On Thu, 22 Aug 2024, Bernd Edlinger wrote:
> This affects only the RISC-V targets, where the compiler options
> -gvariable-location-views and consequently also -ginline-points
> are disabled by default, which is unexpected and disables some
> useful features of the generated debug info.
>
> Due to a bug in the gas assembler the .loc statement
> is not usable to generate location view debug info.
> That is detected by configure:
>
> configure:31500: checking assembler for dwarf2 debug_view support
> configure:31509: .../riscv-unknown-elf/bin/as -o conftest.o conftest.s >&5
> conftest.s: Assembler messages:
> conftest.s:5: Error: .uleb128 only supports constant or subtract expressions
> conftest.s:6: Error: .uleb128 only supports constant or subtract expressions
> configure:31512: $? = 1
> configure: failed program was
> .file 1 "conftest.s"
> .loc 1 3 0 view .LVU1
> nop
> .data
> .uleb128 .LVU1
> .uleb128 .LVU1
>
> configure:31523: result: no
>
> This results in dwarf2out_as_locview_support being set to false,
> and that creates a sequence of events, with the end result that
> most inlined functions either have no DW_AT_entry_pc, or one
> with a wrong entry pc value.
>
> But the location views can also be generated without using any
> .loc statements, therefore we should enable the option
> -gvariable-location-views by default, regardless of the status
> of -gas-locview-support.
>
> Note however, that the combination of the following compiler options
> -g -O2 -gvariable-location-views -gno-as-loc-support
> turned out to create invalid assembler intermediate files,
> with lots of assembler errors like:
> Error: leb128 operand is an undefined symbol: .LVU3
>
> This affects all targets, except RISC-V of course ;-)
> and is fixed by the changes in dwarf2out.cc
>
> Finally the .debug_loclists created without assembler locview support
> did contain location view pairs like v0000000ffffffff v000000000000000
> which is the value from FORCE_RESET_NEXT_VIEW, but that is most likely
> not as expected either, so change that as well.
>
> gcc/ChangeLog:
>
> * dwarf2out.cc (dwarf2out_maybe_output_loclist_view_pair,
> output_loc_list): Correct handling of -gno-as-loc-support,
> use ZERO_VIEW_P to output view number as zero value.
> * toplev.cc (process_options): Do not automatically disable
> -gvariable-location-views when -gno-as-loc-support or
> -gno-as-locview-support is used.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.dg/debug/dwarf2/inline2.c: Add checks for inline entry_pc.
> * gcc.dg/debug/dwarf2/inline6.c: Add -gno-as-loc-support and check
> the resulting location views.
> ---
> gcc/dwarf2out.cc | 16 ++++++++++------
> gcc/testsuite/gcc.dg/debug/dwarf2/inline2.c | 3 +++
> gcc/testsuite/gcc.dg/debug/dwarf2/inline6.c | 7 ++++++-
> gcc/toplev.cc | 4 +---
> 4 files changed, 20 insertions(+), 10 deletions(-)
>
> v2: fixed the boot-strap error triggered by v1 on any target, except RISC-V,
> the issue was triggered by libstdc++-v3/src/c++11/cxx11-ios_failure-lt.s
> which is generated using -gno-as-loc-support, which triggered a latent issue.
>
> v3: added some tests for the fixed bugs.
>
> v4: fixed test failures on some targets, avoid hash sign as it is target
> dependent.
>
> Regression-tested on x86_64-pc-linux-gnu, riscv-unknown-elf
> and riscv64-unknown-elf, OK for trunk?
>
> diff --git a/gcc/dwarf2out.cc b/gcc/dwarf2out.cc
> index 362d695674b..c30dad1513a 100644
> --- a/gcc/dwarf2out.cc
> +++ b/gcc/dwarf2out.cc
> @@ -10374,7 +10374,7 @@ dwarf2out_maybe_output_loclist_view_pair
> (dw_loc_list_ref curr)
> #ifdef DW_LLE_view_pair
> dw2_asm_output_data (1, DW_LLE_view_pair, "DW_LLE_view_pair");
>
> - if (dwarf2out_as_locview_support)
> + if (dwarf2out_as_locview_support && dwarf2out_as_loc_support)
I'm wondering about these hunks - dwarf2out_as_loc_support indicates
the assembler supports .loc and dwarf2out_as_locview_support
indicates it supports location views within .loc, it's odd to have
dwarf2out_as_locview_support set but not dwarf2out_as_loc_support.
How does this happen? May I suggest to adjust
dwarf2out_default_as_locview_support to require
dwarf2out_default_as_loc_support?
> {
> if (ZERO_VIEW_P (curr->vbegin))
> dw2_asm_output_data_uleb128 (0, "Location view begin");
> @@ -10396,8 +10396,10 @@ dwarf2out_maybe_output_loclist_view_pair
> (dw_loc_list_ref curr)
> }
> else
> {
> - dw2_asm_output_data_uleb128 (curr->vbegin, "Location view begin");
> - dw2_asm_output_data_uleb128 (curr->vend, "Location view end");
> + dw2_asm_output_data_uleb128 (ZERO_VIEW_P (curr->vbegin)
> + ? 0 : curr->vbegin, "Location view begin");
> + dw2_asm_output_data_uleb128 (ZERO_VIEW_P (curr->vend)
> + ? 0 : curr->vend, "Location view end");
> }
> #endif /* DW_LLE_view_pair */
>
> @@ -10430,7 +10432,7 @@ output_loc_list (dw_loc_list_ref list_head)
> vcount++;
>
> /* ?? dwarf_split_debug_info? */
> - if (dwarf2out_as_locview_support)
> + if (dwarf2out_as_locview_support && dwarf2out_as_loc_support)
> {
> char label[MAX_ARTIFICIAL_LABEL_BYTES];
>
> @@ -10460,10 +10462,12 @@ output_loc_list (dw_loc_list_ref list_head)
> }
> else
> {
> - dw2_asm_output_data_uleb128 (curr->vbegin,
> + dw2_asm_output_data_uleb128 (ZERO_VIEW_P (curr->vbegin)
> + ? 0 : curr->vbegin,
> "View list begin (%s)",
> list_head->vl_symbol);
> - dw2_asm_output_data_uleb128 (curr->vend,
> + dw2_asm_output_data_uleb128 (ZERO_VIEW_P (curr->vend)
> + ? 0 : curr->vend,
> "View list end (%s)",
> list_head->vl_symbol);
> }
> diff --git a/gcc/testsuite/gcc.dg/debug/dwarf2/inline2.c
> b/gcc/testsuite/gcc.dg/debug/dwarf2/inline2.c
> index 9c36450ae2d..6893ddfa2eb 100644
> --- a/gcc/testsuite/gcc.dg/debug/dwarf2/inline2.c
> +++ b/gcc/testsuite/gcc.dg/debug/dwarf2/inline2.c
> @@ -30,6 +30,9 @@
> layout. */
> /* { dg-final { scan-assembler-times "\\(DIE \\(\[^\n\]*\\)
> DW_TAG_lexical_block" 0 } } */
>
> +/* Each inline instance should have DW_AT_entry_pc and DW_AT_GNU_entry_view.
> */
> +/* { dg-final { scan-assembler-times " DW_AT_entry_pc" 6 } } */
> +/* { dg-final { scan-assembler-times " DW_AT_GNU_entry_view" 6 } } */
>
> /* There are 3 DW_AT_inline attributes: one per abstract inline instance.
> The value of the attribute must be 0x3, meaning the function was
> diff --git a/gcc/testsuite/gcc.dg/debug/dwarf2/inline6.c
> b/gcc/testsuite/gcc.dg/debug/dwarf2/inline6.c
> index fde8c27820d..f5ca02205c0 100644
> --- a/gcc/testsuite/gcc.dg/debug/dwarf2/inline6.c
> +++ b/gcc/testsuite/gcc.dg/debug/dwarf2/inline6.c
> @@ -16,7 +16,7 @@
>
> /* Explicitly use dwarf-5 which uses DW_FORM_implicit_const. */
> /* { dg-do compile } */
> -/* { dg-options "-O -g3 -gdwarf-5 -dA -fgnu89-inline" } */
> +/* { dg-options "-O -g3 -gdwarf-5 -dA -fgnu89-inline -gno-as-loc-support" }
> */
>
> /* There are 6 inlined subroutines:
> - One for each subroutine inlined into main, that's 3.
> @@ -29,6 +29,11 @@
> layout. */
> /* { dg-final { scan-assembler-times "\\(DIE \\(\[^\n\]*\\)
> DW_TAG_lexical_block" 0 } } */
>
> +/* Each inline instance should have DW_AT_entry_pc and DW_AT_GNU_entry_view.
> */
> +/* { dg-final { scan-assembler-times " DW_AT_entry_pc" 6 } } */
> +/* { dg-final { scan-assembler-times " DW_AT_GNU_entry_view" 6 } } */
> +/* { dg-final { scan-assembler-times "uleb128\[^\n\]*LVU\[^\n\]* View list
> (begin|end)" 0 } } */
> +/* { dg-final { scan-assembler-times "uleb128\[^\n\]*0xffffffff\[^\n\]* View
> list (begin|end)" 0 } } */
>
> /* There are 3 DW_AT_inline attributes: one per abstract inline instance.
> The value of the attribute must be 0x3, meaning the function was
> diff --git a/gcc/toplev.cc b/gcc/toplev.cc
> index eee4805b504..292948122de 100644
> --- a/gcc/toplev.cc
> +++ b/gcc/toplev.cc
> @@ -1475,9 +1475,7 @@ process_options ()
> = (flag_var_tracking
> && debug_info_level >= DINFO_LEVEL_NORMAL
> && dwarf_debuginfo_p ()
> - && !dwarf_strict
> - && dwarf2out_as_loc_support
> - && dwarf2out_as_locview_support);
> + && !dwarf_strict);
> }
> else if (debug_variable_location_views == -1 && dwarf_version != 5)
> {
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)
