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Date: Mon, 17 Nov 2008 02:00:00 -0000
Subject: [Bug c/38167]  New: Inline accessor to stdin is breaks on -O2 optimization
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From: "aleksi dot nurmi at helsinki dot fi" <gcc-bugzilla@gcc.gnu.org>
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It appears that the following inline accessor function to stdin doesn't do it's
job if -O2 optimization is turned on, thus letting a null pointer pass and
causing a segfault. This doesn't happen if the function is not declared inline. 

Version: gcc (GCC) 4.2.4 (Ubuntu 4.2.4-1ubuntu3)
Command line: gcc -O2 -o fault fault.c
GNU libc 2.7 is known for its non-constant stdin and is probably required to
actually get a segfault.

Code in readable format:

#include <stdio.h>

struct iostream {
    FILE *f;
};

static struct iostream our_stdin = { 0 };

inline void access_iostream(struct iostream* ios)
{
    if (ios->f == 0)
        if (ios == &our_stdin)
            ios->f = stdin;
}

void read_char(struct iostream* ios)
{
    access_iostream(ios);
    fgetc(ios->f);
}

int main()
{  
    read_char(&our_stdin);

    return 0;
}


-- 
           Summary: Inline accessor to stdin is breaks on -O2 optimization
           Product: gcc
           Version: 4.2.4
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: aleksi dot nurmi at helsinki dot fi
  GCC host triplet: x86_64-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38167