On Tue, 9 Sep 2025, H.J. Lu wrote:
> > > to restore assert if not compiling for shared library. When compiling
> > > for shared library, the recomputed model may be weaker.
> >
> > I don't understand why (for shared libraries), can you explain?
>
> Another shared library or executable may override any global
> symbols with the default visibility in a shared library.
I know that symbols with default visibility can be interposed, but that doesn't
answer the question. Do you have a testcase that demonstrates the issue?
Otherwise, let's say we are talking about
extern __thread int tls_undef;
static __thread int tls_local;
/****/ __thread int tls_global;
With -fpic GCC initially selects local-dynamic for tls_local, global-dynamic
for tls_undef and tls_global. Why would recomputed model for tls_local be
weaker?
> __thread int x;
>
> __attribute__((common))
> __thread int x;
>
> int *f()
> {
> return &x;
> }
> [hjl@gnu-zen4-1 gcc]$ ./xgcc -B./ -O2 -std=c11 -fno-common -S /tmp/x.c
> -fdump-ipa-whole-program
> [hjl@gnu-zen4-1 gcc]$ cat x.c.084i.whole-program
>
> Marking local functions:
>
>
> Marking externally visible functions: f/3
>
>
> Marking externally visible variables: x/1
>
> Clearing variable flags:
>
> Reclaiming functions:
> Reclaiming variables:
> Clearing address taken flags:
> Symbol table:
>
> f/3 (f)
> Type: function definition analyzed
> Visibility: externally_visible semantic_interposition public
> References: x/1 (addr)
> Referring:
> Availability: available
> Function flags: count:1073741824 (estimated locally) body
> Called by:
> Calls:
> x/1 (x)
> Type: variable definition analyzed
> Visibility: externally_visible semantic_interposition public common
> References:
> Referring: f/3 (addr)
> Availability: overwritable
> Varpool flags: tls-local-exec
Thanks. Unrelated to this particular patch, but this is questionable: we have
local-exec for an interposable (Availability: overwritable) symbol. Perhaps
it's better to error out on the redeclaration, when the previous declaration
set a stronger TLS model?
Alexander
