It turns out that linux uses si_trapno very sparingly, and as such it
can be considered extra information for a very narrow selection of
signals, rather than information that is present with every fault
reported in siginfo.
As such move si_trapno inside the union inside of _si_fault. This
results in no change in placement, and makes it eaiser to extend
_si_fault in the future as this reduces the number of special cases.
In particular with si_trapno included in the union it is no longer a
concern that the union must be pointer alligned on most architectures
because the union followes immediately after si_addr which is a
pointer.
Signed-off-by: "Eric W. Biederman" <[email protected]>
---
include/linux/compat.h | 4 +---
include/uapi/asm-generic/siginfo.h | 6 +-----
2 files changed, 2 insertions(+), 8 deletions(-)
diff --git a/include/linux/compat.h b/include/linux/compat.h
index f0d2dd35d408..24462ed63af4 100644
--- a/include/linux/compat.h
+++ b/include/linux/compat.h
@@ -214,12 +214,10 @@ typedef struct compat_siginfo {
/* SIGILL, SIGFPE, SIGSEGV, SIGBUS, SIGTRAP, SIGEMT */
struct {
compat_uptr_t _addr; /* faulting insn/memory ref. */
-#ifdef __ARCH_SI_TRAPNO
- int _trapno; /* TRAP # which caused the signal */
-#endif
#define __COMPAT_ADDR_BND_PKEY_PAD (__alignof__(compat_uptr_t) < sizeof(short) ? \
sizeof(short) : __alignof__(compat_uptr_t))
union {
+ int _trapno; /* TRAP # which caused the signal */
/*
* used when si_code=BUS_MCEERR_AR or
* used when si_code=BUS_MCEERR_AO
diff --git a/include/uapi/asm-generic/siginfo.h b/include/uapi/asm-generic/siginfo.h
index 03d6f6d2c1fe..2abdf1d19aad 100644
--- a/include/uapi/asm-generic/siginfo.h
+++ b/include/uapi/asm-generic/siginfo.h
@@ -63,9 +63,6 @@ union __sifields {
/* SIGILL, SIGFPE, SIGSEGV, SIGBUS, SIGTRAP, SIGEMT */
struct {
void __user *_addr; /* faulting insn/memory ref. */
-#ifdef __ARCH_SI_TRAPNO
- int _trapno; /* TRAP # which caused the signal */
-#endif
#ifdef __ia64__
int _imm; /* immediate value for "break" */
unsigned int _flags; /* see ia64 si_flags */
@@ -75,6 +72,7 @@ union __sifields {
#define __ADDR_BND_PKEY_PAD (__alignof__(void *) < sizeof(short) ? \
sizeof(short) : __alignof__(void *))
union {
+ int _trapno; /* TRAP # which caused the signal */
/*
* used when si_code=BUS_MCEERR_AR or
* used when si_code=BUS_MCEERR_AO
@@ -150,9 +148,7 @@ typedef struct siginfo {
#define si_int _sifields._rt._sigval.sival_int
#define si_ptr _sifields._rt._sigval.sival_ptr
#define si_addr _sifields._sigfault._addr
-#ifdef __ARCH_SI_TRAPNO
#define si_trapno _sifields._sigfault._trapno
-#endif
#define si_addr_lsb _sifields._sigfault._addr_lsb
#define si_lower _sifields._sigfault._addr_bnd._lower
#define si_upper _sifields._sigfault._addr_bnd._upper
--
2.30.1
On Sat, 1 May 2021 at 00:50, Eric W. Biederman <[email protected]> wrote:
>
> It turns out that linux uses si_trapno very sparingly, and as such it
> can be considered extra information for a very narrow selection of
> signals, rather than information that is present with every fault
> reported in siginfo.
>
> As such move si_trapno inside the union inside of _si_fault. This
> results in no change in placement, and makes it eaiser to extend
> _si_fault in the future as this reduces the number of special cases.
> In particular with si_trapno included in the union it is no longer a
> concern that the union must be pointer alligned on most architectures
> because the union followes immediately after si_addr which is a
> pointer.
>
Maybe add "Link:
https://lkml.kernel.org/r/CAK8P3a0+uKYwL1NhY6Hvtieghba2hKYGD6hcKx5n8=4Gtt+pHA@mail.gmail.com"
> Signed-off-by: "Eric W. Biederman" <[email protected]>
Acked-by: Marco Elver <[email protected]>
By no longer guarding it with __ARCH_SI_TRAPNO we run the risk that it
will be used by something else at some point. Is that intentional?
Thanks,
-- Marco
> ---
> include/linux/compat.h | 4 +---
> include/uapi/asm-generic/siginfo.h | 6 +-----
> 2 files changed, 2 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/compat.h b/include/linux/compat.h
> index f0d2dd35d408..24462ed63af4 100644
> --- a/include/linux/compat.h
> +++ b/include/linux/compat.h
> @@ -214,12 +214,10 @@ typedef struct compat_siginfo {
> /* SIGILL, SIGFPE, SIGSEGV, SIGBUS, SIGTRAP, SIGEMT */
> struct {
> compat_uptr_t _addr; /* faulting insn/memory ref. */
> -#ifdef __ARCH_SI_TRAPNO
> - int _trapno; /* TRAP # which caused the signal */
> -#endif
> #define __COMPAT_ADDR_BND_PKEY_PAD (__alignof__(compat_uptr_t) < sizeof(short) ? \
> sizeof(short) : __alignof__(compat_uptr_t))
> union {
> + int _trapno; /* TRAP # which caused the signal */
> /*
> * used when si_code=BUS_MCEERR_AR or
> * used when si_code=BUS_MCEERR_AO
> diff --git a/include/uapi/asm-generic/siginfo.h b/include/uapi/asm-generic/siginfo.h
> index 03d6f6d2c1fe..2abdf1d19aad 100644
> --- a/include/uapi/asm-generic/siginfo.h
> +++ b/include/uapi/asm-generic/siginfo.h
> @@ -63,9 +63,6 @@ union __sifields {
> /* SIGILL, SIGFPE, SIGSEGV, SIGBUS, SIGTRAP, SIGEMT */
> struct {
> void __user *_addr; /* faulting insn/memory ref. */
> -#ifdef __ARCH_SI_TRAPNO
> - int _trapno; /* TRAP # which caused the signal */
> -#endif
> #ifdef __ia64__
> int _imm; /* immediate value for "break" */
> unsigned int _flags; /* see ia64 si_flags */
> @@ -75,6 +72,7 @@ union __sifields {
> #define __ADDR_BND_PKEY_PAD (__alignof__(void *) < sizeof(short) ? \
> sizeof(short) : __alignof__(void *))
> union {
> + int _trapno; /* TRAP # which caused the signal */
> /*
> * used when si_code=BUS_MCEERR_AR or
> * used when si_code=BUS_MCEERR_AO
> @@ -150,9 +148,7 @@ typedef struct siginfo {
> #define si_int _sifields._rt._sigval.sival_int
> #define si_ptr _sifields._rt._sigval.sival_ptr
> #define si_addr _sifields._sigfault._addr
> -#ifdef __ARCH_SI_TRAPNO
> #define si_trapno _sifields._sigfault._trapno
> -#endif
> #define si_addr_lsb _sifields._sigfault._addr_lsb
> #define si_lower _sifields._sigfault._addr_bnd._lower
> #define si_upper _sifields._sigfault._addr_bnd._upper
> --
> 2.30.1
Marco Elver <[email protected]> writes:
> On Sat, 1 May 2021 at 00:50, Eric W. Biederman <[email protected]> wrote:
>>
>> It turns out that linux uses si_trapno very sparingly, and as such it
>> can be considered extra information for a very narrow selection of
>> signals, rather than information that is present with every fault
>> reported in siginfo.
>>
>> As such move si_trapno inside the union inside of _si_fault. This
>> results in no change in placement, and makes it eaiser to extend
>> _si_fault in the future as this reduces the number of special cases.
>> In particular with si_trapno included in the union it is no longer a
>> concern that the union must be pointer alligned on most architectures
>> because the union followes immediately after si_addr which is a
>> pointer.
>>
>
> Maybe add "Link:
> https://lkml.kernel.org/r/CAK8P3a0+uKYwL1NhY6Hvtieghba2hKYGD6hcKx5n8=4Gtt+pHA@mail.gmail.com"
>
>> Signed-off-by: "Eric W. Biederman" <[email protected]>
>
> Acked-by: Marco Elver <[email protected]>
>
> By no longer guarding it with __ARCH_SI_TRAPNO we run the risk that it
> will be used by something else at some point. Is that intentional?
The motivation was letting the code be tested on other architectures.
But once si_trapno falls inside the union instead of being present for
every signal reporting a fault it doesn't really matter.
I think it would be poor taste but harmless to use si_trapno, mostly
because defining a new entry in the union could be more specific and
well defined.
Eric