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Top Forums Programming Why does this example C code run and yet SHOULD either not compile or give a segmentation fault? Post 303033031 by Corona688 on Thursday 28th of March 2019 06:55:31 PM
Old 03-28-2019
Quote:
Originally Posted by wisecracker
IMO gcc should check for any assembly jumps outside the bounds of any individual function, irrespective of how one compiles it.
It's necessary sometimes, if you're building an operating system for example, to insert special instructions here and there without the compiler's interference. That's the kind of thing asm() is for. gcc will insert raw assembly if you ask, but you really have to know what you're doing since it can't protect you( though some more advanced syntax lets you warn gcc about side-effects instead). Plain, non-ASM goto (yes, it exists, very rarely used) wouldn't let you jump out of bounds.
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GENASSYM.CF(5)						      BSD File Formats Manual						    GENASSYM.CF(5)

NAME
genassym.cf -- assym.h definition file DESCRIPTION
The genassym.cf file is used by genassym(1) to make constant C expressions known to assembler source files. Lines starting with '#' are dis- carded by genassym(1). Lines starting with include, ifdef, if, else or endif are preceded with '#' and passed otherwise unmodified to the C compiler. Lines starting with quote get passed on with the quote command removed. The first word after a define command is taken as a CPP identifier and the rest of the line has to be a constant C expression. The output of genassym(1) will assign the numerical value of this expression to the CPP identifier. export X is a shorthand for define X X. struct X remembers X for the member command and does a define X_SIZEOF sizeof(X). member X does a define X offsetof(<last struct>, X). config <ctype> <gcc constraint> <asm print modifier> can be used to customize the output of genassym(1). When producing C output, values are casted to <ctype> (default: long) before they get handed to printf. <gcc constraint> (default: n) is the constraint used in the __asm__ statements. <asm print modifier> (default: empty) can be used to force gcc to output operands in different ways then normal. The "a" modifier e.g. stops gcc from emitting immediate prefixes in front of con- stants for the i386 and m68k port. FILES
/usr/src/sys/arch/${MACHINE}/${MACHINE}/genassym.cf SEE ALSO
genassym(1) HISTORY
The genassym.cf file appeared in NetBSD 1.3. BSD
August 18, 2005 BSD
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