Messages in this thread Patch in this message | | | Date | Mon, 11 Mar 2002 20:00:41 +0000 | From | Russell King <> | Subject | RFC: /proc/kcore |
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A short while ago, I cooked up the following for the ARM architecture to allow /proc/kcore to work. I suspect it needs to be extended to all architectures however; comments from all other architecture maintainers are welcome.
In the ELF headers, we supply the following information for the kernels memory space:
phdr->p_type = PT_LOAD; phdr->p_flags = PF_R|PF_W|PF_X; phdr->p_offset = dataoff; phdr->p_vaddr = PAGE_OFFSET; phdr->p_paddr = __pa(PAGE_OFFSET); phdr->p_filesz = phdr->p_memsz = ((unsigned long)high_memory - PAGE_OFFSET); phdr->p_align = PAGE_SIZE;
So, when we access file offset 'dataoff' we expect the bytes starting at virtual memory address 'PAGE_OFFSET' (or physical address __pa(PAGE_OFFSET)).
'dataoff' comes from get_kcore_size, and is the same as the elf_buflen you see in the patch below, and is the first byte of non-header information.
With a file offset of 'elf_buflen', the original code does:
start = __va(0)
and the only way this will return the byte at PAGE_OFFSET is if __va is defined as (PAGE_OFFSET + (x)). However, a machine where the RAM does not start at physical address zero, this will not be the case.
I therefore expect that the code I have below for ARM should be used for all architectures.
I'd like other people to confirm. If I don't hear anything, I'll generate such a patch, and forward it to Linus, Marcelo and LKML for inclusion in the next kernel releases.
--- orig/fs/proc/kcore.c Mon Oct 1 23:11:24 2001 +++ linux/fs/proc/kcore.c Tue Jan 29 20:57:03 2002 @@ -382,7 +382,17 @@ } #endif /* fill the remainder of the buffer from kernel VM space */ +#ifndef __arm__ start = (unsigned long)__va(*fpos - elf_buflen); +#else + /* + * this would appear to be more correct than the above. + * We said in the ELF header that the data which starts + * at 'elf_buflen' is virtual address PAGE_OFFSET. This + * is not what the above does. + */ + start = PAGE_OFFSET + (*fpos - elf_buflen); +#endif if ((tsz = (PAGE_SIZE - (start & ~PAGE_MASK))) > buflen) tsz = buflen; -- Russell King (rmk@arm.linux.org.uk) The developer of ARM Linux http://www.arm.linux.org.uk/personal/aboutme.html
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