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SFrame version 2 encodes the size of repetitive insn block explicitly
in the format. Add information in the SFrame FDE to convey the size
of the block of repeating instructions. This information is used only
for SFrame FDEs of type SFRAME_FDE_TYPE_PCMASK.
Introduce two extra bytes for padding: this ensures that the memory
accesses to the members of the SFrame Frame Descriptor Entry (FDE) are
naturally aligned.
gas generates SFrame section with version SFRAME_VERSION_2 by default.
libsframe provides two new APIs to:
- get an SFrame FDE data from the decoder context, and
- add an SFrame FDE to the encoder context.
The additional argument (for rep_block_size) is useful for SFrame FDEs
where FDE type is SFRAME_FDE_TYPE_PCMASK.
The linker will generate the output SFrame sections in the
SFRAME_VERSION_2 format. If the input sections offered to the linker
are not all in the SFRAME_VERSION_2 format, the linker issues an error
to the user.
objdump/readelf will show the following message to the user if .sframe
section in SFRAME_VERSION_1 format is seen:
"No further information can be displayed. SFrame version not
supported."
In other words, like the rest of the binutils, only the current SFrame
format version, i.e., SFRAME_VERSION_2 is supported by the textual dump
facilities.
bfd/
* elf-sframe.c (_bfd_elf_merge_section_sframe): Generate an
output SFrame section with version SFRAME_VERSION_2. Also,
error out if the SFrame sections do not all have
SFRAME_VERSION_2.
* elfxx-x86.c (_bfd_x86_elf_create_sframe_plt): Generate SFrame
section for plt entries with version SFRAME_VERSION_2.
gas/
* gen-sframe.c (sframe_set_version): Update to SFRAME_VERSION_2.
(output_sframe): Likewise.
gas/testsuite/
* gas/cfi-sframe/cfi-sframe-aarch64-1.d: Use SFRAME_VERSION_2.
* gas/cfi-sframe/cfi-sframe-aarch64-2.d: Likewise.
* gas/cfi-sframe/cfi-sframe-aarch64-pac-ab-key-1.d: Likewise.
* gas/cfi-sframe/cfi-sframe-common-1.d: Likewise.
* gas/cfi-sframe/cfi-sframe-common-2.d: Likewise.
* gas/cfi-sframe/cfi-sframe-common-3.d: Likewise.
* gas/cfi-sframe/cfi-sframe-common-4.d: Likewise.
* gas/cfi-sframe/cfi-sframe-common-5.d: Likewise.
* gas/cfi-sframe/cfi-sframe-common-6.d: Likewise.
* gas/cfi-sframe/cfi-sframe-common-7.d: Likewise.
* gas/cfi-sframe/cfi-sframe-common-8.d: Likewise.
* gas/cfi-sframe/cfi-sframe-x86_64-1.d: Likewise.
* gas/cfi-sframe/common-empty-1.d: Likewise.
* gas/cfi-sframe/common-empty-2.d: Likewise.
* gas/cfi-sframe/common-empty-3.d: Likewise.
ld/testsuite/
* ld-aarch64/sframe-simple-1.d: Adjust for SFRAME_VERSION_2.
* ld-x86-64/sframe-plt-1.d: Likewise.
* ld-x86-64/sframe-simple-1.d: Likewise.
libsframe/
* libsframe.ver: Add the new APIs.
* sframe.c (sframe_decoder_get_funcdesc_v2): New definition.
(sframe_encoder_add_funcdesc_v2): Likewise.
(sframe_header_sanity_check_p): Include SFRAME_VERSION_2.
(sframe_fre_check_range_p): Get rep_block_size info from SFrame
FDE.
* sframe-dump.c (dump_sframe_header): Add support for
SFRAME_VERSION_2.
(dump_sframe): Inform user if SFrame section in SFRAME_VERSION_1
format is seen.
libsframe/testsuite/
* libsframe.decode/DATA-BE: Regenerated data file.
* libsframe.decode/DATA1: Likewise.
* libsframe.decode/DATA2: Likewise.
* libsframe.find/plt-findfre-1.c: Use new API in the testcase.
include/
* sframe.h: Add member to encode size of the code block of
repeating instructions. Add 2 bytes of padding.
* sframe-api.h (sframe_decoder_get_funcdesc_v2): New
declaration.
(sframe_encoder_add_funcdesc_v2): Likewise.
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For a toy application on x86_64, for example, following is the SFrame
stack trace information for the 3 pltN entries of 16 bytes each:
func idx [1]: pc = 0x401030, size = 48 bytes
STARTPC[m] CFA FP RA
0000000000000000 sp+8 u u
000000000000000b sp+16 u u
The data in first column is the start_ip_offset. Also note that the FDE
is of type SFRAME_FDE_TYPE_PCMASK (denoted by the [m] on LHS).
Where each pltN (note: excluding plt0 entry) entry looks like:
401030: jmp *0x2fca(%rip)
401036: push $0x0
40103b: jmp 401020<_init+0x20>
401040: jmp *0x2fc2(%rip)
401046: push $0x1
40104b: jmp 401020<_init+0x20>
401050: jmp *0x2fba(%rip)
401056: push $0x2
40105b: jmp 401020<_init+0x20>
Now, to find SFrame stack trace information from an FDE of type
SFRAME_FDE_TYPE_PCMASK, sframe_find_fre () was doing an operation
like,
(start_ip_offset & 0xf) >= (pc & 0xf)
This works for pltN entry of size, say, less than 16 bytes. But if the
pltN entries or similar code stubs (for which SFrame FDE of type
SFRAME_FDE_TYPE_PCMASK may be used), evolve to be of size > 16 bytes,
this will cease to work.
To match the range covered by the SFrame FRE, one should instead perform
a modulo operation. The constant for the modulo operation must be the
size of the pltN entry. Further, this constant should ideally be
encoded in the format, as it may be different for each ABI.
In SFrame Version 2 of the format, we will move towards encoding it
explicitly in the SFrame FDE. For now, fix up the logic to at least
move towards modulo operation.
libsframe/
* sframe.c (sframe_fre_check_range_p): New definition.
(sframe_find_fre): Refactor a bit and use the new definition
above.
include/
* sframe.h (SFRAME_FDE_TYPE_PCMASK): Update comment.
libsframe/doc/
* sframe-spec.texi: Fix the text for SFRAME_FDE_TYPE_PCMASK FDE
type.
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include/
* sframe.h: Correct a typo.
libsframe/
* sframe.c: Likewise.
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SFrame format is meant for generating stack traces only.
include/
* sframe.h: Fix comments in the header file.
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An earlier commit 3f107464 defined the SFRAME_FRE_TYPE_*_LIMIT
constants. These constants are used (by gas and libsframe) to pick an
SFrame FRE type based on the function size. Those constants, however,
were buggy, causing the generated SFrame sections to be bloated as
SFRAME_FRE_TYPE_ADDR2/SFRAME_FRE_TYPE_ADDR4 got chosen more often than
necessary.
gas/
* sframe-opt.c (sframe_estimate_size_before_relax): Use
typecast.
(sframe_convert_frag): Likewise.
libsframe/
* sframe.c (sframe_calc_fre_type): Use a more appropriate type
for argument. Adjust the check for SFRAME_FRE_TYPE_ADDR4_LIMIT
to keep it warning-free but meaningful.
include/
* sframe-api.h (sframe_calc_fre_type): Use a more appropriate
type for the argument.
* sframe.h (SFRAME_FRE_TYPE_ADDR1_LIMIT): Correct the constant.
(SFRAME_FRE_TYPE_ADDR2_LIMIT): Likewise.
(SFRAME_FRE_TYPE_ADDR4_LIMIT): Likewise.
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The newer update-copyright.py fixes file encoding too, removing cr/lf
on binutils/bfdtest2.c and ld/testsuite/ld-cygwin/exe-export.exp, and
embedded cr in binutils/testsuite/binutils-all/ar.exp string match.
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ARM 8.3 provides five separate keys that can be used to authenticate
pointers. There are two key for executable (instruction) pointers. The
enum pointer_auth_key in gas/config/tc-aarch64.h currently holds two keys:
enum pointer_auth_key {
AARCH64_PAUTH_KEY_A,
AARCH64_PAUTH_KEY_B
};
Analogous to the above, in SFrame format V1, a bit is reserved in the SFrame
FDE to indicate which key is used for signing the frame's return addresses:
- SFRAME_AARCH64_PAUTH_KEY_A has a value of 0
- SFRAME_AARCH64_PAUTH_KEY_B has a value of 1
Note that the information in this bit will always be used along with the
mangled_ra_p bit, the latter indicates whether the return addresses are
mangled/contain PAC auth bits.
include/ChangeLog:
* sframe.h (SFRAME_AARCH64_PAUTH_KEY_A): New definition.
(SFRAME_AARCH64_PAUTH_KEY_B): Likewise.
(SFRAME_V1_FUNC_INFO): Adjust to accommodate pauth_key.
(SFRAME_V1_FUNC_PAUTH_KEY): New macro.
(SFRAME_V1_FUNC_INFO_UPDATE_PAUTH_KEY): Likewise.
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Use the last remaining bit in the 'SFrame FRE info' word to store whether
the RA is signed/unsigned with PAC authorization code: this bit is named
as the "mangled RA" bit. This bit is still unused for x86-64.
The behaviour of the mangled-RA info bit in SFrame format closely
follows the behaviour of DW_CFA_AARCH64_negate_ra_state in DWARF. During
unwinding, whenever an SFrame FRE with non-zero "mangled RA" bit is
encountered, it means the upper bits of the return address contain Pointer
Authentication code. The unwinder, hence, must use appropriate means to
restore LR correctly in such cases.
include/ChangeLog:
* sframe.h (SFRAME_V1_FRE_INFO_UPDATE_MANGLED_RA_P): New macro.
(SFRAME_V1_FRE_MANGLED_RA_P): Likewise.
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Define constants in sframe.h for the various limits associated with the
range of offsets that can be encoded in the start address of an SFrame
FRE. E.g., sframe_frame_row_entry_addr1 is used when start address
offset can be encoded as 1-byte unsigned value.
Update the code in gas to use these defined constants as it checks for
these limits, and remove the usage of magic numbers.
ChangeLog:
* gas/sframe-opt.c (sframe_estimate_size_before_relax):
(sframe_convert_frag): Do not use magic numbers.
* libsframe/sframe.c (sframe_calc_fre_type): Likewise.
include/ChangeLog:
* sframe.h (SFRAME_FRE_TYPE_ADDR1_LIMIT): New constant.
(SFRAME_FRE_TYPE_ADDR2_LIMIT): Likewise.
(SFRAME_FRE_TYPE_ADDR4_LIMIT): Likewise.
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include/ChangeLog:
* sframe.h (SFRAME_V1_FUNC_INFO): Use specific bits only.
(SFRAME_V1_FRE_INFO): Likewise.
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The header sframe.h defines the SFrame format.
The SFrame format is the Simple Frame format. It can be used to
represent the minimal necessary unwind information required for
backtracing. The current version supports AMD64 and AARCH64.
More details of the SFrame format are included in the documentation
of the header file in this patch.
include/ChangeLog:
* sframe.h: New file.
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