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* [PATCH] AArch64: Add support for -mdirect-extern-access
@ 2022-11-11 14:48 Wilco Dijkstra
  2022-11-16 10:54 ` Richard Sandiford
  0 siblings, 1 reply; 10+ messages in thread
From: Wilco Dijkstra @ 2022-11-11 14:48 UTC (permalink / raw)
  To: GCC Patches; +Cc: Richard Sandiford, Kyrylo Tkachov, maskray

Add a new option -mdirect-extern-access similar to other targets.  This removes
GOT indirections on external symbols with -fPIE, resulting in significantly
better code quality.  With -fPIC it only affects protected symbols, allowing
for more efficient shared libraries which can be linked with standard PIE
binaries (this is what LLVM does by default, so this improves interoperability
with LLVM). This patch doesn't affect ABI, but in the future GCC and LLVM
should converge to using the same ABI.

Regress and bootstrap pass, OK for commit?

gcc/
	* config/aarch64/aarch64.cc (aarch64_binds_local_p): New function.
	(aarch64_symbol_binds_local_p): Refactor, support direct extern access.
	* config/aarch64/aarch64-linux.h (TARGET_BINDS_LOCAL_P):
	Use aarch64_binds_local_p.
	* config/aarch64/aarch64-freebsd.h (TARGET_BINDS_LOCAL_P): Likewise.
	* config/aarch64/aarch64-protos.h: Add aarch64_binds_local_p.
	* doc/gcc/gcc-command-options/option-summary.rst: Add
	-mdirect-extern-access.
	* doc/gcc/gcc-command-options/machine-dependent-options/aarch64-options.rst:
	Add description of -mdirect-extern-access.

gcc/testsuite/
	* gcc.target/aarch64/pr66912-2.c: New test.

---

diff --git a/gcc/config/aarch64/aarch64-freebsd.h b/gcc/config/aarch64/aarch64-freebsd.h
index 13beb3781b61afd82d767884f3c16ff8eead09cc..20bc0f48e484686cd3754613bf20bb3521079d48 100644
--- a/gcc/config/aarch64/aarch64-freebsd.h
+++ b/gcc/config/aarch64/aarch64-freebsd.h
@@ -71,7 +71,7 @@
    strong definitions in dependent shared libraries, will resolve
    to COPY relocated symbol in the executable.  See PR65780.  */
 #undef TARGET_BINDS_LOCAL_P
-#define TARGET_BINDS_LOCAL_P default_binds_local_p_2
+#define TARGET_BINDS_LOCAL_P aarch64_binds_local_p
 
 /* Use the AAPCS type for wchar_t, override the one from
    config/freebsd.h.  */
diff --git a/gcc/config/aarch64/aarch64-linux.h b/gcc/config/aarch64/aarch64-linux.h
index 5e4553d79f5053f2da0eb381e0805f47aec964ae..6c962402155d60b82610d4f65af5182d6faa47ad 100644
--- a/gcc/config/aarch64/aarch64-linux.h
+++ b/gcc/config/aarch64/aarch64-linux.h
@@ -70,7 +70,7 @@
    strong definitions in dependent shared libraries, will resolve
    to COPY relocated symbol in the executable.  See PR65780.  */
 #undef TARGET_BINDS_LOCAL_P
-#define TARGET_BINDS_LOCAL_P default_binds_local_p_2
+#define TARGET_BINDS_LOCAL_P aarch64_binds_local_p
 
 /* Define this to be nonzero if static stack checking is supported.  */
 #define STACK_CHECK_STATIC_BUILTIN 1
diff --git a/gcc/config/aarch64/aarch64-protos.h b/gcc/config/aarch64/aarch64-protos.h
index 238820581c5ee7617f8eed1df2cf5418b1127e19..fac754f78c1d7606ba90e1034820a62466b96b63 100644
--- a/gcc/config/aarch64/aarch64-protos.h
+++ b/gcc/config/aarch64/aarch64-protos.h
@@ -1072,5 +1072,6 @@ const char *aarch64_sls_barrier (int);
 const char *aarch64_indirect_call_asm (rtx);
 extern bool aarch64_harden_sls_retbr_p (void);
 extern bool aarch64_harden_sls_blr_p (void);
+extern bool aarch64_binds_local_p (const_tree);
 
 #endif /* GCC_AARCH64_PROTOS_H */
diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index d1f979ebcf80333d957f8ad8631deef47dc693a5..ab4c42c34da5b15f6739c9b0a7ebaafda9488f2d 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -19185,9 +19185,29 @@ aarch64_tlsdesc_abi_id ()
 static bool
 aarch64_symbol_binds_local_p (const_rtx x)
 {
-  return (SYMBOL_REF_DECL (x)
-	  ? targetm.binds_local_p (SYMBOL_REF_DECL (x))
-	  : SYMBOL_REF_LOCAL_P (x));
+  if (!SYMBOL_REF_DECL (x))
+    return SYMBOL_REF_LOCAL_P (x);
+
+  if (targetm.binds_local_p (SYMBOL_REF_DECL (x)))
+    return true;
+
+  /* In PIE binaries avoid a GOT indirection on non-weak data symbols if
+     aarch64_direct_extern_access is true.  */
+  if (flag_pie && aarch64_direct_extern_access && !SYMBOL_REF_WEAK (x)
+      && !SYMBOL_REF_FUNCTION_P (x))
+    return true;
+
+  return false;
+}
+
+/* Implement TARGET_BINDS_LOCAL_P hook.  */
+
+bool
+aarch64_binds_local_p (const_tree exp)
+{
+  /* Protected symbols are local if aarch64_direct_extern_access is true.  */
+  return default_binds_local_p_3 (exp, flag_shlib != 0, true,
+				  !aarch64_direct_extern_access, !flag_pic);
 }
 
 /* Return true if SYMBOL_REF X is thread local */
diff --git a/gcc/config/aarch64/aarch64.opt b/gcc/config/aarch64/aarch64.opt
index b89b20450710592101b93f4f3b5dc33d152d1eb6..6251a36b544a03955361b445c9f5dfad3740eea8 100644
--- a/gcc/config/aarch64/aarch64.opt
+++ b/gcc/config/aarch64/aarch64.opt
@@ -299,3 +299,7 @@ Constant memset size in bytes from which to start using MOPS sequence.
 -param=aarch64-vect-unroll-limit=
 Target Joined UInteger Var(aarch64_vect_unroll_limit) Init(4) Param
 Limit how much the autovectorizer may unroll a loop.
+
+mdirect-extern-access
+Target Var(aarch64_direct_extern_access) Init(0)
+Do not indirect accesses to external symbols via the GOT.
diff --git a/gcc/doc/gcc/gcc-command-options/machine-dependent-options/aarch64-options.rst b/gcc/doc/gcc/gcc-command-options/machine-dependent-options/aarch64-options.rst
index c2b23a6ee97ef2b7c74119f22c1d3e3d85385f4d..599c37fe299dc142d25d2133a4cd0b861e34fd01 100644
--- a/gcc/doc/gcc/gcc-command-options/machine-dependent-options/aarch64-options.rst
+++ b/gcc/doc/gcc/gcc-command-options/machine-dependent-options/aarch64-options.rst
@@ -389,6 +389,20 @@ These options are defined for AArch64 implementations:
   The default is :samp:`-msve-vector-bits=scalable`, which produces
   vector-length agnostic code.
 
+.. option:: -mdirect-extern-access, -mno-direct-extern-access
+
+  Use direct accesses for external data symbols.  It avoids a GOT indirection
+  on all external data symbols with :option:`-fpie` or :option:`-fPIE`.  This is
+  useful for executables linked with :option:`-static` or :option:`-static-pie`.
+  With :option:`-fpic` or :option:`-fPIC`, it only affects accesses to protected
+  data symbols.  It has no effect on non-position independent code.  The default
+  is :option:`-mno-direct-extern-access`.
+
+  .. warning::
+
+    Use :option:`-mdirect-extern-access` either in shared libraries or in
+    executables, but not in both.  Protected symbols used both in a shared
+    library and executable may cause linker errors or fail to work correctly.
 
 .. _aarch64-feature-modifiers:
 
diff --git a/gcc/doc/gcc/gcc-command-options/option-summary.rst b/gcc/doc/gcc/gcc-command-options/option-summary.rst
index d068f98feac27d95f1402a530a78b553d623d2e9..dbc9b45ae1db12737aca3a6fd246b88a0e9467c2 100644
--- a/gcc/doc/gcc/gcc-command-options/option-summary.rst
+++ b/gcc/doc/gcc/gcc-command-options/option-summary.rst
@@ -634,7 +634,8 @@ in the following sections.
   :option:`-moverride=string`  :option:`-mverbose-cost-dump` |gol|
   :option:`-mstack-protector-guard=guard` :option:`-mstack-protector-guard-reg=sysreg` |gol|
   :option:`-mstack-protector-guard-offset=offset` :option:`-mtrack-speculation` |gol|
-  :option:`-moutline-atomics`
+  :option:`-moutline-atomics` |gol|
+  :option:`-mdirect-extern-access`
 
   *Adapteva Epiphany Options*
 
diff --git a/gcc/testsuite/gcc.target/aarch64/pr66912-2.c b/gcc/testsuite/gcc.target/aarch64/pr66912-2.c
new file mode 100644
index 0000000000000000000000000000000000000000..58e6e1f37116bff77015a7321890ece30c9e6a5c
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/pr66912-2.c
@@ -0,0 +1,41 @@
+/* { dg-do compile { target *-*-linux* } } */
+/* { dg-options "-O2 -fpic" } */
+/* { dg-require-effective-target fpic } */
+
+__attribute__((visibility("protected")))
+int n_common;
+
+__attribute__((weak, visibility("protected")))
+int n_weak_common;
+
+__attribute__((visibility("protected")))
+int n_init = -1;
+
+__attribute__((weak, visibility("protected")))
+int n_weak_init = -1;
+
+int
+f1 ()
+{
+  return n_common;
+}
+
+int
+f2 ()
+{
+  return n_weak_common;
+}
+
+int
+f3 ()
+{
+  return n_init;
+}
+
+int
+f4 ()
+{
+  return n_weak_init;
+}
+
+/* { dg-final { scan-assembler-times ":got" 0 } } */


^ permalink raw reply	[flat|nested] 10+ messages in thread
end of thread, other threads:[~2022-11-17 22:07 UTC | newest]

Thread overview: 10+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2022-11-11 14:48 [PATCH] AArch64: Add support for -mdirect-extern-access Wilco Dijkstra
2022-11-16 10:54 ` Richard Sandiford
2022-11-17 16:42   ` Wilco Dijkstra
2022-11-17 17:30     ` Richard Sandiford
2022-11-17 20:52       ` Ramana Radhakrishnan
2022-11-17 21:20         ` maskray
2022-11-17 21:37           ` Andrew Pinski
2022-11-17 21:46             ` Fangrui Song
2022-11-17 21:55               ` Andrew Pinski
2022-11-17 22:07                 ` Fangrui Song

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