diff mbox series

[pushed] Darwin : Adjust darwin_binds_local_p for PIC code [PR100152].

Message ID AD81B583-F010-4954-87C3-B67AA0DB9CF7@sandoe.co.uk
State New
Headers show
Series [pushed] Darwin : Adjust darwin_binds_local_p for PIC code [PR100152]. | expand

Commit Message

Iain Sandoe April 24, 2021, 12:48 p.m. UTC 
Hi

Darwin's dynamic linker supports interposition and lazy symbol binding.
If we are generating PIC code and a symbol is public, then it could
potentially be indirected via a lazy-resolver stub; we cannot tell at
compile-time if this will be done (since the indirection can be the
result of adding a -flat-namespace option at link-time).  Here we are
conservative and assume that any such symbol cannot bind locally.
The default implementation for binds_local_p handles undefined, weak and
common symbols which are always indirected (for mdynamic-no-pic also).

tested on x86_64-darwin,
pushed to master,
thanks
Iain

gcc/ChangeLog:

	PR target/100152
	* config/darwin.c (darwin_binds_local_p): Assume that any
	public symbol might be interposed for PIC code. Update function
	header comment to reflect current Darwin capability.
---
  gcc/config/darwin.c | 17 +++++++++++++----
  1 file changed, 13 insertions(+), 4 deletions(-)

Comments

Iain Sandoe April 24, 2021, 6:34 p.m. UTC | #1 
Iain Sandoe <iain@sandoe.co.uk> wrote:

> gcc/ChangeLog:
>
> 	PR target/100152
> 	* config/darwin.c (darwin_binds_local_p): Assume that any
> 	public symbol might be interposed for PIC code. Update function
> 	header comment to reflect current Darwin capability.

unfortunately, wider testing showed fallout in sanitizer tests - despite that
this is notionally correct - so I’ve reverted it until those fails can be  
analyzed.

Iain
diff mbox series

Patch

diff --git a/gcc/config/darwin.c b/gcc/config/darwin.c
index 5d173919ee0..36b460a9890 100644
--- a/gcc/config/darwin.c
+++ b/gcc/config/darwin.c
@@ -3134,16 +3134,25 @@  darwin_file_end (void)
  /* TODO: Add a language hook for identifying if a decl is a vtable.  */
  #define DARWIN_VTABLE_P(DECL) 0
 
-/* Cross-module name binding.  Darwin does not support overriding
-   functions at dynamic-link time, except for vtables in kexts.  */
+/* Cross-module name binding.
+   Darwin's dynamic linker supports interposition and lazy symbol binding.
+   If we are generating PIC code and a symbol is public, then it could
+   potentially be indirected via a lazy-resolver stub; we cannot tell at
+   compile-time if this will be done (since the indirection can be the
+   result of adding a -flat-namespace option at link-time).  Here we are
+   conservative and assume that any such symbol cannot bind locally.
+   The default implementation for binds_local_p handles undefined, weak and
+   common symbols which are always indirected.  */
 
  bool
  darwin_binds_local_p (const_tree decl)
  {
    /* We use the "shlib" input to indicate that a symbol should be
-     considered overridable; only relevant for vtables in kernel modules
-     on earlier system versions, and with a TODO to complete.  */
+     considered overridable.  Older versions of the kernel also support
+     interposition for extensions (although this code is a place-holder
+     until there is an implementation for DARWIN_VTABLE_P).  */
    bool force_overridable = TARGET_KEXTABI && DARWIN_VTABLE_P (decl);
+  force_overridable |= MACHOPIC_PURE;
    return default_binds_local_p_3 (decl, force_overridable /* shlib */,
  				  false /* weak dominate */,
  				  false /* extern_protected_data */,