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Diffstat (limited to 'gcc/doc/invoke.texi')
| -rw-r--r-- | gcc/doc/invoke.texi | 24 |
1 files changed, 16 insertions, 8 deletions
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi index 30dd402..0c5e382 100644 --- a/gcc/doc/invoke.texi +++ b/gcc/doc/invoke.texi @@ -1619,16 +1619,10 @@ when used within the DSO@. Enabling this option can have a dramatic effect on load and link times of a DSO as it massively reduces the size of the dynamic export table when the library makes heavy use of templates. -The behavior of this switch is not quite the same as marking the -methods as hidden directly. Normally if there is a class with default -visibility which has a hidden method, the effect of this is that the -method must be defined in only one shared object. This switch does -not have this restriction. - You may mark a method as having a visibility explicitly to negate the effect of the switch for that method. For example, if you do want to -compare pointers to a particular inline method, you might mark it as -having default visibility. +compare pointers to a particular inline method, or the method has +local static data, you might mark it as having default visibility. @item -fno-weak @opindex fno-weak @@ -13506,6 +13500,20 @@ expecting to be compiled with visibility other than the default. You may need to explicitly say @samp{#pragma GCC visibility push(default)} before including any such headers. +@samp{extern} declarations are not affected by @samp{-fvisibility}, so +a lot of code can be recompiled with @samp{-fvisibility=hidden} with +no modifications. However, this means that calls to @samp{extern} +functions with no explicit visibility will use the PLT, so it is more +effective to use @samp{__attribute ((visibility))} and/or +@samp{#pragma GCC visibility} to tell the compiler which @samp{extern} +declarations should be treated as hidden. + +Note that @samp{-fvisibility} does affect C++ vague linkage +entities. This means that, for instance, an exception class that will +be thrown between DSOs must be explicitly marked with default +visibility so that the @samp{type_info} nodes will be unified between +the DSOs. + An overview of these techniques, their benefits and how to use them is at @w{@uref{http://gcc.gnu.org/wiki/Visibility}}. |