#11395: The via-C code generation backend is incompatible with gcc 5.3.1 on m68k
(ELF)
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Reporter: mkarcher | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 7.10.2
Keywords: | Operating System: Linux
Architecture: m68k | Type of failure: GHC doesn't work
| at all
Test Case: | Blocked By:
Blocking: | Related Tickets:
Differential Rev(s): | Wiki Page:
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ghc is generating C code like in the following simplified example:
demo1.c:
{{{
#include
extern void* int_returning_function();
typedef int (*int_f_ptr)();
int main(void)
{
int result;
{
int_f_ptr correctly_typed_pointer;
correctly_typed_pointer =
(int_f_ptr)int_returning_function;
result = correctly_typed_pointer();
}
assert(result == 42);
return 0;
}
}}}
demo2.c:
{{{
int int_returning_function()
{
return 42;
}
}}}
This code fails to work on m68k with gcc-5.3.1 if optimization is turned
on. The real-life example from ghc is rts/Schedule.c:raiseExceptionHelper
as int_returning_function and rts/Exception.cmm:stg_raisezh as main. The
reason it fails is that on m68k, a function returning a pointer returns
the result in %a0, while a function returning an integer returns it in
%d0. If optimization is enabled, gcc elides the function pointer and calls
the function as-if it were called directly. Without optimization, gcc
expects the result to be in %d0, where it actually is.
In my oppinion, gcc is allowed to do that, because according to N843 (C99
draft), 6.2.7 #2 "All declarations that refer to the same object or
function shall have compatible type; otherwise, the behavior is
undefined." is violated in this example. Compatibility of return types is
defined in 6.7.5.3 #11 "For two function types to be compatible, both
shall specify compatible return types. Moreover, [...]" which is clearly
violated.
If you just look at demo1.c and assume that 6.2.7 #2 is *not* violated,
int_returning_function would in fact be a function returning a pointer. In
that case, compiling demo1.c would violate 6.3.2.3 #8 "If a converted
pointer is used to call a function whose type is not compatible with the
pointed-to type, the behavior is undefined." and/or 6.5.2.2 "If the
function is defined with a type that is not compatible with the type (of
the expression) pointed to by the expression that denotes the called
function, the behavior is undefined."
You might want to discuss this issue with the gcc developers, but I don't
see a standard claus justifying the approach of declaring all functions
returning StgFunPtr and casting them to the right type.
If you cross-compile the source tarball Debian claims to be 7.10.3-rc1 to
m68k using gcc 5.3.1, ghc crashes on startup because stg_raisezh gets a
wrong value as frame_type and tries to cancel an STM transaction that does
not exist at all.
--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11395
GHC http://www.haskell.org/ghc/
The Glasgow Haskell Compiler
