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Diffstat (limited to 'gcc/doc/tm.texi')
| -rw-r--r-- | gcc/doc/tm.texi | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi index a4a8e49..29dc73b 100644 --- a/gcc/doc/tm.texi +++ b/gcc/doc/tm.texi @@ -5245,6 +5245,24 @@ be returned; otherwise @var{addr} should be returned unchanged. If this hook is not defined, @var{addr} will be used for function calls. @end deftypefn +@deftypevr {Target Hook} int TARGET_CUSTOM_FUNCTION_DESCRIPTORS +This hook should be defined to a power of 2 if the target will benefit +from the use of custom descriptors for nested functions instead of the +standard trampolines. Such descriptors are created at run time on the +stack and made up of data only, but they are non-standard so the generated +code must be prepared to deal with them. This hook should be defined to 0 +if the target uses function descriptors for its standard calling sequence, +like for example HP-PA or IA-64. Using descriptors for nested functions +eliminates the need for trampolines that reside on the stack and require +it to be made executable. + +The value of the macro is used to parameterize the run-time identification +scheme implemented to distinguish descriptors from function addresses: it +gives the number of bytes by which their address is misaligned compared +with function addresses. The value of 1 will generally work, unless it is +already reserved by the target for another purpose, like for example on ARM. +@end deftypevr + Implementing trampolines is difficult on many machines because they have separate instruction and data caches. Writing into a stack location fails to clear the memory in the instruction cache, so when the program |