On Wed, Feb 13, 2008 at 12:15:06AM -0800, [EMAIL PROTECTED] wrote: > Subject: Elf loader crash while zero-filling .bss > From: "Abel Bernabeu" <[EMAIL PROTECTED]> > > I've finally found a solution for the crash in load_binary_elf I > reported last week: > > http://lkml.org/lkml/2008/1/30/171 > > The attached patch solves my problem. > > set_brk(start, end) allocs just page aligned regions (by "collapsing" both > extremes to the start of the page in which they lay)... That means than > even if both pointers are not equal there are still some chances that > set_brk has allocated no space at all because ELF_PAGEALIGN(elf_bss) == > ELF_PAGEALIGN(elf_brk). > > So the condition was not correct.
This patch is wrong. ELF_PAGEALIGN rounds up to the end of the page, not down to the start of the page. If elf_bss is in the middle of a page, set_brk allocates any additional pages after the one already allocated. elf_bss is the start of the area that needs to be zero initialized, elf_brk is its end. So if elf_bss != elf_brk then there's garbage mapped in BSS from the file and if you don't clear it some of your zero-initialized variables won't be zero initialized at all. In the linked message, set_brk is passed elf_bss so its actual arguments are set_brk (0xa3801, 0x000a4ec8). It should map one page. 0xa3801 should be an already mapped page, and clear_user should succeed in clearing it. -- Daniel Jacobowitz CodeSourcery -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
