[POC 3/5] sframe: add new SFrame library

[Indu Bhagat <indu.bhagat@oracle.com>]

This patch adds an implementation to read SFrame stack trace data from
a .sframe section.  Some APIs are also provided to find stack tracing
information per PC, e.g., given a PC, find the SFrame FRE.

These routines are provided in the sframe_read.h and sframe_read.c.

This implmentation is malloc-free.

Signed-off-by: Indu Bhagat <indu.bhagat@oracle.com>
---
 lib/Makefile             |   1 +
 lib/sframe/Makefile      |   5 +
 lib/sframe/sframe.h      | 263 +++++++++++++++++++++
 lib/sframe/sframe_read.c | 498 +++++++++++++++++++++++++++++++++++++++
 lib/sframe/sframe_read.h |  75 ++++++
 5 files changed, 842 insertions(+)
 create mode 100644 lib/sframe/Makefile
 create mode 100644 lib/sframe/sframe.h
 create mode 100644 lib/sframe/sframe_read.c
 create mode 100644 lib/sframe/sframe_read.h

diff --git a/lib/Makefile b/lib/Makefile
index 876fcdeae34e..cb02d16dbffd 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -198,6 +198,7 @@ obj-$(CONFIG_ZSTD_COMPRESS) += zstd/
 obj-$(CONFIG_ZSTD_DECOMPRESS) += zstd/
 obj-$(CONFIG_XZ_DEC) += xz/
 obj-$(CONFIG_RAID6_PQ) += raid6/
+obj-$(CONFIG_USER_UNWINDER_SFRAME) += sframe/
 
 lib-$(CONFIG_DECOMPRESS_GZIP) += decompress_inflate.o
 lib-$(CONFIG_DECOMPRESS_BZIP2) += decompress_bunzip2.o
diff --git a/lib/sframe/Makefile b/lib/sframe/Makefile
new file mode 100644
index 000000000000..4e4291d9294f
--- /dev/null
+++ b/lib/sframe/Makefile
@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: GPL-2.0
+##################################
+obj-$(CONFIG_USER_UNWINDER_SFRAME) += sframe_read.o \
+
+CFLAGS_sframe_read.o += -I $(srctree)/lib/sframe/
diff --git a/lib/sframe/sframe.h b/lib/sframe/sframe.h
new file mode 100644
index 000000000000..b1290e92839a
--- /dev/null
+++ b/lib/sframe/sframe.h
@@ -0,0 +1,263 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (C) 2023, Oracle and/or its affiliates.
+ */
+
+#ifndef	SFRAME_H
+#define	SFRAME_H
+
+#include <linux/types.h>
+
+/* This file contains definitions for the SFrame stack tracing format, which is
+ * documented at https://sourceware.org/binutils/docs */
+
+#define SFRAME_VERSION_1	1
+#define SFRAME_MAGIC		0xdee2
+#define SFRAME_VERSION	SFRAME_VERSION_1
+
+/* Function Descriptor Entries are sorted on PC. */
+#define SFRAME_F_FDE_SORTED	0x1
+/* Frame-pointer based stack tracing. Defined, but not set. */
+#define SFRAME_F_FRAME_POINTER 0x2
+
+#define SFRAME_CFA_FIXED_FP_INVALID 0
+#define SFRAME_CFA_FIXED_RA_INVALID 0
+
+/* Supported ABIs/Arch. */
+#define SFRAME_ABI_AARCH64_ENDIAN_BIG      1 /* AARCH64 big endian. */
+#define SFRAME_ABI_AARCH64_ENDIAN_LITTLE   2 /* AARCH64 little endian. */
+#define SFRAME_ABI_AMD64_ENDIAN_LITTLE     3 /* AMD64 little endian. */
+
+/* SFrame FRE types. */
+#define SFRAME_FRE_TYPE_ADDR1	0
+#define SFRAME_FRE_TYPE_ADDR2	1
+#define SFRAME_FRE_TYPE_ADDR4	2
+
+/*
+ * SFrame Function Descriptor Entry types.
+ *
+ * The SFrame format has two possible representations for functions.  The
+ * choice of which type to use is made according to the instruction patterns
+ * in the relevant program stub.
+ */
+
+/* Unwinders perform a (PC >= FRE_START_ADDR) to look up a matching FRE. */
+#define SFRAME_FDE_TYPE_PCINC   0
+/*
+ * Unwinders perform a (PC & FRE_START_ADDR_AS_MASK >= FRE_START_ADDR_AS_MASK)
+ * to look up a matching FRE.  Typical usecases are pltN entries, trampolines
+ * etc.
+ */
+#define SFRAME_FDE_TYPE_PCMASK  1
+
+struct sframe_preamble
+{
+	/* Magic number (SFRAME_MAGIC). */
+	uint16_t magic;
+	/* Data format version number (SFRAME_VERSION). */
+	uint8_t version;
+	/* Various flags. */
+	uint8_t flags;
+} __packed;
+
+struct sframe_header
+{
+	struct sframe_preamble preamble;
+	/* Information about the arch (endianness) and ABI. */
+	uint8_t abi_arch;
+	/*
+	 * Offset for the Frame Pointer (FP) from CFA may be fixed for some
+	 * ABIs (e.g, in AMD64 when -fno-omit-frame-pointer is used).  When fixed,
+	 * this field specifies the fixed stack frame offset and the individual
+	 * FREs do not need to track it.  When not fixed, it is set to
+	 * SFRAME_CFA_FIXED_FP_INVALID, and the individual FREs may provide
+	 * the applicable stack frame offset, if any.
+	 */
+	int8_t cfa_fixed_fp_offset;
+	/*
+	 * Offset for the Return Address from CFA is fixed for some ABIs
+	 * (e.g., AMD64 has it as CFA-8).  When fixed, the header specifies the
+	 * fixed stack frame offset and the individual FREs do not track it.  When
+	 * not fixed, it is set to SFRAME_CFA_FIXED_RA_INVALID, and individual
+	 * FREs provide the applicable stack frame offset, if any.
+	 */
+	int8_t cfa_fixed_ra_offset;
+	/*
+	 * Number of bytes making up the auxiliary header, if any.
+	 * Some ABI/arch, in the future, may use this space for extending the
+	 * information in SFrame header.  Auxiliary header is contained in
+	 * bytes sequentially following the sframe_header.
+	 */
+	uint8_t auxhdr_len;
+	/* Number of SFrame FDEs in this SFrame section. */
+	uint32_t num_fdes;
+	/* Number of SFrame Frame Row Entries. */
+	uint32_t num_fres;
+	/* Number of bytes in the SFrame Frame Row Entry section. */
+	uint32_t fre_len;
+	/* Offset of SFrame Function Descriptor Entry section. */
+	uint32_t fdeoff;
+	/* Offset of SFrame Frame Row Entry section. */
+	uint32_t freoff;
+} __packed;
+
+#define SFRAME_V1_HDR_SIZE(sframe_hdr)	\
+  ((sizeof (struct sframe_header) + (sframe_hdr).auxhdr_len))
+
+/* Two possible keys for executable (instruction) pointers signing. */
+#define SFRAME_AARCH64_PAUTH_KEY_A    0 /* Key A. */
+#define SFRAME_AARCH64_PAUTH_KEY_B    1 /* Key B. */
+
+struct sframe_func_desc_entry
+{
+	/*
+	 * Function start address.  Encoded as a signed offset, relative to the
+	 * beginning of the current FDE.
+	 */
+	int32_t func_start_address;
+	/* Size of the function in bytes. */
+	uint32_t func_size;
+	/*
+	 * Offset of the first SFrame Frame Row Entry of the function, relative to the
+	 * beginning of the SFrame Frame Row Entry sub-section.
+	 */
+	uint32_t func_start_fre_off;
+	/* Number of frame row entries for the function. */
+	uint32_t func_num_fres;
+	/*
+	 * Additional information for deciphering the unwind information for the
+	 * function.
+	 *   - 4-bits: Identify the FRE type used for the function.
+	 *   - 1-bit: Identify the FDE type of the function - mask or inc.
+	 *   - 1-bit: PAC authorization A/B key (aarch64).
+	 *   - 2-bits: Unused.
+	 * --------------------------------------------------------------------------
+	 * |     Unused    |  PAC auth A/B key (aarch64) |  FDE type |   FRE type   |
+	 * |               |        Unused (amd64)       |           |              |
+	 * --------------------------------------------------------------------------
+	 * 8               6                             5           4              0
+	 */
+	uint8_t func_info;
+} __packed;
+
+/* Note: Set PAC auth key to SFRAME_AARCH64_PAUTH_KEY_A by default.  */
+#define SFRAME_V1_FUNC_INFO(fde_type, fre_enc_type) \
+  (((SFRAME_AARCH64_PAUTH_KEY_A & 0x1) << 5) | \
+   (((fde_type) & 0x1) << 4) | ((fre_enc_type) & 0xf))
+
+#define SFRAME_V1_FUNC_FRE_TYPE(data)	  ((data) & 0xf)
+#define SFRAME_V1_FUNC_FDE_TYPE(data)	  (((data) >> 4) & 0x1)
+#define SFRAME_V1_FUNC_PAUTH_KEY(data)	  (((data) >> 5) & 0x1)
+
+/*
+ * Size of stack frame offsets in an SFrame Frame Row Entry.  A single
+ * SFrame FRE has all offsets of the same size.  Offset size may vary
+ * across frame row entries.
+ */
+#define SFRAME_FRE_OFFSET_1B	  0
+#define SFRAME_FRE_OFFSET_2B	  1
+#define SFRAME_FRE_OFFSET_4B	  2
+
+/* An SFrame Frame Row Entry can be SP or FP based.  */
+#define SFRAME_BASE_REG_FP	0
+#define SFRAME_BASE_REG_SP	1
+
+/*
+ * The index at which a specific offset is presented in the variable length
+ * bytes of an FRE.
+ */
+#define SFRAME_FRE_CFA_OFFSET_IDX   0
+/*
+ * The RA stack offset, if present, will always be at index 1 in the variable
+ * length bytes of the FRE.
+ */
+#define SFRAME_FRE_RA_OFFSET_IDX    1
+/*
+ * The FP stack offset may appear at offset 1 or 2, depending on the ABI as RA
+ * may or may not be tracked.
+ */
+#define SFRAME_FRE_FP_OFFSET_IDX    2
+
+struct sframe_fre_info
+{
+  /* Information about
+   *   - 1 bit: base reg for CFA
+   *   - 4 bits: Number of offsets (N).  A value of upto 3 is allowed to track
+   *     all three of CFA, FP and RA (fixed implicit order).
+   *   - 2 bits: information about size of the offsets (S) in bytes.
+   *     Valid values are SFRAME_FRE_OFFSET_1B, SFRAME_FRE_OFFSET_2B,
+   *     SFRAME_FRE_OFFSET_4B
+   *   - 1 bit: Mangled RA state bit (aarch64 only).
+   * -----------------------------------------------------------------------------------
+   * | Mangled-RA (aarch64) |  Size of offsets   |   Number of offsets    |   base_reg |
+   * |  Unused (amd64)      |                    |                        |            |
+   * -----------------------------------------------------------------------------------
+   * 8                     7                    5                        1            0
+   */
+  uint8_t fre_info;
+};
+
+/* Macros to compose and decompose FRE info. */
+
+/* Note: Set mangled_ra_p to zero by default. */
+#define SFRAME_V1_FRE_INFO(base_reg_id, offset_num, offset_size) \
+  (((0 & 0x1) << 7) | (((offset_size) & 0x3) << 5) | \
+   (((offset_num) & 0xf) << 1) | ((base_reg_id) & 0x1))
+
+/* Set the mangled_ra_p bit as indicated. */
+#define SFRAME_V1_FRE_INFO_UPDATE_MANGLED_RA_P(mangled_ra_p, fre_info) \
+  ((((mangled_ra_p) & 0x1) << 7) | ((fre_info) & 0x7f))
+
+#define SFRAME_V1_FRE_CFA_BASE_REG_ID(data)	  ((data) & 0x1)
+#define SFRAME_V1_FRE_OFFSET_COUNT(data)	  (((data) >> 1) & 0xf)
+#define SFRAME_V1_FRE_OFFSET_SIZE(data)		  (((data) >> 5) & 0x3)
+#define SFRAME_V1_FRE_MANGLED_RA_P(data)	  (((data) >> 7) & 0x1)
+
+/* SFrame Frame Row Entry definitions. */
+
+/*
+ * Used when SFRAME_FRE_TYPE_ADDR1 is specified as FRE type.
+ * Upper limit of start address in sframe_frame_row_entry_addr1 if 0x100 (not
+ * inclusive).
+ */
+struct sframe_frame_row_entry_addr1
+{
+	/*
+	 * Start address of the frame row entry.  Encoded as an 1-byte unsigned
+	 * offset, relative to the start address of the function.
+	 */
+	uint8_t fre_start_ip_offset;
+	struct sframe_fre_info fre_info;
+} __packed;
+
+/*
+ * Used when SFRAME_FRE_TYPE_ADDR2 is specified as FRE type.
+ * Upper limit of start address in sframe_frame_row_entry_addr2 is 0x10000 (not
+ * inclusive).
+ */
+struct sframe_frame_row_entry_addr2
+{
+	/*
+	 * Start address of the frame row entry.  Encoded as an 2-byte unsigned
+	 * offset, relative to the start address of the function.
+	 */
+	uint16_t fre_start_ip_offset;
+	struct sframe_fre_info fre_info;
+} __packed;
+
+/*
+ * Used when SFRAME_FRE_TYPE_ADDR4 is specified as FRE type.
+ * Upper limit of start address in sframe_frame_row_entry_addr2
+ * is 0x100000000 (not inclusive).
+ */
+struct sframe_frame_row_entry_addr4
+{
+	/*
+	 * Start address of the frame row entry.  Encoded as a 4-byte unsigned
+	 * offset, relative to the start address of the function.
+	 */
+	uint32_t fre_start_ip_offset;
+	struct sframe_fre_info fre_info;
+} __packed;
+
+#endif	/* SFRAME_H */
diff --git a/lib/sframe/sframe_read.c b/lib/sframe/sframe_read.c
new file mode 100644
index 000000000000..9d6558d62c54
--- /dev/null
+++ b/lib/sframe/sframe_read.c
@@ -0,0 +1,498 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2023, Oracle and/or its affiliates.
+ */
+
+#include <linux/string.h>
+
+#include "sframe_read.h"
+
+struct sframe_sec {
+	/* SFrame header. */
+	struct sframe_header header;
+	/* SFrame Function Desc Entries. */
+	void *fdes;
+	/* SFrame Frame Row Entries. */
+	void *fres;
+	/* Number of bytes needed for SFrame FREs. */
+	uint32_t fre_nbytes;
+};
+
+static int sframe_set_errno(int *errp, int error)
+{
+	if (errp != NULL)
+		*errp = error;
+	return SFRAME_ERR;
+}
+
+static uint32_t sframe_sec_get_hdr_size(struct sframe_header *sfh)
+{
+	return SFRAME_V1_HDR_SIZE(*sfh);
+}
+
+static unsigned int sframe_fre_get_offset_count(unsigned char fre_info)
+{
+	return SFRAME_V1_FRE_OFFSET_COUNT(fre_info);
+}
+
+static unsigned int sframe_fre_get_offset_size(unsigned char fre_info)
+{
+	return SFRAME_V1_FRE_OFFSET_SIZE(fre_info);
+}
+
+static unsigned int sframe_get_fre_type(struct sframe_func_desc_entry *fdep)
+{
+	return (fdep) ? SFRAME_V1_FUNC_FRE_TYPE(fdep->func_info) : 0;
+}
+
+static unsigned int sframe_get_fde_type(struct sframe_func_desc_entry *fdep)
+{
+	return (fdep) ? SFRAME_V1_FUNC_FDE_TYPE(fdep->func_info) : 0;
+}
+
+static bool sframe_header_sanity_check_p(struct sframe_header *hp)
+{
+	unsigned char all_flags = SFRAME_F_FDE_SORTED | SFRAME_F_FRAME_POINTER;
+	/* Check that the preamble is valid. */
+	if ((hp->preamble.magic != SFRAME_MAGIC)
+	    || (hp->preamble.version != SFRAME_VERSION)
+	    || ((hp->preamble.flags | all_flags) != all_flags))
+		return false;
+
+	/* Check that the offsets are valid. */
+	if (hp->fdeoff > hp->freoff)
+		return false;
+
+	return true;
+}
+
+static bool sframe_fre_sanity_check_p(struct sframe_fre *frep)
+{
+	unsigned int offset_size, offset_cnt;
+
+	if (frep == NULL)
+		return false;
+
+	offset_size = sframe_fre_get_offset_size(frep->fre_info);
+
+	if (offset_size != SFRAME_FRE_OFFSET_1B
+	    && offset_size != SFRAME_FRE_OFFSET_2B
+	    && offset_size != SFRAME_FRE_OFFSET_4B)
+		return false;
+
+	offset_cnt = sframe_fre_get_offset_count(frep->fre_info);
+	if (offset_cnt > MAX_NUM_STACK_OFFSETS)
+		return false;
+
+	return true;
+}
+
+static int32_t sframe_get_fre_offset(struct sframe_fre *frep, uint32_t idx,
+				     int *errp)
+{
+	int offset_cnt, offset_size;
+
+	if (frep == NULL || !sframe_fre_sanity_check_p(frep))
+		return sframe_set_errno(errp, SFRAME_ERR_FRE_INVAL);
+
+	offset_cnt = sframe_fre_get_offset_count(frep->fre_info);
+	offset_size = sframe_fre_get_offset_size(frep->fre_info);
+
+	if (offset_cnt < idx + 1)
+		return sframe_set_errno(errp, SFRAME_ERR_FREOFFSET_NOPRESENT);
+
+	if (errp != NULL)
+		*errp = 0; /* Offset Valid. */
+
+	if (offset_size == SFRAME_FRE_OFFSET_1B) {
+		int8_t *stack_offsets = (int8_t *)frep->fre_offsets;
+		return stack_offsets[idx];
+	} else if (offset_size == SFRAME_FRE_OFFSET_2B) {
+		int16_t *stack_offsets = (int16_t *)frep->fre_offsets;
+		return stack_offsets[idx];
+	} else {
+		int32_t *stack_offsets = (int32_t *)frep->fre_offsets;
+		return stack_offsets[idx];
+	}
+}
+
+static struct sframe_header *sframe_sec_get_header(struct sframe_sec *sfsec)
+{
+	return sfsec ? &sfsec->header : NULL;
+}
+
+static int sframe_fre_copy(struct sframe_fre *dst,
+			   struct sframe_fre *src)
+{
+	if (dst == NULL || src == NULL)
+		return SFRAME_ERR;
+
+	memcpy(dst, src, sizeof(struct sframe_fre));
+	return 0;
+}
+
+static int sframe_decode_start_ip_offset(const char *fre_buf,
+					 uint32_t *start_ip_offset,
+					 unsigned int fre_type)
+{
+	uint32_t saddr = 0;
+
+	if (fre_type == SFRAME_FRE_TYPE_ADDR1) {
+		uint8_t *uc = (uint8_t *)fre_buf;
+		saddr = (uint32_t)*uc;
+	} else if (fre_type == SFRAME_FRE_TYPE_ADDR2) {
+		uint16_t *ust = (uint16_t *)fre_buf;
+		saddr = (uint32_t)*ust;
+	} else if (fre_type == SFRAME_FRE_TYPE_ADDR4) {
+		uint32_t *uit = (uint32_t *)fre_buf;
+		saddr = (uint32_t)*uit;
+	} else {
+		return SFRAME_ERR_INVAL;
+	}
+
+	*start_ip_offset = saddr;
+	return 0;
+}
+
+/* Get the total size in bytes for the stack offsets. */
+static size_t sframe_fre_stack_offsets_size(unsigned char fre_info)
+{
+	unsigned int offset_size, offset_cnt;
+
+	offset_size = sframe_fre_get_offset_size(fre_info);
+	offset_cnt = sframe_fre_get_offset_count(fre_info);
+
+	if (offset_size == SFRAME_FRE_OFFSET_2B
+	    || offset_size == SFRAME_FRE_OFFSET_4B)	/* 2 or 4 bytes. */
+		return (offset_cnt * (offset_size * 2));
+
+	return offset_cnt;
+}
+
+static size_t sframe_fre_get_start_address_tsize(unsigned int fre_type)
+{
+	/* Type size of the start_addr in an FRE. */
+	size_t saddr_tsize = 0;
+
+	switch (fre_type) {
+	case SFRAME_FRE_TYPE_ADDR1:
+		saddr_tsize = sizeof(uint8_t);
+		break;
+	case SFRAME_FRE_TYPE_ADDR2:
+		saddr_tsize = sizeof(uint16_t);
+		break;
+	case SFRAME_FRE_TYPE_ADDR4:
+		saddr_tsize = sizeof(uint32_t);
+		break;
+	default:
+		/* No other value is expected. */
+		break;
+	}
+	return saddr_tsize;
+}
+
+static size_t sframe_fre_vlen_size(struct sframe_fre *frep,
+				   unsigned int fre_type)
+{
+	unsigned char fre_info;
+	size_t ip_offset_tsize;
+
+	if (frep == NULL)
+		return 0;
+
+	fre_info = frep->fre_info;
+	ip_offset_tsize = sframe_fre_get_start_address_tsize(fre_type);
+
+	/*
+	 * An SFrame FRE is a variable length structure.  It includes the start
+	 * IP offset, FRE info field, and all trailing the stack offsets.
+	 */
+	return (ip_offset_tsize + sizeof(fre_info)
+		+ sframe_fre_stack_offsets_size(fre_info));
+}
+
+/*
+ * Read an SFrame FRE which starts at location FRE_BUF.  The function
+ * updates FRE_SIZE to the size of the FRE as stored in the binary format.
+ *
+ * Returns SFRAME_ERR if failure.
+ */
+static int sframe_sec_read_fre(const char *fre_buf, struct sframe_fre *frep,
+			       unsigned int fre_type, size_t *fre_size)
+{
+	void *stack_offsets;
+	size_t stack_offsets_sz;
+	size_t ip_offset_tsize;
+	size_t esz;
+
+	if (fre_buf == NULL || frep == NULL || fre_size == NULL)
+		return SFRAME_ERR_INVAL;
+
+	/* Copy over the FRE start address. */
+	sframe_decode_start_ip_offset(fre_buf, &frep->start_ip_offset,
+				      fre_type);
+
+	ip_offset_tsize = sframe_fre_get_start_address_tsize(fre_type);
+	/* PS: Note how this API works closely with SFrame binary format. */
+	frep->fre_info = *(unsigned char *)(fre_buf + ip_offset_tsize);
+
+	memset(frep->fre_offsets, 0, MAX_STACK_OFFSET_NBYTES);
+	/* Get stack offsets. */
+	stack_offsets_sz = sframe_fre_stack_offsets_size(frep->fre_info);
+	stack_offsets = ((unsigned char *)fre_buf + ip_offset_tsize
+			 + sizeof(frep->fre_info));
+	memcpy(frep->fre_offsets, stack_offsets, stack_offsets_sz);
+
+	esz = sframe_fre_vlen_size(frep, fre_type);
+	*fre_size = esz;
+
+	return 0;
+}
+
+static struct sframe_func_desc_entry *
+sframe_sec_find_fde(struct sframe_sec *sfsec, int32_t addr, int *errp)
+{
+	struct sframe_header *header;
+	struct sframe_func_desc_entry *fde;
+	int low, high, cnt;
+
+	if (sfsec == NULL) {
+		sframe_set_errno(errp, SFRAME_ERR_INVAL);
+		return NULL;
+	}
+
+	header = sframe_sec_get_header(sfsec);
+	if (header == NULL || header->num_fdes == 0 || sfsec->fdes == NULL) {
+		sframe_set_errno(errp, SFRAME_ERR_INIT_INVAL);
+		return NULL;
+	}
+	/*
+	 * Skip binary search if FDE sub-section is not sorted on PCs.  GNU ld
+	 * sorts the FDEs on start PC by default though.
+	 */
+	if ((header->preamble.flags & SFRAME_F_FDE_SORTED) == 0) {
+		sframe_set_errno(errp, SFRAME_ERR_FDE_NOTSORTED);
+		return NULL;
+	}
+
+	/* Find the FDE that may contain the addr. */
+	fde = (struct sframe_func_desc_entry *)sfsec->fdes;
+	low = 0;
+	high = header->num_fdes;
+	cnt = high;
+	while (low <= high) {
+		int mid = low + (high - low) / 2;
+
+		if (fde[mid].func_start_address == addr)
+			return fde + mid;
+
+		if (fde[mid].func_start_address < addr) {
+			if (mid == (cnt - 1))
+				return fde + (cnt - 1);
+			else if (fde[mid+1].func_start_address > addr)
+				return fde + mid;
+			low = mid + 1;
+		} else
+			high = mid - 1;
+	}
+
+	sframe_set_errno(errp, SFRAME_ERR_FDE_NOTFOUND);
+	return NULL;
+}
+
+static int8_t sframe_sec_get_fixed_fp_offset(struct sframe_sec *sfsec)
+{
+	struct sframe_header *header = sframe_sec_get_header(sfsec);
+	return header->cfa_fixed_fp_offset;
+}
+
+static int8_t sframe_sec_get_fixed_ra_offset(struct sframe_sec *sfsec)
+{
+	struct sframe_header *header = sframe_sec_get_header(sfsec);
+	return header->cfa_fixed_ra_offset;
+}
+
+size_t sframe_sec_sizeof(void)
+{
+	return sizeof (struct sframe_sec);
+}
+
+int sframe_sec_init(struct sframe_sec *sfsec, const char *sf_buf,
+		    size_t sf_size)
+{
+	char *frame_buf;
+	const struct sframe_preamble *preamble;
+	struct sframe_header *header;
+
+	if ((sf_buf == NULL) || (sf_size < sizeof(struct sframe_header)))
+		return SFRAME_ERR_INVAL;
+
+	/* Check for foreign endianness. */
+	preamble = (const struct sframe_preamble *) sf_buf;
+	if (preamble->magic != SFRAME_MAGIC)
+		return SFRAME_ERR_INVAL;
+
+	/* Reset the SFrame section object. */
+	memset(sfsec, 0, sizeof(struct sframe_sec));
+
+	frame_buf = (char *)sf_buf;
+
+	/* Initialize the reference to the SFrame header. */
+	sfsec->header = *(struct sframe_header *) frame_buf;
+	header = &sfsec->header;
+	if (!sframe_header_sanity_check_p(header))
+		return SFRAME_ERR_INVAL;
+
+	/* Initialize the referece to the SFrame FDE section. */
+	frame_buf += sframe_sec_get_hdr_size(header);
+	sfsec->fdes = frame_buf;
+
+	/* Initialize the reference to the the SFrame FRE section. */
+	frame_buf += (header->num_fdes * sizeof(struct sframe_func_desc_entry));
+	sfsec->fres = frame_buf;
+
+	sfsec->fre_nbytes = header->fre_len;
+
+	return 0;
+}
+
+/*
+ * Find the SFrame Frame Row Entry which contains the PC.
+ * Returns error code if failure.
+ */
+int sframe_sec_find_fre(struct sframe_sec *sfsec, int32_t pc,
+			struct sframe_fre *frep)
+{
+	struct sframe_func_desc_entry *fdep;
+	uint32_t start_address, i;
+	struct sframe_fre cur_fre, next_fre;
+	unsigned char *fres;
+	unsigned int fre_type, fde_type;
+	size_t esz;
+	int err = 0;
+	size_t size = 0;
+	/*
+	 * For regular FDEs(i.e. fde_type SFRAME_FDE_TYPE_PCINC),
+	 * where the start address in the FRE is an offset from start pc,
+	 * use a bitmask with all bits set so that none of the address bits are
+	 * ignored.  In this case, we need to return the FRE where
+	 * (PC >= FRE_START_ADDR).
+	 */
+	uint64_t bitmask = 0xffffffff;
+
+	if ((sfsec == NULL) || (frep == NULL))
+		return SFRAME_ERR_INVAL;
+
+	/* Find the FDE which contains the PC, then scan its FRE entries. */
+	fdep = sframe_sec_find_fde(sfsec, pc, &err);
+	if (fdep == NULL || sfsec->fres == NULL)
+		return SFRAME_ERR_INIT_INVAL;
+
+	fre_type = sframe_get_fre_type(fdep);
+	fde_type = sframe_get_fde_type(fdep);
+
+	/*
+	 * For FDEs for repetitive pattern of insns, we need to return the FRE
+	 * such that(PC & FRE_START_ADDR_AS_MASK >= FRE_START_ADDR_AS_MASK).
+	 * so, update the bitmask to the start address.
+	 */
+	/* FIXME - the bitmask. */
+	if (fde_type == SFRAME_FDE_TYPE_PCMASK)
+		bitmask = 0xff;
+
+	fres = (unsigned char *)sfsec->fres + fdep->func_start_fre_off;
+	for (i = 0; i < fdep->func_num_fres; i++) {
+		err = sframe_sec_read_fre((const char *)fres, &next_fre,
+					  fre_type, &esz);
+		start_address = next_fre.start_ip_offset;
+
+		if (((fdep->func_start_address
+		      + (int32_t)start_address) & bitmask) <= (pc & bitmask)) {
+			sframe_fre_copy(&cur_fre, &next_fre);
+
+			/* Get the next FRE in sequence. */
+			if (i < fdep->func_num_fres - 1) {
+				fres += esz;
+				err = sframe_sec_read_fre((const char *)fres,
+							  &next_fre,
+							  fre_type, &esz);
+
+				/* Sanity check the next FRE. */
+				if (!sframe_fre_sanity_check_p(&next_fre))
+					return SFRAME_ERR_FRE_INVAL;
+
+				size = next_fre.start_ip_offset;
+			} else {
+				size = fdep->func_size;
+			}
+
+			if (((fdep->func_start_address
+			      + (int32_t)size) & bitmask) > (pc & bitmask)) {
+				/* Cur FRE contains the PC, return it. */
+				sframe_fre_copy(frep, &cur_fre);
+				return 0;
+			}
+		} else {
+			return SFRAME_ERR_FRE_INVAL;
+		}
+	}
+	return SFRAME_ERR_FDE_INVAL;
+}
+
+unsigned int sframe_fre_get_base_reg_id(struct sframe_fre *frep,
+					int *errp)
+{
+	if (!frep)
+		return sframe_set_errno(errp, SFRAME_ERR_FRE_INVAL);
+
+	return SFRAME_V1_FRE_CFA_BASE_REG_ID(frep->fre_info);
+}
+
+int32_t sframe_fre_get_cfa_offset(struct sframe_sec *sfsec __always_unused,
+				  struct sframe_fre *frep, int *errp)
+{
+	return sframe_get_fre_offset(frep, SFRAME_FRE_CFA_OFFSET_IDX, errp);
+}
+
+int32_t sframe_fre_get_fp_offset(struct sframe_sec *sfsec,
+				 struct sframe_fre *frep, int *errp)
+{
+	uint32_t fp_offset_idx = 0;
+	int8_t fp_offset = sframe_sec_get_fixed_fp_offset(sfsec);
+	/*
+	 * If the FP offset is not being tracked, return the fixed FP offset
+	 * from the SFrame header.
+	 */
+	if (fp_offset != SFRAME_CFA_FIXED_FP_INVALID) {
+		*errp = 0;
+		return fp_offset;
+	}
+
+	/*
+	 * In some ABIs, the stack offset to recover RA (using the CFA) from is
+	 * fixed (like AMD64).  In such cases, the stack offset to recover FP
+	 * will appear at the second index.
+	 */
+	fp_offset_idx = ((sframe_sec_get_fixed_ra_offset(sfsec)
+			  != SFRAME_CFA_FIXED_RA_INVALID)
+			 ? SFRAME_FRE_RA_OFFSET_IDX
+			 : SFRAME_FRE_FP_OFFSET_IDX);
+	return sframe_get_fre_offset(frep, fp_offset_idx, errp);
+}
+
+int32_t sframe_fre_get_ra_offset(struct sframe_sec *sfsec,
+				 struct sframe_fre *frep, int *errp)
+{
+	int8_t ra_offset = sframe_sec_get_fixed_ra_offset(sfsec);
+	/*
+	 * If the RA offset was not being tracked, return the fixed RA offset
+	 * from the SFrame header.
+	 */
+	if (ra_offset != SFRAME_CFA_FIXED_RA_INVALID) {
+		*errp = 0;
+		return ra_offset;
+	}
+
+	/* Otherwise, get the RA offset from the FRE. */
+	return sframe_get_fre_offset(frep, SFRAME_FRE_RA_OFFSET_IDX, errp);
+}
diff --git a/lib/sframe/sframe_read.h b/lib/sframe/sframe_read.h
new file mode 100644
index 000000000000..6632fb76d8b1
--- /dev/null
+++ b/lib/sframe/sframe_read.h
@@ -0,0 +1,75 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (C) 2023, Oracle and/or its affiliates.
+ */
+
+#ifndef SFRAME_READ_H
+#define SFRAME_READ_H
+
+#include <linux/types.h>
+
+#include "sframe.h"
+
+struct sframe_sec;
+
+#define MAX_NUM_STACK_OFFSETS 3
+
+#define MAX_STACK_OFFSET_NBYTES \
+  ((SFRAME_FRE_OFFSET_4B * 2 * MAX_NUM_STACK_OFFSETS))
+
+/*
+ * SFrame Frame Row Entry for the SFrame reader.
+ * Providing such an abstraction helps decouple stack tracer from the
+ * binary format representation of the same.
+ */
+struct sframe_fre {
+	uint32_t start_ip_offset;
+	unsigned char fre_offsets[MAX_STACK_OFFSET_NBYTES];
+	unsigned char fre_info;
+};
+
+#define SFRAME_ERR ((int) -1)
+
+/* SFrame version not supported. */
+#define SFRAME_ERR_VERSION_INVAL	(-2000)
+/* Corrupt SFrame. */
+#define SFRAME_ERR_INVAL		(-2001)
+/* SFrame Section Initialization Error. */
+#define SFRAME_ERR_INIT_INVAL		(-2002)
+/* Corrupt FDE. */
+#define SFRAME_ERR_FDE_INVAL		(-2003)
+/* Corrupt FRE. */
+#define SFRAME_ERR_FRE_INVAL		(-2004)
+/* FDE not found. */
+#define SFRAME_ERR_FDE_NOTFOUND		(-2005)
+/* FDEs not sorted. */
+#define SFRAME_ERR_FDE_NOTSORTED	(-2006)
+/* FRE not found. */
+#define SFRAME_ERR_FRE_NOTFOUND		(-2007)
+/* FRE offset not present. */
+#define SFRAME_ERR_FREOFFSET_NOPRESENT	(-2008)
+
+extern size_t sframe_sec_sizeof(void);
+
+extern int sframe_sec_init(struct sframe_sec *sfsec, const char *cf_buf,
+			   size_t cf_size);
+
+extern int sframe_sec_find_fre(struct sframe_sec *ctx, int32_t pc,
+			   struct sframe_fre *frep);
+
+extern unsigned int sframe_fre_get_base_reg_id(struct sframe_fre *fre,
+					       int *errp);
+extern int32_t sframe_fre_get_cfa_offset(struct sframe_sec *dtcx,
+					 struct sframe_fre *fre,
+					 int *errp);
+extern int32_t sframe_fre_get_fp_offset(struct sframe_sec *sfsec,
+					struct sframe_fre *fre,
+					int *errp);
+extern int32_t sframe_fre_get_ra_offset(struct sframe_sec *sfsec,
+					struct sframe_fre *fre,
+					int *errp);
+extern bool sframe_fre_get_ra_mangled_p(struct sframe_sec *sfsec,
+					struct sframe_fre *fre,
+					int *errp);
+
+#endif /* SFRAME_READ_H */
-- 
2.39.2