[Qemu-devel] [5466] Only use __builtin_* with GCC >= 3.4

[Qemu-devel] [5466] Only use __builtin_* with GCC >= 3.4

[Aurelien Jarno]

Revision: 5466
          http://svn.sv.gnu.org/viewvc/?view=rev&root=qemu&revision=5466
Author:   aurel32
Date:     2008-10-12 11:44:36 +0000 (Sun, 12 Oct 2008)

Log Message:
-----------
Only use __builtin_* with GCC >= 3.4

Fix gcc 3.3 builds, broken in revision 5465.

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

Revision Links:
--------------
    http://svn.sv.gnu.org/viewvc/?view=rev&root=qemu&revision=5465

Modified Paths:
--------------
    trunk/host-utils.h
    trunk/hw/apic.c

Modified: trunk/host-utils.h
===================================================================
--- trunk/host-utils.h	2008-10-12 00:53:17 UTC (rev 5465)
+++ trunk/host-utils.h	2008-10-12 11:44:36 UTC (rev 5466)
@@ -51,7 +51,7 @@
 
 static always_inline int clz32(uint32_t val)
 {
-#if defined(__GNUC__)
+#if defined(__GNUC__) && ((__GNUC__ > 3) || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4))
     if (val)
         return __builtin_clz(val);
     else
@@ -93,7 +93,7 @@
 
 static always_inline int clz64(uint64_t val)
 {
-#if defined(__GNUC__)
+#if defined(__GNUC__) && ((__GNUC__ > 3) || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4))
     if (val)
         return __builtin_clzll(val);
     else
@@ -118,7 +118,7 @@
 
 static always_inline int ctz32 (uint32_t val)
 {
-#if defined(__GNUC__)
+#if defined(__GNUC__) && ((__GNUC__ > 3) || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4))
     if (val)
         return __builtin_ctz(val);
     else
@@ -162,7 +162,7 @@
 
 static always_inline int ctz64 (uint64_t val)
 {
-#if defined(__GNUC__)
+#if defined(__GNUC__) && ((__GNUC__ > 3) || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4))
     if (val)
         return __builtin_ctz(val);
     else
@@ -206,7 +206,7 @@
 
 static always_inline int ctpop32 (uint32_t val)
 {
-#if defined(__GNUC__)
+#if defined(__GNUC__) && ((__GNUC__ > 3) || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4))
     return __builtin_popcount(val);
 #else
     val = (val & 0x55555555) + ((val >>  1) & 0x55555555);
@@ -221,7 +221,7 @@
 
 static always_inline int ctpop64 (uint64_t val)
 {
-#if defined(__GNUC__)
+#if defined(__GNUC__) && ((__GNUC__ > 3) || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4))
     return __builtin_popcountll(val);
 #else
     val = (val & 0x5555555555555555ULL) + ((val >>  1) & 0x5555555555555555ULL);

Modified: trunk/hw/apic.c
===================================================================
--- trunk/hw/apic.c	2008-10-12 00:53:17 UTC (rev 5465)
+++ trunk/hw/apic.c	2008-10-12 11:44:36 UTC (rev 5466)
@@ -107,7 +107,7 @@
 /* Find first bit starting from msb */
 static int fls_bit(uint32_t value)
 {
-#if defined(__GNUC__)
+#if defined(__GNUC__) && ((__GNUC__ > 3) || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4))
     return 31 - __builtin_clz(value);
 #else
     unsigned int ret = 0;
@@ -127,7 +127,7 @@
 /* Find first bit starting from lsb */
 static int ffs_bit(uint32_t value)
 {
-#if defined(__GNUC__)
+#if defined(__GNUC__) && ((__GNUC__ > 3) || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4))
     return __builtin_ffs(value) - 1;
 #else
     unsigned int ret = 0;

Re: [Qemu-devel] [5466] Only use __builtin_* with GCC >= 3.4

[Avi Kivity]

Aurelien Jarno wrote:
> Revision: 5466
>           http://svn.sv.gnu.org/viewvc/?view=rev&root=qemu&revision=5466
> Author:   aurel32
> Date:     2008-10-12 11:44:36 +0000 (Sun, 12 Oct 2008)
>
> Log Message:
> -----------
> Only use __builtin_* with GCC >= 3.4
>
> Fix gcc 3.3 builds, broken in revision 5465.
>
>  
>  static always_inline int clz32(uint32_t val)
>  {
> -#if defined(__GNUC__)
> +#if defined(__GNUC__) && ((__GNUC__ > 3) || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4))
>   

Couldn't this be wrapped in GCC_BUILTINS_AVAILABLE or GCC_ATLEAST_3_4?  
My eyes hurt.


-- 
error compiling committee.c: too many arguments to function

Re: [Qemu-devel] [5466] Only use __builtin_* with GCC >= 3.4

[Jamie Lokier]

Avi Kivity wrote:
> >-#if defined(__GNUC__)
> >+#if defined(__GNUC__) && ((__GNUC__ > 3) || (__GNUC__ == 3 && 
> >__GNUC_MINOR__ >= 4))
> 
> Couldn't this be wrapped in GCC_BUILTINS_AVAILABLE or GCC_ATLEAST_3_4?  
> My eyes hurt.

Glibc uses "#if __GNUC_PREREQ (3,4)" which is quite neat.
Do "grep -R GNUC_PREREQ /usr/include".

I use (and define if not already defined) the same macro in my
programs, on the assumption that the macro's meaning is unlikely to
ever change or be different elsewhere.

-- Jamie

Re: [Qemu-devel] [5466] Only use __builtin_* with GCC >= 3.4

[Avi Kivity]

Jamie Lokier wrote:
> Glibc uses "#if __GNUC_PREREQ (3,4)" which is quite neat.
> Do "grep -R GNUC_PREREQ /usr/include".
>
> I use (and define if not already defined) the same macro in my
> programs, on the assumption that the macro's meaning is unlikely to
> ever change or be different elsewhere.
>   

It's illegal to define or use an identifier beginning with two 
underscores, unless it's documented by the implementation.  What if 
glibc adds a third argument?  All your apps wil break.

You should define your own macros for this, with a non-__ name.

-- 
error compiling committee.c: too many arguments to function

Re: [Qemu-devel] [5466] Only use __builtin_* with GCC >= 3.4

[Jamie Lokier]

Avi Kivity wrote:
> It's illegal to define or use an identifier beginning with two 
> underscores, unless it's documented by the implementation.  What if 
> glibc adds a third argument?  All your apps wil break.
> 
> You should define your own macros for this, with a non-__ name.

I agree.  Portable apps especially should use their own names.

Same applies with just one underscore, I think: they're reserved in
the "implementation" namespace.

But I'd add that avoiding underscore is advisable but not a guarantee.
Sometimes Glibc defines a new macro/variable/function _without_ the
preceding underscore, when you've requested all Glibc extensions by
defining _GNU_SOURCE.  It's not likely for this macro, and conflicts
are obviously much more likely with underscore prefixes.

I've also seen ugly link-time or run-time errors: E.g. defining a
function called `dprintf' or `warn' in the app can break some parts of
Glibc at run-time, with no compile-time error.

This is awkward for third party _libs_ used with a lot of other libs
and apps, as the only realistic protection comes from making sure
every non-static symbol (including internal-use-only ones) has a
prefix that no other lib or app is likely to use.  Fingers crossed.
Once you're dependent on prefix uniqueness, it's a matter of debate or
maybe taste whether using `_myownlib_symbol' (i.e. underscore prefix
before unique prefix) is advisable for internal-use-only names.

-- Jamie

Re: [Qemu-devel] [5466] Only use __builtin_* with GCC >= 3.4

[M. Warner Losh]

In message: <48F21193.3000809@redhat.com>
            Avi Kivity <avi@redhat.com> writes:
: Jamie Lokier wrote:
: > Glibc uses "#if __GNUC_PREREQ (3,4)" which is quite neat.
: > Do "grep -R GNUC_PREREQ /usr/include".
: >
: > I use (and define if not already defined) the same macro in my
: > programs, on the assumption that the macro's meaning is unlikely to
: > ever change or be different elsewhere.
: >   
: 
: It's illegal to define or use an identifier beginning with two 
: underscores, unless it's documented by the implementation.  What if 
: glibc adds a third argument?  All your apps wil break.

Lots of things would break :-(

: You should define your own macros for this, with a non-__ name.

Identifiers starting with __ are reserved for the implementation.
They aren't illegal, per se, just reserved.

Warner