Re: [RFC PATCH 06/10] hurd: Make sure to not use tcb->self

[Joseph Myers <joseph@codesourcery.com>]

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On Thu, 18 May 2023, Sergey Bugaev via Libc-alpha wrote:

> Hello,
> 
> On Thu, May 18, 2023 at 9:55 PM Joseph Myers <joseph@codesourcery.com> wrote:
> >
> > I suspect this of causing linknamespace test failures:
> >
> > Contents of conform/POSIX2008/pthread.h/linknamespace.out:
> >
> > [initial] pthread_create -> [libpthread.a(pt-create.o)] __pthread_setup -> [libpthread.a(pt-setup.o)] hurd_thread_self
> >
> > (On x86_64 there's also a localplt test failure: "Extra PLT reference:
> > libc.so: hurd_thread_self".  In addition, x86_64 has a c++-types-check
> > failure.  Thus, neither Hurd configuration has clean results for
> > compilation tests from build-many-glibcs.py at present.)
> 
> Thank you, and sorry :|
> 
> Do I understand it right that this is because of hurd_thread_self
> being publicly exported and interposable? A quick grep shows that
> nothing else inside glibc was using hurd_thread_self indeed.
> 
> Would the right way to resolve this be introducing a hidden
> __hurd_thread_self and using that? We could also make it

Yes.

Strictly there are two separate issues: (a) calling an exported symbol 
should be done via a hidden alias, to avoid going via the PLT, and (b) 
functions in a standard namespace should not call names in the user's 
namespace, which requires using a name such as __hurd_thread_self instead 
(which should also be marked hidden to make the call optimally efficient).

> What's the C++ type check failure? Surely this patch (nor
> 2f8ecb58a59eb82c43214d000842d99644a662d1 "hurd: Fix x86_64
> _hurd_tls_fork") has modified any public headers?

The C++ type check failure was already present before this patch.

--- sysdeps/mach/hurd/x86_64/c++-types.data     2023-05-02 09:14:30.246903708 +0000
+++ -   2023-05-18 02:08:06.184068438 +0000
@@ -1 +1 @@
-blkcnt64_t:x
+blkcnt64_t:l
@@ -8 +8 @@
-dev_t:j
+dev_t:m
@@ -10 +10 @@
-fsblkcnt64_t:y
+fsblkcnt64_t:m
@@ -12 +12 @@
-fsfilcnt64_t:y
+fsfilcnt64_t:m
@@ -14 +14 @@
-fsid_t:y
+fsid_t:m
@@ -17 +17 @@
-ino64_t:y
+ino64_t:m
@@ -21 +21 @@
-int64_t:x
+int64_t:l
@@ -23 +23 @@
-intptr_t:i
+intptr_t:l
@@ -25 +25 @@
-loff_t:x
+loff_t:l
@@ -27,2 +27,2 @@
-nlink_t:j
-off64_t:x
+nlink_t:m
+off64_t:l
@@ -43,4 +43,4 @@
-pthread_t:i
-quad_t:x
-register_t:i
-rlim64_t:y
+pthread_t:l
+quad_t:l
+register_t:l
+rlim64_t:m
@@ -49 +49 @@
-size_t:j
+size_t:m
@@ -51 +51 @@
-ssize_t:i
+ssize_t:l
@@ -60 +60 @@
-u_int64_t:y
+u_int64_t:m
@@ -64 +64 @@
-u_quad_t:y
+u_quad_t:m

-- 
Joseph S. Myers
joseph@codesourcery.com