Date: Tue, 17 Jul 2012 22:00:30 GMT From: Mark Linimon <linimon@lonesome.com> To: freebsd-amd64@FreeBSD.org Subject: Re: amd64/169927: siginfo, si_code for fpe errors when error occurs using the SSE math processor Message-ID: <201207172200.q6HM0U6Z097180@freefall.freebsd.org>
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The following reply was made to PR amd64/169927; it has been noted by GNATS.
From: Mark Linimon <linimon@lonesome.com>
To: bug-followup@FreeBSD.org
Cc:
Subject: Re: amd64/169927: siginfo, si_code for fpe errors when error
occurs using the SSE math processor
Date: Tue, 17 Jul 2012 16:50:18 -0500
----- Forwarded message from Konstantin Belousov <kostikbel@gmail.com> -----
Date: Tue, 17 Jul 2012 21:26:19 +0300
From: Konstantin Belousov <kostikbel@gmail.com>
To: Bruce Evans <brde@optusnet.com.au>
Cc: freebsd-amd64@freebsd.org
Subject: Re: amd64/169927: siginfo,
si_code for fpe errors when error occurs using the SSE math
processor
On Tue, Jul 17, 2012 at 08:09:15PM +0300, Konstantin Belousov wrote:
> The trap number is available for SA_SIGINFO type of handlers with
> si_trapno member of siginfo_t. I think this is final argument to have
> separate fputrap_{x87,sse} functions.
>
> For amd64, SSE hardware is FPU, so I do not see much wrong with the name.
>
> I changed fputrap_sse() according to your suggestion.
Below is the actually tested patch. After it, I put the test program.
diff --git a/sys/amd64/amd64/fpu.c b/sys/amd64/amd64/fpu.c
index a7812b7..ae241ce 100644
--- a/sys/amd64/amd64/fpu.c
+++ b/sys/amd64/amd64/fpu.c
@@ -73,6 +73,7 @@ __FBSDID("$FreeBSD$");
#define fxrstor(addr) __asm __volatile("fxrstor %0" : : "m" (*(addr)))
#define fxsave(addr) __asm __volatile("fxsave %0" : "=m" (*(addr)))
#define ldmxcsr(csr) __asm __volatile("ldmxcsr %0" : : "m" (csr))
+#define stmxcsr(addr) __asm __volatile("stmxcsr %0" : : "m" (*(addr)))
static __inline void
xrstor(char *addr, uint64_t mask)
@@ -105,6 +106,7 @@ void fnstsw(caddr_t addr);
void fxsave(caddr_t addr);
void fxrstor(caddr_t addr);
void ldmxcsr(u_int csr);
+void stmxcsr(u_int csr);
void xrstor(char *addr, uint64_t mask);
void xsave(char *addr, uint64_t mask);
@@ -113,9 +115,6 @@ void xsave(char *addr, uint64_t mask);
#define start_emulating() load_cr0(rcr0() | CR0_TS)
#define stop_emulating() clts()
-#define GET_FPU_CW(thread) ((thread)->td_pcb->pcb_save->sv_env.en_cw)
-#define GET_FPU_SW(thread) ((thread)->td_pcb->pcb_save->sv_env.en_sw)
-
CTASSERT(sizeof(struct savefpu) == 512);
CTASSERT(sizeof(struct xstate_hdr) == 64);
CTASSERT(sizeof(struct savefpu_ymm) == 832);
@@ -514,11 +513,15 @@ static char fpetable[128] = {
};
/*
- * Preserve the FP status word, clear FP exceptions, then generate a SIGFPE.
+ * Preserve the FP status word, clear FP exceptions for x87, then
+ * generate a SIGFPE.
+ *
+ * Clearing exceptions was necessary mainly to avoid IRQ13 bugs and is
+ * engraved in our i386 ABI. We now depend on longjmp() restoring a
+ * usable state. Restoring the state or examining it might fail if we
+ * didn't clear exceptions.
*
- * Clearing exceptions is necessary mainly to avoid IRQ13 bugs. We now
- * depend on longjmp() restoring a usable state. Restoring the state
- * or examining it might fail if we didn't clear exceptions.
+ * For SSE exceptions, the exceptions are not cleared.
*
* The error code chosen will be one of the FPE_... macros. It will be
* sent as the second argument to old BSD-style signal handlers and as
@@ -531,8 +534,9 @@ static char fpetable[128] = {
* solution for signals other than SIGFPE.
*/
int
-fputrap()
+fputrap_x87(void)
{
+ struct savefpu *pcb_save;
u_short control, status;
critical_enter();
@@ -543,19 +547,40 @@ fputrap()
* wherever they are.
*/
if (PCPU_GET(fpcurthread) != curthread) {
- control = GET_FPU_CW(curthread);
- status = GET_FPU_SW(curthread);
+ pcb_save = curthread->td_pcb->pcb_save;
+ control = pcb_save->sv_env.en_cw;
+ status = pcb_save->sv_env.en_sw;
} else {
fnstcw(&control);
fnstsw(&status);
+ fnclex();
}
- if (PCPU_GET(fpcurthread) == curthread)
- fnclex();
critical_exit();
return (fpetable[status & ((~control & 0x3f) | 0x40)]);
}
+int
+fputrap_sse(void)
+{
+ u_int mxcsr;
+
+ critical_enter();
+
+ /*
+ * Coomparing with the x87 #MF handler, we do not clear
+ * exceptions from the mxcsr.
+ */
+ if (PCPU_GET(fpcurthread) != curthread)
+ mxcsr = curthread->td_pcb->pcb_save->sv_env.en_mxcsr;
+ else
+ stmxcsr(&mxcsr);
+
+ critical_exit();
+
+ return (fpetable[(mxcsr & (~mxcsr >> 7)) & 0x3f]);
+}
+
/*
* Implement device not available (DNA) exception
*
diff --git a/sys/amd64/amd64/trap.c b/sys/amd64/amd64/trap.c
index 75e15e0..57d1cc2 100644
--- a/sys/amd64/amd64/trap.c
+++ b/sys/amd64/amd64/trap.c
@@ -328,7 +328,7 @@ trap(struct trapframe *frame)
break;
case T_ARITHTRAP: /* arithmetic trap */
- ucode = fputrap();
+ ucode = fputrap_x87();
if (ucode == -1)
goto userout;
i = SIGFPE;
@@ -442,7 +442,9 @@ trap(struct trapframe *frame)
break;
case T_XMMFLT: /* SIMD floating-point exception */
- ucode = 0; /* XXX */
+ ucode = fputrap_sse();
+ if (ucode == -1)
+ goto userout;
i = SIGFPE;
break;
}
diff --git a/sys/amd64/include/fpu.h b/sys/amd64/include/fpu.h
index 98a016b..7d0f0ea 100644
--- a/sys/amd64/include/fpu.h
+++ b/sys/amd64/include/fpu.h
@@ -62,7 +62,8 @@ int fpusetregs(struct thread *td, struct savefpu *addr,
char *xfpustate, size_t xfpustate_size);
int fpusetxstate(struct thread *td, char *xfpustate,
size_t xfpustate_size);
-int fputrap(void);
+int fputrap_sse(void);
+int fputrap_x87(void);
void fpuuserinited(struct thread *td);
struct fpu_kern_ctx *fpu_kern_alloc_ctx(u_int flags);
void fpu_kern_free_ctx(struct fpu_kern_ctx *ctx);
fpuex.c:
/* $Id: fpuex.c,v 1.2 2012/07/17 18:22:54 kostik Exp kostik $ */
#include <sys/types.h>
#include <err.h>
#include <errno.h>
#include <signal.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ucontext.h>
#if defined(__amd64__)
#include <machine/fpu.h>
#elif defined(__i386__)
#include <machine/npx.h>
#endif
static void
handler(int signo __unused, siginfo_t *info, void *v)
{
ucontext_t *uap;
mcontext_t *mc;
#if defined(__amd64__)
struct savefpu *sf;
#elif defined(__i386__)
struct savexmm *sf;
#endif
uap = v;
mc = &uap->uc_mcontext;
sf = &mc->mc_fpstate;
printf("intr handler: trapno %d code %d cw 0x%04x sw 0x%04x mxcsr 0x%08x ip 0x%lx\n",
info->si_trapno, info->si_code,
#if defined(__amd64__)
sf->sv_env.en_cw, sf->sv_env.en_sw, sf->sv_env.en_mxcsr,
sf->sv_env.en_rip
#elif defined(__i386__)
sf->sv_env.en_cw, sf->sv_env.en_sw,
sf->sv_env.en_mxcsr, (unsigned long)sf->sv_env.en_fip
#endif
);
exit(0);
}
double a[3];
double x(void) __attribute__((noinline));
double
x(void)
{
a[3] = a[0] / a[1];
return (a[3]);
}
int
main(void)
{
struct sigaction sa;
uint32_t mxcsr;
uint16_t cw;
bzero(&sa, sizeof(sa));
sa.sa_sigaction = handler;
sa.sa_flags = SA_SIGINFO;
if (sigaction(SIGFPE, &sa, NULL) == -1)
err(1, "sigaction SIGFPE");
mxcsr = 0;
__asm __volatile("ldmxcsr %0" : : "m" (mxcsr));
#ifdef __i386__
cw = 0;
__asm __volatile("fldcw %0" : : "m" (cw));
#endif
a[0] = 1.0;
a[1] = 0.0;
x();
return (0);
}
----- End forwarded message -----
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