From 955570f0973d5ba361d5e63d26439947270c7954 Mon Sep 17 00:00:00 2001 From: Jens Remus Date: Fri, 11 Jul 2025 10:29:40 +0200 Subject: [PATCH] s390: Represent FP without RA saved in SFrame If an architecture uses both SFrame RA and FP tracking SFrame assumes that the RA offset is the 2nd offset and the FP offset is the 3rd offset following a SFrame FRE. An architecture does not necessarily need to save both on the stack (or in register) at the same time or even at all. SFrame cannot represent FP without RA saved on stack (or in a register), since it cannot distinguish whether the 2nd offset is the RA or FP offset. For s390x use an invalid SFrame RA offset from CFA value of zero as padding to represent the FP being saved when the RA is not saved. This aligns with the existing invalid SFrame fixed RA offset from CFA value of zero. In a stack tracer this then also naturally falls into place, as it can skip restoring the RA in the topmost frame, if both the fixed RA offset (from SFrame header) and the RA offset (from FDE) are zero, without any need to test architecture-specific flags. include/ * sframe.h (SFRAME_FRE_RA_OFFSET_INVALID): New define. Used as padding offset. * sframe-api.h (sframe_fre_get_ra_offset): Add comment that for s390x an offset value of SFRAME_FRE_RA_OFFSET_INVALID indicates that the RA is not saved. gas/ * gen-sframe.c (get_fre_num_offsets): For s390x account padding RA offset, if FP without RA saved. (sframe_get_fre_offset_size): Likewise. (output_sframe_row_entry): For s390x write a padding RA offset, if FP without RA needs to be represented. (sframe_do_fde): Enable FP without RA saved to be represented on s390x. libsframe/ * sframe.c (sframe_fre_get_ra_offset): Add comment that for s390x an offset value of SFRAME_FRE_RA_OFFSET_INVALID indicates that the RA is not saved. * sframe-dump.c (dump_sframe_func_with_fres): Treat invalid RA offsets as if they were undefined. Display them as "U" to distinguish them. * doc/sframe-spec.texi (s390x): Document s390x-specific use of SFRAME_FRE_RA_OFFSET_INVALID to represent FP without RA saved. gas/testsuite/ * gas/cfi-sframe/cfi-sframe.exp: Rename s390x-specific tests. * gas/cfi-sframe/cfi-sframe-s390x-fpra-offset-err-1.s: Rename to ... * cfi-sframe/cfi-sframe-s390x-fpra-offset-err-1.d: Likewise. * gas/cfi-sframe/cfi-sframe-s390x-fpra-offset-2.s: This. * gas/cfi-sframe/cfi-sframe-s390x-fpra-offset-2.d: Likewise. Update test verification pattern accordingly. * cfi-sframe/cfi-sframe-s390x-fpra-register-err-1.s: Rename to ... * cfi-sframe/cfi-sframe-s390x-fpra-register-err-1.d: Likewise. * gas/cfi-sframe/cfi-sframe-s390x-fpra-register-2.s: This. * gas/cfi-sframe/cfi-sframe-s390x-fpra-register-2.d: Likewise. Update test verification pattern accordingly. Signed-off-by: Jens Remus --- gas/gen-sframe.c | 38 ++++++++++++++----- .../cfi-sframe-s390x-fpra-offset-2.d | 22 +++++++++++ ...r-1.s => cfi-sframe-s390x-fpra-offset-2.s} | 0 .../cfi-sframe-s390x-fpra-offset-err-1.d | 15 -------- .../cfi-sframe-s390x-fpra-register-2.d | 22 +++++++++++ ...1.s => cfi-sframe-s390x-fpra-register-2.s} | 0 .../cfi-sframe-s390x-fpra-register-err-1.d | 15 -------- gas/testsuite/gas/cfi-sframe/cfi-sframe.exp | 4 +- include/sframe-api.h | 2 + include/sframe.h | 22 +++++++++++ libsframe/doc/sframe-spec.texi | 17 ++++++--- libsframe/sframe-dump.c | 4 ++ libsframe/sframe.c | 2 + 13 files changed, 116 insertions(+), 47 deletions(-) create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-fpra-offset-2.d rename gas/testsuite/gas/cfi-sframe/{cfi-sframe-s390x-fpra-offset-err-1.s => cfi-sframe-s390x-fpra-offset-2.s} (100%) delete mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-fpra-offset-err-1.d create mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-fpra-register-2.d rename gas/testsuite/gas/cfi-sframe/{cfi-sframe-s390x-fpra-register-err-1.s => cfi-sframe-s390x-fpra-register-2.s} (100%) delete mode 100644 gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-fpra-register-err-1.d diff --git a/gas/gen-sframe.c b/gas/gen-sframe.c index 2741a8f93af..547e693a7fa 100644 --- a/gas/gen-sframe.c +++ b/gas/gen-sframe.c @@ -340,7 +340,10 @@ get_fre_num_offsets (struct sframe_row_entry *sframe_fre) if (sframe_fre->bp_loc == SFRAME_FRE_ELEM_LOC_STACK) fre_num_offsets++; if (sframe_ra_tracking_p () - && sframe_fre->ra_loc == SFRAME_FRE_ELEM_LOC_STACK) + && (sframe_fre->ra_loc == SFRAME_FRE_ELEM_LOC_STACK + /* For s390x account padding RA offset, if FP without RA saved. */ + || (sframe_get_abi_arch () == SFRAME_ABI_S390X_ENDIAN_BIG + && sframe_fre->bp_loc == SFRAME_FRE_ELEM_LOC_STACK))) fre_num_offsets++; return fre_num_offsets; } @@ -362,9 +365,15 @@ sframe_get_fre_offset_size (struct sframe_row_entry *sframe_fre) cfa_offset_size = get_offset_size_in_bytes (sframe_fre->cfa_offset); if (sframe_fre->bp_loc == SFRAME_FRE_ELEM_LOC_STACK) bp_offset_size = get_offset_size_in_bytes (sframe_fre->bp_offset); - if (sframe_ra_tracking_p () - && sframe_fre->ra_loc == SFRAME_FRE_ELEM_LOC_STACK) - ra_offset_size = get_offset_size_in_bytes (sframe_fre->ra_offset); + if (sframe_ra_tracking_p ()) + { + if (sframe_fre->ra_loc == SFRAME_FRE_ELEM_LOC_STACK) + ra_offset_size = get_offset_size_in_bytes (sframe_fre->ra_offset); + /* For s390x account padding RA offset, if FP without RA saved. */ + else if (sframe_get_abi_arch () == SFRAME_ABI_S390X_ENDIAN_BIG + && sframe_fre->bp_loc == SFRAME_FRE_ELEM_LOC_STACK) + ra_offset_size = get_offset_size_in_bytes (SFRAME_FRE_RA_OFFSET_INVALID); + } /* Get the maximum size needed to represent the offsets. */ max_offset_size = cfa_offset_size; @@ -570,11 +579,20 @@ output_sframe_row_entry (symbolS *fde_start_addr, fre_offset_func_map[idx].out_func (sframe_fre->cfa_offset); fre_write_offsets++; - if (sframe_ra_tracking_p () - && sframe_fre->ra_loc == SFRAME_FRE_ELEM_LOC_STACK) + if (sframe_ra_tracking_p ()) { - fre_offset_func_map[idx].out_func (sframe_fre->ra_offset); - fre_write_offsets++; + if (sframe_fre->ra_loc == SFRAME_FRE_ELEM_LOC_STACK) + { + fre_offset_func_map[idx].out_func (sframe_fre->ra_offset); + fre_write_offsets++; + } + /* For s390x write padding RA offset, if FP without RA saved. */ + else if (sframe_get_abi_arch () == SFRAME_ABI_S390X_ENDIAN_BIG + && sframe_fre->bp_loc == SFRAME_FRE_ELEM_LOC_STACK) + { + fre_offset_func_map[idx].out_func (SFRAME_FRE_RA_OFFSET_INVALID); + fre_write_offsets++; + } } if (sframe_fre->bp_loc == SFRAME_FRE_ELEM_LOC_STACK) { @@ -1804,7 +1822,9 @@ sframe_do_fde (struct sframe_xlate_ctx *xlate_ctx, = get_dw_fde_end_addrS (xlate_ctx->dw_fde); } - if (sframe_ra_tracking_p ()) + /* ABI/arch except s390x cannot represent FP without RA saved. */ + if (sframe_ra_tracking_p () + && sframe_get_abi_arch () != SFRAME_ABI_S390X_ENDIAN_BIG) { struct sframe_row_entry *fre; diff --git a/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-fpra-offset-2.d b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-fpra-offset-2.d new file mode 100644 index 00000000000..305a917e325 --- /dev/null +++ b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-fpra-offset-2.d @@ -0,0 +1,22 @@ +#name: SFrame generation on s390x - FP and then RA saved on stack +#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: 5 + + Function Index : + + func idx \[0\]: pc = 0x0, size = 34 bytes + STARTPC +CFA +FP +RA + + 0+0000 +sp\+160 +u +u + + 0+0006 +sp\+160 +c\-72 +U + + 0+000c +sp\+160 +c\-72 +c\-48 + + 0+001a +sp\+160 +c-72 +U + + 0+0020 +sp\+160 +u +u + +#pass diff --git a/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-fpra-offset-err-1.s b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-fpra-offset-2.s similarity index 100% rename from gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-fpra-offset-err-1.s rename to gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-fpra-offset-2.s diff --git a/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-fpra-offset-err-1.d b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-fpra-offset-err-1.d deleted file mode 100644 index 7d71874111b..00000000000 --- a/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-fpra-offset-err-1.d +++ /dev/null @@ -1,15 +0,0 @@ -#name: SFrame generation on s390x - FP without RA saved on stack -#as: --gsframe -#warning: FP without RA on stack -#objdump: --sframe=.sframe -#... -Contents of the SFrame section .sframe: - - Header : - - Version: SFRAME_VERSION_2 - Flags: SFRAME_F_FDE_FUNC_START_PCREL - Num FDEs: 0 - Num FREs: 0 - -#pass diff --git a/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-fpra-register-2.d b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-fpra-register-2.d new file mode 100644 index 00000000000..7b719fd979f --- /dev/null +++ b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-fpra-register-2.d @@ -0,0 +1,22 @@ +#name: SFrame generation on s390x - FP and then RA saved in FPR registers +#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: 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 +r17 +U + + 0+0008 +sp\+160 +r17 +r16 + + 0+0014 +sp\+160 +r17 +U + + 0+0018 +sp\+160 +u +u + +#pass diff --git a/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-fpra-register-err-1.s b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-fpra-register-2.s similarity index 100% rename from gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-fpra-register-err-1.s rename to gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-fpra-register-2.s diff --git a/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-fpra-register-err-1.d b/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-fpra-register-err-1.d deleted file mode 100644 index f6854c26814..00000000000 --- a/gas/testsuite/gas/cfi-sframe/cfi-sframe-s390x-fpra-register-err-1.d +++ /dev/null @@ -1,15 +0,0 @@ -#name: SFrame generation on s390x - FP without RA saved in registers -#as: --gsframe -#warning: FP without RA on stack -#objdump: --sframe=.sframe -#... -Contents of the SFrame section .sframe: - - Header : - - Version: SFRAME_VERSION_2 - Flags: SFRAME_F_FDE_FUNC_START_PCREL - Num FDEs: 0 - Num FREs: 0 - -#pass diff --git a/gas/testsuite/gas/cfi-sframe/cfi-sframe.exp b/gas/testsuite/gas/cfi-sframe/cfi-sframe.exp index 1e7fc9e03ca..b26ce60c6e5 100644 --- a/gas/testsuite/gas/cfi-sframe/cfi-sframe.exp +++ b/gas/testsuite/gas/cfi-sframe/cfi-sframe.exp @@ -119,7 +119,7 @@ if { [istarget "s390x*-*-*"] && [gas_sframe_check] } then { run_dump_test "cfi-sframe-s390x-err-2" run_dump_test "cfi-sframe-s390x-err-3" run_dump_test "cfi-sframe-s390x-fpra-offset-1" - run_dump_test "cfi-sframe-s390x-fpra-offset-err-1" + 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-err-1" + run_dump_test "cfi-sframe-s390x-fpra-register-2" } diff --git a/include/sframe-api.h b/include/sframe-api.h index cb94f358b3d..ac4f19a66f0 100644 --- a/include/sframe-api.h +++ b/include/sframe-api.h @@ -224,6 +224,8 @@ sframe_fre_get_fp_offset (sframe_decoder_ctx *dctx, /* Get the RA offset from the FRE. If the offset is invalid, sets errp. + For s390x an RA offset value of SFRAME_FRE_RA_OFFSET_INVALID indicates + that the RA is not saved, which is only valid in the topmost frame. For s390x the offset may be an encoded register number, indicated by LSB set to one, which is only valid in the topmost frame. */ extern int32_t diff --git a/include/sframe.h b/include/sframe.h index 7bbdf04db17..28b625b3258 100644 --- a/include/sframe.h +++ b/include/sframe.h @@ -248,6 +248,10 @@ typedef struct sframe_func_desc_entry may or may not be tracked. */ #define SFRAME_FRE_FP_OFFSET_IDX 2 +/* Invalid RA offset. Currently used for s390x as padding to represent FP + without RA saved. */ +#define SFRAME_FRE_RA_OFFSET_INVALID 0 + typedef struct sframe_fre_info { /* Information about @@ -310,6 +314,24 @@ typedef struct sframe_fre_info fi Note that in AAPCS64, a frame record, if created, will save both FP and LR on stack. + + s390x: + offset1 (interpreted as CFA = BASE_REG + offset1) + if RA is being tracked + offset2 (interpreted as RA = CFA + offset2; an offset value of + SFRAME_FRE_RA_OFFSET_INVALID indicates a dummy padding RA offset + to represent FP without RA saved on stack) + if FP is being tracked + offset3 (intrepreted as FP = CFA + offset3) + fi + else + if FP is being tracked + offset2 (intrepreted as FP = CFA + offset2) + fi + fi + Note that in s390x, if a FP/RA offset2/offset3 value has the least- + significant bit set it represents a DWARF register number shifted to the + left by 1 to restore the FP/RA value from. */ /* Used when SFRAME_FRE_TYPE_ADDR1 is specified as FRE type. */ diff --git a/libsframe/doc/sframe-spec.texi b/libsframe/doc/sframe-spec.texi index 1938207233c..6ba6c131edb 100644 --- a/libsframe/doc/sframe-spec.texi +++ b/libsframe/doc/sframe-spec.texi @@ -152,6 +152,9 @@ DWARF register number. FP/RA offset. @item SFRAME_V2_S390X_OFFSET_DECODE_REGNUM: Decode a DWARF register number from an FP/RA offset. + @item SFRAME_FRE_RA_OFFSET_INVALID: Invalid RA offset value (like +SFRAME_CFA_FIXED_RA_INVALID). Used on s390x as padding offset to represent +FP without RA saved. @end itemize @end itemize @@ -890,12 +893,13 @@ The (64-bit) s390x ELF ABI does not mandate the precise location in a function where the return address (RA) and frame pointer (FP) are saved, if at all. Hence the need to track RA in the SFrame stack trace format. As RA is being tracked in this ABI, the second stack offset is always used to locate the RA -stack slot, by interpreting it as: RA = CFA + offset2. RA remains unchanged, -if the offset is not available. Stack tracers are recommended to validate that -the "unchanged RA" pattern, when present, is seen only for the topmost stack -frame. The third stack offset is used to locate the FP stack slot, by -interpreting it as: FP = CFA + offset3. FP remains unchanged, if the offset is -not available. +stack slot, by interpreting it as: RA = CFA + offset2, unless the offset has a +value of @code{SFRAME_FRE_RA_OFFSET_INVALID}. RA remains unchanged, if the +offset is not available or has a value of @code{SFRAME_FRE_RA_OFFSET_INVALID}. +Stack tracers are recommended to validate that the "unchanged RA" pattern, when +present, is seen only for the topmost stack frame. The third stack offset is +used to locate the FP stack slot, by interpreting it as: FP = CFA + offset3. +FP remains unchanged, if the offset is not available. In leaf functions the RA and FP may be saved in other registers, such as floating-point registers (FPRs), instead of on the stack. To represent this @@ -919,6 +923,7 @@ Hence, in summary: @item 1 @tab CFA = @code{BASE_REG} + offset1 @item 2 @tab RA stack slot = CFA + offset2, if (offset2 & 1 == 0) @*RA register number = offset2 >> 1, if (offset2 & 1 == 1) + @*RA not saved if (offset2 == @code{SFRAME_FRE_RA_OFFSET_INVALID}) @item 3 @tab FP stack slot = CFA + offset3, if (offset3 & 1 == 0) @*FP register number = offset3 >> 1, if (offset3 & 1 == 1) @end multitable diff --git a/libsframe/sframe-dump.c b/libsframe/sframe-dump.c index f17ff64e122..d55d3847194 100644 --- a/libsframe/sframe-dump.c +++ b/libsframe/sframe-dump.c @@ -211,6 +211,10 @@ dump_sframe_func_with_fres (sframe_decoder_ctx *sfd_ctx, if (sframe_decoder_get_fixed_ra_offset (sfd_ctx) != SFRAME_CFA_FIXED_RA_INVALID) strcpy (temp, "f"); + /* If an ABI does track RA offset, e.g. s390x, it can be a padding + to represent FP without RA being saved on stack. */ + else if (err[2] == 0 && ra_offset == SFRAME_FRE_RA_OFFSET_INVALID) + sprintf (temp, "U"); else if (err[2] == 0) { if (is_sframe_abi_arch_s390x (sfd_ctx) diff --git a/libsframe/sframe.c b/libsframe/sframe.c index af40e5b4fad..d8d370da90d 100644 --- a/libsframe/sframe.c +++ b/libsframe/sframe.c @@ -733,6 +733,8 @@ sframe_fre_get_fp_offset (sframe_decoder_ctx *dctx, /* Get the RA offset from the FRE. If the offset is invalid, sets errp. + For s390x an RA offset value of SFRAME_FRE_RA_OFFSET_INVALID indicates + that the RA is not saved, which is only valid in the topmost frame. For s390x the offset may be an encoded register number, indicated by LSB set to one, which is only valid in the topmost frame. */ -- 2.47.2