Memory management problem?

[Tobias Koch <tobias.koch@nonterra.com>]

Hi,

I have (cross) compiled a chroot out of Debian testing sources but with musl and busybox at the core. The target is x86_64-cross-linux-musl. Now that I got to the point where I can actually run some builds inside the chroot itself, I noticed that flex segfaults on startup. In the flex sources this snippet is executed:

    num_to_alloc = 1; /* After all that talk, this was set to 1 anyways... */
    (yy_buffer_stack) = (struct yy_buffer_state**) yyalloc(num_to_alloc * sizeof(struct yy_buffer_state*));

    if ( ! (yy_buffer_stack) )
        YY_FATAL_ERROR( "out of dynamic memory in yyensure_buffer_stack()" );

    memset((*yy_buffer_stack), 0, num_to_alloc * sizeof(struct yy_buffer_state*));

The memset is optimized away, because GCC understands that the pointer target is just one native word and does a

    => 0x0000000000401c7e <+64>:64movq   $0x0,(%rax)

instead. Strace shows the following output:

    execve("/tools/bin/flex", ["flex"], [/* 18 vars */]) = 0
    arch_prctl(ARCH_SET_FS, 0x7f87ee4d5b28) = 0
    set_tid_address(0x7f87ee4d5b60)         = 18855
    mprotect(0x7f87ee4d2000, 4096, PROT_READ) = 0
    mprotect(0x63f000, 4096, PROT_READ)     = 0
    brk(NULL)                               = 0x1cd4000
    brk(0x1cd6000)                          = 0x1cd6000
    brk(0x1cd7000)                          = 0x1cd7000
    brk(0x1cd8000)                          = 0x1cd8000
    brk(0x1cda000)                          = 0x1cda000
    brk(0x1cdc000)                          = 0x1cdc000
    brk(0x1cde000)                          = 0x1cde000
    brk(0x1ce0000)                          = 0x1ce0000
    brk(0x1ce2000)                          = 0x1ce2000
    brk(0x1ce4000)                          = 0x1ce4000
    brk(0x1ce6000)                          = 0x1ce6000
    brk(0x1ce8000)                          = 0x1ce8000
    brk(0x1cea000)                          = 0x1cea000
    brk(0x1cec000)                          = 0x1cec000
    brk(0x1cef000)                          = 0x1cef000
    brk(0x1cf0000)                          = 0x1cf0000
    brk(0x1cf1000)                          = 0x1cf1000
    brk(0x1cf2000)                          = 0x1cf2000
    brk(0x1cf3000)                          = 0x1cf3000
    brk(0x1cf4000)                          = 0x1cf4000
    brk(0x1cf6000)                          = 0x1cf6000
    brk(0x1cf8000)                          = 0x1cf8000
    --- SIGSEGV {si_signo=SIGSEGV, si_code=SEGV_MAPERR, si_addr=0xffffffffee4d6d60} ---
    +++ killed by SIGSEGV +++
    Segmentation fault

I'm not sure, if there is a problem with musl or some sort of optimization problem with GCC. If I compile either musl or flex without optimizations, the problem goes away. I have tried version 1.1.16 and git master.

Any hints on how I could get to the bottom of this, would be greatly appreciated.

Tobias