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From: | phcoder |
Subject: | Re: ELF bugfixes |
Date: | Sat, 14 Mar 2009 00:01:13 +0100 |
User-agent: | Thunderbird 2.0.0.19 (X11/20090105) |
Robert Millan wrote:
On Fri, Mar 13, 2009 at 09:41:42PM +0100, phcoder wrote:Robert Millan wrote:No I expressed myself badly. Original code assumed that first segment has PT_LOAD always set (lowest_segment is 0 initally). I removed this assumptionOn Wed, Mar 11, 2009 at 10:21:41PM +0100, phcoder wrote:Robert Millan wrote:Because if first segment doesn't have the PT_LOAD attribute set then it should be considered in this comparisonOn Mon, Mar 02, 2009 at 01:35:06AM +0100, phcoder wrote:+ * include/grub/elf.h: added missing attributesThis should be a bit more descriptive.for (i = 0; i < ehdr->e_phnum; i++) if (phdr(i)->p_type == PT_LOAD && phdr(i)->p_filesz != 0) { - if (phdr(i)->p_paddr < phdr(lowest_segment)->p_paddr)+ if (lowest_segment == -1 + || phdr(i)->p_paddr < phdr(lowest_segment)->p_paddr)lowest_segment = i; - if (phdr(i)->p_paddr > phdr(highest_segment)->p_paddr) + if (highest_segment == -1 + || phdr(i)->p_paddr > phdr(highest_segment)->p_paddr) highest_segment = i; }Why?But you didn't remove the PT_LOAD check. And in the routine below that does the actual segment load, we still check for PT_LOAD. Those should be consistent, right?Why do we care about non-PT_LOAD segments?
We don't but without this fix non-PT_LOAD segment 1 wasn't correctly ignored
Actually our segment table is also our table for transforming between virtual and physical address. I don't see why entry point would be defined against virtual address of lowest physical segementActually now thinking I see that the problem is more deep. The section which is loaded at the lowest address isn't necessarily the section which contains entry point. I'll fix this part cleanly and will resubmit the patch- grub_multiboot_payload_entry_offset = ehdr->e_entry - phdr(lowest_segment)->p_vaddr; + grub_multiboot_payload_entry_offset = ehdr->e_entry - phdr(lowest_segment)->p_paddr;Are you sure about this? IIRC e_entry is in the virtual address space. I think we had some trouble with this (with NetBSD?), which lead to the current use of p_vaddr in this line.No, but AFAICT the entry point is defined relative to that address, regardless of which segment contains it.I think entry point is supposed to be defined in virtual address space. As to why do we check for physical addresses earlier, I'm not entirely sure. I think the idea was that we store the entry point as an offset, so that it can be applied to physical addresses, despite the fact that we obtained it by comparing e_entry with a virtual address. ISTR this being an issue for NetBSD. We should be certain what we do before changing it. In particular, the following commit seem relevant: 2008-02-05 Bean <address@hidden> * loader/i386/pc/multiboot.c (grub_multiboot_load_elf32): Get physical address of entry. I'd also recommend testing your changes with NetBSD's kernel.
Ok will do it -- Regards Vladimir 'phcoder' Serbinenko
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