Re: [PATCH v6 2/4] remoteproc: coredump: Add minidump functionality

Bjorn Andersson
2020-10-26T21:09:21Z

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@codeaurora.org>
> Signed-off-by: Siddharth Gupta <sidgup@codeaurora.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?

> +{
> + 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.

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.

> +
> + 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?

> +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.

> + int idx, ret = 0;

No need to initialize ret as the first usage is an assignment.

Regards,
Bjorn