Message-ID: <ad4c375b-7051-bcce-a86c-febb72267caa@codeaurora.org>
Date:   Thu, 29 Oct 2020 16:54:41 -0700
From:   Siddharth Gupta <sidgup@...eaurora.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     agross@...nel.org, ohad@...ery.com,
        linux-remoteproc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, tsoni@...eaurora.org,
        psodagud@...eaurora.org, rishabhb@...eaurora.org,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v6 2/4] remoteproc: coredump: Add minidump functionality


On 10/26/2020 2:09 PM, Bjorn Andersson wrote:
> On Fri 02 Oct 21:05 CDT 2020, Siddharth Gupta wrote:
>
>> This change adds a new kind of core dump mechanism which instead of dumping
>> entire program segments of the firmware, dumps sections of the remoteproc
>> memory which are sufficient to allow debugging the firmware. This function
>> thus uses section headers instead of program headers during creation of the
>> core dump elf.
>>
>> Signed-off-by: Rishabh Bhatnagar <rishabhb@...eaurora.org>
>> Signed-off-by: Siddharth Gupta <sidgup@...eaurora.org>
>> ---
>>   drivers/remoteproc/remoteproc_coredump.c    | 132 ++++++++++++++++++++++++++++
>>   drivers/remoteproc/remoteproc_elf_helpers.h |  27 ++++++
>>   include/linux/remoteproc.h                  |   1 +
>>   3 files changed, 160 insertions(+)
>>
>> diff --git a/drivers/remoteproc/remoteproc_coredump.c b/drivers/remoteproc/remoteproc_coredump.c
>> index bb15a29..e7d1394 100644
>> --- a/drivers/remoteproc/remoteproc_coredump.c
>> +++ b/drivers/remoteproc/remoteproc_coredump.c
>> @@ -13,6 +13,8 @@
>>   #include "remoteproc_internal.h"
>>   #include "remoteproc_elf_helpers.h"
>>   
>> +#define MAX_STRTBL_SIZE 512
>> +
>>   struct rproc_coredump_state {
>>   	struct rproc *rproc;
>>   	void *header;
>> @@ -323,3 +325,133 @@ void rproc_coredump(struct rproc *rproc)
>>   	 */
>>   	wait_for_completion(&dump_state.dump_done);
>>   }
>> +
>> +/**
>> + * rproc_minidump() - perform minidump
>> + * @rproc:	rproc handle
>> + *
>> + * This function will generate an ELF header for the registered sections of
>> + * segments and create a devcoredump device associated with rproc. Based on
>> + * the coredump configuration this function will directly copy the segments
>> + * from device memory to userspace or copy segments from device memory to
>> + * a separate buffer, which can then be read by userspace.
>> + * The first approach avoids using extra vmalloc memory. But it will stall
>> + * recovery flow until dump is read by userspace.
>> + */
>> +void rproc_minidump(struct rproc *rproc)
> Just to confirm, this does the same thing as rproc_coredump() with the
> difference that instead of storing the segments in program headers, you
> reference them using section headers?

Yes, that is correct.

>
>> +{
>> +	struct rproc_dump_segment *segment;
>> +	void *shdr;
>> +	void *ehdr;
>> +	size_t data_size;
>> +	size_t offset;
>> +	void *data;
>> +	u8 class = rproc->elf_class;
>> +	int shnum;
>> +	struct rproc_coredump_state dump_state;
>> +	unsigned int dump_conf = rproc->dump_conf;
>> +	char *str_tbl = "STR_TBL";
>> +
>> +	if (list_empty(&rproc->dump_segments) ||
>> +	    dump_conf == RPROC_COREDUMP_DISABLED)
>> +		return;
>> +
>> +	if (class == ELFCLASSNONE) {
>> +		dev_err(&rproc->dev, "Elf class is not set\n");
>> +		return;
>> +	}
>> +
>> +	/*
>> +	 * We allocate two extra section headers. The first one is null.
>> +	 * Second section header is for the string table. Also space is
>> +	 * allocated for string table.
>> +	 */
>> +	data_size = elf_size_of_hdr(class) + 2 * elf_size_of_shdr(class) +
>> +		    MAX_STRTBL_SIZE;
> Once you start populating the string table there's no checks that this
> isn't overrun.
I will update the code to dynamically allocate space for the STRTBL.
>
> But really
>
>> +	shnum = 2;
>> +
>> +	list_for_each_entry(segment, &rproc->dump_segments, node) {
>> +		data_size += elf_size_of_shdr(class);
>> +		if (dump_conf == RPROC_COREDUMP_DEFAULT)
>> +			data_size += segment->size;
>> +		shnum++;
>> +	}
>> +
>> +	data = vmalloc(data_size);
>> +	if (!data)
>> +		return;
>> +
>> +	ehdr = data;
>> +	memset(ehdr, 0, elf_size_of_hdr(class));
>> +	/* e_ident field is common for both elf32 and elf64 */
>> +	elf_hdr_init_ident(ehdr, class);
>> +
>> +	elf_hdr_set_e_type(class, ehdr, ET_CORE);
>> +	elf_hdr_set_e_machine(class, ehdr, rproc->elf_machine);
>> +	elf_hdr_set_e_version(class, ehdr, EV_CURRENT);
>> +	elf_hdr_set_e_entry(class, ehdr, rproc->bootaddr);
>> +	elf_hdr_set_e_shoff(class, ehdr, elf_size_of_hdr(class));
>> +	elf_hdr_set_e_ehsize(class, ehdr, elf_size_of_hdr(class));
>> +	elf_hdr_set_e_shentsize(class, ehdr, elf_size_of_shdr(class));
>> +	elf_hdr_set_e_shnum(class, ehdr, shnum);
>> +	elf_hdr_set_e_shstrndx(class, ehdr, 1);
>> +
>> +	/* Set the first section header as null and move to the next one. */
>> +	shdr = data + elf_hdr_get_e_shoff(class, ehdr);
>> +	memset(shdr, 0, elf_size_of_shdr(class));
>> +	shdr += elf_size_of_shdr(class);
>> +
>> +	/* Initialize the string table. */
>> +	offset = elf_hdr_get_e_shoff(class, ehdr) +
>> +		 elf_size_of_shdr(class) * elf_hdr_get_e_shnum(class, ehdr);
>> +	memset(data + offset, 0, MAX_STRTBL_SIZE);
>> +
>> +	/* Fill in the string table section header. */
>> +	memset(shdr, 0, elf_size_of_shdr(class));
>> +	elf_shdr_set_sh_type(class, shdr, SHT_STRTAB);
>> +	elf_shdr_set_sh_offset(class, shdr, offset);
>> +	elf_shdr_set_sh_size(class, shdr, MAX_STRTBL_SIZE);
>> +	elf_shdr_set_sh_entsize(class, shdr, 0);
>> +	elf_shdr_set_sh_flags(class, shdr, 0);
>> +	elf_shdr_set_sh_name(class, shdr, set_section_name(str_tbl, ehdr, class));
>> +	offset += elf_shdr_get_sh_size(class, shdr);
>> +	shdr += elf_size_of_shdr(class);
> I assume this last part creates the null entry? How about mentioning
> that in a comment - and perhaps why there needs to be a null entry.
Okay sure. I will add that comment.
>
>> +
>> +	list_for_each_entry(segment, &rproc->dump_segments, node) {
>> +		memset(shdr, 0, elf_size_of_shdr(class));
>> +		elf_shdr_set_sh_type(class, shdr, SHT_PROGBITS);
>> +		elf_shdr_set_sh_offset(class, shdr, offset);
>> +		elf_shdr_set_sh_addr(class, shdr, segment->da);
>> +		elf_shdr_set_sh_size(class, shdr, segment->size);
>> +		elf_shdr_set_sh_entsize(class, shdr, 0);
>> +		elf_shdr_set_sh_flags(class, shdr, SHF_WRITE);
>> +		elf_shdr_set_sh_name(class, shdr,
>> +				     set_section_name(segment->priv, ehdr, class));
>> +
>> +		/* No need to copy segments for inline dumps */
>> +		if (dump_conf == RPROC_COREDUMP_DEFAULT)
>> +			rproc_copy_segment(rproc, data + offset, segment, 0,
>> +					   segment->size);
>> +		offset += elf_shdr_get_sh_size(class, shdr);
>> +		shdr += elf_size_of_shdr(class);
>> +	}
>> +
>> +	if (dump_conf == RPROC_COREDUMP_DEFAULT) {
>> +		dev_coredumpv(&rproc->dev, data, data_size, GFP_KERNEL);
>> +		return;
>> +	}
>> +
>> +	/* Initialize the dump state struct to be used by rproc_coredump_read */
>> +	dump_state.rproc = rproc;
>> +	dump_state.header = data;
>> +	init_completion(&dump_state.dump_done);
>> +
>> +	dev_coredumpm(&rproc->dev, NULL, &dump_state, data_size, GFP_KERNEL,
>> +		      rproc_coredump_read, rproc_coredump_free);
>> +
>> +	/* Wait until the dump is read and free is called. Data is freed
>> +	 * by devcoredump framework automatically after 5 minutes.
>> +	 */
>> +	wait_for_completion(&dump_state.dump_done);
>> +}
>> +EXPORT_SYMBOL(rproc_minidump);
>> diff --git a/drivers/remoteproc/remoteproc_elf_helpers.h b/drivers/remoteproc/remoteproc_elf_helpers.h
>> index 4b6be7b..d83ebca 100644
>> --- a/drivers/remoteproc/remoteproc_elf_helpers.h
>> +++ b/drivers/remoteproc/remoteproc_elf_helpers.h
>> @@ -11,6 +11,7 @@
>>   #include <linux/elf.h>
>>   #include <linux/types.h>
>>   
>> +#define MAX_NAME_LENGTH 16
> This name is too generic. Why is it 16?

I will update the name to  MAX_SHDR_NAME_LEN. In our usecase we didn't 
expect a length of the section name to exceed
16 characters (MAX_REGION_NAME_LENGTH defined in qcom_minidump.h in 
patch 03/04). It might change later if users
want to increase the size. What would you prefer the max name length for 
the section header to be?

>
>> +static inline unsigned int set_section_name(const char *name, void *ehdr,
>> +					    u8 class)
>> +{
>> +	u16 shstrndx = elf_hdr_get_e_shstrndx(class, ehdr);
>> +	void *shdr;
>> +	char *strtab;
>> +	static int strtable_idx = 1;
> This can't be static as this will only start at 1 on the first
> invocation of rproc_minidump().
>
> I think it would be perfectly fine if you simply scan the string list to
> find the next available slot.
Right. I will update this as well.
>
>> +	int idx, ret = 0;
> No need to initialize ret as the first usage is an assignment.
>
> Regards,
> Bjorn

I will make this change as well.

Thanks,
Siddharth

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