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Date: Fri, 17 Feb 2017 17:48:08 +0000
From: Tobias Koch <tobias.koch@...terra.com>
To: musl <musl@...ts.openwall.com>
Subject: Memory management problem?
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
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