linux-kernel - [PATCH v1 14/14] compiler-gcc: Remove obsolete RELOC

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Message-ID: <20260120195407.1163051-15-hpa@zytor.com>
Date: Tue, 20 Jan 2026 11:54:06 -0800
From: "H. Peter Anvin" <hpa@...or.com>
To: Thomas Gleixner <tglx@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Uros Bizjak <ubizjak@...il.com>, Petr Mladek <pmladek@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>, Kees Cook <kees@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Kiryl Shutsemau <kas@...nel.org>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>
Cc: "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        linux-coco@...ts.linux.dev, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH v1 14/14] compiler-gcc: Remove obsolete RELOC_HIDE() macro

From: Uros Bizjak <ubizjak@...il.com>

Remove the RELOC_HIDE() macro from include/linux/compiler-gcc.h.

The GCC specific macro was historically used to workaround very old
compiler bugs (including pre-4.1 ppc64 GCC). These compilers are long
obsolete.

The generic RELOC_HIDE() macro should be used instead.

The removal of the GCC specific macro results in the
following code size reduction:

     text    data     bss     dec     hex filename
  28526453        4823511  737108 34087072        20820a0 vmlinux-old.o
  28520945        4823463  737108 34081516        2080aec vmlinux-new.o

  ./bloat-o-meter vmlinux-old.o vmlinux-new.o
  add/remove: 4/14 grow/shrink: 189/674 up/down: 4433/-7865 (-3432)
  ...
  Total: Before=24103512, After=24100080, chg -0.01%

Signed-off-by: Uros Bizjak <ubizjak@...il.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
---
 include/linux/compiler-gcc.h | 25 -------------------------
 include/linux/compiler.h     |  8 ++++++++
 2 files changed, 8 insertions(+), 25 deletions(-)

diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index 5de824a0b3d7..081e658754b9 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -10,31 +10,6 @@
 		     + __GNUC_MINOR__ * 100	\
 		     + __GNUC_PATCHLEVEL__)
 
-/*
- * This macro obfuscates arithmetic on a variable address so that gcc
- * shouldn't recognize the original var, and make assumptions about it.
- *
- * This is needed because the C standard makes it undefined to do
- * pointer arithmetic on "objects" outside their boundaries and the
- * gcc optimizers assume this is the case. In particular they
- * assume such arithmetic does not wrap.
- *
- * A miscompilation has been observed because of this on PPC.
- * To work around it we hide the relationship of the pointer and the object
- * using this macro.
- *
- * Versions of the ppc64 compiler before 4.1 had a bug where use of
- * RELOC_HIDE could trash r30. The bug can be worked around by changing
- * the inline assembly constraint from =g to =r, in this particular
- * case either is valid.
- */
-#define RELOC_HIDE(ptr, off)						\
-({									\
-	unsigned long __ptr;						\
-	__asm__ ("" : "=r"(__ptr) : "0"(ptr));				\
-	(typeof(ptr)) (__ptr + (off));					\
-})
-
 #if defined(LATENT_ENTROPY_PLUGIN) && !defined(__CHECKER__)
 #define __latent_entropy __attribute__((latent_entropy))
 #endif
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 04487c9bd751..6affb7b44be7 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -148,6 +148,14 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
 	= (unsigned long)&sym;
 #endif
 
+/*
+ * This macro obfuscates arithmetic on a variable address so that the compiler
+ * shouldn't recognize the original var, and make assumptions about it.
+ *
+ * This is needed because the C standard makes it undefined to do pointer
+ * arithmetic on "objects" outside their boundaries and compilers assume
+ * this is the case. In particular they assume such arithmetic does not wrap.
+ */
 #ifndef RELOC_HIDE
 # define RELOC_HIDE(ptr, off)					\
   ({ unsigned long __ptr;					\
-- 
2.52.0