Re: [Tinycc-devel] Feature request: _Thread_local (and a possible bug)

[Robert Clausecker]

Hello Thomas,

Thank you for your effort. Unfortunately, the change breaks tcc.

When I compile the following file:

    __thread int x;

I get the error

    *** Error in `tcc': malloc(): memory corruption: 0x0000000001d74c40 ***

and tcc does not terminate afterwards.

Also, I have the impression that the commit you made does not implement
__thread correctly. The following C code should compile to the assembly
further below on x86-64:

__thread int x;

int get_x(void) {
        return x;
}

void set_x(int a) {
        x = a;
}

int *x_addr(void) {
        return &x;
}

/* --- */

        .text
        .globl get_x
get_x:  movl %fs:address@hidden,%eax
        ret

        .globl set_x
set_x:  movl %edi,%fs:address@hidden
        ret

        .globl x_addr
x_addr: movq %fs:0,%rax
        addq address@hidden,%rax
        ret

        .globl x
        .section .tbss
        .type x,@object
        .size x, 4
x:      .zero 4

I see nothing in the patch you made that indicates any special access
conventions to thread-local variables (such as %fs-relative
instructions). It might very well be possible that I missed that, but I
can't test because tcc does not compile the code at all on my machine.

Yours, Robert Clausecker