sh: handle Linux core notes in the generic ELF vector
Improves SH core file support by prioritizing targets that correctly handle core note information.
This patch addresses a bug in the SH target’s ELF core file handling where the default elf32-shl target was chosen over elf32-sh-linux, leading to incorrect core file interpretation and missing register information for GDB. The fix modifies bfd_check_format_matches to prefer targets with a higher section count when multiple targets match equally, thus prioritizing elf32-sh-linux and resolving the issue.
- contributor
Explains the problem: Linux SH core files were not correctly parsed due to target matching priority, leading to missing register information.
“A Linux sh core file matches elf32-shl, elf32-sh-linux, elf32-shl-nbsd and elf32-shl-vxworks with equal priority, and bfd_check_format_matches picks the first, elf32-shl. Only the Linux vector handled NT_PRSTATUS and NT_PRPSINFO notes, so the core had no .reg section and gdb found no registers.”
- proposer
Proposes a solution to improve target selection for SH ELF core files by prioritizing targets with more sections when ambiguity arises.
“This patch aims to improve core file support in cases where binutils was configured with the target needed to interpret notes not being the default target. In such cases multiple targets may match the object file with nothing to choose between them. As per the PR, elf32-shl, elf32-sh-linux, elf32-shl-nbsd and elf32-shl-vxworks all match with the same priority,”
Technical Tradeoffs
- Prioritizing targets by section count is a heuristic that improves correctness for SH core files but might not be universally optimal for all ELF targets.
- The change aims to fix a specific bug rather than refactor the entire target matching logic, which could be more complex.
In Details
This patch modifies bfd_check_format_matches for the SH target. Previously, when multiple targets (e.g., elf32-shl, elf32-sh-linux) had equal priority, elf32-shl was chosen. This is problematic because only elf32-sh-linux correctly parses NT_PRSTATUS/NT_PRPSINFO notes, essential for GDB register information. The change prioritizes targets with more sections to ensure the correct SH Linux core file format is selected.
- core notes
- Sections within a core dump file that contain auxiliary information about the process state, such as process status (NT_PRSTATUS) or process information (NT_PRPSINFO).
- ELF
- Executable and Linkable Format, a standard file format for object files, executable files, shared libraries, and core dumps on many Unix-like systems.
- bfd_check_format_matches
- A function within the BFD library responsible for determining which target format best matches an input object file when multiple formats could potentially apply.
- target
- In the context of binutils, a 'target' refers to a specific architecture and operating system configuration (e.g., 'sh-linux'). Different targets have different ways of structuring object files and interpreting debugging information.