| Message ID | 1686875.o51Xv5tRQl@polaris |
|---|---|
| State | New |
| Headers | show |
Eric Botcazou <ebotcazou@adacore.com> writes: > Similarly to x86, PowerPC and SPARC, this enables the use of custom run- > time descriptors in Ada, thus eliminating the need for trampolines and > executable stack in presence of pointers to nested functions. > > Unfortunately I don't have access to MIPS hardware any more, but the > scheme was tested on the architecture at some point. OK for the > mainline? > > > 2016-11-13 Eric Botcazou <ebotcazou@adacore.com> > > PR ada/67205 > * config/mips/mips.c (TARGET_CUSTOM_FUNCTION_DESCRIPTORS): Define. Hi Eric, Thanks for the patch. I'm a bit concerned about the interaction this will have with microMIPS which can (albeit not implemented today) use 2-byte alignment on function entry points. Is the solution for other targets to mandate 4-byte alignment when using function descriptors? If so then I don't see a problem with this. We will have to account for that when GCC allows 2-byte aligned microMIPS functions. Thanks, Matthew
> Thanks for the patch. I'm a bit concerned about the interaction this > will have with microMIPS which can (albeit not implemented today) use > 2-byte alignment on function entry points. > > Is the solution for other targets to mandate 4-byte alignment when > using function descriptors? Yes, the compiler will overalign functions for languages using descriptors (only Ada as of this writing): 2-byte alignment if the setting is 1, 4-byte alignment if the setting is 2, 8-byte alignment if the setting is 4, etc. That's done by the FUNCTION_ALIGNMENT macro defined in defaults.h. > If so then I don't see a problem with this. We will have to account for > that when GCC allows 2-byte aligned microMIPS functions. OK, thanks. -- Eric Botcazou
Index: config/mips/mips.c =================================================================== --- config/mips/mips.c (revision 242334) +++ config/mips/mips.c (working copy) @@ -22387,6 +22387,10 @@ mips_promote_function_mode (const_tree t #undef TARGET_HARD_REGNO_SCRATCH_OK #define TARGET_HARD_REGNO_SCRATCH_OK mips_hard_regno_scratch_ok +/* The architecture reserves bit 0 for MIPS16 so use bit 1 for descriptors. */ +#undef TARGET_CUSTOM_FUNCTION_DESCRIPTORS +#define TARGET_CUSTOM_FUNCTION_DESCRIPTORS 2 + struct gcc_target targetm = TARGET_INITIALIZER; #include "gt-mips.h"
Similarly to x86, PowerPC and SPARC, this enables the use of custom run-time descriptors in Ada, thus eliminating the need for trampolines and executable stack in presence of pointers to nested functions. Unfortunately I don't have access to MIPS hardware any more, but the scheme was tested on the architecture at some point. OK for the mainline? 2016-11-13 Eric Botcazou <ebotcazou@adacore.com> PR ada/67205 * config/mips/mips.c (TARGET_CUSTOM_FUNCTION_DESCRIPTORS): Define. -- Eric Botcazou