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s390: Initial support to generate .sframe from CFI directives in assembler
This introduces initial support to generate .sframe from CFI directives
in assembler on s390 64-bit (s390x). Due to SFrame V2 format
limitations it has the following limitations, some of them getting
addressed by subsequent patches, which cause generation of SFrame FDE
to be skipped:
- SFrame FP/RA tracking only supports register contents being 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.
This issue is detailed further and resolved in the subsequent commit
"s390: Represent FP/RA saved in register in SFrame".
- SFrame FP/RA tracking cannot represent FP without RA saved. This is
because the format assumes SFrame FDE offset2 to be the RA offset, if
there are two offsets, and offset3 to be the FP offset, if there are
three offsets. There is no mean to distinguish whether offset2 is the
RA or FP offset, if there are only two offsets.
This issue is detailed further and resolved in the subsequent commit
"s390: Represent FP without RA saved in SFrame".
- SFrame assumes a dedicated FP register number. The s390x ELF ABI [1]
does only designate register 11 as preferred FP register number. In
general GCC and Clang on s390x use register 11 as frame pointer.
GCC on s390x can be observed to use register 14 as frame pointer in
the stack clash protector in the function prologue.
glibc on s390x contains hand-written assembler code that uses
register 12 as frame pointer.
This s390x support is largely based on the AArch64 support from commit
b52c4ee466 ("gas: generate .sframe from CFI directives").
The SFrame ABI/arch identifier SFRAME_ABI_S390X_ENDIAN_BIG is introduced
for s390x and added to the SFrame format specification.
The s390x ELF ABI [1] specifies the following C calling conventions for
s390x architecture:
- Register 15 is the stack pointer (SP).
- Register 14 contains the return address (RA) at function entry.
- There is no dedicated frame pointer register. Register 11 is the
preferred frame pointer (FP). [2] GCC and Clang in general use
register 11 as frame pointer.
- The CFA is defined as SP at call site +160. [3] The SP at call site
can therefore be derived from the CFA using a SP value offset from CFA
of -160.
The s390x ELF ABI [1] does not assign any standard save slot to each
register in the register save area of a stack frame. Neither the
return address (RA, r14) nor preferred frame pointer (FP, r11)
necessarily need to be saved. Therefore SFrame RA and FP tracking is
used.
Support for SFrame on s390 is only enabled for the 64-bit s390x ELF ABI
(z/Architecture with 64-bit addressing mode). It is disabled for the
32-bit s390 ELF ABI (ESA/390 or z/Architecture with 32-bit addressing
mode).
s390x-specific SFrame assembler and linker tests are added, including
error tests for use of a non-preferred frame pointer (FP) register and
specification of a non-default return address (RA) register.
[1]: s390x ELF ABI, https://github.com/IBM/s390x-abi/releases
[2]: s390x ELF ABI, commit f00421825979 ("Add information about the frame
pointer register"),
https://github.com/IBM/s390x-abi/commit/f00421825979
[3]: s390x ELF ABI, commit 4e38ad9c8a88 ("Document the CFA"),
https://github.com/IBM/s390x-abi/commit/4e38ad9c8a88
include/
* sframe.h: Add reference to s390x architecture in comments.
(SFRAME_ABI_S390X_ENDIAN_BIG): Define SFrame ABI/arch identifier
for s390x.
(SFRAME_S390X_SP_VAL_OFFSET): Define s390x-specific SP value
offset from CFA.
libsframe/
* sframe.c (need_swapping): Add SFRAME_ABI_S390X_ENDIAN_BIG.
* doc/sframe-spec.texi (SFRAME_ABI_S390X_ENDIAN_BIG, s390x,
SFRAME_S390X_SP_VAL_OFFSET): Document SFrame ABI/arch identifier
for s390x, add references to s390x architecture, and document
s390x-specifics, such as the SP value offset from CFA of -160.
gas/
* config/tc-s390.h: s390x support to generate .sframe from CFI
directives in assembler.
(support_sframe_p): Define.
(SFRAME_CFA_SP_REG, SFRAME_CFA_FP_REG, SFRAME_CFA_RA_REG):
Define.
(sframe_ra_tracking_p): Define.
(sframe_cfa_ra_offset): Define.
(sframe_get_abi_arch): Define.
* config/tc-s390.c: s390x support to generate .sframe from CFI
directives in assembler.
(s390_sframe_cfa_sp_reg, s390_sframe_cfa_fp_reg,
s390_sframe_cfa_ra_reg): New. Initialize to DWARF register
numbers of stack pointer (SP, r15), preferred frame pointer
(FP, r11), and return address (RA, r14) registers.
(s390_support_sframe_p): New function. Return true if s390x.
(s390_sframe_ra_tracking_p): New function. Return true.
(s390_sframe_cfa_ra_offset): New function. Return
SFRAME_CFA_FIXED_RA_INVALID.
(s390_sframe_get_abi_arch): New function. Return
SFRAME_ABI_S390X_ENDIAN_BIG if s390x, otherwise zero.
* gen-sframe.c: Add reference to s390x architecture in comments.
(sframe_xlate_do_val_offset): Add support for s390x-specific
SFRAME_S390X_SP_VAL_OFFSET.
* NEWS: Add news entry.
gas/testsuite/
* gas/cfi-sframe/cfi-sframe.exp: Enable common SFrame tests for
s390x. Add s390x-specific SFrame (error) tests.
* gas/cfi-sframe/cfi-sframe-s390x-1.d: New s390x-specific SFrame
test.
* gas/cfi-sframe/cfi-sframe-s390x-1.s: Likewise.
* gas/cfi-sframe/cfi-sframe-s390x-2.d: Likewise.
* gas/cfi-sframe/cfi-sframe-s390x-2.s: Likewise.
* gas/cfi-sframe/cfi-sframe-s390x-err-1.d: New s390x-specific
SFrame error test that uses a non-default frame-pointer register
as CFA base register.
* gas/cfi-sframe/cfi-sframe-s390x-err-1.s: Likewise.
* gas/cfi-sframe/cfi-sframe-s390x-err-2.d: Likewise.
* gas/cfi-sframe/cfi-sframe-s390x-err-2.s: Likewise.
* gas/cfi-sframe/cfi-sframe-s390x-err-3.d: New s390x-specific
SFrame error test that uses a non-default return address
register.
* gas/cfi-sframe/cfi-sframe-s390x-err-3.s: Likewise.
* gas/cfi-sframe/cfi-sframe-s390x-fpra-offset-1.d: New s390x-
specific SFrame test that saves RA and FP individually on the
stack.
* gas/cfi-sframe/cfi-sframe-s390x-fpra-offset-1.s: Likewise.
* gas/cfi-sframe/cfi-sframe-s390x-fpra-offset-err-1.d: New
s390x-specific SFrame error test that saves FP and RA
individually, to trigger FP without RA saved.
* gas/cfi-sframe/cfi-sframe-s390x-fpra-offset-err-1.s: Likewise.
* gas/cfi-sframe/cfi-sframe-s390x-fpra-register-err-1.d: New
s390x-specific SFrame error test that saves FP and RA
individually in registers.
* gas/cfi-sframe/cfi-sframe-s390x-fpra-register-err-1.s:
Likewise.
* gas/cfi-sframe/cfi-sframe-s390x-fpra-register-err-2.d: New
s390x-specific SFrame error test that saves RA and FP
individually in registers.
* gas/cfi-sframe/cfi-sframe-s390x-fpra-register-err-2.s:
Likewise.
ld/testsuite/
* ld-s390/s390.exp: Add simple SFrame test.
* ld-s390/sframe-simple-1.d: New simple SFrame test.
* ld-s390/sframe-bar.s: Likewise.
* ld-s390/sframe-foo.s: Likewise.
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
This commit is contained in:
Jens Remus
@@ -81,8 +81,8 @@ The SFrame stack trace information is provided in a loaded section, known as the
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@code{.sframe} section. When available, the @code{.sframe} section appears in
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a new segment of its own, PT_GNU_SFRAME.
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The SFrame format is currently supported only for select ABIs, namely, AMD64
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and AAPCS64.
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The SFrame format is currently supported only for select ABIs, namely, AMD64,
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AAPCS64, and s390x.
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A portion of the SFrame format follows an unaligned on-disk representation.
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Some data structures, however, (namely the SFrame header and the SFrame
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@@ -139,6 +139,14 @@ bytes to the start PC of the associated function from the field itself.
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bytes to the start PC of the associated function from the start of the SFrame
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section.
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@end itemize
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@item
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Add a new ABI/arch identifier SFRAME_ABI_S390X_ENDIAN_BIG for the s390
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architecture (64-bit) s390x ABI. Other s390x-specific backward compatible
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changes including the following helper definitions have been incrementally
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added to SFrame version 2 only:
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@itemize @minus
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@item SFRAME_S390X_SP_VAL_OFFSET: SP value offset from CFA.
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@end itemize
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@end itemize
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SFrame version 1 is now obsolete and should not be used.
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@@ -421,6 +429,10 @@ in the format.
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@item @code{SFRAME_ABI_AMD64_ENDIAN_LITTLE}
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@tab 3 @tab AMD64 little-endian
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@tindex SFRAME_ABI_S390X_ENDIAN_BIG
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@item @code{SFRAME_ABI_S390X_ENDIAN_BIG}
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@tab 4 @tab s390x big-endian
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@end multitable
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The presence of an explicit identification of ABI/arch in SFrame may allow
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@@ -794,6 +806,7 @@ auxiliary SFrame header, etc., if used, must also be outlined here.
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@menu
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* AMD64::
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* AArch64::
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* s390x::
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@end menu
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@node AMD64
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@@ -850,6 +863,50 @@ Hence, in summary:
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@item 3 @tab FP = CFA + offset3
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@end multitable
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@node s390x
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@section s390x
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A stack tracer implementation must initialize the SP to the designated SP
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register value, the FP to the preferred FP register value, and the RA to the
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designated RA register value in the topmost stack frame of the callchain. This
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is required, as either the SP or FP is used as CFA base register and as the FP
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and/or RA are not necessarily saved on the stack. For RA this may only be the
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case in the topmost stack frame of the callchain. For FP this may be the case
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in any stack frame.
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Irrespective of the ABI, the first stack offset is always used to locate the
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CFA, by interpreting it as: CFA = @code{BASE_REG} + offset1.
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The identification of the @code{BASE_REG} is done by using the
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@code{fre_cfa_base_reg_id} field in the SFrame FRE info word.
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The (64-bit) s390x ELF ABI does not mandate the precise location in a function
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where the return address (RA) and frame pointer (FP) are saved, if at all.
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Hence the need to track RA in the SFrame stack trace format. As RA is being
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tracked in this ABI, the second stack offset is always used to locate the RA
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stack slot, by interpreting it as: RA = CFA + offset2. RA remains unchanged,
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if the offset is not available. Stack tracers are recommended to validate that
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the "unchanged RA" pattern, when present, is seen only for the topmost stack
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frame. The third stack offset is used to locate the FP stack slot, by
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interpreting it as: FP = CFA + offset3. FP remains unchanged, if the offset is
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not available.
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Given the nature of things, the number of stack offsets seen on s390x per
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SFrame FRE is either 1, 2, or 3.
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Hence, in summary:
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@multitable {Offset ID} {Interpretation in s390x in X}
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@headitem Offset ID @tab Interpretation in s390x
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@item 1 @tab CFA = @code{BASE_REG} + offset1
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@item 2 @tab RA = CFA + offset2
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@item 3 @tab FP = CFA + offset3
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@end multitable
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The s390x ELF ABI defines the CFA as stack pointer (SP) at call site +160. The
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SP can therefore be obtained using the SP value offset from CFA
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@code{SFRAME_S390X_SP_VAL_OFFSET} of -160 as follows:
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SP = CFA + @code{SFRAME_S390X_SP_VAL_OFFSET}
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@node Generating Stack Traces using SFrame
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@appendix Generating Stack Traces using SFrame
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@@ -913,7 +970,7 @@ SFrame section.
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fp_offset = sframe_fre_get_fp_offset (fre);
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cfa = base_reg_val + cfa_offset;
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next_frame->sp = cfa;
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next_frame->sp = cfa [+ SFRAME_S390X_SP_VAL_OFFSET on s390x];
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ra_stack_loc = cfa + ra_offset;
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// Get the address stored in the stack location.
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@@ -166,6 +166,7 @@ need_swapping (int endian)
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case SFRAME_ABI_AMD64_ENDIAN_LITTLE:
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return !is_little;
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case SFRAME_ABI_AARCH64_ENDIAN_BIG:
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case SFRAME_ABI_S390X_ENDIAN_BIG:
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return is_little;
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default:
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break;
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