With CONFIG_DRM_USE_DYNAMIC_DEBUG=y, several build configs had problems with __dyndbg* sections getting lost in drm drivers. Fix this by following the model demonstrated in codetag.lds.h.
Introduce include/asm-generic/dyndbg.lds.h, to bundle dynamic-debug's multiple sections together, into 2 macros: vmlinux.lds.h DATA_DATA: move the 2 BOUNDED_SECTION_BY(__dyndbg*) calls into dyndbg.lds.h DYNDBG_SECTIONS(). vmlinux.lds.h now includes the new file and calls the new macro. MOD_DYNDBG_SECTIONS declares the 2 BOUNDED_SECTION_BY calls, but wraps them with output section syntax to keep them as known and separate ELF sections in the module.ko. The KEEP fixes the lost section. dyndbg.lds.h includes (reuses) bounded-section.lds.h scripts/module.lds.S: now calls MOD_DYNDBG_SECTIONS right before the CODETAG macro (consistent with their placements in vmlinux.lds.h), and also includes dyndbg.lds.h This isolates vmlinux.lds.h from further __dyndbg section additions. CC: Arnd Bergmann <[email protected]> Signed-off-by: Jim Cromie <[email protected]> --- v2 - Address linker script review feedback for relocatable modules. v1 of MOD_DYNDBG_SECTIONS() used the BOUNDED_SECTION_BY() macro, which proved problematic for kernel modules for two reasons: 1. Unwanted Empty Sections: BOUNDED_SECTION_BY() automatically generates `__start` and `__stop` symbols. When applied to `MOD_DYNDBG_SECTIONS()`, the linker assumes the sections are populated due to the symbol definitions, forcing an empty `__dyndbg` and `__dyndbg_classes` output section in every compiled module, even those without dynamic debug configuration. Since the module loader uses `section_objs()` to locate data via ELF headers instead of relying on `__start`/`__stop` symbols, these assignments are completely unnecessary. 2. Non-zero Output Addresses: During relocatable linking (e.g., `ld.bfd -r`), omitting an explicit base address causes the section to inherit the current location counter. This results in non-zero sh_addr values in `.ko` files, which is confusing, degrades compressibility, and can cause issues with external tools parsing the ELF. Fix both issues by dropping `BOUNDED_SECTION_BY()` in favor of a simple `KEEP(*(...))` constraint and explicitly defining the sections with a `0` base address: `__dyndbg 0 : ALIGN(8) { ... }`. --- MAINTAINERS | 1 + include/asm-generic/dyndbg.lds.h | 19 +++++++++++++++++++ include/asm-generic/vmlinux.lds.h | 6 ++---- scripts/module.lds.S | 2 ++ 4 files changed, 24 insertions(+), 4 deletions(-) diff --git a/MAINTAINERS b/MAINTAINERS index 882214b0e7db..54bb257b60ee 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -9070,6 +9070,7 @@ DYNAMIC DEBUG M: Jason Baron <[email protected]> M: Jim Cromie <[email protected]> S: Maintained +F: include/asm-generic/dyndbg.lds.h F: include/linux/dynamic_debug.h F: lib/dynamic_debug.c F: lib/test_dynamic_debug.c diff --git a/include/asm-generic/dyndbg.lds.h b/include/asm-generic/dyndbg.lds.h new file mode 100644 index 000000000000..844f1cb82020 --- /dev/null +++ b/include/asm-generic/dyndbg.lds.h @@ -0,0 +1,19 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +#ifndef __ASM_GENERIC_DYNDBG_LDS_H +#define __ASM_GENERIC_DYNDBG_LDS_H + +#include <asm-generic/bounded_sections.lds.h> +#define DYNDBG_SECTIONS() \ + . = ALIGN(8); \ + BOUNDED_SECTION_BY(__dyndbg, ___dyndbg) \ + BOUNDED_SECTION_BY(__dyndbg_classes, ___dyndbg_classes) + +#define MOD_DYNDBG_SECTIONS() \ + __dyndbg 0 : ALIGN(8) { \ + KEEP(*(__dyndbg)) \ + } \ + __dyndbg_classes 0 : ALIGN(8) { \ + KEEP(*(__dyndbg_classes)) \ + } + +#endif /* __ASM_GENERIC_DYNDBG_LDS_H */ diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index d9d2eb708355..54897d742c6c 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -332,6 +332,7 @@ /* * .data section */ +#include <asm-generic/dyndbg.lds.h> #define DATA_DATA \ *(.xiptext) \ *(DATA_MAIN) \ @@ -345,10 +346,7 @@ *(.data..do_once) \ STRUCT_ALIGN(); \ *(__tracepoints) \ - /* implement dynamic printk debug */ \ - . = ALIGN(8); \ - BOUNDED_SECTION_BY(__dyndbg_classes, ___dyndbg_classes) \ - BOUNDED_SECTION_BY(__dyndbg, ___dyndbg) \ + DYNDBG_SECTIONS() \ CODETAG_SECTIONS() \ LIKELY_PROFILE() \ BRANCH_PROFILE() \ diff --git a/scripts/module.lds.S b/scripts/module.lds.S index b62683061d79..2e62dc5bd5d4 100644 --- a/scripts/module.lds.S +++ b/scripts/module.lds.S @@ -10,6 +10,7 @@ #endif #include <asm-generic/codetag.lds.h> +#include <asm-generic/dyndbg.lds.h> SECTIONS { /DISCARD/ : { @@ -61,6 +62,7 @@ SECTIONS { *(.rodata..L*) } + MOD_DYNDBG_SECTIONS() MOD_SEPARATE_CODETAG_SECTIONS() } -- 2.54.0
