Re: dtc(1): reproducible segmentation fault

> On Oct 23, 2015, at 07:10, George Abdelmalik <gabdelmalik_at_uniridge.com.au> wrote:
> 
> Hi,
> 
> With recent amd64 11.0-current system (as of earlier this week) I can reproduciblycw
> get a SIGSEGV when running a command such as
> 
> $ dtc -o zb.dtb /usr/src/sys/boot/fdt/dts/arm/zedboard.dts
> Segmentation fault (core dumped)
> 
> I've investigated the issue and found that the problem is at line
> 241 of the /usr/src/usr.bin/dtc/input_buffer.cc where the call to
> mmap(2) fails. Snippet below:
> 
> 233 mmap_input_buffer::mmap_input_buffer(int fd) : input_buffer(0, 0)
> 234 {
> 235         struct stat sb;
> 236         if (fstat(fd, &sb))
> 237         {
> 238                 perror("Failed to stat file");
> 239         }
> 240         size = sb.st_size;
> 241         buffer = (const char*)mmap(0, size, PROT_READ,
> 242                 MAP_PREFAULT_READ, fd, 0);
> 243         if (buffer == 0)
> 244         {
> 245                 perror("Failed to mmap file");
> 246         }
> 247 }
> 
> The code incorrectly tests againts 0 instead of MAP_FAILED for failure
> which is why the the perror message isn't seen at the terminal, the SIGSEGV
> happens later when an attempt to access the buffer array is made.
> 
> Also the final parts of truss output are:
> 
> ..
> ..
> getrusage(0,{ u=0.000000,s=0.002578,in=2,out=0 }) = 0 (0x0)
> mmap(0x0,2097152,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON,-1,0x0) = 34384904192 (0x801800000)
> openat(AT_FDCWD,"xxx.dtb",O_WRONLY|O_CREAT|O_TRUNC,0666) = 3 (0x3)
> getrusage(0,{ u=0.000000,s=0.002697,in=2,out=0 }) = 0 (0x0)
> openat(AT_FDCWD,"/usr/src/sys/boot/fdt/dts/arm/zedboard.dts",O_RDONLY,00) = 4 (0x4)
> fstat(4,{ mode=-rw-r--r-- ,inode=73360,size=5360,blksize=5632 }) = 0 (0x0)
> fstat(4,{ mode=-rw-r--r-- ,inode=73360,size=5360,blksize=5632 }) = 0 (0x0)
> mmap(0x0,5360,PROT_READ,MAP_PREFAULT_READ,4,0x0) ERR#22 'Invalid argument'
> close(4)                     = 0 (0x0)
> SIGNAL 11 (SIGSEGV)
> process killed, signal = 11 (core dumped)
> 
> Any help debugging this futher would be much appreciated. I just can't understand why
> the mmap in question would fail, and what's invalid about its arguments?

Hi George,
    Could you please post the bug report (with your dts file) on bugs.freebsd.org and CC Ian Lepore and Warner Losh?
Thanks!
-NGie