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Date: Fri, 06 May 2022 11:17:35 +0200
From: Sven Schnelle <svens@...ux.ibm.com>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: linux-kernel@...r.kernel.org,
Peter Zijlstra <peterz@...radead.org>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
Michael Ellerman <mpe@...erman.id.au>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Paul Mackerras <paulus@...ba.org>,
Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>,
Albert Ou <aou@...s.berkeley.edu>,
Heiko Carstens <hca@...ux.ibm.com>,
Vasily Gorbik <gor@...ux.ibm.com>,
Alexander Gordeev <agordeev@...ux.ibm.com>,
Christian Borntraeger <borntraeger@...ux.ibm.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
"H. Peter Anvin" <hpa@...or.com>,
linux-arm-kernel@...ts.infradead.org,
linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org,
linux-s390@...r.kernel.org
Subject: Re: [PATCH] bug: Use normal relative pointers in 'struct bug_entry'
Josh Poimboeuf <jpoimboe@...nel.org> writes:
> With CONFIG_GENERIC_BUG_RELATIVE_POINTERS, the addr/file relative
> pointers are calculated weirdly: based on the beginning of the bug_entry
> struct address, rather than their respective pointer addresses.
>
> Make the relative pointers less surprising to both humans and tools by
> calculating them the normal way.
>
> Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
Acked-by: Sven Schnelle <svens@...ux.ibm.com> # s390
> ---
> arch/arm64/include/asm/asm-bug.h | 4 ++--
> arch/powerpc/include/asm/bug.h | 5 +++--
> arch/riscv/include/asm/bug.h | 4 ++--
> arch/s390/include/asm/bug.h | 5 +++--
> arch/x86/include/asm/bug.h | 2 +-
> lib/bug.c | 15 +++++++--------
> 6 files changed, 18 insertions(+), 17 deletions(-)
>
> diff --git a/arch/arm64/include/asm/asm-bug.h b/arch/arm64/include/asm/asm-bug.h
> index 03f52f84a4f3..c762038ba400 100644
> --- a/arch/arm64/include/asm/asm-bug.h
> +++ b/arch/arm64/include/asm/asm-bug.h
> @@ -14,7 +14,7 @@
> 14472: .string file; \
> .popsection; \
> \
> - .long 14472b - 14470b; \
> + .long 14472b - .; \
> .short line;
> #else
> #define _BUGVERBOSE_LOCATION(file, line)
> @@ -25,7 +25,7 @@
> #define __BUG_ENTRY(flags) \
> .pushsection __bug_table,"aw"; \
> .align 2; \
> - 14470: .long 14471f - 14470b; \
> + 14470: .long 14471f - .; \
> _BUGVERBOSE_LOCATION(__FILE__, __LINE__) \
> .short flags; \
> .popsection; \
> diff --git a/arch/powerpc/include/asm/bug.h b/arch/powerpc/include/asm/bug.h
> index ecbae1832de3..76252576d889 100644
> --- a/arch/powerpc/include/asm/bug.h
> +++ b/arch/powerpc/include/asm/bug.h
> @@ -13,7 +13,8 @@
> #ifdef CONFIG_DEBUG_BUGVERBOSE
> .macro __EMIT_BUG_ENTRY addr,file,line,flags
> .section __bug_table,"aw"
> -5001: .4byte \addr - 5001b, 5002f - 5001b
> +5001: .4byte \addr - .
> + .4byte 5002f - .
> .short \line, \flags
> .org 5001b+BUG_ENTRY_SIZE
> .previous
> @@ -24,7 +25,7 @@
> #else
> .macro __EMIT_BUG_ENTRY addr,file,line,flags
> .section __bug_table,"aw"
> -5001: .4byte \addr - 5001b
> +5001: .4byte \addr - .
> .short \flags
> .org 5001b+BUG_ENTRY_SIZE
> .previous
> diff --git a/arch/riscv/include/asm/bug.h b/arch/riscv/include/asm/bug.h
> index d3804a2f9aad..1aaea81fb141 100644
> --- a/arch/riscv/include/asm/bug.h
> +++ b/arch/riscv/include/asm/bug.h
> @@ -30,8 +30,8 @@
> typedef u32 bug_insn_t;
>
> #ifdef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
> -#define __BUG_ENTRY_ADDR RISCV_INT " 1b - 2b"
> -#define __BUG_ENTRY_FILE RISCV_INT " %0 - 2b"
> +#define __BUG_ENTRY_ADDR RISCV_INT " 1b - ."
> +#define __BUG_ENTRY_FILE RISCV_INT " %0 - ."
> #else
> #define __BUG_ENTRY_ADDR RISCV_PTR " 1b"
> #define __BUG_ENTRY_FILE RISCV_PTR " %0"
> diff --git a/arch/s390/include/asm/bug.h b/arch/s390/include/asm/bug.h
> index 0b25f28351ed..aebe1e22c7be 100644
> --- a/arch/s390/include/asm/bug.h
> +++ b/arch/s390/include/asm/bug.h
> @@ -15,7 +15,8 @@
> "1: .asciz \""__FILE__"\"\n" \
> ".previous\n" \
> ".section __bug_table,\"awM\",@progbits,%2\n" \
> - "2: .long 0b-2b,1b-2b\n" \
> + "2: .long 0b-.\n" \
> + " .long 1b-.\n" \
> " .short %0,%1\n" \
> " .org 2b+%2\n" \
> ".previous\n" \
> @@ -30,7 +31,7 @@
> asm_inline volatile( \
> "0: mc 0,0\n" \
> ".section __bug_table,\"awM\",@progbits,%1\n" \
> - "1: .long 0b-1b\n" \
> + "1: .long 0b-.\n" \
> " .short %0\n" \
> " .org 1b+%1\n" \
> ".previous\n" \
> diff --git a/arch/x86/include/asm/bug.h b/arch/x86/include/asm/bug.h
> index aaf0cb0db4ae..a3ec87d198ac 100644
> --- a/arch/x86/include/asm/bug.h
> +++ b/arch/x86/include/asm/bug.h
> @@ -18,7 +18,7 @@
> #ifdef CONFIG_X86_32
> # define __BUG_REL(val) ".long " __stringify(val)
> #else
> -# define __BUG_REL(val) ".long " __stringify(val) " - 2b"
> +# define __BUG_REL(val) ".long " __stringify(val) " - ."
> #endif
>
> #ifdef CONFIG_DEBUG_BUGVERBOSE
> diff --git a/lib/bug.c b/lib/bug.c
> index 45a0584f6541..c223a2575b72 100644
> --- a/lib/bug.c
> +++ b/lib/bug.c
> @@ -6,8 +6,7 @@
>
> CONFIG_BUG - emit BUG traps. Nothing happens without this.
> CONFIG_GENERIC_BUG - enable this code.
> - CONFIG_GENERIC_BUG_RELATIVE_POINTERS - use 32-bit pointers relative to
> - the containing struct bug_entry for bug_addr and file.
> + CONFIG_GENERIC_BUG_RELATIVE_POINTERS - use 32-bit relative pointers for bug_addr and file
> CONFIG_DEBUG_BUGVERBOSE - emit full file+line information for each BUG
>
> CONFIG_BUG and CONFIG_DEBUG_BUGVERBOSE are potentially user-settable
> @@ -53,10 +52,10 @@ extern struct bug_entry __start___bug_table[], __stop___bug_table[];
>
> static inline unsigned long bug_addr(const struct bug_entry *bug)
> {
> -#ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
> - return bug->bug_addr;
> +#ifdef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
> + return (unsigned long)&bug->bug_addr_disp + bug->bug_addr_disp;
> #else
> - return (unsigned long)bug + bug->bug_addr_disp;
> + return bug->bug_addr;
> #endif
> }
>
> @@ -131,10 +130,10 @@ void bug_get_file_line(struct bug_entry *bug, const char **file,
> unsigned int *line)
> {
> #ifdef CONFIG_DEBUG_BUGVERBOSE
> -#ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
> - *file = bug->file;
> +#ifdef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
> + *file = (const char *)&bug->file_disp + bug->file_disp;
> #else
> - *file = (const char *)bug + bug->file_disp;
> + *file = bug->file;
> #endif
> *line = bug->line;
> #else
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