linux-kernel - Re: [Patch 18/21] Generate the data sections for ELF Core

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Date:	Wed, 15 Dec 2010 15:19:54 +0800
From:	Cong Wang <amwang@...hat.com>
To:	"Suzuki K. Poulose" <suzuki@...ibm.com>
CC:	linux-kernel@...r.kernel.org,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	Christoph Hellwig <hch@....de>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Daisuke HATAYAMA <d.hatayama@...fujitsu.com>,
	Andi Kleen <andi@...stfloor.org>,
	Roland McGrath <roland@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [Patch 18/21] Generate the data sections for ELF Core

于 2010年12月14日 18:22, Suzuki K. Poulose 写道:
...
> +	/*
> +	 * Read from the vma segments
> +	 * a. verify if the *fpos is within a phdr
> +	 * b. Use access_process_vm() to get data page by page
> +	 * c. copy_to_user into user buffer
> +	 */


This kind of comments is useless, "code tells you how, comments tell you why."


> +
> +	while (buflen) {
> +		size_t bufsz, offset, bytes;
> +		char *readbuf;
> +		struct elf_phdr *phdr = get_pos_elfphdr(cp, *fpos);
> +
> +		if (!phdr)
> +			break;
> +
> +		bufsz = (buflen>  PAGE_SIZE) ? PAGE_SIZE : buflen;
> +		readbuf = kmalloc(bufsz, GFP_KERNEL);
> +		if (!readbuf) {
> +			ret = -ENOMEM;
> +			goto out;
> +		}
> +
> +		offset = *fpos - phdr->p_offset;
> +		bytes = access_process_vm(cp->task, (phdr->p_vaddr + offset),
> +						readbuf, bufsz, 0);
> +		if (!bytes) {
> +			ret = -EIO;
> +			goto out;


Why you don't kfree(readbuf) here?

> +		}
> +		if (copy_to_user(buffer, readbuf, bytes)) {
> +			ret = -EFAULT;
> +			kfree(readbuf);
> +			goto out;
> +		} else
> +			acc += bytes;
> +
> +		kfree(readbuf);
> +		buflen -= bytes;
> +		buffer += bytes;
> +		*fpos += bytes;
> +	}
> +
> +	/* Fill extnum section header if present */
> +	if (buflen&&
> +		elf_hdr->e_shoff&&
> +		(*fpos>= elf_hdr->e_shoff)&&
> +		(*fpos<  (elf_hdr->e_shoff + sizeof(struct elf_shdr)))) {


This indention seems ugly.

> +
> +		off_t offset = *fpos - elf_hdr->e_shoff;

Are you sure it is 'off_t' not 'loff_t'?

> +		size_t shdrsz = sizeof(struct elf_shdr) - offset;
> +
> +		shdrsz = (buflen<  shdrsz) ? buflen : shdrsz;
> +		if (copy_to_user(buffer, ((char *)cp->shdr) + offset, shdrsz)) {
> +			ret = -EFAULT;
> +			goto out;
> +		} else {
> +			acc += shdrsz;
> +			buflen -= shdrsz;
> +			buffer += shdrsz;
> +		}
> +	}
>
> +done:
> +	ret = acc;
>   out:
>   	return ret;
>   }

Thanks.
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