Re: [Qemu-devel] qemu-2007-10-24 build error

["Edgar E. Iglesias" <edgar.iglesias@axis.com>]

On Wed, Oct 24, 2007 at 04:33:49PM +0100, Thiemo Seufer wrote:
> Edgar E. Iglesias wrote:
> > On Wed, Oct 24, 2007 at 12:33:24PM +0200, J. Mayer wrote:
> > > On Wed, 2007-10-24 at 09:36 +0900, Hwang YunSong(?????????) wrote:
> > > > 
> > > > gcc32 -g -o qemu-system-cris vl.o osdep.o readline.o monitor.o pci.o
> > > > console.o loader.o isa_mmio.o cutils.o block.o block-raw.o block-cow.o
> > > > block-qcow.o aes.o block-vmdk.o block-cloop.o block-dmg.o
> > > > block-bochs.o block-vpc.o block-vvfat.o block-qcow2.o
> > > > block-parallels.o irq.o i2c.o smbus.o scsi-disk.o cdrom.o lsi53c895a.o
> > > > usb.o usb-hub.o usb-linux.o usb-hid.o usb-ohci.o usb-msd.o usb-wacom.o
> > > > eeprom93xx.o eepro100.o ne2000.o pcnet.o rtl8139.o etraxfs.o ptimer.o
> > > > etraxfs_timer.o etraxfs_ser.o gdbstub.o sdl.o x_keymap.o vnc.o d3des.o
> > > > slirp/cksum.o slirp/if.o slirp/ip_icmp.o slirp/ip_input.o
> > > > slirp/ip_output.o slirp/slirp.o slirp/mbuf.o slirp/misc.o slirp/sbuf.o
> > > > slirp/socket.o slirp/tcp_input.o slirp/tcp_output.o slirp/tcp_subr.o
> > > > slirp/tcp_timer.o slirp/udp.o slirp/bootp.o slirp/debug.o slirp/tftp.o
> > > > libqemu.a -lm -lz -lgnutls -L/usr/lib -lSDL -lpthread -lrt -lutil 
> > > > libqemu.a(helper.o): In function `do_interrupt': 
> > > > /usr/src/Haansoft/BUILD/qemu/target-cris/helper.c:137: undefined
> > > > reference to `__builtin_clz' 
> > > > libqemu.a(translate-op.o): In function `dyngen_code': 
> > > > /home/hys545/qemu/cris-softmmu/op.h:1566: undefined reference to
> > > > `__builtin_clz' 
> > > > libqemu.a(op.o): In function `op_lz_T0_T1': 
> > > > /usr/src/Haansoft/BUILD/qemu/target-cris/op.c:1009: undefined
> > > > reference to `__builtin_clz' 
> > > > collect2: ld returned 1 exit status 
> > > 
> > > It does not seem to be a good idea, imho, to use gcc builtins directly
> > > from micro-ops. But your compiler should implement __builtin_clz. As far
> > 
> > Hi,
> > 
> > I submitted a patch that at compile-time fallbacks to clz code without builtins. Do you see any additional issues with using the builtins?
> > 
> > I think the speed-up with GCC ports implementing fast builtin variants of operations like clz would be significant enough to justify their use but if there is disagreement I'll send in a new patch removing the builtin_clz alltogether.
> 
> If the builtin ends up calling into libgcc (this can happen depending
> on the host / host compiler), then the dynamic code generation breaks.
> 
> It is safer not to force the compiler to use builtins.

Right, if calls are made things could break. Thanks for clarifying that. 

Here's a new patch to remove the builtin altogether. When building the system simulator for CRIS I found another one which will cause build problems with older GCC's so I replaced that one aswell.

Best regards
-- 
Edgar E. Iglesias
Axis Communications AB

diff --git a/target-cris/helper.c b/target-cris/helper.c
index 3db3bea..43fcdd1 100644
--- a/target-cris/helper.c
+++ b/target-cris/helper.c
@@ -87,6 +87,32 @@ static void cris_shift_ccs(CPUState *env)
 	env->pregs[SR_CCS] = ccs;
 }
 
+static int cris_clz(uint32_t x)
+{
+	int n;
+	/* Binary search for leading zeros.  */
+
+	n = 1;
+	if ((x >> 16) == 0) {
+		n = n + 16; 
+		x = x << 16;
+	}
+	if ((x >> 24) == 0) {
+		n = n + 8;
+		x = x << 8;
+	}
+	if ((x >> 28) == 0) {
+		n = n + 4; 
+		x = x << 4;
+	}
+	if ((x >> 30) == 0) {
+		n = n + 2; 
+		x = x << 2;
+	}
+	n = n - (x >> 31);
+	return n;
+}
+
 void do_interrupt(CPUState *env)
 {
 	uint32_t ebp, isr;
@@ -135,7 +161,7 @@ void do_interrupt(CPUState *env)
 				}
 
 				irqnum = 31 -
-					__builtin_clz(env->pending_interrupts);
+					cris_clz(env->pending_interrupts);
 				irqnum += 0x30;
 				ebp = env->pregs[SR_EBP];
 				isr = ldl_code(ebp + irqnum * 4);
diff --git a/target-cris/op.c b/target-cris/op.c
index 3ce9888..12188b4 100644
--- a/target-cris/op.c
+++ b/target-cris/op.c
@@ -1006,7 +1006,28 @@ void OPPROTO op_lz_T0_T1 (void)
 	if (T1 == 0)
 		T0 = 32;
 	else
-		T0 = __builtin_clz(T1);
+	{
+		/* Binary search for leading zeros.  */
+
+		T0 = 1;
+		if ((T1 >> 16) == 0) {
+			T0 = T0 + 16; 
+			T1 = T1 << 16;
+		}
+		if ((T1 >> 24) == 0) {
+			T0 = T0 + 8;
+			T1 = T1 << 8;
+		}
+		if ((T1 >> 28) == 0) {
+			T0 = T0 + 4; 
+			T1 = T1 << 4;
+		}
+		if ((T1 >> 30) == 0) {
+			T0 = T0 + 2; 
+			T1 = T1 << 2;
+		}
+		T0 = T0 - (T1 >> 31);
+	}
 	RETURN();
 }