[RFC PATCH v3 1/2] s390: Initial support to generate .sframe from CFI directives in assembler

[Jens Remus <jremus@linux.ibm.com>]

This introduces initial support to generate .sframe from CFI directives
in assembler on s390x. Due to the following SFrame limitations it is
incomplete and does not work for most real-world applications (i.e.
generation of SFrame FDE is skipped):

- SFrame FP/RA tracking assumes the register contents to be saved on
  the stack (i.e. .cfi_offset). It does not support FP/RA register
  contents being saved in other registers (i.e. .cfi_register). GCC
  on s390x can be observed to save the FP/RA register contents in
  floating-point registers, but only in leaf functions.

- SFrame assumes a static FP register number. The s390x ELF ABI [1]
  does not specify any FP register number. GCC and clang on s390x
  usually use register 11 as frame pointer.
  GCC on s390x can also be observed to use register 14 (e.g. binutils
  and glibc builds) in the stack clash protector in the funcion
  prologue.
  glibc on s390x contains hand-written assembler code that uses
  register 12 for the frame pointer.

This s390x support is largely based on the AArch64 support from commit
b52c4ee46657 ("gas: generate .sframe from CFI directives").

SFrame ABI/arch identifier SFRAME_ABI_S390_ENDIAN_BIG is introduced
for s390 and added to the SFrame specification.

According to the s390x ELF ABI [1] the following calling conventions
are used on s390x architecture:
- Register 15 is used as stack pointer (SP). The CFA is initially
  located at offset +160 from the SP.
- Register 14 is used as return address (RA).
- There is no dedicated frame pointer. GCC and LLVM currently use
  register 11 as frame pointer.

The s390x ELF ABI [1] standard stack frame layout has the following
conventions:
- The return address (RA, r15) may be saved at offset -40 from the
  CFA. Unlike x86 AMD64 architecture it is not necessarily saved on
  the stack. Also compilers may use a non-standard stack frame layout,
  such as but not limited to GCC with option -mpacked-stack.
  Therefore SFrame RA tracking is used.
- The potential frame pointer (FP, r11) may be saved at offset -72
  from the CFA. It is not necessarily saved on the stack and compilers
  may use a non-standard stack frame layout (see above).
  Therefore SFrame FP tracking is used.

Support for SFrame is only enabled for z/Architecture (s390x) with
64-bit architecture mode. It is disabled for 32-bit architecture mode
and ESA/390 (s390).

Add s390-specific SFrame test cases. As for the error test cases add
ones that use a non-default frame pointer (FP) register number and ones
that save the return address (RA) in a non-default RA register number.

[1] ELF ABI s390x Supplement:
    https://github.com/IBM/s390x-abi/releases
[2] ELF ABI s390 Supplement:
    https://refspecs.linuxfoundation.org/ELF/zSeries/lzsabi0_s390.html
    https://refspecs.linuxfoundation.org/ELF/zSeries/lzsabi0_s390.pdf

include/
	* sframe.h (SFRAME_ABI_S390_ENDIAN_BIG): Define SFrame ABI/arch
	identifier for s390x. Reference s390x architecture in comments.

libsframe/
	* doc/sframe-spec.texi: Document SFrame ABI/arch identifier for
	s390x and reference s390x architecture.

gas/
	* config/tc-s390.h: s390x support to generate .sframe from CFI
	directives in assembler.
	* config/tc-s390.c: Likewise.
	* gen-sframe.c: Reference s390x architecture in comments.

gas/testsuite/
	* gas/cfi-sframe/cfi-sframe.exp: Enable common SFrame test cases
	for s390x. Add s390-specific SFrame test cases.
	* gas/cfi-sframe/cfi-sframe-s390-1.s: New s390-specific SFrame
	test case.
	* gas/cfi-sframe/cfi-sframe-s390-1.d: Likewise.
	* gas/cfi-sframe/cfi-sframe-s390-2.s: Likewise.
	* gas/cfi-sframe/cfi-sframe-s390-2.d: Likewise.
	* gas/cfi-sframe/cfi-sframe-s390-err-1.s: New s390-specific
	SFrame error test case that uses a non-default register number
	for the frame pointer.
	* gas/cfi-sframe/cfi-sframe-s390-err-1.d: Likewise.
	* gas/cfi-sframe/cfi-sframe-s390-err-2.s: Likewise.
	* gas/cfi-sframe/cfi-sframe-s390-err-2.d: Likewise.
	* gas/cfi-sframe/cfi-sframe-s390-err-3.s: New s390-specific
	SFrame error test case that uses a non-default register number
	to save the return address.
	* gas/cfi-sframe/cfi-sframe-s390-err-3.d: Likewise.
	* gas/cfi-sframe/cfi-sframe-s390-err-4.s: New s390-specific
	SFrame error test case that uses a non-default return column
	(return address) register number.
	* gas/cfi-sframe/cfi-sframe-s390-err-4.d: Likewise.
	* gas/cfi-sframe/cfi-sframe-s390-err-5.s: New s390-specific
	SFrame error test case for FP without RA on stack.
	* gas/cfi-sframe/cfi-sframe-s390-err-5.d: Likewise.

Reviewed-by: Andreas Krebbel <krebbel@linux.ibm.com>
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---

Notes (jremus):
    Changes v2 -> v3:
    - Update error test cases to changed SFrame warning message texts from
      patch "gas: User readable warnings if SFrame FDE is not generated".
    - New error test case 5 where FP is saved on stack while RA is not.
    - Updated the following notes.
    
    The SFrame support for s390x provided by this patch still has some open
    issues, which need to be addressed. Any ideas or assistance to overcome
    the SFrame limitations listed in the commit description are very
    welcome.
    
    Based on Indus suggestions in the discussion of v2 the following
    approach seems most promising (details follow below):
    - Enhance SFrame to represent FP without RA on stack.
    - Enhance SFrame to represent FP/RA-register saved in FPR-register
      (.cfi_register) on s390x only for compiler-generated leaf functions.
    
    SFrame related warnings from v3 test builds:
    
    Note that the increase in ".cfi_register specifying FP" (v2 -> v3) is
    due to no longer skipping FDE for ".cfi_register specifying SP" in v3.
    Previously some FDEs were skipped for the latter reason, which did not
    surface the former.
    Also note that "FP without RA on stack" is new in v3. I will send RFC
    patches to enable SFrame to represent this case in two flavors
    separately.
    
    Example #1: Warnings when compiling binutils with SFrame
    
    $ ../configure CC="gcc -B$HOME/temp/binutils-sframe/bin -Wa,--gsframe" \
      CXX="g++ -B$HOME/temp/binutils-sframe/bin -Wa,--gsframe" \
      --prefix=$HOME/temp/binutils-sframe
    $ make -j $(nproc) 2>&1 | tee make.log
    $ grep --only-matching "Warning:.*" make.log | sort | uniq -c
          1 Warning: skipping SFrame FDE due to .cfi_def_cfa defining
            non-SP/FP register 14 as CFA base register
        234 Warning: skipping SFrame FDE due to .cfi_register specifying FP
            register
          1 Warning: skipping SFrame FDE due to FP without RA on stack
    
    Example #2: Warnings when compiling glibc with SFrame
    
    $ ../configure CC="gcc -B$HOME/temp/binutils-sframe/bin -Wa,--gsframe" \
      CXX="g++ -B$HOME/temp/binutils-sframe/bin -Wa,--gsframe" \
      --prefix=$HOME/temp/glibc-sframe
    $ make -j $(nproc) 2>&1 | tee make.log
    $ grep --only-matching "Warning:.*" make.log | sort | uniq -c
          7 Warning: skipping SFrame FDE due to .cfi_def_cfa defining
            non-SP/FP register 14 as CFA base register
          2 Warning: skipping SFrame FDE due to .cfi_def_cfa_register
            defining non-SP/FP register 12 as CFA base register
        310 Warning: skipping SFrame FDE due to .cfi_register specifying FP
            register
          2 Warning: skipping SFrame FDE due to DWARF CFI op CFI_escape
            (0x103)
        180 Warning: skipping SFrame FDE due to FP without RA on stack
          2 Warning: skipping SFrame FDE due to non-default return-address
            register 0
    
    .cfi_def_cfa 14, ... originates from GCC generated prologue code, which
    uses register %r14 as frame-pointer (FP) register in the stack clash
    protector. GCC could potentially be changed to use register %r11 as FP
    register in this case.
    
    .cfi_def_cfa_register 12 originates from hand-written assembler code
    sysdeps/s390/s390-64/dl-trampoline.S, which uses register %r12 as frame
    pointer (FP).
    
    .cfi_return_column 0 and .cfi_escape both originate from hand-written
    assembler code sysdeps/s390/s390-64/s390x-mcount.S, which is compiled
    twice (with and without -DSHARED).
    mcount/fentry may only use registers that, according to the s390x ABI,
    are volatile (i.e. not saved or reserved) and do not have any role
    (e.g. argument, stack pointer, return address). This boils down to
    registers %r0 and %r1. Register %r0 is used as "return register" to
    branch to the function actually called. Register %r1 is used as temp.
    
    - .cfi_escape 0x14, 0x15, 0x14: Is used to code
      ".cfi_val_offset r15, -160", which would require binutils 2.28+ (glibc
      currently supports a minimum binutils 2.25). This CFI directive states
      that the contents of register %r15 are CFA-160 (not to be confused
      with saved at CFA-160).
      This specific warning in the build of glibc on s390x can be ignored,
      as ".cfi_val_offset <SP-register>, ..." can be ignored. The reason is
      that SFrame does not track the SP (on stack, in a register, as a CFA
      offset). Instead the SP value at entry can be computed from the CFA
      tracking information (see description of patch "gas: Don't skip SFrame
      FDE if .cfi_register specifies SP register") for details.
    
    - .cfi_return_column 0: See v2 comments below for details.
    
    .cfi_register 11, <FPR-reg> originates from GCC generated prologue code,
    which may save the frame-pointer (FP) register %r11 in a floating-point
    register (FPR), but only in leaf functions.
    SFrame could be enhanced to represent .cfi_register <FP|RA-reg> for
    compiler-generated leaf functions on s390x. I have a hack, which uses
    the LSB (lowest significant bit) of the FP/RA offset to indicate that
    the offset value is not an offset, but a DWARF register number shifted
    to the left by one. The LSB can be used as indication, as CFA offsets
    must be a multiple of the data-alignment factor -8 on s390x. In DWARF
    CFI any CFA offsets are actually encoded as factored offsets using this
    architecture-dependent data-alignment factor. This is only an option,
    unless SFrame would take the opportunity to do the same and store any
    CFA offsets as factored offsets and save the architecture-dependent
    data-alignment factor in the SFrame Header.
    
    "FP without RA on stack" currently cannot be represented by SFrame. I
    reviewed several of the reported instances. All of them were for GCC
    generated code for variadic functions (taking a variable number of
    arguments). GCC saves all unused argument registers, which are
    potentially part of the variable argument list (starting somewhere
    between %r2 and %r6), as well as any registers required to be saved on
    the stack. For that purpose it uses a single STM (Store Multiple)
    instruction, whose range then includes includes the FP register %r11
    due to the need to save RA register %r14, if a function call can occur
    required. For return it then only restores the RA register %r14 and SP
    register %r15, since it did not modify the FP register %r11.
    Note that another source for "FP without RA on stack" is GCC option
    "-mpreserve-args". In a test build of glibc their number increases
    from 180 to 548.
    
    SFrame related warnings from v2 test builds for reference:
    
    Example #1: Warnings when compiling binutils with SFrame
    
    $ ../configure CC="gcc -B$HOME/temp/binutils-gcc/bin -Wa,--gsframe" \
      CXX="g++ -B$HOME/temp/binutils-gcc/bin -Wa,--gsframe" \
      --prefix=$HOME/temp/binutils-sframe
    $ make -j $(nprocs) 2>&1 | tee make.log
    $ grep --only-matching "Warning:.*" make.log | sort | uniq -c
          1 Warning: skipping SFrame FDE due to .cfi_def_cfa specifying CFA
            base register other than SP or FP (14 instead of 15 or 11)
        205 Warning: skipping SFrame FDE due to .cfi_register specifying FP
            register (11)
         56 Warning: skipping SFrame FDE due to .cfi_register specifying SP
            register (15)
    
    Example #2: Warnings when compiling glibc with SFrame
    
    $ ../configure CC="gcc -B$HOME/temp/binutils-sframe/bin -Wa,--gsframe" \
      CXX="g++ -B$HOME/temp/binutils-sframe/bin -Wa,--gsframe" \
      --prefix=$HOME/temp/glibc-sframe
    $ make -j $(nprocs) 2>&1 | tee make.log
    $ grep --only-matching "Warning:.*" make.log | sort | uniq -c
          2 Warning: skipping SFrame FDE due to .cfi_def_cfa_register
            specifying CFA base register other than SP or FP (12 instead of
            15 or 11)
          7 Warning: skipping SFrame FDE due to .cfi_def_cfa specifying CFA
            base register other than SP or FP (14 instead of 15 or 11)
        225 Warning: skipping SFrame FDE due to .cfi_register specifying FP
            register (11)
        187 Warning: skipping SFrame FDE due to .cfi_register specifying SP
            register (15)
          2 Warning: skipping SFrame FDE due to DWARF CFI op CFI_escape
            (0x103)
          2 Warning: skipping SFrame FDE due to non-default DWARF return
            column (0 instead of 14)
    
    .cfi_def_cfa 14, ... originates from GCC generated code, which uses
    register %r14 as frame pointer (FP).
    
    .cfi_def_cfa_register 12 originates from hand-written assembler code
    sysdeps/s390/s390-64/dl-trampoline.S, which uses register %r12 as frame
    pointer (FP).
    
    .cfi_return_column 0 and .cfi_escape both originate from hand-written
    assembler code sysdeps/s390/s390-64/s390x-mcount.S, which is compiled
    twice (with and without -DSHARED).
    
    - .cfi_escape 0x14, 0x15, 0x14: Is used to code
      ".cfi_val_offset r15, -160", which would require binutils 2.28+ (glibc
      currently supports a minimum binutils 2.25). This CFI directive states
      that the contents of register %r15 are CFA-160 (not to be confused
      with saved at CFA-160).
    
    - .cfi_return_column 0: The following comment explains why register %r0
      contains the return address:
    
      "The _mcount implementation now has to call __mcount_internal with the
      address of .LP0 as first parameter and the return address as second
      parameter. &.LP0 was loaded to %r1 and the return address is in %r14.
      _mcount may not modify any register.
    
      Alternatively, at the start of each function __fentry__ is called
      using a single
    
              brasl  0,__fentry__
    
      instruction.  In this case %r0 points to the callee, and %r14 points
      to the caller.  These values need to be passed to __mcount_internal
      using the same sequence as for _mcount, so the code below is shared
      between both functions.
      The only major difference is that __fentry__ cannot return through
      %r0, in which the return address is located, because br instruction
      is a no-op with this register.  Therefore %r1, which is clobbered by
      the PLT anyway, is used."
    
      Excerpt of the relevant glibc source code:
    
              .globl C_SYMBOL_NAME(MCOUNT_SYMBOL)
              .type C_SYMBOL_NAME(MCOUNT_SYMBOL), @function
              cfi_startproc
              .align ALIGNARG(4)
      C_LABEL(MCOUNT_SYMBOL)
              cfi_return_column (glue(r, MCOUNT_CALLEE_REG))
              /* Save the caller-clobbered registers.  */
              aghi  %r15,-224
              cfi_adjust_cfa_offset (224)
              /* binutils 2.28+: .cfi_val_offset r15, -160 */
              .cfi_escape \
                      /* DW_CFA_val_offset */ 0x14, \
                      /* r15 */               0x0f, \
                      /* scaled offset */     0x14
              stmg  %r14,%r5,160(%r15)
    
              cfi_offset (r14, -224)
              cfi_offset (r0, -224+16)
      ...

 gas/config/tc-s390.c                          | 55 +++++++++++++++++++
 gas/config/tc-s390.h                          | 31 +++++++++++
 gas/gen-sframe.c                              |  2 +-
 .../gas/cfi-sframe/cfi-sframe-s390-1.d        | 23 ++++++++
 .../gas/cfi-sframe/cfi-sframe-s390-1.s        | 37 +++++++++++++
 .../gas/cfi-sframe/cfi-sframe-s390-2.d        | 23 ++++++++
 .../gas/cfi-sframe/cfi-sframe-s390-2.s        | 37 +++++++++++++
 .../gas/cfi-sframe/cfi-sframe-s390-err-1.d    | 15 +++++
 .../gas/cfi-sframe/cfi-sframe-s390-err-1.s    | 37 +++++++++++++
 .../gas/cfi-sframe/cfi-sframe-s390-err-2.d    | 15 +++++
 .../gas/cfi-sframe/cfi-sframe-s390-err-2.s    | 37 +++++++++++++
 .../gas/cfi-sframe/cfi-sframe-s390-err-3.d    | 15 +++++
 .../gas/cfi-sframe/cfi-sframe-s390-err-3.s    |  6 ++
 .../gas/cfi-sframe/cfi-sframe-s390-err-4.d    | 15 +++++
 .../gas/cfi-sframe/cfi-sframe-s390-err-4.s    |  5 ++
 .../gas/cfi-sframe/cfi-sframe-s390-err-5.d    | 15 +++++
 .../gas/cfi-sframe/cfi-sframe-s390-err-5.s    | 22 ++++++++
 gas/testsuite/gas/cfi-sframe/cfi-sframe.exp   | 14 ++++-
 include/sframe.h                              |  7 ++-
 libsframe/doc/sframe-spec.texi                |  8 ++-
 20 files changed, 412 insertions(+), 7 deletions(-)
 create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-1.d
 create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-1.s
 create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-2.d
 create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-2.s
 create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-1.d
 create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-1.s
 create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-2.d
 create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-2.s
 create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-3.d
 create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-3.s
 create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-4.d
 create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-4.s
 create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-5.d
 create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-5.s

diff --git a/gas/config/tc-s390.c b/gas/config/tc-s390.c
index 659c6af392bd..1f8b67adbdea 100644
--- a/gas/config/tc-s390.c
+++ b/gas/config/tc-s390.c
@@ -24,6 +24,8 @@
 #include "subsegs.h"
 #include "dwarf2dbg.h"
 #include "dw2gencfi.h"
+#include "sframe.h"
+#include "gen-sframe.h"
 
 #include "opcode/s390.h"
 #include "elf/s390.h"
@@ -97,6 +99,17 @@ const char FLT_CHARS[] = "dD";
 /* The dwarf2 data alignment, adjusted for 32 or 64 bit.  */
 int s390_cie_data_alignment;
 
+/* Register numbers used for SFrame stack trace info.  */
+
+/* Stack-pointer DWARF register number according to s390x ELF ABI.  */
+unsigned int s390_sframe_cfa_sp_reg = 15;
+
+/* Frame-pointer DWARF register number accoring to s390x GCC/LLVM convention.  */
+unsigned int s390_sframe_cfa_fp_reg = 11;
+
+/* Return-address DWARF register number according to s390x ELF ABI.  */
+unsigned int s390_sframe_cfa_ra_reg = DWARF2_DEFAULT_RETURN_COLUMN;
+
 /* The target specific pseudo-ops which we support.  */
 
 /* Define the prototypes for the pseudo-ops */
@@ -2860,6 +2873,48 @@ tc_s390_regname_to_dw2regnum (char *regname)
   return regnum;
 }
 
+/* Whether SFrame stack trace info is supported.  */
+
+bool
+s390_support_sframe_p (void)
+{
+  /* At this time, SFrame is supported for s390x (64-bit) only.  */
+  return (s390_arch_size == 64);
+}
+
+/* Specify if RA tracking is needed.  */
+
+bool
+s390_sframe_ra_tracking_p (void)
+{
+  return true;
+}
+
+/* Specify the fixed offset to recover RA from CFA.
+   (useful only when RA tracking is not needed).  */
+
+offsetT
+s390_sframe_cfa_ra_offset (void)
+{
+  return (offsetT) SFRAME_CFA_FIXED_RA_INVALID;
+}
+
+/* Get the abi/arch indentifier for SFrame.  */
+
+unsigned char
+s390_sframe_get_abi_arch (void)
+{
+  unsigned char sframe_abi_arch = 0;
+
+  if (s390_support_sframe_p ())
+    {
+      gas_assert (target_big_endian);
+      sframe_abi_arch = SFRAME_ABI_S390_ENDIAN_BIG;
+    }
+
+  return sframe_abi_arch;
+}
+
 void
 s390_elf_final_processing (void)
 {
diff --git a/gas/config/tc-s390.h b/gas/config/tc-s390.h
index cd353045a822..c8f172d8737b 100644
--- a/gas/config/tc-s390.h
+++ b/gas/config/tc-s390.h
@@ -98,3 +98,34 @@ extern int s390_cie_data_alignment;
 extern void s390_elf_final_processing (void);
 
 #define elf_tc_final_processing s390_elf_final_processing
+
+/* SFrame  */
+
+/* Whether SFrame stack trace info is supported.  */
+extern bool s390_support_sframe_p (void);
+#define support_sframe_p s390_support_sframe_p
+
+/* The stack-pointer register number for SFrame stack trace info.  */
+extern unsigned int s390_sframe_cfa_sp_reg;
+#define SFRAME_CFA_SP_REG s390_sframe_cfa_sp_reg
+
+/* The frame-pointer register number for SFrame stack trace info.  */
+extern unsigned int s390_sframe_cfa_fp_reg;
+#define SFRAME_CFA_FP_REG s390_sframe_cfa_fp_reg
+
+/* The return address register number for SFrame stack trace info.  */
+extern unsigned int s390_sframe_cfa_ra_reg;
+#define SFRAME_CFA_RA_REG s390_sframe_cfa_ra_reg
+
+/* Specify if RA tracking is needed.  */
+extern bool s390_sframe_ra_tracking_p (void);
+#define sframe_ra_tracking_p s390_sframe_ra_tracking_p
+
+/* Specify the fixed offset to recover RA from CFA.
+   (useful only when RA tracking is not needed).  */
+extern offsetT s390_sframe_cfa_ra_offset (void);
+#define sframe_cfa_ra_offset s390_sframe_cfa_ra_offset
+
+/* The abi/arch indentifier for SFrame.  */
+unsigned char s390_sframe_get_abi_arch (void);
+#define sframe_get_abi_arch s390_sframe_get_abi_arch
diff --git a/gas/gen-sframe.c b/gas/gen-sframe.c
index 7e815f9603ef..93a5eebcc9d8 100644
--- a/gas/gen-sframe.c
+++ b/gas/gen-sframe.c
@@ -675,7 +675,7 @@ output_sframe_internal (void)
 #endif
   out_one (fixed_ra_offset);
 
-  /* None of the AMD64, or AARCH64 ABIs need the auxiliary header.
+  /* None of the AMD64, AARCH64, or S390 ABIs need the auxiliary header.
      When the need does arise to use this field, the appropriate backend
      must provide this information.  */
   out_one (0); /* Auxiliary SFrame header length.  */
diff --git a/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-1.d b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-1.d
new file mode 100644
index 000000000000..211804a2309a
--- /dev/null
+++ b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-1.d
@@ -0,0 +1,23 @@
+#objdump: --sframe=.sframe
+#name: SFrame generation on s390
+#...
+Contents of the SFrame section .sframe:
+
+  Header :
+
+    Version: SFRAME_VERSION_2
+    Flags: NONE
+    Num FDEs: 1
+    Num FREs: 6
+
+  Function Index :
+
+    func idx \[0\]: pc = 0x0, size = 40 bytes
+    STARTPC +CFA +FP +RA +
+    0+0000 +sp\+160 +u +u +
+    0+0006 +sp\+160 +c\-72 +c\-48 +
+    0+000c +sp\+336 +c\-72 +c\-48 +
+    0+0010 +fp\+336 +c\-72 +c\-48 +
+    0+001c +sp\+160 +u +u +
+    0+001e +fp\+336 +c\-72 +c\-48 +
+#pass
diff --git a/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-1.s b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-1.s
new file mode 100644
index 000000000000..56d8425ae2b1
--- /dev/null
+++ b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-1.s
@@ -0,0 +1,37 @@
+	.cfi_sections .sframe
+	.cfi_startproc
+	stmg	%r6,%r15,48(%r15)
+	.cfi_offset 6, -112
+	.cfi_offset 7, -104
+	.cfi_offset 8, -96
+	.cfi_offset 9, -88
+	.cfi_offset 10, -80
+	.cfi_offset 11, -72
+	.cfi_offset 12, -64
+	.cfi_offset 13, -56
+	.cfi_offset 14, -48
+	.cfi_offset 15, -40
+	lay	%r15,-176(%r15)
+	.cfi_def_cfa_offset 336
+	lgr	%r11,%r15
+	.cfi_def_cfa_register 11
+	lay	%r15,-128(%r15)
+.Lreturn:
+	lmg	%r6,%r15,224(%r11)
+	.cfi_remember_state
+	.cfi_restore 15
+	.cfi_restore 14
+	.cfi_restore 13
+	.cfi_restore 12
+	.cfi_restore 11
+	.cfi_restore 10
+	.cfi_restore 9
+	.cfi_restore 8
+	.cfi_restore 7
+	.cfi_restore 6
+	.cfi_def_cfa 15, 160
+	br	%r14
+	.cfi_restore_state
+	lay     %r15,-128(%r15)
+	j	.Lreturn
+	.cfi_endproc
diff --git a/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-2.d b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-2.d
new file mode 100644
index 000000000000..211804a2309a
--- /dev/null
+++ b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-2.d
@@ -0,0 +1,23 @@
+#objdump: --sframe=.sframe
+#name: SFrame generation on s390
+#...
+Contents of the SFrame section .sframe:
+
+  Header :
+
+    Version: SFRAME_VERSION_2
+    Flags: NONE
+    Num FDEs: 1
+    Num FREs: 6
+
+  Function Index :
+
+    func idx \[0\]: pc = 0x0, size = 40 bytes
+    STARTPC +CFA +FP +RA +
+    0+0000 +sp\+160 +u +u +
+    0+0006 +sp\+160 +c\-72 +c\-48 +
+    0+000c +sp\+336 +c\-72 +c\-48 +
+    0+0010 +fp\+336 +c\-72 +c\-48 +
+    0+001c +sp\+160 +u +u +
+    0+001e +fp\+336 +c\-72 +c\-48 +
+#pass
diff --git a/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-2.s b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-2.s
new file mode 100644
index 000000000000..4d58cdaf64a7
--- /dev/null
+++ b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-2.s
@@ -0,0 +1,37 @@
+	.cfi_sections .sframe
+	.cfi_startproc
+	stmg	%r6,%r15,48(%r15)
+	.cfi_rel_offset 6, 48
+	.cfi_rel_offset 7, 56
+	.cfi_rel_offset 8, 64
+	.cfi_rel_offset 9, 72
+	.cfi_rel_offset 10, 80
+	.cfi_rel_offset 11, 88
+	.cfi_rel_offset 12, 96
+	.cfi_rel_offset 13, 104
+	.cfi_rel_offset 14, 112
+	.cfi_rel_offset 15, 120
+	lay	%r15,-176(%r15)
+	.cfi_def_cfa_offset 336
+	lgr	%r11,%r15
+	.cfi_def_cfa_register 11
+	lay	%r15,-128(%r15)
+.Lreturn:
+	lmg	%r6,%r15,224(%r11)
+	.cfi_remember_state
+	.cfi_restore 15
+	.cfi_restore 14
+	.cfi_restore 13
+	.cfi_restore 12
+	.cfi_restore 11
+	.cfi_restore 10
+	.cfi_restore 9
+	.cfi_restore 8
+	.cfi_restore 7
+	.cfi_restore 6
+	.cfi_def_cfa 15, 160
+	br	%r14
+	.cfi_restore_state
+	lay     %r15,-128(%r15)
+	j	.Lreturn
+	.cfi_endproc
diff --git a/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-1.d b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-1.d
new file mode 100644
index 000000000000..5875e568bd66
--- /dev/null
+++ b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-1.d
@@ -0,0 +1,15 @@
+#name: SFrame generation on s390
+#as: --gsframe
+#warning: skipping SFrame FDE due to .cfi_def_cfa_register defining non-SP/FP register 10 as CFA base register
+#objdump: --sframe=.sframe
+#...
+Contents of the SFrame section .sframe:
+
+  Header :
+
+    Version: SFRAME_VERSION_2
+    Flags: NONE
+    Num FDEs: 0
+    Num FREs: 0
+
+#pass
diff --git a/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-1.s b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-1.s
new file mode 100644
index 000000000000..85e36c39d2a3
--- /dev/null
+++ b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-1.s
@@ -0,0 +1,37 @@
+	.cfi_sections .sframe
+	.cfi_startproc
+	stmg	%r6,%r15,48(%r15)
+	.cfi_offset 6, -112
+	.cfi_offset 7, -104
+	.cfi_offset 8, -96
+	.cfi_offset 9, -88
+	.cfi_offset 10, -80
+	.cfi_offset 11, -72
+	.cfi_offset 12, -64
+	.cfi_offset 13, -56
+	.cfi_offset 14, -48
+	.cfi_offset 15, -40
+	lay	%r15,-176(%r15)
+	.cfi_def_cfa_offset 336
+	lgr	%r10,%r15
+	.cfi_def_cfa_register 10	# non-default frame pointer register
+	lay	%r15,-128(%r15)
+.Lreturn:
+	lmg	%r6,%r15,224(%r10)
+	.cfi_remember_state
+	.cfi_restore 15
+	.cfi_restore 14
+	.cfi_restore 13
+	.cfi_restore 12
+	.cfi_restore 11
+	.cfi_restore 10
+	.cfi_restore 9
+	.cfi_restore 8
+	.cfi_restore 7
+	.cfi_restore 6
+	.cfi_def_cfa 15, 160
+	br	%r14
+	.cfi_restore_state
+	lay     %r15,-128(%r15)
+	j	.Lreturn
+	.cfi_endproc
diff --git a/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-2.d b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-2.d
new file mode 100644
index 000000000000..e1da5c19f21e
--- /dev/null
+++ b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-2.d
@@ -0,0 +1,15 @@
+#name: SFrame generation on s390
+#as: --gsframe
+#warning: skipping SFrame FDE due to .cfi_def_cfa defining non-SP/FP register 10 as CFA base register
+#objdump: --sframe=.sframe
+#...
+Contents of the SFrame section .sframe:
+
+  Header :
+
+    Version: SFRAME_VERSION_2
+    Flags: NONE
+    Num FDEs: 0
+    Num FREs: 0
+
+#pass
diff --git a/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-2.s b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-2.s
new file mode 100644
index 000000000000..0bb274a9e991
--- /dev/null
+++ b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-2.s
@@ -0,0 +1,37 @@
+	.cfi_sections .sframe
+	.cfi_startproc
+	stmg	%r6,%r15,48(%r15)
+	.cfi_offset 6, -112
+	.cfi_offset 7, -104
+	.cfi_offset 8, -96
+	.cfi_offset 9, -88
+	.cfi_offset 10, -80
+	.cfi_offset 11, -72
+	.cfi_offset 12, -64
+	.cfi_offset 13, -56
+	.cfi_offset 14, -48
+	.cfi_offset 15, -40
+	lay	%r15,-176(%r15)
+	.cfi_def_cfa_offset 336
+	lgr	%r10,%r15
+	.cfi_def_cfa 10, 336	# non-default frame pointer register
+	lay	%r15,-128(%r15)
+.Lreturn:
+	lmg	%r6,%r15,224(%r10)
+	.cfi_remember_state
+	.cfi_restore 15
+	.cfi_restore 14
+	.cfi_restore 13
+	.cfi_restore 12
+	.cfi_restore 11
+	.cfi_restore 10
+	.cfi_restore 9
+	.cfi_restore 8
+	.cfi_restore 7
+	.cfi_restore 6
+	.cfi_def_cfa 15, 160
+	br	%r14
+	.cfi_restore_state
+	lay     %r15,-128(%r15)
+	j	.Lreturn
+	.cfi_endproc
diff --git a/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-3.d b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-3.d
new file mode 100644
index 000000000000..4b3262f02f02
--- /dev/null
+++ b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-3.d
@@ -0,0 +1,15 @@
+#name: SFrame generation on s390
+#as: --gsframe
+#warning: skipping SFrame FDE due to .cfi_register specifying RA register
+#objdump: --sframe=.sframe
+#...
+Contents of the SFrame section .sframe:
+
+  Header :
+
+    Version: SFRAME_VERSION_2
+    Flags: NONE
+    Num FDEs: 0
+    Num FREs: 0
+
+#pass
diff --git a/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-3.s b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-3.s
new file mode 100644
index 000000000000..f0a5bd577304
--- /dev/null
+++ b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-3.s
@@ -0,0 +1,6 @@
+	.cfi_sections .sframe
+	.cfi_startproc
+	lgr	%r7,%r14
+	.cfi_register 14, 7	# non-default return address register
+	br	%r7
+	.cfi_endproc
diff --git a/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-4.d b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-4.d
new file mode 100644
index 000000000000..cdfdd4a8e6ab
--- /dev/null
+++ b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-4.d
@@ -0,0 +1,15 @@
+#name: SFrame generation on s390
+#as: --gsframe
+#warning: skipping SFrame FDE due to non-default return-address register 7
+#objdump: --sframe=.sframe
+#...
+Contents of the SFrame section .sframe:
+
+  Header :
+
+    Version: SFRAME_VERSION_2
+    Flags: NONE
+    Num FDEs: 0
+    Num FREs: 0
+
+#pass
diff --git a/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-4.s b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-4.s
new file mode 100644
index 000000000000..cfdea75e0b95
--- /dev/null
+++ b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-4.s
@@ -0,0 +1,5 @@
+	.cfi_sections .sframe
+	.cfi_startproc
+	.cfi_return_column 7	# non-default return address register
+	br	%r7
+	.cfi_endproc
diff --git a/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-5.d b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-5.d
new file mode 100644
index 000000000000..57af27d26419
--- /dev/null
+++ b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-5.d
@@ -0,0 +1,15 @@
+#name: SFrame generation on s390
+#as: --gsframe
+#warning: skipping SFrame FDE due to FP without RA on stack
+#objdump: --sframe=.sframe
+#...
+Contents of the SFrame section .sframe:
+
+  Header :
+
+    Version: SFRAME_VERSION_2
+    Flags: NONE
+    Num FDEs: 0
+    Num FREs: 0
+
+#pass
diff --git a/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-5.s b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-5.s
new file mode 100644
index 000000000000..c0c3911496b2
--- /dev/null
+++ b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-5.s
@@ -0,0 +1,22 @@
+	.cfi_sections .sframe
+	.cfi_startproc
+	stmg	%r4,%r15,32(%r15)
+	.cfi_offset 6, -112
+	.cfi_offset 7, -104
+	.cfi_offset 8, -96
+	.cfi_offset 9, -88
+	.cfi_offset 10, -80
+	.cfi_offset 11, -72
+	.cfi_offset 12, -64
+	.cfi_offset 13, -56
+	.cfi_offset 14, -48
+	.cfi_offset 15, -40
+	lay	%r15,-192(%r15)
+	.cfi_def_cfa_offset 352
+.Lreturn:
+	lmg	%r14,%r15,304(%r15)
+	.cfi_restore 15
+	.cfi_restore 14
+	.cfi_def_cfa_offset 160
+	br	%r14
+	.cfi_endproc
diff --git a/gas/testsuite/gas/cfi-sframe/cfi-sframe.exp b/gas/testsuite/gas/cfi-sframe/cfi-sframe.exp
index cfae28d39aaf..f97fa9e170a2 100644
--- a/gas/testsuite/gas/cfi-sframe/cfi-sframe.exp
+++ b/gas/testsuite/gas/cfi-sframe/cfi-sframe.exp
@@ -64,7 +64,8 @@ proc gas_x86_64_check { } {
 }
 
 # common tests
-if  { ([istarget "x86_64-*-*"] || [istarget "aarch64*-*-*"]) \
+if  { ([istarget "x86_64-*-*"] || [istarget "aarch64*-*-*"] ||
+       [istarget "s390x-*-*"]) \
        && [gas_sframe_check] } then {
 
     global ASFLAGS
@@ -99,3 +100,14 @@ if { [istarget "aarch64*-*-*"] && [gas_sframe_check] } then {
     run_dump_test "cfi-sframe-aarch64-2"
     run_dump_test "cfi-sframe-aarch64-pac-ab-key-1"
 }
+
+# s390 specific tests
+if { [istarget "s390x*-*-*"] && [gas_sframe_check] } then {
+    run_dump_test "cfi-sframe-s390-1"
+    run_dump_test "cfi-sframe-s390-2"
+    run_dump_test "cfi-sframe-s390-err-1"
+    run_dump_test "cfi-sframe-s390-err-2"
+    run_dump_test "cfi-sframe-s390-err-3"
+    run_dump_test "cfi-sframe-s390-err-4"
+    run_dump_test "cfi-sframe-s390-err-5"
+}
diff --git a/include/sframe.h b/include/sframe.h
index b3d0c2e937d3..90bc92a32f84 100644
--- a/include/sframe.h
+++ b/include/sframe.h
@@ -93,6 +93,7 @@ extern "C"
 #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.  */
+#define SFRAME_ABI_S390_ENDIAN_BIG         4 /* S390 big endian.  */
 
 /* SFrame FRE types.  */
 #define SFRAME_FRE_TYPE_ADDR1	0
@@ -190,7 +191,7 @@ typedef struct sframe_func_desc_entry
      - 2-bits: Unused.
      ------------------------------------------------------------------------
      |     Unused    |  PAC auth A/B key (aarch64) |  FDE type |   FRE type   |
-     |               |        Unused (amd64)       |           |              |
+     |               |     Unused (amd64, s390)    |           |              |
      ------------------------------------------------------------------------
      8               6                             5           4              0     */
   uint8_t sfde_func_info;
@@ -248,7 +249,7 @@ typedef struct sframe_fre_info
      - 1 bit: Mangled RA state bit (aarch64 only).
      ----------------------------------------------------------------------------------
      | Mangled-RA (aarch64) |  Size of offsets   |   Number of offsets    |   base_reg |
-     |  Unused (amd64)      |                    |                        |            |
+     | Unused (amd64, s390) |                    |                        |            |
      ----------------------------------------------------------------------------------
      8                     7                    5                        1            0
 
@@ -274,7 +275,7 @@ typedef struct sframe_fre_info
 
 /* SFrame Frame Row Entry definitions.
 
-   Used for both AMD64 and AARCH64.
+   Used for AMD64, AARCH64, and S390.
 
    An SFrame Frame Row Entry is a self-sufficient record which contains
    information on how to generate the stack trace for the specified range of
diff --git a/libsframe/doc/sframe-spec.texi b/libsframe/doc/sframe-spec.texi
index d0f99bd698eb..a81faf49f5c1 100644
--- a/libsframe/doc/sframe-spec.texi
+++ b/libsframe/doc/sframe-spec.texi
@@ -74,8 +74,8 @@ The SFrame stack trace information is provided in a loaded section, known as the
 @code{.sframe} section.  When available, the @code{.sframe} section appears in
 a new segment of its own, PT_GNU_SFRAME.
 
-The SFrame format is currently supported only for select ABIs, namely, AMD64
-and AAPCS64.
+The SFrame format is currently supported only for select ABIs, namely, AMD64,
+AAPCS64, and s390.
 
 A portion of the SFrame format follows an unaligned on-disk representation.
 Some data structures, however, (namely the SFrame header and the SFrame
@@ -366,6 +366,10 @@ in the format.
 @item @code{SFRAME_ABI_AMD64_ENDIAN_LITTLE}
 @tab 3 @tab AMD64 little-endian
 
+@tindex SFRAME_ABI_S390_ENDIAN_BIG
+@item @code{SFRAME_ABI_S390_ENDIAN_BIG}
+@tab 4 @tab s390 big-endian
+
 @end multitable
 
 The presence of an explicit identification of ABI/arch in SFrame may allow
-- 
2.40.1