[RFC,v3,2/2] s390: SFrame track FP/RA saved in register
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Commit Message
GCC on s390x, when in a leaf function, can be observed to save the
frame pointer (FP) and/or return address (RA) register in a floating-
point registers (FPR) instead of on the stack. This is declared using
the following CFI directive:
.cfi_register <fp/ra-regno>, <fpr-regno>
SFrame cannot represent the FP and/or RA being saved in another
register. It does only track the CFA base register (SP/FP), CFA offset
from CFA base register, and FP and RA save area offsets from CFA.
On s390x the FP and/or RA are only saved in another FPR when in a leaf
function. That is a function that does not call any other functions.
Therefore it can ever only be the topmost function in a call chain.
During function return, if the RA would be restored into a non-default
RA register, the function would also only ever be the topmost function
on the call stack.
An unwinder by default has access to all registers of the function that
if the topmost on the call stack. Therefore no further information would
be required for those registers.
Represent the FP/RA in another register on s390, by encoding the
register number shifted by one to the left with the least-significant
bit set in the offset as follows:
offset = (regno << 1) | 1
Add s390-specific SFrame (error) test cases for FP/RA being saved in
FPRs in leaf-function.
gas/
* gen-sframe.c (s390_sframe_xlate_do_register): New s390-
specific function to represent FP/RA in another register on
s390.
(sframe_xlate_do_register): Invoke s390_sframe_xlate_do_register
on s390.
libsframe/
* sframe-dump.c (is_sframe_abi_arch_s390): New helper to test
whether ABI/arch is s390.
(dump_sframe_func_with_fres): Dump FP/RA in another register on
s390.
gas/testsuite/
* gas/cfi-sframe/cfi-sframe.exp: Update s390-specific SFrame
(error) test cases.
* gas/cfi-sframe/cfi-sframe-s390-3.s: New s390-specific SFrame
test case for FP/RA saved in register on s390.
* gas/cfi-sframe/cfi-sframe-s390-3.d: Likewise.
* gas/cfi-sframe/cfi-sframe-s390-err-6.s: New s390-specific
SFrame error test case for FP without RA saved in register.
* gas/cfi-sframe/cfi-sframe-s390-err-6.d: Likewise.
* gas/cfi-sframe/cfi-sframe-s390-err-3.s: s390-specific SFrame
error test case 3 no longer triggers an error and is renamed as
test case 4.
* gas/cfi-sframe/cfi-sframe-s390-err-3.d: Likewise.
* gas/cfi-sframe/cfi-sframe-s390-4.s: Likewise.
* gas/cfi-sframe/cfi-sframe-s390-4.d: Likewise. Added expected
SFrame dump output.
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
* gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-4.d: # GCL: missing file
* gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-3.d -> gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-6.d: # GCL: missing file
* gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-3.s -> gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-4.s: # GCL: missing file
---
Notes (jremus):
Changes v2 -> v3:
- New patch.
Currently there is no mean to determine whether a function is a leaf
function. Neither an annotation that a section of the assembler code
does not call any function. Both would guarantee that the code will
only ever appear topmost on the call stack, so that the unwinder by
default has access to all registers.
Therefore SFrame generation cannot determine whether saving of FP/RA
registers in other registers such as FPR is actually valid. It needs
to trust the CFI, as it would need to to anyway.
The s390-specific functionality could be made dependent on TC_S390
at compile-time instead of on sframe_get_abi_arch() at run-time.
sframe_fre_set_{bp|ra}_track() could be renamed to
sframe_fre_set_{fp|ra}_track_offset() and new
sframe_fre_set_{fp|ra}_track_register() could be introduced. These
would call some architecture-specific callback to perform the encoding
of the dw2renum as offset.
gas/gen-sframe.c | 35 +++++++++++++++++++
.../gas/cfi-sframe/cfi-sframe-s390-3.d | 22 ++++++++++++
.../gas/cfi-sframe/cfi-sframe-s390-3.s | 15 ++++++++
.../gas/cfi-sframe/cfi-sframe-s390-4.d | 21 +++++++++++
...frame-s390-err-3.s => cfi-sframe-s390-4.s} | 0
...e-s390-err-3.d => cfi-sframe-s390-err-6.d} | 2 +-
.../gas/cfi-sframe/cfi-sframe-s390-err-6.s | 15 ++++++++
gas/testsuite/gas/cfi-sframe/cfi-sframe.exp | 4 ++-
libsframe/sframe-dump.c | 22 ++++++++++--
9 files changed, 132 insertions(+), 4 deletions(-)
create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-3.d
create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-3.s
create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-4.d
rename gas/testsuite/gas/cfi-sframe/{cfi-sframe-s390-err-3.s => cfi-sframe-s390-4.s} (100%)
rename gas/testsuite/gas/cfi-sframe/{cfi-sframe-s390-err-3.d => cfi-sframe-s390-err-6.d} (74%)
create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-6.s
Comments
Am 12.04.2024 um 18:36 schrieb Jens Remus:
> GCC on s390x, when in a leaf function, can be observed to save the
> frame pointer (FP) and/or return address (RA) register in a floating-
> point registers (FPR) instead of on the stack. This is declared using
> the following CFI directive:
>
> .cfi_register <fp/ra-regno>, <fpr-regno>
>
> SFrame cannot represent the FP and/or RA being saved in another
> register. It does only track the CFA base register (SP/FP), CFA offset
> from CFA base register, and FP and RA save area offsets from CFA.
>
> On s390x the FP and/or RA are only saved in another FPR when in a leaf
> function. That is a function that does not call any other functions.
> Therefore it can ever only be the topmost function in a call chain.
> During function return, if the RA would be restored into a non-default
> RA register, the function would also only ever be the topmost function
> on the call stack.
> An unwinder by default has access to all registers of the function that
> if the topmost on the call stack. Therefore no further information would
> be required for those registers.
>
> Represent the FP/RA in another register on s390, by encoding the
> register number shifted by one to the left with the least-significant
> bit set in the offset as follows:
>
> offset = (regno << 1) | 1
>
> Add s390-specific SFrame (error) test cases for FP/RA being saved in
> FPRs in leaf-function.
>
> gas/
> * gen-sframe.c (s390_sframe_xlate_do_register): New s390-
> specific function to represent FP/RA in another register on
> s390.
> (sframe_xlate_do_register): Invoke s390_sframe_xlate_do_register
> on s390.
>
> libsframe/
> * sframe-dump.c (is_sframe_abi_arch_s390): New helper to test
> whether ABI/arch is s390.
> (dump_sframe_func_with_fres): Dump FP/RA in another register on
> s390.
>
> gas/testsuite/
> * gas/cfi-sframe/cfi-sframe.exp: Update s390-specific SFrame
> (error) test cases.
> * gas/cfi-sframe/cfi-sframe-s390-3.s: New s390-specific SFrame
> test case for FP/RA saved in register on s390.
> * gas/cfi-sframe/cfi-sframe-s390-3.d: Likewise.
> * gas/cfi-sframe/cfi-sframe-s390-err-6.s: New s390-specific
> SFrame error test case for FP without RA saved in register.
> * gas/cfi-sframe/cfi-sframe-s390-err-6.d: Likewise.
> * gas/cfi-sframe/cfi-sframe-s390-err-3.s: s390-specific SFrame
> error test case 3 no longer triggers an error and is renamed as
> test case 4.
> * gas/cfi-sframe/cfi-sframe-s390-err-3.d: Likewise.
> * gas/cfi-sframe/cfi-sframe-s390-4.s: Likewise.
> * gas/cfi-sframe/cfi-sframe-s390-4.d: Likewise. Added expected
> SFrame dump output.
I will fix the indentation in the next version.
>
> Signed-off-by: Jens Remus <jremus@linux.ibm.com>
>
> * gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-4.d: # GCL: missing file
> * gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-3.d -> gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-6.d: # GCL: missing file
> * gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-3.s -> gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-4.s: # GCL: missing file
Above three lines have erroneously creeped in, while experimenting with
custom (prepare-)commit-msg Git hooks to generate/validate the GNU
Changelog entries. (sigh!) I will remove them in the next version.
> ---
...
Regards,
Jens
@@ -1150,6 +1150,37 @@ sframe_xlate_do_val_offset (struct sframe_xlate_ctx *xlate_ctx ATTRIBUTE_UNUSED,
return SFRAME_XLATE_OK;
}
+/* S390-specific translate DW_CFA_register into SFrame context.
+ Return SFRAME_XLATE_OK if success. */
+
+static int
+s390_sframe_xlate_do_register (struct sframe_xlate_ctx *xlate_ctx,
+ struct cfi_insn_data *cfi_insn)
+{
+ /* The scratchpad FRE currently being updated with each cfi_insn
+ being interpreted. This FRE eventually gets linked in into the
+ list of FREs for the specific function. */
+ struct sframe_row_entry *cur_fre = xlate_ctx->cur_fre;
+
+ gas_assert (cur_fre);
+
+ /* Change the rule for the register indicated by the register number to
+ be the specified register. Encode the register number as offset by
+ shifting it to the left by one and setting the least-significant bit
+ (LSB). The LSB can be used to differentiate offsets from register
+ numbers, as offsets from CFA are always a multiple of -8 on s390x. */
+ if (cfi_insn->u.rr.reg1 == SFRAME_CFA_FP_REG)
+ sframe_fre_set_bp_track (cur_fre, cfi_insn->u.rr.reg2 << 1 | 1);
+#ifdef SFRAME_FRE_RA_TRACKING
+ else if (sframe_ra_tracking_p ()
+ && cfi_insn->u.rr.reg1 == SFRAME_CFA_RA_REG)
+ sframe_fre_set_ra_track (cur_fre, cfi_insn->u.rr.reg2 << 1 | 1);
+#endif
+
+ /* Safe to skip. */
+ return SFRAME_XLATE_OK;
+}
+
/* Translate DW_CFA_register into SFrame context.
Return SFRAME_XLATE_OK if success. */
@@ -1157,6 +1188,10 @@ static int
sframe_xlate_do_register (struct sframe_xlate_ctx *xlate_ctx ATTRIBUTE_UNUSED,
struct cfi_insn_data *cfi_insn)
{
+ /* Conditionally invoke S390-specific implementation. */
+ if (sframe_get_abi_arch () == SFRAME_ABI_S390_ENDIAN_BIG)
+ return s390_sframe_xlate_do_register (xlate_ctx, cfi_insn);
+
/* Previous value of register1 is register2. However, if the specified
register1 is not interesting (FP or RA reg), the current DW_CFA_register
instruction can be safely skipped without sacrificing the asynchronicity of
new file mode 100644
@@ -0,0 +1,22 @@
+#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: 5
+
+ Function Index :
+
+ func idx \[0\]: pc = 0x0, size = 26 bytes
+ STARTPC +CFA +FP +RA +
+ 0+0000 +sp\+160 +u +u +
+ 0+0004 +sp\+160 +u +r16 +
+ 0+0008 +sp\+160 +r17 +r16 +
+ 0+0014 +sp\+160 +u +r16 +
+ 0+0018 +sp\+160 +u +u +
+#pass
new file mode 100644
@@ -0,0 +1,15 @@
+ .cfi_sections .sframe
+ .cfi_startproc
+ ldgr %f0,%r14
+ .cfi_register 14, 16
+ ldgr %f2,%r11
+ .cfi_register 11, 17
+ la %r11,0
+ la %r14,0
+.Lreturn:
+ lgdr %r11,%f2
+ .cfi_restore 11
+ lgdr %r14,%f0
+ .cfi_restore 14
+ br %r14
+ .cfi_endproc
new file mode 100644
@@ -0,0 +1,21 @@
+#name: SFrame generation on s390
+#as: --gsframe
+#objdump: --sframe=.sframe
+#...
+Contents of the SFrame section .sframe:
+
+ Header :
+
+ Version: SFRAME_VERSION_2
+ Flags: NONE
+ Num FDEs: 1
+ Num FREs: 2
+
+ Function Index :
+
+ func idx \[0\]: pc = 0x0, size = 6 bytes
+ STARTPC +CFA +FP +RA +
+ 0+0000 +sp\+160 +u +u +
+ 0+0004 +sp\+160 +u +r7 +
+
+#pass:
similarity index 100%
rename from gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-3.s
rename to gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-4.s
similarity index 74%
rename from gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-3.d
rename to gas/testsuite/gas/cfi-sframe/cfi-sframe-s390-err-6.d
@@ -1,6 +1,6 @@
#name: SFrame generation on s390
#as: --gsframe
-#warning: skipping SFrame FDE due to .cfi_register specifying RA register
+#warning: skipping SFrame FDE due to FP without RA on stack
#objdump: --sframe=.sframe
#...
Contents of the SFrame section .sframe:
new file mode 100644
@@ -0,0 +1,15 @@
+ .cfi_sections .sframe
+ .cfi_startproc
+ ldgr %f2,%r11
+ .cfi_register 11, 17
+ ldgr %f0,%r14
+ .cfi_register 14, 16
+ la %r11,0
+ la %r14,0
+.Lreturn:
+ lgdr %r14,%f0
+ .cfi_restore 14
+ lgdr %r11,%f2
+ .cfi_restore 11
+ br %r14
+ .cfi_endproc
@@ -105,9 +105,11 @@ if { [istarget "aarch64*-*-*"] && [gas_sframe_check] } then {
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-s390-3"
+ run_dump_test "cfi-sframe-s390-4"
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"
+ run_dump_test "cfi-sframe-s390-err-6"
}
@@ -40,6 +40,14 @@ is_sframe_abi_arch_aarch64 (sframe_decoder_ctx *sfd_ctx)
return aarch64_p;
}
+/* Return TRUE if the SFrame section is associated with the s390 ABIs. */
+
+static bool
+is_sframe_abi_arch_s390 (sframe_decoder_ctx *sfd_ctx)
+{
+ return sframe_decoder_get_abi_arch (sfd_ctx) == SFRAME_ABI_S390_ENDIAN_BIG;
+}
+
static void
dump_sframe_header (sframe_decoder_ctx *sfd_ctx)
{
@@ -175,7 +183,12 @@ dump_sframe_func_with_fres (sframe_decoder_ctx *sfd_ctx,
/* Dump SP/FP info. */
if (err[1] == 0)
- sprintf (temp, "c%+d", fp_offset);
+ {
+ if (is_sframe_abi_arch_s390 (sfd_ctx) && (fp_offset & 1))
+ sprintf (temp, "r%d", fp_offset >> 1);
+ else
+ sprintf (temp, "c%+d", fp_offset);
+ }
else
strcpy (temp, "u");
printf ("%-10s", temp);
@@ -187,7 +200,12 @@ dump_sframe_func_with_fres (sframe_decoder_ctx *sfd_ctx,
!= SFRAME_CFA_FIXED_RA_INVALID)
strcpy (temp, "f");
else if (err[2] == 0)
- sprintf (temp, "c%+d", ra_offset);
+ {
+ if (is_sframe_abi_arch_s390 (sfd_ctx) && (ra_offset & 1))
+ sprintf (temp, "r%d", ra_offset >> 1);
+ else
+ sprintf (temp, "c%+d", ra_offset);
+ }
else
strcpy (temp, "u");