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* [glibc] hurd: Fix x86_64 _hurd_tls_fork
@ 2023-05-17 21:01 Samuel Thibault
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From: Samuel Thibault @ 2023-05-17 21:01 UTC (permalink / raw)
To: glibc-cvs
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=2f8ecb58a59eb82c43214d000842d99644a662d1
commit 2f8ecb58a59eb82c43214d000842d99644a662d1
Author: Sergey Bugaev <bugaevc@gmail.com>
Date: Wed May 17 22:14:33 2023 +0300
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 <bugaevc@gmail.com>
Message-Id: <20230517191436.73636-8-bugaevc@gmail.com>
Diff:
---
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 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,
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2023-05-17 21:01 [glibc] hurd: Fix x86_64 _hurd_tls_fork Samuel Thibault
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