diff options
Diffstat (limited to 'gcc/doc/tm.texi')
| -rw-r--r-- | gcc/doc/tm.texi | 25 |
1 files changed, 18 insertions, 7 deletions
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi index 778ecc9..e99989f 100644 --- a/gcc/doc/tm.texi +++ b/gcc/doc/tm.texi @@ -6477,6 +6477,13 @@ specify an alignment within the section directive need pay attention to This flag is true if the target supports @code{TARGET_ASM_NAMED_SECTION}. @end deftypefn +@anchor{TARGET_HAVE_SWITCHABLE_BSS_SECTIONS} +@deftypefn {Target Hook} bool TARGET_HAVE_SWITCHABLE_BSS_SECTIONS +This flag is true if we can create zeroed data by switching to a BSS +section and then using @code{ASM_OUTPUT_SKIP} to allocate the space. +This is true on most ELF targets. +@end deftypefn + @deftypefn {Target Hook} {unsigned int} TARGET_SECTION_TYPE_FLAGS (tree @var{decl}, const char *@var{name}, int @var{reloc}) Choose a set of section attributes for use by @code{TARGET_ASM_NAMED_SECTION} based on a variable or function decl, a section name, and whether or not the @@ -6705,13 +6712,17 @@ defining this macro. If unable, use the expression before and after that, output the additional assembler syntax for defining the name, and a newline. -This macro controls how the assembler definitions of uninitialized global -variables are output. This macro exists to properly support languages like -C++ which do not have @code{common} data. However, this macro currently -is not defined for all targets. If this macro and -@code{ASM_OUTPUT_ALIGNED_BSS} are not defined then @code{ASM_OUTPUT_COMMON} -or @code{ASM_OUTPUT_ALIGNED_COMMON} or -@code{ASM_OUTPUT_ALIGNED_DECL_COMMON} is used. +There are two ways of handling global BSS. One is to define either +this macro or its aligned counterpart, @code{ASM_OUTPUT_ALIGNED_BSS}. +The other is to have @code{TARGET_ASM_SELECT_SECTION} return a +switchable BSS section (@pxref{TARGET_HAVE_SWITCHABLE_BSS_SECTIONS}). +You do not need to do both. + +Some languages do not have @code{common} data, and require a +non-common form of global BSS in order to handle uninitialized globals +efficiently. C++ is one example of this. However, if the target does +not support global BSS, the front end may choose to make globals +common in order to save space in the object file. @end defmac @defmac ASM_OUTPUT_ALIGNED_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment}) |