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 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 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
> > > > ---
> > > > 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
> > > >
> > > > +#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.
>
> 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_ALWAYSALT_DIRECT_CALL(X86_FEATURE_ALWAYS)
-#define ALTINSTR_SIZE 14
-
#ifndef __ASSEMBLER__
#include
@@ -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
-#define EXTABLE_SIZE 12
+#ifndef COMPILE_OFFSETS
+#include
+#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 d4aae98b3
Re: [PATCH v2 45/62] x86/extable: Define ELF section entry size for exception tables
On Fri, Jun 6, 2025 at 3:48 AM Josh Poimboeuf 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 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 > > > --- > > > 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 > > > > > > +#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. can be used in C code too. Normally it wouldn't be needed but the inline asm case is a valid use. Brian Gerst
Re: [PATCH v2 45/62] x86/extable: Define ELF section entry size for exception tables
On Thu, Jun 05, 2025 at 11:58:23PM -0400, Brian Gerst wrote: > On Fri, May 9, 2025 at 4:51 PM Josh Poimboeuf 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 > > --- > > 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 > > > > +#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. -- Josh
Re: [PATCH v2 45/62] x86/extable: Define ELF section entry size for exception tables
On Fri, May 9, 2025 at 4:51 PM Josh Poimboeuf 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 > --- > 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 > > +#define EXTABLE_SIZE 12 Put this in asm-offsets.c instead. That removes the need for the BUILD_BUG_ON(). Brian Gerst
Re: [PATCH v2 45/62] x86/extable: Define ELF section entry size for exception tables
On Wed, May 28, 2025 at 10:40:55AM -0400, Joe Lawrence wrote:
> On 5/9/25 4:17 PM, Josh Poimboeuf 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
> > ---
> > 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
> >
> > +#define EXTABLE_SIZE 12
> >
> > + > [ ... snip ... ]
> >
>
> EXTABLE_SIZE defined in arch/x86/ ...
>
> > diff --git a/kernel/extable.c b/kernel/extable.c
> > index 71f482581cab..0ae3ee2ef266 100644
> > --- a/kernel/extable.c
> > +++ b/kernel/extable.c
> > @@ -55,6 +55,8 @@ const struct exception_table_entry
> > *search_exception_tables(unsigned long addr)
> > {
> > const struct exception_table_entry *e;
> >
> > + BUILD_BUG_ON(EXTABLE_SIZE != sizeof(struct exception_table_entry));
> > +
>
> but referenced in kernel/ where a non-x86 build like ppc64le build won't
> know what EXTABLE_SIZE is :(
Thanks, I'll move the BUILD_BUG_ON() to the x86 extable code:
diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index bf8dab18be97..d4aae98b3739 100644
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -303,6 +303,8 @@ 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/kernel/extable.c b/kernel/extable.c
index 0ae3ee2ef266..71f482581cab 100644
--- a/kernel/extable.c
+++ b/kernel/extable.c
@@ -55,8 +55,6 @@ const struct exception_table_entry
*search_exception_tables(unsigned long addr)
{
const struct exception_table_entry *e;
- BUILD_BUG_ON(EXTABLE_SIZE != sizeof(struct exception_table_entry));
-
e = search_kernel_exception_table(addr);
if (!e)
e = search_module_extables(addr);
Re: [PATCH v2 45/62] x86/extable: Define ELF section entry size for exception tables
On 5/9/25 4:17 PM, Josh Poimboeuf 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
> ---
> 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
>
> +#define EXTABLE_SIZE 12
>
> + > [ ... snip ... ]
>
EXTABLE_SIZE defined in arch/x86/ ...
> diff --git a/kernel/extable.c b/kernel/extable.c
> index 71f482581cab..0ae3ee2ef266 100644
> --- a/kernel/extable.c
> +++ b/kernel/extable.c
> @@ -55,6 +55,8 @@ const struct exception_table_entry
> *search_exception_tables(unsigned long addr)
> {
> const struct exception_table_entry *e;
>
> + BUILD_BUG_ON(EXTABLE_SIZE != sizeof(struct exception_table_entry));
> +
but referenced in kernel/ where a non-x86 build like ppc64le build won't
know what EXTABLE_SIZE is :(
--
Joe
[PATCH v2 45/62] x86/extable: Define ELF section entry size for exception tables
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
---
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
+#define EXTABLE_SIZE 12
+
/* Exception table entry */
#ifdef __ASSEMBLER__
-# define _ASM_EXTABLE_TYPE(from, to, type) \
- .pushsection "__ex_table","a" ; \
- .balign 4 ; \
- .long (from) - . ; \
- .long (to) - . ;\
- .long type ;\
+# define _ASM_EXTABLE_TYPE(from, to, type) \
+ .pushsection "__ex_table", "aM", @progbits, EXTABLE_SIZE; \
+ .balign 4 ; \
+ .long (from) - . ; \
+ .long (to) - . ;\
+ .long type ;\
.popsection
# ifdef CONFIG_KPROBES
@@ -189,7 +191,8 @@ static __always_inline __pure void *rip_rel_ptr(void *p)
".purgem extable_type_reg\n"
# define _ASM_EXTABLE_TYPE(from, to, type) \
- " .pushsection \"__ex_table\",\"a\"\n" \
+ " .pushsection __ex_table, \"aM\", @progbits, " \
+ __stringify(EXTABLE_SIZE) "\n" \
" .balign 4\n" \
" .long (" #from ") - .\n" \
" .long (" #to ") - .\n"\
@@ -197,7 +200,8 @@ static __always_inline __pure void *rip_rel_ptr(void *p)
" .popsection\n"
# define _ASM_EXTABLE_TYPE_REG(from, to, type, reg)
\
- " .pushsection \"__ex_table\",\"a\"\n"
\
+ " .pushsection __ex_table, \"aM\", @progbits, "
\
+ __stringify(EXTABLE_SIZE) "\n"
\
" .balign 4\n"
\
" .long (" #from ") - .\n"
\
" .long (" #to ") - .\n"
\
diff --git a/kernel/extable.c b/kernel/extable.c
index 71f482581cab..0ae3ee2ef266 100644
--- a/kernel/extable.c
+++ b/kernel/extable.c
@@ -55,6 +55,8 @@ const struct exception_table_entry
*search_exception_tables(unsigned long addr)
{
const struct exception_table_entry *e;
+ BUILD_BUG_ON(EXTABLE_SIZE != sizeof(struct exception_table_entry));
+
e = search_kernel_exception_table(addr);
if (!e)
e = search_module_extables(addr);
--
2.49.0
