From d1e780507b6ed4b67e5e0e4e4b7c9796dc537210 Mon Sep 17 00:00:00 2001

From: Bhupesh Sharma <bhsharma@redhat.com>

Date: Tue, 6 Mar 2018 02:13:00 +0900

Subject: [PATCH 2/3] arm64: Add support to read symbols like _stext from

 '/proc/kallsyms'

On ARM64 platforms the VA_BITS supported by a linux kernel being run

can be selected by setting 'ARM64_VA_BITS_*' (see 'arch/arm64/Kconfig'

for details).

Now, to determine the 'info->page_offset' in arm64 makedumpfile

context ('arch/arm64.c') we need to determine the VA_BITS which was

selected by the underlying linux kernel.

There can be several ways to determine the VA_BITS, out of which

reading the '_stext' symbol and calculating the 'va_bits' using the

same is the simplest yet portable method.

For reading the kernel symbols like '_stext', we can read the

'/proc/kallsyms' file which contains these symbols and

works even in case of KASLR enabled arm64 kernels, as in those cases,

the '_stext' symbol will end up being randomized and hence

cannot be correctly read from the 'vmlinux' file.

Signed-off-by: Bhupesh Sharma <bhsharma@redhat.com>

---

 arch/arm64.c | 77 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++----

 1 file changed, 73 insertions(+), 4 deletions(-)

diff --git a/makedumpfile-1.6.2/arch/arm64.c b/makedumpfile-1.6.2/arch/arm64.c

index 25d7a1f4db98..c9dab677f2c9 100644

--- a/makedumpfile-1.6.2/arch/arm64.c

+++ b/makedumpfile-1.6.2/arch/arm64.c

@@ -48,6 +48,12 @@ static unsigned long kimage_voffset;

 #define SZ_64K			(64 * 1024)

 #define SZ_128M			(128 * 1024 * 1024)

+#define PAGE_OFFSET_36 ((0xffffffffffffffffUL) << 36)

+#define PAGE_OFFSET_39 ((0xffffffffffffffffUL) << 39)

+#define PAGE_OFFSET_42 ((0xffffffffffffffffUL) << 42)

+#define PAGE_OFFSET_47 ((0xffffffffffffffffUL) << 47)

+#define PAGE_OFFSET_48 ((0xffffffffffffffffUL) << 48)

+

 #define pgd_val(x)		((x).pgd)

 #define pud_val(x)		(pgd_val((x).pgd))

 #define pmd_val(x)		(pud_val((x).pud))

@@ -140,8 +146,6 @@ pud_offset(pgd_t *pgda, pgd_t *pgdv, unsigned long vaddr)

 static int calculate_plat_config(void)

 {

-	va_bits = NUMBER(VA_BITS);

-

 	/* derive pgtable_level as per arch/arm64/Kconfig */

 	if ((PAGESIZE() == SZ_16K && va_bits == 36) ||

 			(PAGESIZE() == SZ_64K && va_bits == 42)) {

@@ -177,6 +181,44 @@ get_phys_base_arm64(void)

 	return TRUE;

 }

+ulong

+get_stext_symbol(void)

+{

+	int found;

+	FILE *fp;

+	char buf[BUFSIZE];

+	char *kallsyms[MAXARGS];

+	ulong kallsym;

+

+	if (!file_exists("/proc/kallsyms")) {

+		ERRMSG("(%s) does not exist, will not be able to read symbols. %s\n",

+		       "/proc/kallsyms", strerror(errno));

+		return FALSE;

+	}

+

+	if ((fp = fopen("/proc/kallsyms", "r")) == NULL) {

+		ERRMSG("Cannot open (%s) to read symbols. %s\n",

+		       "/proc/kallsyms", strerror(errno));

+		return FALSE;

+	}

+

+	found = FALSE;

+	kallsym = 0;

+

+	while (!found && fgets(buf, BUFSIZE, fp) &&

+	      (parse_line(buf, kallsyms) == 3)) {

+		if (hexadecimal(kallsyms[0], 0) &&

+		    STREQ(kallsyms[2], "_stext")) {

+			kallsym = htol(kallsyms[0], 0);

+			found = TRUE;

+			break;

+		}

+	}

+	fclose(fp);

+

+	return(found ? kallsym : FALSE);

+}

+

 int

 get_machdep_info_arm64(void)

 {

@@ -188,12 +230,10 @@ get_machdep_info_arm64(void)

 	kimage_voffset = NUMBER(kimage_voffset);

 	info->max_physmem_bits = PHYS_MASK_SHIFT;

 	info->section_size_bits = SECTIONS_SIZE_BITS;

-	info->page_offset = 0xffffffffffffffffUL << (va_bits - 1);

 	DEBUG_MSG("kimage_voffset   : %lx\n", kimage_voffset);

 	DEBUG_MSG("max_physmem_bits : %lx\n", info->max_physmem_bits);

 	DEBUG_MSG("section_size_bits: %lx\n", info->section_size_bits);

-	DEBUG_MSG("page_offset      : %lx\n", info->page_offset);

 	return TRUE;

 }

@@ -219,6 +259,35 @@ get_xen_info_arm64(void)

 int

 get_versiondep_info_arm64(void)

 {

+	ulong _stext;

+

+	_stext = get_stext_symbol();

+	if (!_stext) {

+		ERRMSG("Can't get the symbol of _stext.\n");

+		return FALSE;

+	}

+

+	/* Derive va_bits as per arch/arm64/Kconfig */

+	if ((_stext & PAGE_OFFSET_36) == PAGE_OFFSET_36) {

+		va_bits = 36;

+	} else if ((_stext & PAGE_OFFSET_39) == PAGE_OFFSET_39) {

+		va_bits = 39;

+	} else if ((_stext & PAGE_OFFSET_42) == PAGE_OFFSET_42) {

+		va_bits = 42;

+	} else if ((_stext & PAGE_OFFSET_47) == PAGE_OFFSET_47) {

+		va_bits = 47;

+	} else if ((_stext & PAGE_OFFSET_48) == PAGE_OFFSET_48) {

+		va_bits = 48;

+	} else {

+		ERRMSG("Cannot find a proper _stext for calculating VA_BITS\n");

+		return FALSE;

+	}

+

+	info->page_offset = (0xffffffffffffffffUL) << (va_bits - 1);

+

+	DEBUG_MSG("page_offset=%lx, va_bits=%d\n", info->page_offset,

+			va_bits);

+

 	return TRUE;

 }

-- 

2.7.4