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authorLibravatar Junio C Hamano <gitster@pobox.com>2020-09-30 15:26:24 +0000
committerLibravatar Junio C Hamano <gitster@pobox.com>2020-09-30 13:26:54 -0700
commit0ad621f61e4b2adc3a7bad088c25ebf2c8b9f43d (patch)
treea50c0af62adeba71d64d70f93369ca793075aecc
parentcmake (Windows): recommend using Visual Studio's built-in CMake support (diff)
downloadtgif-0ad621f61e4b2adc3a7bad088c25ebf2c8b9f43d.tar.xz
hashmap_for_each_entry(): workaround MSVC's runtime check failure #3
The OFFSETOF_VAR(var, member) macro is implemented in terms of offsetof(typeof(*var), member) with compilers that know typeof(), but its fallback implemenation compares &(var->member) and (var) and count the distance in bytes, i.e. ((uintptr_t)&(var)->member - (uintptr_t)(var)) MSVC's runtime check, when fed an uninitialized 'var', flags this as a use of an uninitialized variable (and that is legit---uninitialized contents of 'var' is subtracted) in a debug build. After auditing all 6 uses of OFFSETOF_VAR(), 1 of them does feed a potentially uninitialized 'var' to the macro in the beginning of the for() loop: #define hashmap_for_each_entry(map, iter, var, member) \ for (var = hashmap_iter_first_entry_offset(map, iter, \ OFFSETOF_VAR(var, member)); \ var; \ var = hashmap_iter_next_entry_offset(iter, \ OFFSETOF_VAR(var, member))) We can work around this by making sure that var has _some_ value when OFFSETOF_VAR() is called. Strictly speaking, it invites undefined behaviour to use NULL here if we end up with pointer comparison, but MSVC runtime seems to be happy with it, and most other systems have typeof() and don't even need pointer comparison fallback code. Signed-off-by: Junio C Hamano <gitster@pobox.com> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
-rw-r--r--hashmap.h3
1 files changed, 2 insertions, 1 deletions
diff --git a/hashmap.h b/hashmap.h
index ef220de4c6..b011b394fe 100644
--- a/hashmap.h
+++ b/hashmap.h
@@ -449,7 +449,8 @@ static inline struct hashmap_entry *hashmap_iter_first(struct hashmap *map,
* containing a @member which is a "struct hashmap_entry"
*/
#define hashmap_for_each_entry(map, iter, var, member) \
- for (var = hashmap_iter_first_entry_offset(map, iter, \
+ for (var = NULL, /* for systems without typeof */ \
+ var = hashmap_iter_first_entry_offset(map, iter, \
OFFSETOF_VAR(var, member)); \
var; \
var = hashmap_iter_next_entry_offset(iter, \