6.2. THREAD LOCAL STORAGE
Win32UninitializedTLSdataOne solution is to add__declspec( thread )modifier to the global variable, then it will be allocated in
theTLS(line 9):1 #include <stdint.h>
2 #include <windows.h>
3 #include <winnt.h>
4
5 // from the Numerical Recipes book:
6 #define RNG_a 1664525
7 #define RNG_c 1013904223
8
9 __declspec( thread ) uint32_t rand_state;
10
11 void my_srand (uint32_t init)
12 {
13 rand_state=init;
14 }
15
16 int my_rand ()
17 {
18 rand_state=rand_state*RNG_a;
19 rand_state=rand_state+RNG_c;
20 return rand_state & 0x7fff;
21 }
22
23 int main()
24 {
25 my_srand(0x12345678);
26 printf ("%d\n", my_rand());
27 };
Hiew shows us that there is a new PE section in the executable file:.tls.Listing 6.15: Optimizing MSVC 2013 x86
_TLS SEGMENT
_rand_state DD 01H DUP (?)
_TLS ENDS_DATA SEGMENT
$SG84851 DB '%d', 0aH, 00H
_DATA ENDS
_TEXT SEGMENT_init$ = 8 ; size = 4
_my_srand PROC
; FS:0=address of TIB
mov eax, DWORD PTR fs:__tls_array ; displayed in IDA as FS:2Ch
; EAX=address of TLS of process
mov ecx, DWORD PTR __tls_index
mov ecx, DWORD PTR [eax+ecx*4]
; ECX=current TLS segment
mov eax, DWORD PTR _init$[esp-4]
mov DWORD PTR _rand_state[ecx], eax
ret 0
_my_srand ENDP_my_rand PROC
; FS:0=address of TIB
mov eax, DWORD PTR fs:__tls_array ; displayed in IDA as FS:2Ch
; EAX=address of TLS of process
mov ecx, DWORD PTR __tls_index
mov ecx, DWORD PTR [eax+ecx*4]
; ECX=current TLS segment
imul eax, DWORD PTR _rand_state[ecx], 1664525
add eax, 1013904223 ; 3c6ef35fH