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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

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;