@c Copyright (C) 1995-1997 Free Software Foundation, Inc. @c This is part of the G77 manual. @c For copying conditions, see the file g77.texi. @c The text of this file appears in the file BUGS @c in the G77 distribution, as well as in the G77 manual. @c 1996-02-24 @ifclear BUGSONLY @node Actual Bugs @section Actual Bugs We Haven't Fixed Yet @end ifclear This section identifies bugs that @code{g77} @emph{users} might run into. This includes bugs that are actually in the @code{gcc} back end (GBE) or in @code{libf2c}, because those sets of code are at least somewhat under the control of (and necessarily intertwined with) @code{g77}, so it isn't worth separating them out. For information on bugs that might afflict people who configure, port, build, and install @code{g77}, @ref{Problems Installing}. @itemize @bullet @cindex SIGNAL() intrinsic @cindex intrinsics, SIGNAL() @item Work is needed on the @code{SIGNAL()} intrinsic to ensure that pointers and integers are properly handled on all targets, including 64-bit machines. @cindex -fugly-comma option @cindex options, -fugly-comma @item When using @samp{-fugly-comma}, @code{g77} assumes an extra @samp{%VAL(0)} argument is to be passed to intrinsics taking no arguments, such as @code{IARGC()}, which in turn reject such a call. Although this has been worked around for 0.5.18 due to changes in the handling of intrinsics, @code{g77} needs to do the ugly-argument-appending trick only for external-function invocation, as this would probably be more consistent with compilers that default to using that trick. @item Something about @code{g77}'s straightforward handling of label references and definitions sometimes prevents the GBE from unrolling loops. Until this is solved, try inserting or removing @code{CONTINUE} statements as the terminal statement, using the @code{END DO} form instead, and so on. @item The @code{g77} command itself should more faithfully process options the way the @code{gcc} command does. For example, @code{gcc} accepts abbreviated forms of long options, @code{g77} generally doesn't. @item Some confusion in diagnostics concerning failing @code{INCLUDE} statements from within @code{INCLUDE}'d or @code{#include}'d files. @cindex integer constants @cindex constants, integer @item @code{g77} assumes that @code{INTEGER(KIND=1)} constants range from @samp{-2**31} to @samp{2**31-1} (the range for two's-complement 32-bit values), instead of determining their range from the actual range of the type for the configuration (and, someday, for the constant). Further, it generally doesn't implement the handling of constants very well in that it makes assumptions about the configuration that it no longer makes regarding variables (types). Included with this item is the fact that @code{g77} doesn't recognize that, on IEEE-754/854-compliant systems, @samp{0./0.} should produce a NaN and no warning instead of the value @samp{0.} and a warning. This is to be fixed in version 0.6, when @code{g77} will use the @code{gcc} back end's constant-handling mechanisms to replace its own. @cindex compiler speed @cindex speed, of compiler @cindex compiler memory usage @cindex memory usage, of compiler @cindex large aggregate areas @cindex initialization @cindex DATA statement @cindex statements, DATA @item @code{g77} uses way too much memory and CPU time to process large aggregate areas having any initialized elements. For example, @samp{REAL A(1000000)} followed by @samp{DATA A(1)/1/} takes up way too much time and space, including the size of the generated assembler file. This is to be mitigated somewhat in version 0.6. Version 0.5.18 improves cases like this---specifically, cases of @emph{sparse} initialization that leave large, contiguous areas uninitialized---significantly. However, even with the improvements, these cases still require too much memory and CPU time. (Version 0.5.18 also improves cases where the initial values are zero to a much greater degree, so if the above example ends with @samp{DATA A(1)/0/}, the compile-time performance will be about as good as it will ever get, aside from unrelated improvements to the compiler.) Note that @code{g77} does display a warning message to notify the user before the compiler appears to hang. @xref{Large Initialization,,Initialization of Large Aggregate Areas}, for information on how to change the point at which @code{g77} decides to issue this warning. @cindex debugging @cindex common blocks @cindex equivalence areas @cindex local equivalence areas @item @code{g77} doesn't emit variable and array members of common blocks for use with a debugger (the @samp{-g} command-line option). The code is present to do this, but doesn't work with at least one debug format---perhaps it works with others. And it turns out there's a similar bug for local equivalence areas, so that has been disabled as well. As of Version 0.5.19, a temporary kludge solution is provided whereby some rudimentary information on a member is written as a string that is the member's value as a character string. @xref{Code Gen Options,,Options for Code Generation Conventions}, for information on the @samp{-fdebug-kludge} option. @cindex code, displaying main source @cindex displaying main source code @cindex debugging main source code @cindex printing main source @item When debugging, after starting up the debugger but before being able to see the source code for the main program unit, the user must currently set a breakpoint at @samp{MAIN__} (or @samp{MAIN___} or @samp{MAIN_} if @samp{MAIN__} doesn't exist) and run the program until it hits the breakpoint. At that point, the main program unit is activated and about to execute its first executable statement, but that's the state in which the debugger should start up, as is the case for languages like C. @cindex debugger @item Debugging @code{g77}-compiled code using debuggers other than @code{gdb} is likely not to work. Getting @code{g77} and @code{gdb} to work together is a known problem---getting @code{g77} to work properly with other debuggers, for which source code often is unavailable to @code{g77} developers, seems like a much larger, unknown problem, and is a lower priority than making @code{g77} and @code{gdb} work together properly. On the other hand, information about problems other debuggers have with @code{g77} output might make it easier to properly fix @code{g77}, and perhaps even improve @code{gdb}, so it is definitely welcome. Such information might even lead to all relevant products working together properly sooner. @cindex padding @cindex structures @cindex common blocks @cindex equivalence areas @item @code{g77} currently inserts needless padding for things like @samp{COMMON A,IPAD} where @samp{A} is @code{CHARACTER*1} and @samp{IPAD} is @code{INTEGER(KIND=1)} on machines like x86, because the back end insists that @samp{IPAD} be aligned to a 4-byte boundary, but the processor has no such requirement (though it's good for performance). It is possible that this is not a real bug, and could be considered a performance feature, but it might be important to provide the ability to Fortran code to specify minimum padding for aggregate areas such as common blocks---and, certainly, there is the potential, with the current setup, for interface differences in the way such areas are laid out between @code{g77} and other compilers. @item Some crashes occur when compiling under Solaris on x86 machines. Nothing has been heard about any such problems for some time, so this is considering a closed item as of 0.5.20. Please submit any bug reports pertinent to @code{g77}'s support for Solaris/x86 systems. @cindex RS/6000 support @cindex support, RS/6000 @item RS/6000 support is not complete as of the gcc 2.6.3 back end. The 2.7.0 back end appears to fix this problem, or at least mitigate it significantly, but there is at least one known problem that is likely to be a code-generation bug in @file{gcc-2.7.0} plus @file{g77-0.5.16}. This problem shows up only when compiling the Fortran program with @samp{-O}. Nothing has been heard about any RS/6000 problems for some time, so this is considering a closed item as of 0.5.20. Please submit any bug reports pertinent to @code{g77}'s support for RS/6000 systems. @cindex SGI support @cindex support, SGI @item SGI support is known to be a bit buggy. The known problem shows up only when compiling the Fortran program with @samp{-O}. It is possible these problems have all been fixed in 0.5.20 by emulating complex arithmetic in the front end. Please submit any bug reports pertinent to @code{g77}'s support for SGI systems. @cindex Alpha, support @cindex support, Alpha @item @code{g77} doesn't work perfectly on 64-bit configurations such as the Alpha. This problem is expected to be largely resolved as of version 0.5.20, and version 0.6 should solve most or all related problems (such as 64-bit machines other than DEC Alphas). One known bug that causes a compile-time crash occurs when compiling code such as the following with optimization: @example SUBROUTINE CRASH (TEMP) INTEGER*2 HALF(2) REAL TEMP HALF(1) = NINT (TEMP) END @end example It is expected that a future version of @code{g77} will have a fix for this problem, almost certainly by the time @code{g77} supports the forthcoming version 2.8.0 of @code{gcc}. @cindex COMPLEX support @cindex support, COMPLEX @item Maintainers of gcc report that the back end definitely has ``broken'' support for @code{COMPLEX} types. Based on their input, it seems many of the problems affect only the more-general facilities for gcc's @code{__complex__} type, such as @code{__complex__ int} (where the real and imaginary parts are integers) that GNU Fortran does not use. Version 0.5.20 of @code{g77} works around this problem by not using the back end's support for @code{COMPLEX}. The new option @samp{-fno-emulate-complex} avoids the work-around, reverting to using the same ``broken'' mechanism as that used by versions of @code{g77} prior to 0.5.20. @cindex ELF support @cindex support, ELF @cindex -fPIC option @cindex options, -fPIC @item There seem to be some problems with passing constants, and perhaps general expressions (other than simple variables/arrays), to procedures when compiling on some systems (such as i386) with @samp{-fPIC}, as in when compiling for ELF targets. The symptom is that the assembler complains about invalid opcodes. More investigation is needed, but the problem is almost certainly in the gcc back end, and it apparently occurs only when compiling sufficiently complicated functions @emph{without} the @samp{-O} option. @end itemize