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Commit cc9f72e4 authored Jul 16, 2017 by Eric W. Biederman

signal/sparc: Document a conflict with SI_USER with SIGFPE



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>

parent 80dce5e3

arch/sparc/include/uapi/asm/siginfo.h

+7 −0

Original line number	Original line	Diff line number	Diff line
	@@ -16,6 +16,13 @@

	#define SI_NOINFO 32767 /* no information in siginfo_t */		#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		* SIGEMT si_codes
	*/		*/

arch/sparc/kernel/traps_32.c

+1 −1

Original line number	Original line	Diff line number	Diff line
	@@ -306,7 +306,7 @@ void do_fpe_trap(struct pt_regs *regs, unsigned long pc, unsigned long npc,
	info.si_errno = 0;		info.si_errno = 0;
	info.si_addr = (void __user *)pc;		info.si_addr = (void __user *)pc;
	info.si_trapno = 0;		info.si_trapno = 0;
	info.si_code = __SI_FAULT;		info.si_code = FPE_FIXME;
	if ((fsr & 0x1c000) == (1 << 14)) {		if ((fsr & 0x1c000) == (1 << 14)) {
	if (fsr & 0x10)		if (fsr & 0x10)
	info.si_code = FPE_FLTINV;		info.si_code = FPE_FLTINV;

arch/sparc/kernel/traps_64.c

+1 −1

Original line number	Original line	Diff line number	Diff line
	@@ -2258,7 +2258,7 @@ static void do_fpe_common(struct pt_regs *regs)
	info.si_errno = 0;		info.si_errno = 0;
	info.si_addr = (void __user *)regs->tpc;		info.si_addr = (void __user *)regs->tpc;
	info.si_trapno = 0;		info.si_trapno = 0;
	info.si_code = __SI_FAULT;		info.si_code = FPE_FIXME;
	if ((fsr & 0x1c000) == (1 << 14)) {		if ((fsr & 0x1c000) == (1 << 14)) {
	if (fsr & 0x10)		if (fsr & 0x10)
	info.si_code = FPE_FLTINV;		info.si_code = FPE_FLTINV;