Implement Structured Exception Handling (SEH) on AArch64
Evgeny Karpov submits v11 of a patch series to implement SEH on AArch64, including big-endian host support and fixes.
Evgeny Karpov presents the eleventh version of a patch series aimed at implementing Structured Exception Handling (SEH) for the AArch64 architecture in Binutils. This version incorporates support for big-endian hosts, fixes a ‘phantom prologue’ encoding issue, and includes other minor refinements. Previous versions addressed indentation, limitations, unwinding information reordering, register validation, renaming, and added extensive SEH tests.
- proposer
Submits v11 of the SEH implementation for AArch64, detailing changes including big-endian support and bug fixes.
“Hello, Thank you for reviewing v10! v11 contains support for big endian host, a fix for phantom prologue and some other minor changes.”
- proposer
Describes the implementation's reliance on shared helpers and Microsoft's SEH documentation.
“The patch reuses shared helpers for SEH and implements SEH on AArch64. The implementation is based on (https://learn.microsoft.com/en-us/cpp/build/arm64-exception-handling?view=msvc-170) and pdata/xdata SEH records are emitted from md_finish.”
Technical Tradeoffs
- Support for big-endian hosts adds complexity to the implementation.
- Correctly encoding exception handling information (pdata/xdata) requires careful handling of function sizes and unwind codes.
In Details
Evgeny Karpov's v11 patch series introduces AArch64 support for Structured Exception Handling (SEH) into Binutils, primarily targeting the assembler (gas). This implementation aligns with Microsoft's AArch64 SEH model, generating .pdata and .xdata records during the md_finish phase. Key challenges include calculating function sizes on big-endian hosts and ensuring correct prologue/epilogue unwinding codes. This work is crucial for enabling SEH-compliant C++ exception handling on AArch64 targets within the GCC toolchain ecosystem.
- SEH
- Structured Exception Handling. A mechanism for handling runtime errors and exceptions, commonly used on Windows platforms. This patch brings SEH support to AArch64.
- AArch64
- The 64-bit ARM architecture.
- Binutils
- A collection of binary manipulation tools, including the GNU assembler (
gas), linker (ld), and others, essential for software development. - big endian
- A byte order where the most significant byte is stored at the lowest memory address.
- phantom prologue
- A specific encoding issue related to exception handling prologues that needs to be handled correctly for SEH.
- .pdata/.xdata
- Sections in PE/COFF object files that store exception handling information, including function prologue/epilogue details and unwind codes.
- unwinding
- The process of moving up the call stack during exception handling to find a suitable handler.
- md_finish
- Likely refers to the end of the machine description phase in the assembler, where final output sections like exception handling data are generated.