powerpc/asm: Add a patch_site macro & helpers for patching instructions

Add a macro and some helper C functions for patching single asm
instructions.

The gas macro means we can do something like:

  1:	nop
  	patch_site 1b, patch__foo

Which is less visually distracting than defining a GLOBAL symbol at 1,
and also doesn't pollute the symbol table which can confuse eg. perf.

These are obviously similar to our existing feature sections, but are
not automatically patched based on CPU/MMU features, rather they are
designed to be manually patched by C code at some arbitrary point.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/include/asm/code-patching-asm.h b/arch/powerpc/include/asm/code-patching-asm.h
new file mode 100644 (file)
index 0000000..ed7b144
--- /dev/null
+++ b/arch/powerpc/include/asm/code-patching-asm.h
@@ -0,0 +1,18 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright 2018, Michael Ellerman, IBM Corporation.
+ */
+#ifndef _ASM_POWERPC_CODE_PATCHING_ASM_H
+#define _ASM_POWERPC_CODE_PATCHING_ASM_H
+
+/* Define a "site" that can be patched */
+.macro patch_site label name
+       .pushsection ".rodata"
+       .balign 4
+       .global \name
+\name:
+       .4byte  \label - .
+       .popsection
+.endm
+
+#endif /* _ASM_POWERPC_CODE_PATCHING_ASM_H */

diff --git a/arch/powerpc/include/asm/code-patching.h b/arch/powerpc/include/asm/code-patching.h
index 9ecc7bfc8ae7bd678c66167f0bf61b9b63ac49c4..31733a95bbd052bda1038f8160b127181d3cffc2 100644 (file)
--- a/arch/powerpc/include/asm/code-patching.h
+++ b/arch/powerpc/include/asm/code-patching.h
@@ -33,6 +33,8 @@ unsigned int create_cond_branch(const unsigned int *addr,
 int patch_branch(unsigned int *addr, unsigned long target, int flags);
 int patch_instruction(unsigned int *addr, unsigned int instr);
 int raw_patch_instruction(unsigned int *addr, unsigned int instr);
+int patch_instruction_site(s32 *addr, unsigned int instr);
+int patch_branch_site(s32 *site, unsigned long target, int flags);
 
 int instr_is_relative_branch(unsigned int instr);
 int instr_is_relative_link_branch(unsigned int instr);

diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c
index e0d881ab304e97482721c3e307ec0232c7a9fbb3..850f3b8f4da5e55346afbbe939987b0a0642aa7d 100644 (file)
--- a/arch/powerpc/lib/code-patching.c
+++ b/arch/powerpc/lib/code-patching.c
@@ -195,6 +195,22 @@ int patch_branch(unsigned int *addr, unsigned long target, int flags)
        return patch_instruction(addr, create_branch(addr, target, flags));
 }
 
+int patch_branch_site(s32 *site, unsigned long target, int flags)
+{
+       unsigned int *addr;
+
+       addr = (unsigned int *)((unsigned long)site + *site);
+       return patch_instruction(addr, create_branch(addr, target, flags));
+}
+
+int patch_instruction_site(s32 *site, unsigned int instr)
+{
+       unsigned int *addr;
+
+       addr = (unsigned int *)((unsigned long)site + *site);
+       return patch_instruction(addr, instr);
+}
+
 bool is_offset_in_branch_range(long offset)
 {
        /*