https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126277
Bug ID: 126277
Summary: gcobol: DEBUG-* special registers reference missing
`__gg__data_debug_*` symbols
Product: gcc
Version: 17.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: cobol
Assignee: unassigned at gcc dot gnu.org
Reporter: peeterjoot at protonmail dot com
Target Milestone: ---
Created attachment 65054
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=65054&action=edit
debug-register-data-symbol.cob from the report above (also specified inline)
# Summary
Any program that references a Debug-module special register (`DEBUG-LINE`,
`DEBUG-NAME`, `DEBUG-CONTENTS`, …) **compiles** but **fails to link** with:
```
undefined reference to `__gg__data_debug_line'
```
(and likewise `__gg__data_debug_name` when that register is used).
The frontend and `libgcobol` disagree on the external symbol name for the
runtime data of these registers. Other special registers (`SPACE`, `ZEROS`, …)
pair `__ggsr__*` metadata with a matching `__gg__data_*` buffer; `DEBUG-*`
fields use a shared buffer named `__gg__debug_item_data` instead, so the
`__gg__data_debug_*` symbols the frontend emits do not exist.
# Environment
- Compiler: gcobol from GCC trunk (`gcobol (GCC) 17.0.0 20260710
(experimental)`)
- Also observed with the packaged Ubuntu gcobol when Debug special registers
are referenced
- Platform: Linux aarch64 (also expected on x86-64)
- No special options required
# Reproducer
`debug-register-data-symbol.cob` (in this directory):
```cobol
IDENTIFICATION DIVISION.
PROGRAM-ID. DBGLINE.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 WS-LINE PIC X(6).
PROCEDURE DIVISION.
MOVE DEBUG-LINE TO WS-LINE
DISPLAY WS-LINE
STOP RUN.
```
```
gcobol -o /tmp/dbgline debug-register-data-symbol.cob
```
(A `USE FOR DEBUGGING` declarative that MOVEs `DEBUG-LINE` / `DEBUG-NAME` hits
the same undefined symbols; NIST COBOL85 `DB101A`–`DB104A` / `DB204A` fail this
way.)
# Observed
Compile of the COBOL source succeeds; the link step fails:
```
undefined reference to `__gg__data_debug_line'
collect2: error: ld returned 1 exit status
```
Installed `libgcobol` exports (via `nm -D`):
```
D __gg__debug_item_data
D __ggsr__debug_item
D __ggsr__debug_line
D __ggsr__debug_name
D __ggsr__debug_contents
…
```
but **not** `__gg__data_debug_line` / `__gg__data_debug_name` / …
For comparison, ordinary special registers do export both sides, e.g.
`__ggsr__space` + `__gg__data_space`.
# Expected
The program links and runs. Reading `DEBUG-LINE` should use the existing
runtime register backed by `__gg__debug_item_data` (offset 0 within the
`DEBUG-ITEM` group), the same storage `__ggsr__debug_line.data` already points
at in `libgcobol/constants.cc`.
# Root cause (frontend / libgcobol mismatch)
In `gcc/cobol/genapi.cc`, `psa_global()` declares two externals for every
special register:
1. `__ggsr__<name>` — the `cblc_field_t` (this matches `libgcobol`)
2. `__gg__data_<name>` — a presumed dedicated data buffer
```c
// finding their name … "__ggsr__" is prepended
snprintf(ach, sizeof(ach), "__ggsr__%s", new_var->name);
…
new_var->var_decl_node = gg_declare_variable(…, ach, …,
vs_external_reference);
strcpy(ach, "__gg__data_");
strcat(ach, new_var->name);
…
new_var->data_decl_node = gg_declare_variable(UCHAR, ach, …,
vs_external_reference);
```
In `libgcobol/constants.cc`, the Debug registers are **not** given per-field
`__gg__data_*` buffers. The whole `DEBUG-ITEM` group shares one array:
```c
unsigned char __gg__debug_item_data[132] = …;
struct cblc_field_t __ggsr__debug_line = {
.data = __gg__debug_item_data + 0,
…
};
struct cblc_field_t __ggsr__debug_name = {
.data = __gg__debug_item_data + 7,
…
};
```
So the linker finds `__ggsr__debug_line` but not `__gg__data_debug_line`.
`symbols.cc` also notes that special registers must be kept in sync with
`constants.cc`:
> When adding special registers, be sure to create the actual cblc_field_t
> in libgcobol/constants.cc.
The metadata side was added; the `__gg__data_*` naming expected by `psa_global`
was not.
# Suggested fix (either side)
1. **libgcobol:** export `__gg__data_debug_line` (etc.) as aliases / symbols at
the appropriate offsets into `__gg__debug_item_data` (and likely
`__gg__data_debug_item` for the group), matching the convention used for
`SPACE`/`ZEROS`; or
2. **Frontend (`psa_global`):** for `DEBUG-*` registers, reference
`__gg__debug_item_data` (plus offset) instead of synthesizing
`__gg__data_<name>`.
# Impact
Programs that use the Debug module special registers — including the NIST
COBOL85 Debug-module tests that successfully parse `USE FOR DEBUGGING` —
cannot be linked. Found while attempting to build the NIST COBOL85 suite with
gcobol.
# Disclaimer:
The root cause analysis for this bug report was generated by cursor, when I
pointed it at the gcc repo to help understand the link error -- I have not
vouched for it's correctness.
