From 2f8ecb58a59eb82c43214d000842d99644a662d1 Mon Sep 17 00:00:00 2001 From: Sergey Bugaev Date: Wed, 17 May 2023 22:14:33 +0300 Subject: hurd: Fix x86_64 _hurd_tls_fork It is illegal to call thread_get_state () on mach_thread_self (), so this codepath cannot be used as-is to fork the calling thread's TLS. Fortunately we can use THREAD_SELF (aka %fs:0x0) to find out the value of our fs_base without calling into the kernel. Fixes: f6cf701efc61c9ad910372bda14b9a235db310a8 "hurd: Implement TLS for x86_64" Checked on x86_64-gnu: fork () now works! Signed-off-by: Sergey Bugaev Message-Id: <20230517191436.73636-8-bugaevc@gmail.com> --- sysdeps/mach/hurd/x86_64/tls.h | 25 +++++++++++++++++++------ 1 file changed, 19 insertions(+), 6 deletions(-) (limited to 'sysdeps/mach') diff --git a/sysdeps/mach/hurd/x86_64/tls.h b/sysdeps/mach/hurd/x86_64/tls.h index 35dcef447e..6487ed3580 100644 --- a/sysdeps/mach/hurd/x86_64/tls.h +++ b/sysdeps/mach/hurd/x86_64/tls.h @@ -140,12 +140,25 @@ _hurd_tls_fork (thread_t child, thread_t orig, error_t err; struct i386_fsgs_base_state state; mach_msg_type_number_t state_count = i386_FSGS_BASE_STATE_COUNT; - err = __thread_get_state (orig, i386_FSGS_BASE_STATE, - (thread_state_t) &state, - &state_count); - if (err) - return err; - assert (state_count == i386_FSGS_BASE_STATE_COUNT); + + extern thread_t hurd_thread_self (void); + if (orig != hurd_thread_self ()) + { + err = __thread_get_state (orig, i386_FSGS_BASE_STATE, + (thread_state_t) &state, + &state_count); + if (err) + return err; + assert (state_count == i386_FSGS_BASE_STATE_COUNT); + } + else + { + /* It is illegal to call thread_get_state () on mach_thread_self (). + But we're only interested in the value of fs_base, and since we're + this thread, we know it points to our TCB. */ + state.fs_base = (unsigned long) THREAD_SELF; + state.gs_base = 0; + } return __thread_set_state (child, i386_FSGS_BASE_STATE, (thread_state_t) &state, -- cgit v1.2.3-70-g09d2