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gas: sframe: Represent .cfi_undefined RA as FRE without offsets

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In DWARF CFI an "undefined" register rule for the return address (RA)
register indicates that there is no return address and the stack trace
is complete.

Represent DW_CFA_undefined as SFrame FRE without any offsets, so that a
stack tracer implementation can use this as indication that an outermost
frame has been reached and the stack trace is complete.

This representation is backward compatible, as existing stack tracers
should already deal with the case, that an SFrame FRE a so far invalid
offset count of zero and stop the trace.

include/
	* sframe.h (SFRAME_V2_FRE_RA_UNDEFINED_P): New macro to test
	FRE info word for RA undefined (FRE without any offsets).

binutils/
	* NEWS: Mention SFrame can represent an undefined RA as FRE
	without	any offsets.

gas/
	* gen-sframe.h (struct sframe_row_entry): Add ra_undefined_p
	flag.
	* gen-sframe.c (sframe_row_entry_new): Initialize ra_undefined_p
	flag to not set.
	(sframe_row_entry_initialize): Treat ra_undefined_p flag as
	sticky.
	(sframe_fre_set_ra_track): Reset ra_undefined_p flag.
	(sframe_xlate_do_restore): Reset ra_undefined_p flag to saved
	state.
	(sframe_xlate_do_same_value): Reset ra_undefined_p flag.
	(sframe_xlate_do_cfi_undefined): For RA set ra_undefined_p flag.
	(output_sframe_row_entry): Represent RA undefined as SFrame FRE
	without any offsets and FRE info word fields zeroed.
	* NEWS: Mention assembler represents .cfi_undefined RA in SFrame
	as FRE without any offsets.

libsframe/
	* doc/sframe-spec.texi (Changes from Version 1 to Version 2):
	Mention that a SFrame FRE without any offsets flag indicates an
	outermost frame with an undefined RA.
	(fre_offset_count): Document that a FRE offset count of zero
	indicates an outermost frame with an undefined RA.
	* sframe.c (sframe_get_fre_ra_undefined_p): Use macro
	SFRAME_V2_FRE_RA_UNDEFINED_P.
	(sframe_fre_get_fp_offset, sframe_fre_get_ra_offset): Do not
	return fixed FP/RA offset if RA undefined.
	* sframe-dump.c (dump_sframe_func_with_fres): Show FRE without
	any offsets as "RA undefined".

gas/testsuite/
	* gas/cfi-sframe/cfi-sframe.exp: Run tests for .cfi_undefined RA
	on AArch64, s390x, and x86-64.
	* gas/cfi-sframe/cfi-sframe-aarch64-ra-undefined-1.d: Add test
	for .cfi_undefined RA on AArch64.
	* gas/cfi-sframe/cfi-sframe-aarch64-ra-undefined-1.s: Likewise.
	* as/cfi-sframe/cfi-sframe-s390x-ra-undefined-1.d: Add test
	for .cfi_undefined RA on s390x.
	* gas/cfi-sframe/cfi-sframe-s390x-ra-undefined-1.s: Likewise.
	* gas/cfi-sframe/cfi-sframe-x86_64-ra-undefined-1.d: Add test
	for .cfi_undefined RA on x86-64.
	* gas/cfi-sframe/cfi-sframe-x86_64-ra-undefined-1.s: Likewise.

Signed-off-by: Jens Remus <jremus@linux.ibm.com>
This commit is contained in:
Jens Remus
2025-10-15 17:45:48 +02:00
parent 6ca8915c61
commit 5079bf8959
15 changed files with 191 additions and 16 deletions
Download Patch File Download Diff File Expand all files Collapse all files

5
binutils/NEWS
View File

@@ -1,5 +1,10 @@
-*- text -*-
* SFrame stack trace format now represents an undefined return address as
an SFrame FRE without any offsets. libsframe provides a new API to test
for RA undefined, which is used when dumping SFrame information (e.g. using
objdump and readelf) to show such FREs as "RA undefined".
* Add --got-contents option to readelf to display the contents of
Global Offset Table (GOT) sections.

3
gas/NEWS
View File

@@ -1,5 +1,8 @@
-*- text -*-
* Emit an SFrame FRE with zero offsets to convey an undefined return address
in the SFrame stack trace format.
* ELF targets can now have section entity size specified for arbitrary
sections, using the new attribute letter 'E'.

61
gas/gen-sframe.c
View File

@@ -164,6 +164,7 @@ sframe_fre_set_ra_track (struct sframe_row_entry *fre, offsetT ra_offset)
{
fre->ra_loc = SFRAME_FRE_ELEM_LOC_STACK;
fre->ra_offset = ra_offset;
fre->ra_undefined_p = false;
fre->merge_candidate = false;
}
@@ -511,6 +512,8 @@ sframe_row_entry_new (void)
initialize it in sframe_row_entry_initialize () with the sticky
bit if set. */
fre->mangled_ra_p = false;
/* Reset the RA undefined status by to zero by default. */
fre->ra_undefined_p = false;
return fre;
}
@@ -552,6 +555,7 @@ output_sframe_row_entry (symbolS *fde_start_addr,
unsigned int fre_num_offsets;
unsigned int fre_offset_size;
unsigned int fre_base_reg;
bool fre_mangled_ra_p;
expressionS exp;
unsigned int fre_addr_size;
@@ -581,14 +585,30 @@ output_sframe_row_entry (symbolS *fde_start_addr,
}
/* Create the fre_info using the CFA base register, number of offsets and max
size of offset in this frame row entry. */
fre_base_reg = get_fre_base_reg_id (sframe_fre);
fre_num_offsets = get_fre_num_offsets (sframe_fre);
fre_offset_size = sframe_get_fre_offset_size (sframe_fre);
size of offset in this frame row entry. Represent RA undefined as FRE
without any offsets and all FRE info word fields zeroed. */
if (sframe_fre->ra_undefined_p)
{
fre_base_reg = 0;
fre_num_offsets = 0;
fre_offset_size = 0;
fre_mangled_ra_p = 0;
}
else
{
fre_base_reg = get_fre_base_reg_id (sframe_fre);
fre_num_offsets = get_fre_num_offsets (sframe_fre);
fre_offset_size = sframe_get_fre_offset_size (sframe_fre);
fre_mangled_ra_p = sframe_fre->mangled_ra_p;
}
fre_info = sframe_set_fre_info (fre_base_reg, fre_num_offsets,
fre_offset_size, sframe_fre->mangled_ra_p);
fre_offset_size, fre_mangled_ra_p);
out_one (fre_info);
/* Represent RA undefined as FRE without any offsets. */
if (sframe_fre->ra_undefined_p)
return;
idx = sframe_fre_offset_func_map_index (fre_offset_size);
gas_assert (idx < SFRAME_FRE_OFFSET_FUNC_MAP_INDEX_MAX);
@@ -944,6 +964,10 @@ sframe_row_entry_initialize (struct sframe_row_entry *cur_fre,
/* Treat RA mangling as a sticky bit. It retains its value until another
.cfi_negate_ra_state is seen. */
cur_fre->mangled_ra_p = prev_fre->mangled_ra_p;
/* Treat RA undefined as a sticky bit. It retains its value until a
.cfi_offset RA, .cfi_register RA, .cfi_restore RA, or .cfi_same_value RA
is seen. */
cur_fre->ra_undefined_p = prev_fre->ra_undefined_p;
}
/* Return SFrame register name for SP, FP, and RA, or NULL if other. */
@@ -1319,6 +1343,7 @@ sframe_xlate_do_restore (struct sframe_xlate_ctx *xlate_ctx,
gas_assert (cur_fre);
cur_fre->ra_loc = cie_fre->ra_loc;
cur_fre->ra_offset = cie_fre->ra_offset;
cur_fre->ra_undefined_p = cie_fre->ra_undefined_p;
cur_fre->merge_candidate = false;
}
return SFRAME_XLATE_OK;
@@ -1665,9 +1690,15 @@ sframe_xlate_do_cfi_escape (const struct sframe_xlate_ctx *xlate_ctx,
/* Translate DW_CFA_undefined into SFrame context.
DW_CFA_undefined op indicates that from now on, the previous value of
register can’t be restored anymore. In SFrame stack trace, we cannot
represent such a semantic. So, we skip generating an SFrame FDE for this,
when a register of interest is used with DW_CFA_undefined.
register can’t be restored anymore. In DWARF, for the return address (RA)
register, this indicates to an unwinder that there is no return address
and the unwind is complete.
In SFrame, represent the use of the RA register with DW_CFA_undefined as
SFrame FRE without any offsets. Stack tracers can use this as indication
that an outermost frame has been reached and the stack trace is complete.
The use of other registers of interest with DW_CFA_undefined cannot be
represented in SFrame. Therefore skip generating an SFrame FDE.
Return SFRAME_XLATE_OK if success. */
@@ -1676,15 +1707,24 @@ sframe_xlate_do_cfi_undefined (const struct sframe_xlate_ctx *xlate_ctx ATTRIBUT
const struct cfi_insn_data *cfi_insn)
{
if (cfi_insn->u.r == SFRAME_CFA_FP_REG
|| cfi_insn->u.r == SFRAME_CFA_RA_REG
|| cfi_insn->u.r == SFRAME_CFA_SP_REG)
{
as_warn (_("no SFrame FDE emitted; %s reg %u in .cfi_undefined"),
sframe_register_name (cfi_insn->u.r), cfi_insn->u.r);
return SFRAME_XLATE_ERR_NOTREPRESENTED; /* Not represented. */
}
else if (cfi_insn->u.r == SFRAME_CFA_RA_REG)
{
/* Represent RA undefined (i.e. outermost frame) as FRE without any
offsets. */
struct sframe_row_entry *cur_fre = xlate_ctx->cur_fre;
gas_assert (cur_fre);
/* Set RA undefined status bit. */
cur_fre->ra_undefined_p = true;
cur_fre->merge_candidate = false;
}
/* Safe to skip. */
return SFRAME_XLATE_OK;
}
@@ -1732,6 +1772,7 @@ sframe_xlate_do_same_value (const struct sframe_xlate_ctx *xlate_ctx,
{
cur_fre->ra_loc = SFRAME_FRE_ELEM_LOC_REG;
cur_fre->ra_offset = 0;
cur_fre->ra_undefined_p = false;
cur_fre->merge_candidate = false;
}
else if (cfi_insn->u.r == SFRAME_CFA_FP_REG)

3
gas/gen-sframe.h
View File

@@ -65,6 +65,9 @@ struct sframe_row_entry
/* Whether the return address is mangled with pauth code. */
bool mangled_ra_p;
/* Whether RA is undefined. */
bool ra_undefined_p;
/* Track CFA base (architectural) register ID. */
unsigned int cfa_base_reg;
/* Offset from the CFA base register for recovering CFA. */

20
gas/testsuite/gas/cfi-sframe/cfi-sframe-aarch64-ra-undefined-1.d Normal file
View File

@@ -0,0 +1,20 @@
#as: --gsframe
#objdump: --sframe=.sframe
#name: SFrame generation on aarch64 - .cfi_undefined RA
#...
Contents of the SFrame section .sframe:
Header :
Version: SFRAME_VERSION_2
Flags: SFRAME_F_FDE_FUNC_START_PCREL
Num FDEs: 1
Num FREs: 4
Function Index :
func idx \[0\]: pc = 0x0, size = 16 bytes
STARTPC +CFA +FP +RA +
0+0000 +sp\+0 +u +u +
0+0004 +sp\+16 +c\-16 +c\-8 +
0+0008 +RA undefined
0+000c +RA undefined

13
gas/testsuite/gas/cfi-sframe/cfi-sframe-aarch64-ra-undefined-1.s Normal file
View File

@@ -0,0 +1,13 @@
.cfi_startproc
stp fp, lr, [sp, #-16]!
.cfi_def_cfa_offset 16
.cfi_offset 29, -16
.cfi_offset 30, -8
nop
.cfi_undefined 30
ldp fp, lr, [sp], #16
.cfi_restore 20
.cfi_restore 19
.cfi_def_cfa_offset 0
ret lr
.cfi_endproc

21
gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-ra-undefined-1.d Normal file
View File

@@ -0,0 +1,21 @@
#name: SFrame generation on s390x - .cfi_undefined RA
#as: --gsframe
#objdump: --sframe=.sframe
#...
Contents of the SFrame section .sframe:
Header :
Version: SFRAME_VERSION_2
Flags: SFRAME_F_FDE_FUNC_START_PCREL
Num FDEs: 1
Num FREs: 4
Function Index :
func idx \[0\]: pc = 0x0, size = 18 bytes
STARTPC +CFA +FP +RA +
0+0000 +sp\+160 +u +u +
0+0006 +sp\+160 +u +c\-48 +
0+000a +RA undefined
0+0010 +sp\+160 +u +u +

11
gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-ra-undefined-1.s Normal file
View File

@@ -0,0 +1,11 @@
.cfi_startproc
stmg %r14,%r15,112(%r15)
.cfi_offset 14, -48
.cfi_offset 15, -40
nop
.cfi_undefined 14
lmg %r14,%r15,112(%r15)
.cfi_restore 15
.cfi_restore 14
br %r14
.cfi_endproc

22
gas/testsuite/gas/cfi-sframe/cfi-sframe-x86_64-ra-undefined-1.d Normal file
View File

@@ -0,0 +1,22 @@
#as: --gsframe -O0
#objdump: --sframe=.sframe
#name: SFrame generation on x86_64 - .cfi_undefined RA
#...
Contents of the SFrame section .sframe:
Header :
Version: SFRAME_VERSION_2
Flags: SFRAME_F_FDE_FUNC_START_PCREL
CFA fixed RA offset: \-8
Num FDEs: 1
Num FREs: 4
Function Index :
func idx \[0\]: pc = 0x0, size = 6 bytes
STARTPC +CFA +FP +RA +
0+0000 +sp\+8 +u +f +
0+0001 +sp\+16 +c\-16 +f +
0+0004 +fp\+16 +c\-16 +f +
0+0005 +RA undefined

11
gas/testsuite/gas/cfi-sframe/cfi-sframe-x86_64-ra-undefined-1.s Normal file
View File

@@ -0,0 +1,11 @@
.cfi_startproc
pushq %rbp
.cfi_def_cfa_offset 16
.cfi_offset 6, -16
movq %rsp, %rbp
.cfi_def_cfa_register 6
nop
.cfi_undefined 16
.cfi_def_cfa 7, 8
ret
.cfi_endproc

3
gas/testsuite/gas/cfi-sframe/cfi-sframe.exp
View File

@@ -66,6 +66,7 @@ if { [istarget "x86_64-*-*"] && [gas_sframe_check] } then {
run_dump_test "cfi-sframe-x86_64-empty-2"
run_dump_test "cfi-sframe-x86_64-empty-3"
run_dump_test "cfi-sframe-x86_64-empty-4"
run_dump_test "cfi-sframe-x86_64-ra-undefined-1"
set ASFLAGS "$old_ASFLAGS"
}
}
@@ -77,6 +78,7 @@ if { [istarget "aarch64*-*-*"] && [gas_sframe_check] } then {
run_dump_test "cfi-sframe-aarch64-3"
run_dump_test "cfi-sframe-aarch64-4"
run_dump_test "cfi-sframe-aarch64-pac-ab-key-1"
run_dump_test "cfi-sframe-aarch64-ra-undefined-1"
}
# s390x specific tests
@@ -91,4 +93,5 @@ if { [istarget "s390x*-*-*"] && [gas_sframe_check] } then {
run_dump_test "cfi-sframe-s390x-fpra-offset-2"
run_dump_test "cfi-sframe-s390x-fpra-register-1"
run_dump_test "cfi-sframe-s390x-fpra-register-2"
run_dump_test "cfi-sframe-s390x-ra-undefined-1"
}

1
include/sframe.h
View File

@@ -287,6 +287,7 @@ typedef struct sframe_fre_info
#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)
#define SFRAME_V2_FRE_RA_UNDEFINED_P(data) (SFRAME_V1_FRE_OFFSET_COUNT (data) == 0)
/* SFrame Frame Row Entry definitions.

10
libsframe/doc/sframe-spec.texi
View File

@@ -171,6 +171,11 @@ by CFA offset alignment factor and then revert CFA offset adjustment).
@end itemize
@item
[Errata 1] An ELF SFrame section has the type SHT_GNU_SFRAME.
@item
[Errata 2] An SFrame FRE info word offset count of zero indicates that the
return address (RA) is undefined for the range of PCs covered by the SFrame FRE.
A stack tracer may use this as indication that an outermost frame has been
reached and the stack trace is complete.
@end itemize
SFrame version 1 is now obsolete and should not be used.
@@ -777,7 +782,10 @@ SFRAME_FRE_OFFSET_4B.
@item 1-4
@tab @code{fre_offset_count}
@tab A max value of 15 is allowed. Typically, a value of upto 3 is sufficient
for most ABIs to track all three of CFA, FP and RA.
for most ABIs to track all three of CFA, FP and RA. A value of zero indicates
that the return address (RA) is undefined. A stack tracer may use this as
indication that an outermost frame has been reached and the stack trace is
complete.
@item 0
@tab @code{fre_cfa_base_reg_id}

15
libsframe/sframe-dump.c
View File

@@ -130,6 +130,7 @@ dump_sframe_func_with_fres (sframe_decoder_ctx *sfd_ctx,
uint64_t func_start_pc_vma = 0;
uint64_t fre_start_pc_vma = 0;
const char *base_reg_str[] = {"fp", "sp"};
bool ra_undefined_p = false;
int32_t cfa_offset = 0;
int32_t fp_offset = 0;
int32_t ra_offset = 0;
@@ -180,15 +181,25 @@ dump_sframe_func_with_fres (sframe_decoder_ctx *sfd_ctx,
: func_start_pc_vma + fre.fre_start_addr);
/* FIXME - fixup the err caching in array.
assert no error for base reg id. */
assert no error for base reg id and RA undefined. */
base_reg_id = sframe_fre_get_base_reg_id (&fre, &err[0]);
ra_undefined_p = sframe_fre_get_ra_undefined_p (sfd_ctx, &fre, &err[0]);
cfa_offset = sframe_fre_get_cfa_offset (sfd_ctx, &fre, &err[0]);
fp_offset = sframe_fre_get_fp_offset (sfd_ctx, &fre, &err[1]);
ra_offset = sframe_fre_get_ra_offset (sfd_ctx, &fre, &err[2]);
/* Dump CFA info. */
/* Dump VMA. */
printf ("\n");
printf (" %016"PRIx64, fre_start_pc_vma);
/* Dump RA undefined (FRE without any offsets). */
if (ra_undefined_p)
{
printf (" RA undefined");
continue;
}
/* Dump CFA info. */
sprintf (temp, "%s+%d", base_reg_str[base_reg_id], cfa_offset);
printf (" %-10s", temp);

8
libsframe/sframe.c
View File

@@ -134,7 +134,7 @@ sframe_get_fre_ra_mangled_p (uint8_t fre_info)
static bool
sframe_get_fre_ra_undefined_p (uint8_t fre_info)
{
return SFRAME_V1_FRE_OFFSET_COUNT (fre_info) == 0;
return SFRAME_V2_FRE_RA_UNDEFINED_P (fre_info);
}
/* Access functions for info from function descriptor entry. */
@@ -729,7 +729,8 @@ sframe_fre_get_fp_offset (sframe_decoder_ctx *dctx,
int8_t fp_offset = sframe_decoder_get_fixed_fp_offset (dctx);
/* 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)
if (fp_offset != SFRAME_CFA_FIXED_FP_INVALID
&& !sframe_get_fre_ra_undefined_p (fre->fre_info))
{
if (errp)
*errp = 0;
@@ -760,7 +761,8 @@ sframe_fre_get_ra_offset (sframe_decoder_ctx *dctx,
int8_t ra_offset = sframe_decoder_get_fixed_ra_offset (dctx);
/* 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)
if (ra_offset != SFRAME_CFA_FIXED_RA_INVALID
&& !sframe_get_fre_ra_undefined_p (fre->fre_info))
{
if (errp)
*errp = 0;