[PATCH] makedumpfile: readpage_elf: handle 0-pages not stored in the ELF file

[Ivan Delalande]

Handle pages filled with zeros that are not stored in the ELF file
directly, but have addresses between p_filesz and p_memsz of a segment.

This allows makedumpfile to dump-dmesg from a previously makedumpfile-ed
vmcore where all 0-pages were excluded (dump_level & 1) for example.

Signed-off-by: Ivan Delalande <colona at arista.com>
---
 elf_info.c     | 22 ++++++++++++++++++++++
 elf_info.h     |  1 +
 makedumpfile.c | 16 ++++++++++++++++
 3 files changed, 39 insertions(+)

diff --git a/elf_info.c b/elf_info.c
index 8bce942..340e885 100644
--- a/elf_info.c
+++ b/elf_info.c
@@ -42,6 +42,7 @@ struct pt_load_segment {
 	unsigned long long	phys_end;
 	unsigned long long	virt_start;
 	unsigned long long	virt_end;
+	size_t			mem_size;
 };
 
 static int			nr_cpus;             /* number of cpu */
@@ -166,6 +167,7 @@ dump_Elf_load(Elf64_Phdr *prog, int num_load)
 	pls->virt_start  = prog->p_vaddr;
 	pls->virt_end    = pls->virt_start + prog->p_filesz;
 	pls->file_offset = prog->p_offset;
+	pls->mem_size    = prog->p_memsz;
 
 	DEBUG_MSG("LOAD (%d)\n", num_load);
 	DEBUG_MSG("  phys_start : %llx\n", pls->phys_start);
@@ -584,6 +586,26 @@ offset_to_pt_load_end(off_t offset)
 }
 
 /*
+ * Return true if a page is in the zone between p_filesz and p_memsz of a
+ * segment, which is a page filled with zero and not stored in the ELF file.
+ */
+int
+paddr_is_null(unsigned long long paddr)
+{
+	int i;
+	struct pt_load_segment *pls;
+
+	for (i = 0; i < num_pt_loads; i++) {
+		pls = &pt_loads[i];
+		if ((paddr >= pls->phys_start)
+		    && (paddr + info->page_size
+			<= pls->phys_start + pls->mem_size))
+			return TRUE;
+	}
+	return FALSE;
+}
+
+/*
  * Judge whether the page is fractional or not.
  */
 int
diff --git a/elf_info.h b/elf_info.h
index e712253..4823311 100644
--- a/elf_info.h
+++ b/elf_info.h
@@ -36,6 +36,7 @@ unsigned long long page_head_to_phys_start(unsigned long long head_paddr);
 unsigned long long page_head_to_phys_end(unsigned long long head_paddr);
 off_t offset_to_pt_load_start(off_t offset);
 off_t offset_to_pt_load_end(off_t offset);
+int paddr_is_null(unsigned long long paddr);
 unsigned long long vaddr_to_paddr_general(unsigned long long vaddr);
 off_t vaddr_to_offset_slow(int fd, char *filename, unsigned long long vaddr);
 unsigned long long get_max_paddr(void);
diff --git a/makedumpfile.c b/makedumpfile.c
index fa0b779..120bfdc 100644
--- a/makedumpfile.c
+++ b/makedumpfile.c
@@ -654,6 +654,14 @@ readpage_elf(unsigned long long paddr, void *bufptr)
 	phys_end = paddr + info->page_size;
 
 	/*
+	 * Check the 0-filled pages that are not in the ELF file.
+	 */
+	if (!offset1 && !offset2 && paddr_is_null(paddr)) {
+		memset(bufptr, 0, info->page_size);
+		return TRUE;
+	}
+
+	/*
 	 * Check the case phys_start isn't aligned by page size like below:
 	 *
 	 *                           phys_start
@@ -728,6 +736,14 @@ readpage_elf_parallel(int fd_memory, unsigned long long paddr, void *bufptr)
 	phys_end = paddr + info->page_size;
 
 	/*
+	 * Check the 0-filled pages that are not in the ELF file.
+	 */
+	if (!offset1 && !offset2 && paddr_is_null(paddr)) {
+		memset(bufptr, 0, info->page_size);
+		return TRUE;
+	}
+
+	/*
 	 * Check the case phys_start isn't aligned by page size like below:
 	 *
 	 *                           phys_start
-- 
2.7.0

-- 
Ivan "Colona" Delalande
Arista Networks