/* ----------------------------------------------------------------------------- * * (c) The GHC Team, 1998-2009 * * Stuff for implementing proper tail jumps. * * Do not #include this file directly: #include "Rts.h" instead. * * To understand the structure of the RTS headers, see the wiki: * http://hackage.haskell.org/trac/ghc/wiki/Commentary/SourceTree/Includes * * ---------------------------------------------------------------------------*/ #ifndef TAILCALLS_H #define TAILCALLS_H /* ----------------------------------------------------------------------------- Unmangled tail-jumping: use the mini interpretter. -------------------------------------------------------------------------- */ #ifdef USE_MINIINTERPRETER #define JMP_(cont) return((StgFunPtr)(cont)) #define FB_ #define FE_ #else extern void __DISCARD__(void); /* ----------------------------------------------------------------------------- Tail calling on x86 -------------------------------------------------------------------------- */ #if i386_HOST_ARCH /* Note about discard: possibly there to fool GCC into clearing up before we do the jump eg. if there are some arguments left on the C stack that GCC hasn't popped yet. Also possibly to fool any optimisations (a function call often acts as a barrier). Not sure if any of this is necessary now -- SDM Comment to above note: I don't think the __DISCARD__() in JMP_ is necessary. Arguments should be popped from the C stack immediately after returning from a function, as long as we pass -fno-defer-pop to gcc. Moreover, a goto to a first-class label acts as a barrier for optimisations in the same way a function call does. -= chak */ /* The goto here seems to cause gcc -O2 to delete all the code after it - including the FE_ marker and the epilogue code - exactly what we want! -- SDM */ #define JMP_(cont) \ { \ void *__target; \ __DISCARD__(); \ __target = (void *)(cont); \ goto *__target; \ } #endif /* i386_HOST_ARCH */ /* ----------------------------------------------------------------------------- Tail calling on x86_64 -------------------------------------------------------------------------- */ #if x86_64_HOST_ARCH /* NOTE about __DISCARD__(): On x86_64 this is necessary to work around bugs in the register variable support in gcc. Without the __DISCARD__() call, gcc will silently throw away assignements to global register variables that happen before the jump. Here's the example: extern void g(void); static void f(void) { R1 = g; __DISCARD__() goto *R1; } without the dummy function call, gcc throws away the assignment to R1 (gcc 3.4.3) gcc bug #20359. */ #define JMP_(cont) \ { \ __DISCARD__(); \ goto *(void *)(cont); \ } #endif /* x86_64_HOST_ARCH */ /* ----------------------------------------------------------------------------- Tail calling on Sparc -------------------------------------------------------------------------- */ #ifdef sparc_HOST_ARCH #define JMP_(cont) ((F_) (cont))() /* Oh so happily, the above turns into a "call" instruction, which, on a SPARC, is nothing but a "jmpl" with the return address in %o7 [which we don't care about]. */ /* Don't need these for sparc mangling */ #define FB_ #define FE_ #endif /* sparc_HOST_ARCH */ /* ----------------------------------------------------------------------------- Tail calling on Alpha -------------------------------------------------------------------------- */ #ifdef alpha_HOST_ARCH #if IN_STG_CODE register void *_procedure __asm__("$27"); #endif #define JMP_(cont) \ do { _procedure = (void *)(cont); \ __DISCARD__(); \ goto *_procedure; \ } while(0) /* Don't need these for alpha mangling */ #define FB_ #define FE_ #endif /* alpha_HOST_ARCH */ /* ----------------------------------------------------------------------------- Tail calling on HP Description of HP's weird procedure linkage, many thanks to Andy Bennet : I've been digging a little further into the problem of how HP-UX does dynamic procedure calls. My solution in the last e-mail inserting an extra 'if' statement into the JMP_ I think is probably the best general solution I can come up with. There are still a few problems with it however: It wont work, if JMP_ ever has to call anything in a shared library, if this is likely to be required it'll need something more elaborate. It also wont work with PA-RISC 2.0 wide mode (64-bit) which uses a different format PLT. I had some feedback from someone in HP's compiler lab and the problem relates to the linker on HP-UX, not gcc as I first suspected. The reason the 'hsc' executable works is most likely due to a change in 'ld's behaviour for performance reasons between your revision and mine. The major issue relating to this is shared libraries and how they are implented under HP-UX. The whole point of the Procedure Label Table (PLT) is to allow a function pointer to hold the address of the function and a pointer to the library's global data lookup table (DLT) used by position independent code (PIC). This makes the PLT absolutely essential for shared library calls. HP has two linker introduced assembly functions for dealing with dynamic calls, $$dyncall and $$dyncall_external. The former does a check to see if the address is a PLT pointer and dereferences if necessary or just calls the address otherwise; the latter skips the check and just does the indirect jump no matter what. Since $$dyncall_external runs faster due to its not having the test, the linker nowadays prefers to generate calls to that, rather than $$dyncall. It makes this decision based on the presence of any shared library. If it even smells an sl's existence at link time, it rigs the runtime system to generate PLT references for everything on the assumption that the result will be slightly more efficient. This is what is crashing GHC since the calls it is generating have no understanding of the procedure label proper. The only way to get real addresses is to link everything archive, including system libraries, at which point it assumes you probably are going to be using calls similar to GHC's (its rigged for HP's +ESfic compiler option) but uses $$dyncall if necessary to cope, just in case you aren't. -------------------------------------------------------------------------- */ #ifdef hppa1_1_hp_hpux_HOST #define JMP_(cont) \ do { void *_procedure = (void *)(cont); \ if (((int) _procedure) & 2) \ _procedure = (void *)(*((int *) (_procedure - 2))); \ goto *_procedure; \ } while(0) #endif /* hppa1_1_hp_hpux_HOST */ /* ----------------------------------------------------------------------------- Tail calling on PowerPC -------------------------------------------------------------------------- */ #ifdef powerpc_HOST_ARCH #define JMP_(cont) \ { \ void *target; \ target = (void *)(cont); \ __DISCARD__(); \ goto *target; \ } /* The __DISCARD__ is there because Apple's April 2002 Beta of GCC 3.1 sometimes generates incorrect code otherwise. It tends to "forget" to update global register variables in the presence of decrement/increment operators: JMP_(*(--Sp)) is wrongly compiled as JMP_(Sp[-1]). Calling __DISCARD__ in between works around this problem. */ /* I would _love_ to use the following instead, but some versions of Apple's GCC fail to generate code for it if it is called for a casted data pointer - which is exactly what we are going to do... #define JMP_(cont) ((F_) (cont))() */ #endif /* powerpc_HOST_ARCH */ #ifdef powerpc64_HOST_ARCH #define JMP_(cont) ((F_) (cont))() #endif /* ----------------------------------------------------------------------------- Tail calling on IA64 -------------------------------------------------------------------------- */ #ifdef ia64_HOST_ARCH /* The compiler can more intelligently decide how to do this. We therefore * implement it as a call and optimise to a jump at mangle time. * * Sometimes GCC likes to move instructions between the function call and * the "--- TAILCALL ---". To stop it from finding instructions to put * there, we insert a jump to the end of the function after the TAILCALL. */ #define JMP_(cont) \ ((F_) (cont))(); \ __asm__ volatile ("--- TAILCALL ---"); \ goto _function_end; #define FE_ _function_end: __asm__ volatile ("--- END ---"); /* Don't emit calls to __DISCARD__ as this causes hassles */ #define __DISCARD__() #endif /* ----------------------------------------------------------------------------- Tail calling on MIPS -------------------------------------------------------------------------- */ #ifdef mips_HOST_ARCH #if IN_STG_CODE register void *_procedure __asm__("$25"); #endif #define JMP_(cont) \ { \ _procedure = (void *)(cont); \ __DISCARD__(); \ goto *_procedure; \ } /* Don't need these for MIPS mangling */ #define FB_ #define FE_ #endif /* mips_HOST_ARCH */ /* ----------------------------------------------------------------------------- FUNBEGIN and FUNEND. These are markers indicating the start and end of Real Code in a function. All instructions between the actual start and end of the function and these markers is shredded by the mangler. -------------------------------------------------------------------------- */ /* The following __DISCARD__() has become necessary with gcc 2.96 on x86. * It prevents gcc from moving stack manipulation code from the function * body (aka the Real Code) into the function prologue, ie, from moving it * over the --- BEGIN --- marker. It should be noted that (like some * other black magic in GHC's code), there is no essential reason why gcc * could not move some stack manipulation code across the __DISCARD__() - * it just doesn't choose to do it at the moment. * -= chak */ #ifndef FB_ #define FB_ __asm__ volatile ("--- BEGIN ---"); __DISCARD__ (); #endif #ifndef FE_ #define FE_ __asm__ volatile ("--- END ---"); #endif #endif /* !USE_MINIINTERPRETER */ #endif /* TAILCALLS_H */