On 6/24/20 5:50 AM, Paolo Bonzini wrote:
From: Eric Blake <ebl...@redhat.com>
I'm not aware of any immediate bugs in qemu where a second runtime
evalution of the arguments to MIN() or MAX() causes a problem, but
evaluation
Update the MIN/MAX macros to only evaluate their argument once at
runtime;
Use of MIN when MIN_CONST is needed:
In file included from /home/eblake/qemu/qemu-img.c:25:
/home/eblake/qemu/include/qemu/osdep.h:249:5: error: braced-group within
expression allowed only inside a function
249 | ({ \
| ^
/home/eblake/qemu/qemu-img.c:92:12: note: in expansion of macro ‘MIN’
UTF-8 mojibake in the commit message ;(
Signed-off-by: Eric Blake <ebl...@redhat.com>
Message-Id: <20200604215236.2798244-1-ebl...@redhat.com>
Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
---
+#define MIN_CONST(a, b) \
+ __builtin_choose_expr( \
+ __builtin_constant_p(a) && __builtin_constant_p(b), \
+ (a) < (b) ? (a) : (b), \
+ ((void)0))
This one is correct...
+#undef MAX
+#define MAX(a, b) \
+ ({ \
+ typeof(1 ? (a) : (b)) _a = (a), _b = (b); \
+ _a > _b ? _a : _b; \
+ })
+#define MAX_CONST(a, b) \
+ __builtin_choose_expr( \
+ __builtin_constant_p(a) && __builtin_constant_p(b), \
+ (a) > (b) ? (a) : (b), \
+ __builtin_unreachable())
...but this one should also use ((void)0), to match the commit message.
+
+/* Minimum function that returns zero only if both values are zero.
* Intended for use with unsigned values only. */
And checkpatch complains about the formatting here.
Ah well. I had all these things fixed in my tree, but failed to post a
v5. Not worth holding up this pull request in isolation, but if there
are any other build issues, I'll post a v5 of this patch, otherwise a
followup.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org
