Re: [PATCH 1/8] signal/alpha: Document a conflict with SI_USER for SIGTRAP

From: Helge Deller
Date: Sun Jul 02 2017 - 10:15:14 EST

* Eric W. Biederman <ebiederm@xxxxxxxxxxxx>:
> Setting si_code to __SI_FAULT results in a userspace seeing
> an si_code of 0. This is the same si_code as SI_USER. Posix
> and common sense requires that SI_USER not be a signal specific
> si_code. As such this use of 0 for the si_code is a pretty
> horribly broken ABI.
> Given that alpha is on it's last legs I don't know that it is worth
> fixing this, but it is worth documenting what is going on so that
> no one decides to copy this bad decision.

The ABI was already broken, so IMHO I think it's better to somehow "fix"
it instead. Agreed, alpha and some other architectures are already aged,
but nevertheless most of them build in debian-ports. Below is a
suggested fix which reuses/misuses other existing trap codes instead.


Signed-off-by: Helge Deller <deller@xxxxxx>

diff --git a/arch/alpha/kernel/traps.c b/arch/alpha/kernel/traps.c
index 65bb102..2ed37dd 100644
--- a/arch/alpha/kernel/traps.c
+++ b/arch/alpha/kernel/traps.c
@@ -278,7 +278,7 @@ do_entIF(unsigned long type, struct pt_regs *regs)
case 1: /* bugcheck */
info.si_signo = SIGTRAP;
info.si_errno = 0;
- info.si_code = __SI_FAULT;
+ info.si_code = TRAP_HWBKPT;
info.si_addr = (void __user *) regs->pc;
info.si_trapno = 0;
send_sig_info(SIGTRAP, &info, current);
@@ -318,7 +318,7 @@ do_entIF(unsigned long type, struct pt_regs *regs)
signo = SIGFPE;
- code = __SI_FAULT;
+ code = FPE_FLTSUB;

@@ -340,7 +340,7 @@ do_entIF(unsigned long type, struct pt_regs *regs)
signo = SIGTRAP;
- code = __SI_FAULT;
+ code = TRAP_HWBKPT;

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