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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 303033016 by wisecracker on Thursday 28th of March 2019 11:56:57 AM
Old 03-28-2019
Quote:
Originally Posted by Corona688
Because argv[0] actually exists, even in a program with no arguments - it's the name of the calling program. Again, why should it segfault? What exact fault should it be catching here? Segmentation fault means "touched memory I don't have permission to use", and if you don't do that, you don't get a segfault, even if you leap around like a flea on a hot griddle.
IMO gcc should check for any assembly jumps outside the bounds of any individual function, irrespective of how one compiles it. Just because the first code uses two near identical functions is irrelevant the 'asm()' function is taking functions out of their boundaries.
And, I don't intend, ever, to use this bad coding method at all. It was an exercise in finding out as I was researching about 'goto' inside a function.

--- Post updated at 03:56 PM ---

Quote:
Originally Posted by jim mcnamara
How do you compile ? Try gcc -Wall -ansi mycode.c -o mycode

I'm guessing, completely. You have to read your manpage for gcc, look for the options for your hardware e.g., SPARC
Compile with the strictest settings you can find. This will eliminate some of the problems you see: gcc compiling stuff that should fail.
Try to use -std=c99 if your compiler supports it, for example. Since you run on OSX and Amiga (I think), I have to punt on what the exact command should be.

PS: a good clean compile means zero warnings/errors

Hi Jim...
Absolutely.
However I shouldn't have to type all that just to find out, gcc filename.c should be sufficient.
Code:
Last login: Thu Mar 28 14:56:34 on ttys000
AMIGA:amiga~> cd Desktop/Code/C
AMIGA:amiga~/Desktop/Code/C> gcc -Wall -ansi obfuscate_asm.c -o obfuscate_asm
obfuscate_asm.c:14:2: warning: implicit declaration of function 'asm'
      [-Wimplicit-function-declaration]
        asm("nop;"
        ^
obfuscate_asm.c:40:2: warning: implicit declaration of function 'asm'
      [-Wimplicit-function-declaration]
        asm("jmp    getout;"
        ^
2 warnings generated.
Undefined symbols for architecture x86_64:
  "_asm", referenced from:
      _main in obfuscate_asm-09a969.o
      _obfuscate in obfuscate_asm-09a969.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
 AMIGA:amiga~/Desktop/Code/C> _

It should have been __asm__ volatile() but I used the generic 'asm()' as it seems 'universal' even on my AMIGA C compilers.

Thanks for your help...

EDIT:
I didn't add this as an edit, it did so itself.
Last edited by wisecracker; 03-28-2019 at 01:00 PM.. Reason: See EDIT:
 

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