Re: [PATCH 0/1] MR2434: include: Add memory clobber to GCC asm statement in NtCurrentTeb().

[Mateusz Wajchęprzełóż (＠mati271828)]

> I don't see how can `NtCurrentTeb()` change between calls within the same function ("function" here means what is resulted after inlining)? Do you have a (hypothetical) example of such code?

TEB changes within `fiberProc` function:
```
#include <windows.h>
#include <stdio.h>

static inline __attribute__((always_inline)) void* getTEB()
{
    void* teb;
    __asm__ (".byte 0x65\n\tmovq (0x30),%0" : "=r" (teb));
    return teb;
}

static inline __attribute__((always_inline)) void* getTEB_volatile()
{
    void* teb;
    __asm__ volatile (".byte 0x65\n\tmovq (0x30),%0" : "=r" (teb));
    return teb;
}

void* testFiber;
void* mainThrFiber;
void* secondThrFiber;

static void WINAPI fiberProc(void* arg);
static DWORD WINAPI threadProc(void* arg);

int main()
{
    mainThrFiber = ConvertThreadToFiber(NULL);
    testFiber = CreateFiber(0, fiberProc, NULL);

printf("main TEB=%p; volatile TEB=%p\n", getTEB(), getTEB_volatile());

puts("main -> fiber");
    SwitchToFiber(testFiber);
    puts("main <- fiber");

HANDLE hThr = CreateThread(NULL, 0, threadProc, NULL, 0, NULL);
    WaitForSingleObject(hThr, INFINITE);

return 0;
}

DWORD WINAPI threadProc(void* arg)
{
    secondThrFiber = ConvertThreadToFiber(NULL);

printf("thread TEB=%p; volatile TEB=%p\n", getTEB(), getTEB_volatile());

puts("thread -> fiber");
    SwitchToFiber(testFiber);
    puts("thread <- fiber");

return 0;
}

void WINAPI fiberProc(void* arg)
{
    printf("fiber TEB=%p; volatile TEB=%p\n", getTEB(), getTEB_volatile());
    SwitchToFiber(mainThrFiber);
    printf("fiber TEB=%p; volatile TEB=%p\n", getTEB(), getTEB_volatile());

SwitchToFiber(secondThrFiber);
}

```