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linux/arch/powerpc/include/asm/feature-fixups.h
Bill Wendling f47462c9d8 powerpc: Work around inline asm issues in alternate feature sections 
The clang toolchain treats inline assembly a bit differently than
straight assembly code. In particular, inline assembly doesn't have
the complete context available to resolve expressions. This is
intentional to avoid divergence in the resulting assembly code.

We can work around this issue by borrowing a workaround done for ARM,
i.e. not directly testing the labels themselves, but by moving the
current output pointer by a value that should always be zero. If this
value is not null, then we will trigger a backward move, which is
explicitly forbidden.

Signed-off-by: Bill Wendling <morbo@google.com>
[mpe: Put it in a macro and only do the workaround for clang]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201120224034.191382-4-morbo@google.com
2020-11-26 22:05:43 +11:00

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/* SPDX-License-Identifier: GPL-2.0-or-later */
#ifndef __ASM_POWERPC_FEATURE_FIXUPS_H
#define __ASM_POWERPC_FEATURE_FIXUPS_H
#include <asm/asm-const.h>
/*
*/
/*
* Feature section common macros
*
* Note that the entries now contain offsets between the table entry
* and the code rather than absolute code pointers in order to be
* useable with the vdso shared library. There is also an assumption
* that values will be negative, that is, the fixup table has to be
* located after the code it fixes up.
*/
#if defined(CONFIG_PPC64) && !defined(__powerpc64__)
/* 64 bits kernel, 32 bits code (ie. vdso32) */
#define FTR_ENTRY_LONG .8byte
#define FTR_ENTRY_OFFSET .long 0xffffffff; .long
#elif defined(CONFIG_PPC64)
#define FTR_ENTRY_LONG .8byte
#define FTR_ENTRY_OFFSET .8byte
#else
#define FTR_ENTRY_LONG .long
#define FTR_ENTRY_OFFSET .long
#endif
#define START_FTR_SECTION(label) label##1:
#define FTR_SECTION_ELSE_NESTED(label) \
label##2: \
.pushsection __ftr_alt_##label,"a"; \
.align 2; \
label##3:
#ifndef CONFIG_CC_IS_CLANG
#define CHECK_ALT_SIZE(else_size, body_size) \
.ifgt (else_size) - (body_size); \
.error "Feature section else case larger than body"; \
.endif;
#else
/*
* If we use the ifgt syntax above, clang's assembler complains about the
* expression being non-absolute when the code appears in an inline assembly
* statement.
* As a workaround use an .org directive that has no effect if the else case
* instructions are smaller than the body, but fails otherwise.
*/
#define CHECK_ALT_SIZE(else_size, body_size) \
.org . + ((else_size) > (body_size));
#endif
#define MAKE_FTR_SECTION_ENTRY(msk, val, label, sect) \
label##4: \
.popsection; \
.pushsection sect,"a"; \
.align 3; \
label##5: \
FTR_ENTRY_LONG msk; \
FTR_ENTRY_LONG val; \
FTR_ENTRY_OFFSET label##1b-label##5b; \
FTR_ENTRY_OFFSET label##2b-label##5b; \
FTR_ENTRY_OFFSET label##3b-label##5b; \
FTR_ENTRY_OFFSET label##4b-label##5b; \
CHECK_ALT_SIZE((label##4b-label##3b), (label##2b-label##1b)); \
.popsection;
/* CPU feature dependent sections */
#define BEGIN_FTR_SECTION_NESTED(label) START_FTR_SECTION(label)
#define BEGIN_FTR_SECTION START_FTR_SECTION(97)
#define END_FTR_SECTION_NESTED(msk, val, label) \
FTR_SECTION_ELSE_NESTED(label) \
MAKE_FTR_SECTION_ENTRY(msk, val, label, __ftr_fixup)
#define END_FTR_SECTION(msk, val) \
END_FTR_SECTION_NESTED(msk, val, 97)
#define END_FTR_SECTION_NESTED_IFSET(msk, label) \
END_FTR_SECTION_NESTED((msk), (msk), label)
#define END_FTR_SECTION_IFSET(msk) END_FTR_SECTION((msk), (msk))
#define END_FTR_SECTION_IFCLR(msk) END_FTR_SECTION((msk), 0)
/* CPU feature sections with alternatives, use BEGIN_FTR_SECTION to start */
#define FTR_SECTION_ELSE FTR_SECTION_ELSE_NESTED(97)
#define ALT_FTR_SECTION_END_NESTED(msk, val, label) \
MAKE_FTR_SECTION_ENTRY(msk, val, label, __ftr_fixup)
#define ALT_FTR_SECTION_END_NESTED_IFSET(msk, label) \
ALT_FTR_SECTION_END_NESTED(msk, msk, label)
#define ALT_FTR_SECTION_END_NESTED_IFCLR(msk, label) \
ALT_FTR_SECTION_END_NESTED(msk, 0, label)
#define ALT_FTR_SECTION_END(msk, val) \
ALT_FTR_SECTION_END_NESTED(msk, val, 97)
#define ALT_FTR_SECTION_END_IFSET(msk) \
ALT_FTR_SECTION_END_NESTED_IFSET(msk, 97)
#define ALT_FTR_SECTION_END_IFCLR(msk) \
ALT_FTR_SECTION_END_NESTED_IFCLR(msk, 97)
/* MMU feature dependent sections */
#define BEGIN_MMU_FTR_SECTION_NESTED(label) START_FTR_SECTION(label)
#define BEGIN_MMU_FTR_SECTION START_FTR_SECTION(97)
#define END_MMU_FTR_SECTION_NESTED(msk, val, label) \
FTR_SECTION_ELSE_NESTED(label) \
MAKE_FTR_SECTION_ENTRY(msk, val, label, __mmu_ftr_fixup)
#define END_MMU_FTR_SECTION(msk, val) \
END_MMU_FTR_SECTION_NESTED(msk, val, 97)
#define END_MMU_FTR_SECTION_NESTED_IFSET(msk, label) \
END_MMU_FTR_SECTION_NESTED((msk), (msk), label)
#define END_MMU_FTR_SECTION_IFSET(msk) END_MMU_FTR_SECTION((msk), (msk))
#define END_MMU_FTR_SECTION_IFCLR(msk) END_MMU_FTR_SECTION((msk), 0)
/* MMU feature sections with alternatives, use BEGIN_FTR_SECTION to start */
#define MMU_FTR_SECTION_ELSE_NESTED(label) FTR_SECTION_ELSE_NESTED(label)
#define MMU_FTR_SECTION_ELSE MMU_FTR_SECTION_ELSE_NESTED(97)
#define ALT_MMU_FTR_SECTION_END_NESTED(msk, val, label) \
MAKE_FTR_SECTION_ENTRY(msk, val, label, __mmu_ftr_fixup)
#define ALT_MMU_FTR_SECTION_END_NESTED_IFSET(msk, label) \
ALT_MMU_FTR_SECTION_END_NESTED(msk, msk, label)
#define ALT_MMU_FTR_SECTION_END_NESTED_IFCLR(msk, label) \
ALT_MMU_FTR_SECTION_END_NESTED(msk, 0, label)
#define ALT_MMU_FTR_SECTION_END(msk, val) \
ALT_MMU_FTR_SECTION_END_NESTED(msk, val, 97)
#define ALT_MMU_FTR_SECTION_END_IFSET(msk) \
ALT_MMU_FTR_SECTION_END_NESTED_IFSET(msk, 97)
#define ALT_MMU_FTR_SECTION_END_IFCLR(msk) \
ALT_MMU_FTR_SECTION_END_NESTED_IFCLR(msk, 97)
/* Firmware feature dependent sections */
#define BEGIN_FW_FTR_SECTION_NESTED(label) START_FTR_SECTION(label)
#define BEGIN_FW_FTR_SECTION START_FTR_SECTION(97)
#define END_FW_FTR_SECTION_NESTED(msk, val, label) \
FTR_SECTION_ELSE_NESTED(label) \
MAKE_FTR_SECTION_ENTRY(msk, val, label, __fw_ftr_fixup)
#define END_FW_FTR_SECTION(msk, val) \
END_FW_FTR_SECTION_NESTED(msk, val, 97)
#define END_FW_FTR_SECTION_IFSET(msk) END_FW_FTR_SECTION((msk), (msk))
#define END_FW_FTR_SECTION_IFCLR(msk) END_FW_FTR_SECTION((msk), 0)
/* Firmware feature sections with alternatives */
#define FW_FTR_SECTION_ELSE_NESTED(label) FTR_SECTION_ELSE_NESTED(label)
#define FW_FTR_SECTION_ELSE FTR_SECTION_ELSE_NESTED(97)
#define ALT_FW_FTR_SECTION_END_NESTED(msk, val, label) \
MAKE_FTR_SECTION_ENTRY(msk, val, label, __fw_ftr_fixup)
#define ALT_FW_FTR_SECTION_END_NESTED_IFSET(msk, label) \
ALT_FW_FTR_SECTION_END_NESTED(msk, msk, label)
#define ALT_FW_FTR_SECTION_END_NESTED_IFCLR(msk, label) \
ALT_FW_FTR_SECTION_END_NESTED(msk, 0, label)
#define ALT_FW_FTR_SECTION_END(msk, val) \
ALT_FW_FTR_SECTION_END_NESTED(msk, val, 97)
#define ALT_FW_FTR_SECTION_END_IFSET(msk) \
ALT_FW_FTR_SECTION_END_NESTED_IFSET(msk, 97)
#define ALT_FW_FTR_SECTION_END_IFCLR(msk) \
ALT_FW_FTR_SECTION_END_NESTED_IFCLR(msk, 97)
#ifndef __ASSEMBLY__
#define ASM_FTR_IF(section_if, section_else, msk, val) \
stringify_in_c(BEGIN_FTR_SECTION) \
section_if "; " \
stringify_in_c(FTR_SECTION_ELSE) \
section_else "; " \
stringify_in_c(ALT_FTR_SECTION_END((msk), (val)))
#define ASM_FTR_IFSET(section_if, section_else, msk) \
ASM_FTR_IF(section_if, section_else, (msk), (msk))
#define ASM_FTR_IFCLR(section_if, section_else, msk) \
ASM_FTR_IF(section_if, section_else, (msk), 0)
#define ASM_MMU_FTR_IF(section_if, section_else, msk, val) \
stringify_in_c(BEGIN_MMU_FTR_SECTION) \
section_if "; " \
stringify_in_c(MMU_FTR_SECTION_ELSE) \
section_else "; " \
stringify_in_c(ALT_MMU_FTR_SECTION_END((msk), (val)))
#define ASM_MMU_FTR_IFSET(section_if, section_else, msk) \
ASM_MMU_FTR_IF(section_if, section_else, (msk), (msk))
#define ASM_MMU_FTR_IFCLR(section_if, section_else, msk) \
ASM_MMU_FTR_IF(section_if, section_else, (msk), 0)
#endif /* __ASSEMBLY__ */
/* LWSYNC feature sections */
#define START_LWSYNC_SECTION(label) label##1:
#define MAKE_LWSYNC_SECTION_ENTRY(label, sect) \
label##2: \
.pushsection sect,"a"; \
.align 2; \
label##3: \
FTR_ENTRY_OFFSET label##1b-label##3b; \
.popsection;
#define STF_ENTRY_BARRIER_FIXUP_SECTION \
953: \
.pushsection __stf_entry_barrier_fixup,"a"; \
.align 2; \
954: \
FTR_ENTRY_OFFSET 953b-954b; \
.popsection;
#define STF_EXIT_BARRIER_FIXUP_SECTION \
955: \
.pushsection __stf_exit_barrier_fixup,"a"; \
.align 2; \
956: \
FTR_ENTRY_OFFSET 955b-956b; \
.popsection;
#define UACCESS_FLUSH_FIXUP_SECTION \
959: \
.pushsection __uaccess_flush_fixup,"a"; \
.align 2; \
960: \
FTR_ENTRY_OFFSET 959b-960b; \
.popsection;
#define ENTRY_FLUSH_FIXUP_SECTION \
957: \
.pushsection __entry_flush_fixup,"a"; \
.align 2; \
958: \
FTR_ENTRY_OFFSET 957b-958b; \
.popsection;
#define RFI_FLUSH_FIXUP_SECTION \
951: \
.pushsection __rfi_flush_fixup,"a"; \
.align 2; \
952: \
FTR_ENTRY_OFFSET 951b-952b; \
.popsection;
#define NOSPEC_BARRIER_FIXUP_SECTION \
953: \
.pushsection __barrier_nospec_fixup,"a"; \
.align 2; \
954: \
FTR_ENTRY_OFFSET 953b-954b; \
.popsection;
#define START_BTB_FLUSH_SECTION \
955: \
#define END_BTB_FLUSH_SECTION \
956: \
.pushsection __btb_flush_fixup,"a"; \
.align 2; \
957: \
FTR_ENTRY_OFFSET 955b-957b; \
FTR_ENTRY_OFFSET 956b-957b; \
.popsection;
#ifndef __ASSEMBLY__
#include <linux/types.h>
extern long stf_barrier_fallback;
extern long entry_flush_fallback;
extern long __start___stf_entry_barrier_fixup, __stop___stf_entry_barrier_fixup;
extern long __start___stf_exit_barrier_fixup, __stop___stf_exit_barrier_fixup;
extern long __start___uaccess_flush_fixup, __stop___uaccess_flush_fixup;
extern long __start___entry_flush_fixup, __stop___entry_flush_fixup;
extern long __start___rfi_flush_fixup, __stop___rfi_flush_fixup;
extern long __start___barrier_nospec_fixup, __stop___barrier_nospec_fixup;
extern long __start__btb_flush_fixup, __stop__btb_flush_fixup;
void apply_feature_fixups(void);
void setup_feature_keys(void);
#endif
#endif /* __ASM_POWERPC_FEATURE_FIXUPS_H */
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