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Full Discussion: Why does this example C code run and yet SHOULD either not compile or give a segmentation fault?
Top Forums Programming Why does this example C code run and yet SHOULD either not compile or give a segmentation fault? Post 303032978 by jim mcnamara on Wednesday 27th of March 2019 06:33:32 PM
Old 03-27-2019
This is basically another way to do the undefined operation thing.

asm:
Not part of standard C, so whatever asm does is implementation defined, i.e., the people who wrote gcc
Since it's not mentioned in ISO C standard (n1570 draft-- C2011), but mentioned in annex J (common extensions):

Quote:
J.5.10 The asm keyword

1 The asm keyword may be used to insert assembly language directly into the translator output (6.8). The most common implementation is via a statement of the form:

asm ( character-string-literal );
Annex J is informative, not normative, so an implementation need not provide inline assembly, and if it does it's not prescribed in which form. But it's a widespread extension, though not portable since compilers do indeed implement it differently.

In the C++ standard (n3376 draft of the C++11 standard), it is NOT mentioned in the body of the standard.

Quote:
7.4 The asm declaration [dcl.asm]

1 An asm declaration has the form

asm-definition:

asm ( string-literal ) ;

The asm declaration is conditionally-supported; its meaning is implementation-defined. [ Note: Typically it is used to pass information through the implementation to an assembler. - end note ]
I think Rudi correct. Try using return statements. That return values used by the calling code. Other than learning what not to do for reasonable code, what does this do for you? If you had not asked here your might have accidentally created a horrible bug in a piece of code that you thought was okay. It's okay with me, but it does not seem all that helpful....
Last edited by jim mcnamara; 03-28-2019 at 12:06 PM..
This User Gave Thanks to jim mcnamara For This Post:
wisecracker
 

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LEARN ABOUT FREEBSD

tblgen

TBLGEN(1)							       LLVM								 TBLGEN(1)

NAME

       tblgen - Target Description To C++ Code Generator

SYNOPSIS

       tblgen [options] [filename]

DESCRIPTION

       tblgen translates from target description (.td) files into C++ code that can be included in the definition of an LLVM target library.  Most
       users of LLVM will not need to use this program.  It is only for assisting with writing an LLVM target backend.

       The input and output of tblgen is beyond the scope of this short introduction; please see the introduction to TableGen.

       The filename argument specifies the name of a Target Description (.td) file to read as input.

OPTIONS

       -help  Print a summary of command line options.

       -o filename
	      Specify the output file name.  If filename is -, then tblgen sends its output to standard output.

       -I directory
	      Specify where to find other target description files for inclusion.  The directory value should be a  full  or  partial  path  to  a
	      directory that contains target description files.

       -asmparsernum N
	      Make -gen-asm-parser emit assembly writer number N.

       -asmwriternum N
	      Make -gen-asm-writer emit assembly writer number N.

       -class className
	      Print the enumeration list for this class.

       -print-records
	      Print all records to standard output (default).

       -print-enums
	      Print enumeration values for a class.

       -print-sets
	      Print expanded sets for testing DAG exprs.

       -gen-emitter
	      Generate machine code emitter.

       -gen-register-info
	      Generate registers and register classes info.

       -gen-instr-info
	      Generate instruction descriptions.

       -gen-asm-writer
	      Generate the assembly writer.

       -gen-disassembler
	      Generate disassembler.

       -gen-pseudo-lowering
	      Generate pseudo instruction lowering.

       -gen-dag-isel
	      Generate a DAG (Directed Acycle Graph) instruction selector.

       -gen-asm-matcher
	      Generate assembly instruction matcher.

       -gen-dfa-packetizer
	      Generate DFA Packetizer for VLIW targets.

       -gen-fast-isel
	      Generate a "fast" instruction selector.

       -gen-subtarget
	      Generate subtarget enumerations.

       -gen-intrinsic
	      Generate intrinsic information.

       -gen-tgt-intrinsic
	      Generate target intrinsic information.

       -gen-enhanced-disassembly-info
	      Generate enhanced disassembly info.

       -version
	      Show the version number of this program.

EXIT STATUS

       If tblgen succeeds, it will exit with 0.  Otherwise, if an error occurs, it will exit with a non-zero value.

AUTHOR

       Maintained by The LLVM Team (http://llvm.org/).

COPYRIGHT

       2003-2014, LLVM Project

3.5								    2015-01-10								 TBLGEN(1)
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