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signal/sparc: Document a conflict with SI_USER with SIGFPE

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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.

This was introduced in 2.3.41 so this mess has had a long time for
people to be able to start depending on it.

As this bug has existed for 17 years already I don't know if it is
worth fixing.  It is definitely worth documenting what is going
on so that no one decides to copy this bad decision.

Cc: "David S. Miller" <davem@davemloft.net>
Cc: sparclinux@vger.kernel.org
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
This commit is contained in:
Eric W. Biederman
2017-07-16 20:04:58 -05:00
parent 80dce5e374
commit cc9f72e474
3 changed files with 9 additions and 2 deletions
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7
arch/sparc/include/uapi/asm/siginfo.h
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@@ -16,6 +16,13 @@
#define SI_NOINFO 32767 /* no information in siginfo_t */
/*
* SIGFPE si_codes
*/
#ifdef __KERNEL__
#define FPE_FIXME (__SI_FAULT|0) /* Broken dup of SI_USER */
#endif /* __KERNEL__ */
/*
* SIGEMT si_codes
*/