| Message ID | 5016BE96.9000106@codesourcery.com |
|---|---|
| State | New |
| Headers | show |
Sandra Loosemore <sandra@codesourcery.com> writes: > The MIPS back end has an option -mno-float that is supported by > bare-metal configs using the SDE library. However, this option is not > properly documented in the manual, and MIPS_ARCH_FLOAT_SPEC doesn't know > about it as one of the explicit floating-point configuration changes > that should override architecture defaults. This patch addresses both > problems. OK to commit? OK, you're touching a sore spot here, but... > +@item -mno-float > +@opindex mno-float > +Prevents the use of all floating-point operations. This option is presently > +supported only by some bare-metal MIPS configurations. ...unfortunately, it doesn't prevent the use floating-point operations. That's why it's such a bad option. The only difference from the compiler proper's point of view between -msoft-float and -mno-float is that they define different preprocessor macros. The onus is instead on the programmer to avoid writing anything that might tempt the compiler into using floating-point operations. If the user gets it wrong, they get (at best) a link-time error rather than a compile-time error. I think we should document it that way. E.g. something like: @item -mno-float @opindex mno-float Equivalent to @option{-msoft-float}, but asserts that the user is trying to avoid all floating-point operations. This option is presently supported only by some bare-metal MIPS configurations, where it selects a special set of libraries that lack all floating-point support (including, for example, the floating-point @code{printf} formats). If code compiled with @code{-mno-float} accidentally contains floating-point operations, it is likely to suffer a link-time or run-time failure. but you're better at the wordsmithing than I am. Perhaps we should document the __mips_no_float preprocessor macro too, since that's how things like printf() know that they don't need the floating-point stuff. The mips.h part is OK though, thanks. Feel free to apply it separately if that's more convenient than keeping the patch together. Richard
Index: gcc/doc/invoke.texi =================================================================== --- gcc/doc/invoke.texi (revision 189950) +++ gcc/doc/invoke.texi (working copy) @@ -733,7 +733,8 @@ Objective-C and Objective-C++ Dialects}. -mabi=@var{abi} -mabicalls -mno-abicalls @gol -mshared -mno-shared -mplt -mno-plt -mxgot -mno-xgot @gol -mgp32 -mgp64 -mfp32 -mfp64 -mhard-float -msoft-float @gol --msingle-float -mdouble-float -mdsp -mno-dsp -mdspr2 -mno-dspr2 @gol +-mno-float -msingle-float -mdouble-float @gol +-mdsp -mno-dsp -mdspr2 -mno-dspr2 @gol -mmcu -mmno-mcu @gol -mfpu=@var{fpu-type} @gol -msmartmips -mno-smartmips @gol @@ -15633,6 +15634,11 @@ Use floating-point coprocessor instructi Do not use floating-point coprocessor instructions. Implement floating-point calculations using library calls instead. +@item -mno-float +@opindex mno-float +Prevents the use of all floating-point operations. This option is presently +supported only by some bare-metal MIPS configurations. + @item -msingle-float @opindex msingle-float Assume that the floating-point coprocessor only supports single-precision Index: gcc/config/mips/mips.h =================================================================== --- gcc/config/mips/mips.h (revision 189950) +++ gcc/config/mips/mips.h (working copy) @@ -713,7 +713,7 @@ struct mips_cpu_info { link-compatible. */ #define MIPS_ARCH_FLOAT_SPEC \ - "%{mhard-float|msoft-float|march=mips*:; \ + "%{mhard-float|msoft-float|mno-float|march=mips*:; \ march=vr41*|march=m4k|march=4k*|march=24kc|march=24kec \ |march=34kc|march=74kc|march=1004kc|march=5kc \ |march=octeon|march=xlr: -msoft-float; \