diff options
Diffstat (limited to 'gcc/doc')
| -rw-r--r-- | gcc/doc/invoke.texi | 35 |
1 files changed, 33 insertions, 2 deletions
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi index 650099ec1ff..0a2a6f45d7c 100644 --- a/gcc/doc/invoke.texi +++ b/gcc/doc/invoke.texi @@ -281,7 +281,8 @@ Objective-C and Objective-C++ Dialects}. -Woverride-init-side-effects -Woverlength-strings @gol -Wpacked -Wpacked-bitfield-compat -Wpadded @gol -Wparentheses -Wno-pedantic-ms-format @gol --Wplacement-new -Wpointer-arith -Wno-pointer-to-int-cast @gol +-Wplacement-new -Wplacement-new=@var{n} @gol +-Wpointer-arith -Wno-pointer-to-int-cast @gol -Wno-pragmas -Wredundant-decls -Wno-return-local-addr @gol -Wreturn-type -Wsequence-point -Wshadow -Wno-shadow-ivar @gol -Wshift-overflow -Wshift-overflow=@var{n} @gol @@ -4894,6 +4895,7 @@ width specifiers @code{I32}, @code{I64}, and @code{I} used on Windows targets, which depend on the MS runtime. @item -Wplacement-new +@itemx -Wplacement-new=@var{n} @opindex Wplacement-new @opindex Wno-placement-new Warn about placement new expressions with undefined behavior, such as @@ -4906,7 +4908,36 @@ char buf [64]; new (buf) int[64]; @end smallexample This warning is enabled by default. - + +@table @gcctabopt +@item -Wplacement-new=1 +This is the default warning level of @option{-Wplacement-new}. At this +level the warning is not issued for some strictly undefined constructs that +GCC allows as extensions for compatibility with legacy code. For example, +the following @code{new} expression is not diagnosed at this level even +though it has undefined behavior according to the C++ standard because +it writes past the end of the one-element array. +@smallexample +struct S @{ int n, a[1]; @}; +S *s = (S *)malloc (sizeof *s + 31 * sizeof s->a[0]); +new (s->a)int [32](); +@end smallexample + +@item -Wplacement-new=2 +At this level, in addition to diagnosing all the same constructs as at level +1, a diagnostic is also issued for placement new expressions that construct +an object in the last member of structure whose type is an array of a single +element and whose size is less than the size of the object being constructed. +While the previous example would be diagnosed, the following construct makes +use of the flexible member array extension to avoid the warning at level 2. +@smallexample +struct S @{ int n, a[]; @}; +S *s = (S *)malloc (sizeof *s + 32 * sizeof s->a[0]); +new (s->a)int [32](); +@end smallexample + +@end table + @item -Wpointer-arith @opindex Wpointer-arith @opindex Wno-pointer-arith |