On Sun, May 15, 2011 at 04:16:20PM +0300, Blue Swirl wrote: > On Sun, May 15, 2011 at 3:49 PM, Aurelien Jarno <aurel...@aurel32.net> wrote: > > On Sun, May 15, 2011 at 03:30:17PM +0300, Blue Swirl wrote: > >> On Sun, May 15, 2011 at 2:36 PM, Aurelien Jarno <aurel...@aurel32.net> > >> wrote: > >> > On Sun, May 15, 2011 at 02:12:27PM +0300, Blue Swirl wrote: > >> >> On Sun, May 15, 2011 at 1:19 PM, Aurelien Jarno <aurel...@aurel32.net> > >> >> wrote: > >> >> > I still don't get where are this list of possible changes? Did I miss > >> >> > something in another thread? > >> >> > >> >> I'm referring to the patches I sent. > >> > > >> > Ok, patches 1, 2 and 4 to 7 looks ok at a first glance, though I think > >> > patches 6 and 7 should be done for all hosts or none of them. > >> > >> The changes can be done in steps, but of course removing temp_buf from > >> CPUState would need all targets to be converted first. > >> > >> >> > On the TCG generated code, the env structure is used almost for every > >> >> > op, so it really makes sense to keep it in a register instead of > >> >> > having to > >> >> > reload the address of env regularly from memory. Given it only affects > >> >> > TCG generated code, I don't see the point of portability here. > >> >> > >> >> For example, maybe the bugs in Sparc glibc could be avoided by using > >> >> one of %i set of registers (not accessible from helpers) for AREG0 > >> >> within generated code instead of %g registers which seem to be > >> >> fragile. > >> > > >> > First of all, but it's a different subject, I am not sure there are > >> > sparc glibc bugs, I'd rather says QEMU mis-uses some register. For > >> > example the following code is probably wrong: > >> > > >> > /* Note: must be synced with dyngen-exec.h */ > >> > #ifdef CONFIG_SOLARIS > >> > #define TCG_AREG0 TCG_REG_G2 > >> > #elif defined(__sparc_v9__) > >> > #define TCG_AREG0 TCG_REG_G5 > >> > #else > >> > #define TCG_AREG0 TCG_REG_G6 > >> > #endif > >> > > >> > __sparc_v9__ can set on the 32-bit ABI, when the compiler targets V8+, > >> > so the condition is probably wrong there. Secondly the SPARC ABI [1] on > >> > page 23 that %g5 to %g7 are reserved for system. I don't think QEMU has > >> > the right to use this registers. > >> > >> Yes, but the situation is not so nice. Please see this post for status > >> as of 2010: > >> http://article.gmane.org/gmane.comp.emulators.qemu/63610 > >> > >> This is from Debian glibc 2.11.2-10: > >> $ file /lib/libc-2.11.2.so > >> /lib/libc-2.11.2.so: ELF 32-bit MSB shared object, SPARC32PLUS, > >> version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux > >> 2.6.18, stripped > >> $ objdump -d /lib/libc.so.6 |grep %g1|wc -l > >> 69648 > >> $ objdump -d /lib/libc.so.6 |grep %g2|wc -l > >> 37299 > >> $ objdump -d /lib/libc.so.6 |grep %g3|wc -l > >> 20635 > >> $ objdump -d /lib/libc.so.6 |grep %g4|wc -l > >> 11603 > >> $ objdump -d /lib/libc.so.6 |grep %g5|wc -l > >> 448 > >> $ objdump -d /lib/libc.so.6 |grep %g6|wc -l > >> 150 > >> $ objdump -d /lib/libc.so.6 |grep %g7|wc -l > >> 3052 > >> > >> Glibc is compiled for Sparc32plus, so it should only use %g6 and %g7, > > > > From the calling convention point of view, sparc32 and sparc32plus are > > the same ABI, so %g5 is also reserved for system use. > > > >> or %g1 and %g5 for scratch purposes. However, it is the application > >> registers %g2 to %g4 that are used heaviest. Looking inside the > >> objdump it's easy to see that the uses are not for example saving or > >> restoring, but actually using them without saving the previous value > >> first: > > > > Well, we have to define system and application. System is defined as > > library in Chapter 6, and I don't see the libc there, and is probably > > considered as part of the application. > > No, for example unistd.h is described and even X11. GCC also says that > libraries should be compiled without using the registers: > > http://gcc.gnu.org/onlinedocs/gcc-4.6.0/gcc/SPARC-Options.html#SPARC-Options > > >> 000211e0 <__divdi3>: > >> 211e0: 9d e3 bf a0 save %sp, -96, %sp > >> 211e4: 90 10 00 18 mov %i0, %o0 > >> 211e8: 92 10 00 19 mov %i1, %o1 > >> 211ec: 94 10 00 1a mov %i2, %o2 > >> 211f0: 96 10 00 1b mov %i3, %o3 > >> 211f4: 80 a6 20 00 cmp %i0, 0 > >> 211f8: 06 40 00 10 bl,pn %icc, 21238 <__divdi3+0x58> > >> 211fc: a0 10 20 00 clr %l0 > >> 21200: 80 a2 a0 00 cmp %o2, 0 > >> 21204: 26 40 00 13 bl,a,pn %icc, 21250 <__divdi3+0x70> > >> 21208: a0 38 00 10 xnor %g0, %l0, %l0 > >> 2120c: 7f ff fe ed call 20dc0 <__ashldi3+0x40> > >> 21210: 98 10 20 00 clr %o4 > >> 21214: 84 10 00 08 mov %o0, %g2 > >> > >> ...whoops... > >> > >> 21218: 80 a4 20 00 cmp %l0, 0 > >> 2121c: 02 40 00 04 be,pn %icc, 2122c <__divdi3+0x4c> > >> 21220: 86 10 00 09 mov %o1, %g3 > >> > >> ...whoops... > >> > >> 21224: 86 a0 00 09 subcc %g0, %o1, %g3 > >> 21228: 84 60 00 02 subc %g0, %g2, %g2 > >> 2122c: b2 10 00 03 mov %g3, %i1 > >> 21230: 81 cf e0 08 rett %i7 + 8 > >> 21234: 90 10 00 02 mov %g2, %o0 > >> 21238: 92 a0 00 19 subcc %g0, %i1, %o1 > >> 2123c: 90 60 00 18 subc %g0, %i0, %o0 > >> 21240: 80 a2 a0 00 cmp %o2, 0 > >> 21244: 16 4f ff f2 bge %icc, 2120c <__divdi3+0x2c> > >> 21248: a0 10 3f ff mov -1, %l0 > >> 2124c: a0 38 00 10 xnor %g0, %l0, %l0 > >> 21250: 96 a0 00 0b subcc %g0, %o3, %o3 > >> 21254: 10 6f ff ee b %xcc, 2120c <__divdi3+0x2c> > >> 21258: 94 60 00 0a subc %g0, %o2, %o2 > >> 2125c: 01 00 00 00 nop > >> > >> This is libc from OpenBSD/Sparc64 4.9: > >> $ objdump -d /usr/lib/libc.so.58.0 |grep %g1|wc -l > >> 40562 > >> $ objdump -d /usr/lib/libc.so.58.0 |grep %g2|wc -l > >> 20384 > >> $ objdump -d /usr/lib/libc.so.58.0 |grep %g3|wc -l > >> 10240 > >> $ objdump -d /usr/lib/libc.so.58.0 |grep %g4|wc -l > >> 6606 > >> $ objdump -d /usr/lib/libc.so.58.0 |grep %g5|wc -l > >> 3811 > >> $ objdump -d /usr/lib/libc.so.58.0 |grep %g6|wc -l > >> 4 > >> $ objdump -d /usr/lib/libc.so.58.0 |grep %g7|wc -l > >> 20 > >> > >> Not so great there either. > >> > >> > Anyway, I don't see why keeping TCG_AREG0 inside the TCG generated code > >> > would prevent you to use a register from the %i set for it. > >> > >> The helpers currently use global env register, but %i registers can't > >> be accessed from the next level of function call nesting hierarchy so > >> they can't be used for global env. > >> > > > > That's the current situation yes. Using %i registers for TCG_AREG0 does > > mean you can't use a global env register in the helpers, but it doesn't > > mean that internal TCG code can't use them for TCG_AREG0. > > Exactly. > > > What I am telling you since the beginning is that: > > - I have no objection that we stop using a fixed register in GCC > > generated code (that is completely removing HELPER_CFLAGS). However I > > don't really see the point of doing that, though the Sparc issue might > > be an argument. > > - I do have objection to remove TCG_AREG0 from inside the TCG generated > > code, this register is used for almost every TCG op, and I don't see > > any real argument for not keeping it. > > I'm pretty much open at this point for all alternatives. >
So what about getting rid of TCG_AREG0 for GCC generated code only, at least as a first step? So what about the following changes: - Change TCG_AREG0 of all targets to a callee saved register (if possible, e.g. sparc) - Change the prologue of all TCG targets to take env as an argument, and save it into TCG_AREG0. - Change all helpers to explicitly take an env pointer instead of using the fixed register. Note that it also includes softmmu helpers, but the TCG load/store instructions should be kept unchanged. - Remove HELPER_CFLAGS from makefiles when all helpers have been changed. - TCG_AREG0 can then be changed to another register if needed. And later we can do more steps to get a complete removal of TCG_AREG0, including in TCG code, though I still think it is a really bad idea. -- Aurelien Jarno GPG: 1024D/F1BCDB73 aurel...@aurel32.net http://www.aurel32.net