remoteproc: coredump: Add minidump functionality

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.

Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Co-developed-by: Rishabh Bhatnagar <rishabhb@codeaurora.org>
Signed-off-by: Rishabh Bhatnagar <rishabhb@codeaurora.org>
Signed-off-by: Siddharth Gupta <sidgup@codeaurora.org>
Link: https://lore.kernel.org/r/1605819935-10726-3-git-send-email-sidgup@codeaurora.org
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

drivers/remoteproc/remoteproc_coredump.c

@@ -323,3 +323,143 @@ void rproc_coredump(struct rproc *rproc)
 	 */
 	wait_for_completion(&dump_state.dump_done);
 }
+
+/**
+ * rproc_coredump_using_sections() - perform coredump using section headers
+ * @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_coredump_using_sections(struct rproc *rproc)
+{
+	struct rproc_dump_segment *segment;
+	void *shdr;
+	void *ehdr;
+	size_t data_size;
+	size_t strtbl_size = 0;
+	size_t strtbl_index = 1;
+	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);
+	shnum = 2;
+
+	/* the extra byte is for the null character at index 0 */
+	strtbl_size += strlen(str_tbl) + 2;
+
+	list_for_each_entry(segment, &rproc->dump_segments, node) {
+		data_size += elf_size_of_shdr(class);
+		strtbl_size += strlen(segment->priv) + 1;
+		if (dump_conf == RPROC_COREDUMP_ENABLED)
+			data_size += segment->size;
+		shnum++;
+	}
+
+	data_size += strtbl_size;
+
+	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);
+
+	/*
+	 * The zeroth index of the section header is reserved and is rarely used.
+	 * Set the section header as null (SHN_UNDEF) 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, 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, 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, elf_strtbl_add(str_tbl, ehdr, class, &strtbl_index));
+	offset += elf_shdr_get_sh_size(class, shdr);
+	shdr += elf_size_of_shdr(class);
+
+	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,
+				     elf_strtbl_add(segment->priv, ehdr, class, &strtbl_index));
+
+		/* No need to copy segments for inline dumps */
+		if (dump_conf == RPROC_COREDUMP_ENABLED)
+			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_ENABLED) {
+		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_coredump_using_sections);

drivers/remoteproc/remoteproc_elf_helpers.h

@@ -65,6 +65,7 @@ ELF_GEN_FIELD_GET_SET(hdr, e_type, u16)
 ELF_GEN_FIELD_GET_SET(hdr, e_version, u32)
 ELF_GEN_FIELD_GET_SET(hdr, e_ehsize, u32)
 ELF_GEN_FIELD_GET_SET(hdr, e_phentsize, u16)
+ELF_GEN_FIELD_GET_SET(hdr, e_shentsize, u16)
 
 ELF_GEN_FIELD_GET_SET(phdr, p_paddr, u64)
 ELF_GEN_FIELD_GET_SET(phdr, p_vaddr, u64)
@@ -75,6 +76,9 @@ ELF_GEN_FIELD_GET_SET(phdr, p_offset, u64)
 ELF_GEN_FIELD_GET_SET(phdr, p_flags, u32)
 ELF_GEN_FIELD_GET_SET(phdr, p_align, u64)
 
+ELF_GEN_FIELD_GET_SET(shdr, sh_type, u32)
+ELF_GEN_FIELD_GET_SET(shdr, sh_flags, u32)
+ELF_GEN_FIELD_GET_SET(shdr, sh_entsize, u16)
 ELF_GEN_FIELD_GET_SET(shdr, sh_size, u64)
 ELF_GEN_FIELD_GET_SET(shdr, sh_offset, u64)
 ELF_GEN_FIELD_GET_SET(shdr, sh_name, u32)
@@ -93,4 +97,26 @@ ELF_STRUCT_SIZE(shdr)
 ELF_STRUCT_SIZE(phdr)
 ELF_STRUCT_SIZE(hdr)
 
+static inline unsigned int elf_strtbl_add(const char *name, void *ehdr, u8 class, size_t *index)
+{
+	u16 shstrndx = elf_hdr_get_e_shstrndx(class, ehdr);
+	void *shdr;
+	char *strtab;
+	size_t idx, ret;
+
+	shdr = ehdr + elf_size_of_hdr(class) + shstrndx * elf_size_of_shdr(class);
+	strtab = ehdr + elf_shdr_get_sh_offset(class, shdr);
+	idx = index ? *index : 0;
+	if (!strtab || !name)
+		return 0;
+
+	ret = idx;
+	strcpy((strtab + idx), name);
+	idx += strlen(name) + 1;
+	if (index)
+		*index = idx;
+
+	return ret;
+}
+
 #endif /* REMOTEPROC_ELF_LOADER_H */

include/linux/remoteproc.h

@@ -657,6 +657,7 @@ int rproc_boot(struct rproc *rproc);
 void rproc_shutdown(struct rproc *rproc);
 int rproc_set_firmware(struct rproc *rproc, const char *fw_name);
 void rproc_report_crash(struct rproc *rproc, enum rproc_crash_type type);
+void rproc_coredump_using_sections(struct rproc *rproc);
 int rproc_coredump_add_segment(struct rproc *rproc, dma_addr_t da, size_t size);
 int rproc_coredump_add_custom_segment(struct rproc *rproc,
 				      dma_addr_t da, size_t size,