| Message ID | 20230517191436.73636-8-bugaevc@gmail.com |
|---|---|
| State | New |
| Headers | show |
| Series | Stack setup & misc fixes for x86_64-gnu | expand |
Applied, thanks! Sergey Bugaev via Libc-alpha, le mer. 17 mai 2023 22:14:33 +0300, a ecrit: > 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 <bugaevc@gmail.com> > --- > It would be nice if GNU Mach allowed > > thread_get_state (mach_thread_self (), i386_FSGS_BASE_STATE) > > like it already allows thread_set_state for this case. But even if > gnumach adds suppport for this, doing it in userspace without an extra > RPC is still better. > > sysdeps/mach/hurd/x86_64/tls.h | 25 +++++++++++++++++++------ > 1 file changed, 19 insertions(+), 6 deletions(-) > > diff --git a/sysdeps/mach/hurd/x86_64/tls.h b/sysdeps/mach/hurd/x86_64/tls.h > index 35dcef44..6487ed35 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, > -- > 2.40.1 >
diff --git a/sysdeps/mach/hurd/x86_64/tls.h b/sysdeps/mach/hurd/x86_64/tls.h index 35dcef44..6487ed35 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,
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 <bugaevc@gmail.com> --- It would be nice if GNU Mach allowed thread_get_state (mach_thread_self (), i386_FSGS_BASE_STATE) like it already allows thread_set_state for this case. But even if gnumach adds suppport for this, doing it in userspace without an extra RPC is still better. sysdeps/mach/hurd/x86_64/tls.h | 25 +++++++++++++++++++------ 1 file changed, 19 insertions(+), 6 deletions(-)