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Hlms: give msThreadId default visibility so a static build links into a PIE #586

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Merged
eugenegff merged 1 commit into from
Aug 1, 2026
Merged

Hlms: give msThreadId default visibility so a static build links into a PIE #586

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31 changes: 31 additions & 0 deletions OgreMain/include/OgreHlms.h
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Original file line number Diff line number Diff line change
Expand Up @@ -149,7 +149,38 @@ namespace Ogre

#ifdef OGRE_SHADER_THREADING_BACKWARDS_COMPATIBLE_API
# ifdef OGRE_SHADER_THREADING_USE_TLS
# ifdef OGRE_GCC_VISIBILITY
/** Left visible on purpose, even though _OgreExport hides every other
member of this class in a static build (OGRE_SHADER_THREADING_USE_TLS
is a static-only setting, so that is the only build this declaration
appears in).

A translation unit that sees only the declaration cannot know that
the definition in OgreHlms.cpp is constant-initialized, so it emits
the Itanium ABI thread-local access wrapper (_ZTW...), which weakly
references the thread-local init function
_ZTHN4Ogre4Hlms10msThreadIdE - a symbol that a constant-initialized
variable never defines anywhere. Resolving that dangling weak
reference to zero is the linker's job, and it needs the indirection
of a GOT entry, which the compiler only emits for a symbol that may
bind externally; a hidden symbol it addresses directly, and the
resulting relocation cannot be linked into a position-independent
executable:

relocation R_X86_64_PC32 against undefined hidden symbol
`_ZTHN4Ogre4Hlms10msThreadIdE' can not be used when making a
PIE object

Only optimized builds hit it. Unoptimized ones leave the reference
inside the wrapper's own COMDAT section, which the linker discards
in favour of the clean copy OgreHlms.cpp contributes; inlining the
wrapper moves the relocation into ordinary code, where it survives
to the final link.
*/
static __attribute__( ( visibility( "default" ) ) ) thread_local uint32 msThreadId;
# else
static thread_local uint32 msThreadId;
# endif
# else
static constexpr uint32 msThreadId = 0u;
# endif
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