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Message-ID: <zsvgiietkr4qwrlnmvsov7xmgqe7khqmgluvr6f6hsqaw3sp4q@drakq47ntmhr>
Date: Mon, 9 Jun 2025 10:07:36 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Brian Gerst <brgerst@...il.com>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org,
Petr Mladek <pmladek@...e.com>, Miroslav Benes <mbenes@...e.cz>,
Joe Lawrence <joe.lawrence@...hat.com>, live-patching@...r.kernel.org, Song Liu <song@...nel.org>,
laokz <laokz@...mail.com>, Jiri Kosina <jikos@...nel.org>,
Marcos Paulo de Souza <mpdesouza@...e.com>, Weinan Liu <wnliu@...gle.com>,
Fazla Mehrab <a.mehrab@...edance.com>, Chen Zhongjin <chenzhongjin@...wei.com>,
Puranjay Mohan <puranjay@...nel.org>
Subject: Re: [PATCH v2 45/62] x86/extable: Define ELF section entry size for
exception tables
On Fri, Jun 06, 2025 at 09:26:30PM -0400, Brian Gerst wrote:
> On Fri, Jun 6, 2025 at 3:48 AM Josh Poimboeuf <jpoimboe@...nel.org> wrote:
> >
> > On Thu, Jun 05, 2025 at 11:58:23PM -0400, Brian Gerst wrote:
> > > On Fri, May 9, 2025 at 4:51 PM Josh Poimboeuf <jpoimboe@...nel.org> wrote:
> > > >
> > > > In preparation for the objtool klp diff subcommand, define the entry
> > > > size for the __ex_table section in its ELF header. This will allow
> > > > tooling to extract individual entries.
> > > >
> > > > Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
> > > > ---
> > > > arch/x86/include/asm/asm.h | 20 ++++++++++++--------
> > > > kernel/extable.c | 2 ++
> > > > 2 files changed, 14 insertions(+), 8 deletions(-)
> > > >
> > > > diff --git a/arch/x86/include/asm/asm.h b/arch/x86/include/asm/asm.h
> > > > index f963848024a5..62dff336f206 100644
> > > > --- a/arch/x86/include/asm/asm.h
> > > > +++ b/arch/x86/include/asm/asm.h
> > > > @@ -138,15 +138,17 @@ static __always_inline __pure void *rip_rel_ptr(void *p)
> > > >
> > > > # include <asm/extable_fixup_types.h>
> > > >
> > > > +#define EXTABLE_SIZE 12
> > >
> > > Put this in asm-offsets.c instead.
> >
> > But that's only for .S code right? This is also needed for inline asm.
>
> <asm/asm-offsets.h> can be used in C code too. Normally it wouldn't
> be needed but the inline asm case is a valid use.
Ah, nice. This is much better. Thanks!
diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h
index e206e0f96568..eb24d9ba30d7 100644
--- a/arch/x86/include/asm/alternative.h
+++ b/arch/x86/include/asm/alternative.h
@@ -16,8 +16,6 @@
#define ALT_DIRECT_CALL(feature) ((ALT_FLAG_DIRECT_CALL << ALT_FLAGS_SHIFT) | (feature))
#define ALT_CALL_ALWAYS ALT_DIRECT_CALL(X86_FEATURE_ALWAYS)
-#define ALTINSTR_SIZE 14
-
#ifndef __ASSEMBLER__
#include <linux/stddef.h>
@@ -200,7 +198,7 @@ static inline int alternatives_text_reserved(void *start, void *end)
#define ALTINSTR_ENTRY(ft_flags) \
".pushsection .altinstructions, \"aM\", @progbits, " \
- __stringify(ALTINSTR_SIZE) "\n" \
+ __stringify(ALT_INSTR_SIZE) "\n" \
" .long 771b - .\n" /* label */ \
" .long 774f - .\n" /* new instruction */ \
" .4byte " __stringify(ft_flags) "\n" /* feature + flags */ \
@@ -363,7 +361,7 @@ void nop_func(void);
741: \
.skip -(((744f-743f)-(741b-740b)) > 0) * ((744f-743f)-(741b-740b)),0x90 ;\
742: \
- .pushsection .altinstructions, "aM", @progbits, ALTINSTR_SIZE ; \
+ .pushsection .altinstructions, "aM", @progbits, ALT_INSTR_SIZE ;\
altinstr_entry 740b,743f,flag,742b-740b,744f-743f ; \
.popsection ; \
.pushsection .altinstr_replacement,"ax" ; \
diff --git a/arch/x86/include/asm/asm.h b/arch/x86/include/asm/asm.h
index 62dff336f206..eb0b33f02be3 100644
--- a/arch/x86/include/asm/asm.h
+++ b/arch/x86/include/asm/asm.h
@@ -138,7 +138,9 @@ static __always_inline __pure void *rip_rel_ptr(void *p)
# include <asm/extable_fixup_types.h>
-#define EXTABLE_SIZE 12
+#ifndef COMPILE_OFFSETS
+#include <asm/asm-offsets.h>
+#endif
/* Exception table entry */
#ifdef __ASSEMBLER__
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index d01ab5fa631f..4888e1c8be6a 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -593,8 +593,6 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
u8 *instr, *replacement;
struct alt_instr *a, *b;
- BUILD_BUG_ON(ALTINSTR_SIZE != sizeof(struct alt_instr));
-
DPRINTK(ALT, "alt table %px, -> %px", start, end);
/*
diff --git a/arch/x86/kernel/asm-offsets.c b/arch/x86/kernel/asm-offsets.c
index 6259b474073b..805da27854ee 100644
--- a/arch/x86/kernel/asm-offsets.c
+++ b/arch/x86/kernel/asm-offsets.c
@@ -123,4 +123,8 @@ static void __used common(void)
OFFSET(ARIA_CTX_rounds, aria_ctx, rounds);
#endif
+ BLANK();
+ DEFINE(EXTABLE_SIZE, sizeof(struct exception_table_entry));
+ DEFINE(UNWIND_HINT_SIZE, sizeof(struct unwind_hint));
+ DEFINE(ALT_INSTR_SIZE, sizeof(struct alt_instr));
}
diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c
index 4624d6d916a2..977ee75e047c 100644
--- a/arch/x86/kernel/unwind_orc.c
+++ b/arch/x86/kernel/unwind_orc.c
@@ -199,8 +199,6 @@ static struct orc_entry *orc_find(unsigned long ip)
{
static struct orc_entry *orc;
- BUILD_BUG_ON(UNWIND_HINT_SIZE != sizeof(struct unwind_hint));
-
if (ip == 0)
return &null_orc_entry;
diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index d4aae98b3739..bf8dab18be97 100644
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -303,8 +303,6 @@ int fixup_exception(struct pt_regs *regs, int trapnr, unsigned long error_code,
const struct exception_table_entry *e;
int type, reg, imm;
- BUILD_BUG_ON(EXTABLE_SIZE != sizeof(struct exception_table_entry));
-
#ifdef CONFIG_PNPBIOS
if (unlikely(SEGMENT_IS_PNP_CODE(regs->cs))) {
extern u32 pnp_bios_fault_eip, pnp_bios_fault_esp;
diff --git a/include/linux/objtool.h b/include/linux/objtool.h
index d4137a46ee70..e93f0c28b54b 100644
--- a/include/linux/objtool.h
+++ b/include/linux/objtool.h
@@ -8,8 +8,6 @@
#include <asm/asm.h>
-#define UNWIND_HINT_SIZE 12
-
#ifndef __ASSEMBLY__
#define UNWIND_HINT(type, sp_reg, sp_offset, signal) \
diff --git a/kernel/bounds.c b/kernel/bounds.c
index 29b2cd00df2c..02b619eb6106 100644
--- a/kernel/bounds.c
+++ b/kernel/bounds.c
@@ -6,6 +6,7 @@
*/
#define __GENERATING_BOUNDS_H
+#define COMPILE_OFFSETS
/* Include headers that define the enum constants of interest */
#include <linux/page-flags.h>
#include <linux/mmzone.h>
diff --git a/scripts/mod/devicetable-offsets.c b/scripts/mod/devicetable-offsets.c
index d3d00e85edf7..ef2ffb68f69d 100644
--- a/scripts/mod/devicetable-offsets.c
+++ b/scripts/mod/devicetable-offsets.c
@@ -1,4 +1,5 @@
// SPDX-License-Identifier: GPL-2.0
+#define COMPILE_OFFSETS
#include <linux/kbuild.h>
#include <linux/mod_devicetable.h>
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