diff options
Diffstat (limited to 'src/runtime/sys_linux_386.s')
| -rw-r--r-- | src/runtime/sys_linux_386.s | 42 |
1 files changed, 30 insertions, 12 deletions
diff --git a/src/runtime/sys_linux_386.s b/src/runtime/sys_linux_386.s index 0f6d4bbb5e..f9dec7597c 100644 --- a/src/runtime/sys_linux_386.s +++ b/src/runtime/sys_linux_386.s @@ -379,9 +379,18 @@ TEXT runtime·sigaltstack(SB),NOSPLIT,$-8 #define SEG_NOT_PRESENT 0x20 #define USEABLE 0x40 +// `-1` means the kernel will pick a TLS entry on the first setldt call, +// which happens during runtime init, and that we'll store back the saved +// entry and reuse that on subsequent calls when creating new threads. +DATA runtime·tls_entry_number+0(SB)/4, $-1 +GLOBL runtime·tls_entry_number(SB), NOPTR, $4 + // setldt(int entry, int address, int limit) +// We use set_thread_area, which mucks with the GDT, instead of modify_ldt, +// which would modify the LDT, but is disabled on some kernels. +// The name, setldt, is a misnomer, although we leave this name as it is for +// the compatibility with other platforms. TEXT runtime·setldt(SB),NOSPLIT,$32 - MOVL entry+0(FP), BX // entry MOVL address+4(FP), CX // base address /* @@ -400,18 +409,19 @@ TEXT runtime·setldt(SB),NOSPLIT,$32 ADDL $0x8, CX // address MOVL CX, 0(CX) + // get entry number + MOVL runtime·tls_entry_number(SB), DX + // set up user_desc LEAL 16(SP), AX // struct user_desc - MOVL BX, 0(AX) - MOVL CX, 4(AX) - MOVL $0xfffff, 8(AX) + MOVL DX, 0(AX) // unsigned int entry_number + MOVL CX, 4(AX) // unsigned long base_addr + MOVL $0xfffff, 8(AX) // unsigned int limit MOVL $(SEG_32BIT|LIMIT_IN_PAGES|USEABLE|CONTENTS_DATA), 12(AX) // flag bits - // call modify_ldt - MOVL $1, BX // func = 1 (write) - MOVL AX, CX // user_desc - MOVL $16, DX // sizeof(user_desc) - MOVL $123, AX // syscall - modify_ldt + // call set_thread_area + MOVL AX, BX // user_desc + MOVL $243, AX // syscall - set_thread_area CALL *runtime·_vdso(SB) // breakpoint on error @@ -419,10 +429,18 @@ TEXT runtime·setldt(SB),NOSPLIT,$32 JLS 2(PC) INT $3 - // compute segment selector - (entry*8+7) - MOVL entry+0(FP), AX + // read allocated entry number back out of user_desc + LEAL 16(SP), AX // get our user_desc back + MOVL 0(AX), AX + + // store entry number if the kernel allocated it + CMPL DX, $-1 + JNE 2(PC) + MOVL AX, runtime·tls_entry_number(SB) + + // compute segment selector - (entry*8+3) SHLL $3, AX - ADDL $7, AX + ADDL $3, AX MOVW AX, GS RET |