.h>
#include <setjmp.h>
int main(void) {
int i;
jmp_buf jmp;
i = rand();
if (setjmp(jmp) == 0) {
i = rand();
printf("%d\n", i);
longjmp(jmp, 1);
} else {
printf("%d\n", i);
}
}
: ?
: . -!
, gcc. -O0, , :
; int main(void) {
push ebp ; ( stack frame)
mov ebp, esp ; EBP ESP ( )
sub esp, E0h
...
call _rand ; EAX
mov [ebp-D4h], eax ; i = rand(); i (EBP-D4h)
...
; if (... == 0) { ; setjmp()
call _rand
mov [ebp-D4h], eax ; i = rand();
; printf("%d\n", i);
mov eax, [ebp-D4h] ; i
mov esi, eax
lea edi, format ; "%d\n"
mov eax, 0
call _printf
...
; } else { ; setjmp()
mov eax, [ebp-D4h] ; i,
mov esi, eax
lea edi, format ; "%d\n"
mov eax, 0
call _printf
, i ( EBP - D4h). , :
- 256 char int jmp_buf, 4 200 , 20 - , 224 (E0h) 100h,
- ESP setjmp()
FFF8h - E0h = FF18h ( FEF8h), jmp
- i, i (
FF18h) - longjmp()
FF18h, , i , - , (jmp), main() ( )
-O1, :
; stack frame , ESP
sub esp, E8h
...
call _rand
mov [esp+E8h-DCh], eax ; i = rand(); , -O0
...
; -O1 - , else ,
; if (setjmp() == 0) ( - ),
; ;
; if (... == 0) {
call _rand
mov esi, eax ; ! i
; printf("%d\n", i);
lea edi, format ; "%d\n"
mov eax, 0
call _printf
...
; } else {
mov esi, [esp+E8h-DCh] ; ! i
lea edi, format ; "%d\n"
mov eax, 0
call _printf
, -O1 gcc :
test.c:6:11: warning: variable ‘i’ might be clobbered by ‘longjmp’ or ‘vfork’ [-Wclobbered]
? i , ( if) gcc, i printf(), ESI, ( ESI printf(), . ABI, . 22 — RDI (format), RSI (i), …). - :
ESP + E8h - DCh rand()- ESI
- printf() ( ) ()
- longjmp() , ,
- printf() ( else) , , ,
- ESI, (, printf() longjmp())
, :
stack[i] = rand(); // i = rand(); (1)
if (setjmp(jmp) == 0) {
ESI = rand(); // i = rand(); (2)
printf("%d\n", ESI); // (2)
longjmp(jmp, 1); //
} else {
printf("%d\n", stack[i]); // (1)
// :
printf("%d\n", ESI); // , -
// "" ( printf() longjmp())
}
, , gcc rand() ESI ( -O3). SO , x86_64 ( ) , EAX. ? , gcc printf() else longjmp(), rand() printf() — , i .
— .
volatile
« » — volatile ( — «»). , , , :
volatile int i;
-O1 if:
; :
call _rand
mov esi, eax
; :
call _rand
mov [rsp+E8h-DCh], eax
mov esi, [rsp+E8h-DCh]
; :
call _rand
mov esi, eax
mov [rsp+E8h-DCh], eax
, ():
if (setjmp(jmp) == 0) {
ESI = stack[i] = rand();
IRL
, — -volatile , SJLJ . — , SJLJ
, , — , « », , , - (). , DrMefistO.
Quake World WinMain(), jmp_buf, , « continue»:
// WinQuake/host.c
jmp_buf host_abortserver;
void Host_EndGame (char *message, ...)
{
...
if (cls.demonum != -1)
CL_NextDemo ();
else
CL_Disconnect ();
longjmp (host_abortserver, 1);
}
void Host_Error (char *error, ...)
{
...
if (cls.state == ca_dedicated)
Sys_Error ("Host_Error: %s\n",string); // dedicated servers exit
CL_Disconnect ();
cls.demonum = -1;
inerror = false;
longjmp (host_abortserver, 1);
}
void _Host_Frame (float time)
{
static double time1 = 0;
static double time2 = 0;
static double time3 = 0;
int pass1, pass2, pass3;
if (setjmp (host_abortserver) )
return; // something bad happened, or the server disconnected
...
}
// QW/client/sys_win.c
int WINAPI WinMain (...)
{
...
while (1)
{
...
newtime = Sys_DoubleTime ();
time = newtime - oldtime;
Host_Frame (time);
oldtime = newtime;
}
/* return success of application */
return TRUE;
}
, — . , setjmp() glibc , . :
- , , SJLJ/
saneex.c - -…- (
, ) , - — , - , — zero-cost exceptions (, , zero-cost try), try, () — goto , , , «» , -,
«» zero-cost exceptions , volatile-, , ( longjmp()). , :
, saneex.c zero-cost ( — ), setjmp(), ? , ? — .
« », main() 100 try/catch throw().
C:
#include <stdio.h>
#include <time.h>
#include "saneex.h"
int main(void) {
for (int i = 0; i < 100000; i++) {
try {
// ("" = ):
throw(msgex("A quick fox jumped over a red dog and a nyancat was spawned"));
// ("" = ):
time(NULL);
} catchall {
fprintf(stderr, "%s\n", curex().message);
} endtry
}
}
++ ( , cerr << fprintf()):
#include <iostream>
#include <vector>
#include <stdexcept>
#include <time.h>
int main() {
std::vector<int> vec{ 3, 4, 3, 1 };
for (int i = 0; i < 100000; i++) {
try {
// ("" = ):
int i{ vec.at(4) };
// ("" = ):
time(NULL);
}
catch (std::out_of_range & e) {
// << fprintf() 25-50%
//std::cerr << "Accessing a non-existent element: " << e.what() << '\n';
fprintf(stderr, "%s\n", e.what());
}
catch (std::exception & e) {
//std::cerr << "Exception thrown: " << e.what() << '\n';
fprintf(stderr, "%s\n", e.what());
}
catch (...) {
//std::cerr << "Some fatal error\n";
fprintf(stderr, "Some fatal error");
}
}
return 0;
}
( 64-):
- Windows 10 2019 LTSC PowerShell
Measure-Command { test.exe 2>$null } - Live CD Ubuntu time
Windows __try/__except, :
#include <windows.h>
#include <stdio.h>
#include <vector>
int filterExpression(EXCEPTION_POINTERS* ep) {
ep->ContextRecord->Eip += 8;
return EXCEPTION_EXECUTE_HANDLER;
}
int main() {
static int zero;
for (int i = 0; i < 100000; i++) {
__try {
zero = 1 / zero;
__asm {
nop
nop
nop
nop
nop
nop
nop
}
printf("Past the exception.\n");
}
__except (filterExpression(GetExceptionInformation())) {
printf("Handler called.\n");
}
}
}
— , :
error C2712: Cannot use __try in functions that require object unwinding
, , . 1100-1300 (Debug Release, x86) — , VS, , g++.
№ ()¹ saneex
1. VS 2019 v16.0.0 Debug x64 saneex.c 9713 / 8728 = 1.1 1.8 / 1.8
2. VS 2019 v16.0.0 Debug x64 saneex.c 95 / 46 = 2 4.5 / 2.3
3. VS 2019 v16.0.0 Debug x64 C++ 5449 / 4750² = 1.6
4. VS 2019 v16.0.0 Debug x64 C++ 21 / 20 = 1
5. VS 2019 v16.0.0 Release x64 saneex.c 8542³ / 182 = 47 1.8 / 0.4
6. VS 2019 v16.0.0 Release x64 saneex.c 80³ / 23 = 3.5 8 / 1.8
7. VS 2019 v16.0.0 Release x64 C++ 4669³ / 420 = 11
8. VS 2019 v16.0.0 Release x64 C++ 10³ / 13 = 0.8
9. gcc 9.2.1 -O0 x64 saneex.c 71 / 351 = 0.2 0.2 / 0.6
10. gcc 9.2.1 -O0 x64 saneex.c 6 / 39 = 0.2 1.5 / 1.1
11. g++ 9.2.1 -O0 x64 C++ 378 / 630 = 0.6
12. g++ 9.2.1 -O0 x64 C++ 4 / 37 = 0.1
13. gcc 9.2.1 -O3 x64 saneex.c 66 / 360 = 0.2 0.2 / 0.6
14. gcc 9.2.1 -O3 x64 saneex.c 5 / 23 = 0.2 1 / 0.6
15. g++ 9.2.1 -O3 x64 C++ 356 / 605 = 0.6
16. g++ 9.2.1 -O3 x64 C++ 5 / 38 = 0.1
¹ Windows 7 SP1 x64 VS 2017 v15.9.17 gcc cygwin.
² : fprintf() cerr <<, 3 : 1386/1527 .
³ VS , .
… :
- / «» VS. — .
cerr << fprintf() VS 3-4 ( 3). ?- try throw — (4-28 100 ).
- «» Debug VS,
saneex.c , ( 2.3 VS, 5 gcc/g++), try throw — , . !
… . !
use-case — try throw (« , »), setjmp(), , , , . , , setjmp() OpenBSD (1.45) — Solaris. 2005 . «» — , .
, …
— saneex.c
, :
- Visual Studio
- , throw() , finally catch ( )
- ( static)
- - (__thread/_Thread_local)
- public domain (CC0)
GitHub. , . saneex-demo.c :
01. #include <stdio.h>
02. #include "saneex.h"
03.
04. int main(void) {
05. sxTag = "SaneC's Exceptions Demo";
06.
07. try {
08. printf("Enter a message to fail with: [] [1] [2] [!] ");
09.
10. char msg[50];
11. thrif(!fgets(msg, sizeof(msg), stdin), "fgets() error");
12.
13. int i = strlen(msg) - 1;
14. while (i >= 0 && msg[i] <= ' ') { msg[i--] = 0; }
15.
16. if (msg[0]) {
17. errno = atoi(msg);
18. struct SxTraceEntry e = newex();
19. e = sxprintf(e, "Your message: %s", msg);
20. e.uncatchable = msg[0] == '!';
21. throw(e);
22. }
23.
24. puts("End of try body");
25.
26. } catch (1) {
27. puts("Caught in catch (1)");
28. sxPrintTrace();
29.
30. } catch (2) {
31. puts("Caught in catch (2)");
32. errno = 123;
33. rethrow(msgex("calling rethrow() with code 123"));
34.
35. } catchall {
36. printf("Caught in catchall, message is: %s\n", curex().message);
37.
38. } finally {
39. puts("Now in finally");
40.
41. } endtry
42.
43. puts("End of main()");
44. }
, :
End of try body
Now in finally
End of main()
- , , (1),
catch (1) (26.), :
Caught in catch (1)
Your message: 1 hello, habr!
...at saneex-demo.c:18, code 1
Now in finally
End of main()
Caught in catch (2)
Now in finally
Uncaught exception (code 123) - terminating. Tag: SaneC's Exceptions Demo
Your message: 2 TM! kak tam blok4ain?
...at saneex-demo.c:18, code 2
calling rethrow() with code 123
...at saneex-demo.c:33, code 123
rethrown by ENDTRY
...at saneex-demo.c:41, code 123
!, «» (uncatchable; 20.) — try , ( catch, finally), — abort():
Caught in catch (1)
Your message: ! it is a good day to die
...UNCATCHABLE at saneex-demo.c:18, code 0
Now in finally
Uncaught exception (code 0) - terminating. Tag: SaneC's Exceptions Demo
Your message: ! it is a good day to die
...UNCATCHABLE at saneex-demo.c:18, code 0
UNCATCHABLE rethrown by ENDTRY
...at saneex-demo.c:41, code 0
Caught in catchall, message is: Your message: 3 we need more gold
Now in finally
End of main()
«»
. , ( MSVC¹), C11 (TLS):
#define SX_THREAD_LOCAL _Thread_local
¹ Microsoft - open source,
sxTag (05.) — , stderr. — (__DATE__ __TIME__).
SxTraceEntry ( stack trace). — (struct SxTraceEntry) {...}:
newex() — ; __FILE__, __LINE__ = errno ( , fgets(); 11.)
- 1 1 ( setjmp() 0 ),
catch (0)
msgex(m) — newex(), ( )exex(m, e) — msgex(), ; free() :
try {
TimeoutException *e = malloc(sizeof(*e));
e->elapsed = timeElapsed;
e->limit = MAX_TIMEOUT;
errno = 146;
throw(exex("Connection timed out", e));
} catch (146) {
printf("%s after %d\n", curex().message,
// void *SxTraceEntry.extra:
((TimeoutException *) curex().extra)->elapsed);
} endtry
, , designated initializers C99 ( Visual Studio 2013+):
throw( (struct SxTraceEntry) {.message = "kaboom!"} );
:
throw(e) — SxTraceEntryrethrow(e) — throw(), stack trace; catch/catchallthrif(x, m) — ; if (x) SxTraceEntry x + m «»thri(x) — thrif(), m
«» — fgets() (11.), . fgets() ( EOF: ./a.out </dev/null), . :
thri(read(0xBaaD, buf, nbyte));
// errno = 9, "Bad file descriptor"
// Assertion error: read(0xBaaD, buf, nbyte);
… « »
( !):
- endtry — ( try)
- return try endtry — , ; PR
«», volatile. «» — (. longjmp()), , try, catch/catchall/finally endtry, volatile. . :
int foo = 1;
try {
foo = 2;
// foo
} catchall {
// !
} finally {
// !
} endtry
// !
volatile :
volatile int foo = 1;
try {
...
:
- () :
struct SxTryContext — try, — , jmp_buf ; , :
try {
try {
//
} endtry
} endtry
struct SxTraceEntry — stack trace, , ; , try:
try { // SxTryContext
try { // SxTryContext
// SxTraceEntry
throw(msgex(" !"));
// SxTraceEntry
} catchall {
// SxTraceEntry
rethrow(msgex(" !"));
// SxTraceEntry (*)
} endtry
} endtry
rethrow() throw(), SxTraceEntry (*) , — (stack trace ). , sxAddTraceEntry(e).
try和其他结构元素是宏（-您的K.O.）。{ }后面的括号是可选的。最后，一切都归结为以下伪代码：
try { int _sxLastJumpCode = setjmp(add_context()¹);
bool handled = false;
if (_sxLastJumpCode == 0) {
throw(msgex("Mama mia!")); clearTrace();
sxAddTraceEntry(msgex(...));
if (count_contexts() == 0) {
fprintf(stderr, "Shurik, vs propalo!");
sxPrintTrace();
exit(curex().code);
} else {
longjmp(top_context());
}
} catch (9000) { } else if (_sxLastJumpCode == 9000) {
handled = true;
} catchall { } else {
handled = true;
} finally { }
// finally { }
} endtry remove_context();
if (!handled) {
// throw()
}
¹带_的名称未在库中使用，它们是抽象的。
我认为，在对 SJLJ的工作原理进行详细说明之后，这里不需要评论其他内容，因此，让我请您发言。