OvmfPkg: Replace include guards with #pragma once

2026-02-23T21:01:28+00:00

Replace traditional `#ifndef`/`#define`/`#endif` include guards with `#pragma` once. `#pragma once` is a widely supported preprocessor directive that prevents header files from being included multiple times. It is supported by all toolchains used to build edk2: GCC, Clang/LLVM, and MSVC. Note: Headers taken directly from external projects, such as those in OvmfPkg/Include/IndustryStandard/Xen/ were not modified since they may be periodically re-synced and do not follow other edk2 coding stadards. Compared to macro-based include guards, `#pragma once`: - Eliminates the risk of macro name collisions or copy/paste errors where two headers inadvertently use the same guard macro. - Eliminate inconsistency in the way include guard macros are named (e.g., some files use `__FILE_H__`, others use `FILE_H_`, etc.). - Reduces boilerplate (three lines replaced by one). - Avoids polluting the macro namespace with guard symbols. - Can improve build times as the preprocessor can skip re-opening the file entirely, rather than re-reading it to find the matching `#endif` ("multiple-include optimization"). - Note that some compilers may already optimize traditional include guards, by recognzining the idiomatic pattern. This change is made acknowledging that overall portability of the code will technically be reduced, as `#pragma once` is not part of the C/C++ standards. However, this is considered acceptable given: 1. edk2 already defines a subset of supported compilers in BaseTools/Conf/tools_def.template, all of which have supported `#pragma once` for over two decades. 2. There have been concerns raised to the project about inconsistent include guard naming and potential macro collisions. Approximate compiler support dates: - MSVC: Supported since Visual C++ 4.2 (1996) - GCC: Supported since 3.4 (2004) (http://gnu.ist.utl.pt/software/gcc/gcc-3.4/changes.html) - Clang (LLVM based): Since initial release in 2007 Signed-off-by: Michael Kubacki

OvmfPkg: Add library to handle TPL from within nested interrupt handlers

2022-12-23T14:44:48+00:00

UEFI requires us to support nested interrupts, but provides no way for an interrupt handler to call RestoreTPL() without implicitly re-enabling interrupts. In a virtual machine, it is possible for a large burst of interrupts to arrive. We must prevent such a burst from leading to stack underrun, while continuing to allow nested interrupts to occur. This can be achieved by allowing, when provably safe to do so, an inner interrupt handler to return from the interrupt without restoring the TPL and with interrupts remaining disabled after IRET, with the deferred call to RestoreTPL() then being issued from the outer interrupt handler. This is necessarily messy and involves direct manipulation of the interrupt stack frame, and so should not be implemented as open-coded logic within each interrupt handler. Add the Nested Interrupt TPL Library (NestedInterruptTplLib) to provide helper functions that can be used by nested interrupt handlers in place of RaiseTPL()/RestoreTPL(). Example call tree for a timer interrupt occurring at TPL_APPLICATION with a nested timer interrupt that makes its own call to RestoreTPL(): outer TimerInterruptHandler() InterruptedTPL == TPL_APPLICATION ... IsrState->InProgressRestoreTPL = TPL_APPLICATION; gBS->RestoreTPL (TPL_APPLICATION); EnableInterrupts(); dispatch a TPL_CALLBACK event gEfiCurrentTpl = TPL_CALLBACK; nested timer interrupt occurs inner TimerInterruptHandler() InterruptedTPL == TPL_CALLBACK ... IsrState->InProgressRestoreTPL = TPL_CALLBACK; gBS->RestoreTPL (TPL_CALLBACK); EnableInterrupts(); DisableInterrupts(); IsrState->InProgressRestoreTPL = TPL_APPLICATION; IRET re-enables interrupts ... finish dispatching TPL_CALLBACK events ... gEfiCurrentTpl = TPL_APPLICATION; DisableInterrupts(); IsrState->InProgressRestoreTPL = 0; sees IsrState->DeferredRestoreTPL == FALSE and returns IRET re-enables interrupts Example call tree for a timer interrupt occurring at TPL_APPLICATION with a nested timer interrupt that defers its call to RestoreTPL() to the outer instance of the interrupt handler: outer TimerInterruptHandler() InterruptedTPL == TPL_APPLICATION ... IsrState->InProgressRestoreTPL = TPL_APPLICATION; gBS->RestoreTPL (TPL_APPLICATION); EnableInterrupts(); dispatch a TPL_CALLBACK event ... finish dispatching TPL_CALLBACK events ... gEfiCurrentTpl = TPL_APPLICATION; nested timer interrupt occurs inner TimerInterruptHandler() InterruptedTPL == TPL_APPLICATION; ... sees InterruptedTPL == IsrState->InProgressRestoreTPL IsrState->DeferredRestoreTPL = TRUE; DisableInterruptsOnIret(); IRET returns without re-enabling interrupts DisableInterrupts(); IsrState->InProgressRestoreTPL = 0; sees IsrState->DeferredRestoreTPL == TRUE and loops IsrState->InProgressRestoreTPL = TPL_APPLICATION; gBS->RestoreTPL (TPL_APPLICATION); <-- deferred call EnableInterrupts(); DisableInterrupts(); IsrState->InProgressRestoreTPL = 0; sees IsrState->DeferredRestoreTPL == FALSE and returns IRET re-enables interrupts Cc: Paolo Bonzini Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=4162 Signed-off-by: Michael Brown Acked-by: Laszlo Ersek

Tianocore/edk2.git/OvmfPkg/Include/Library/NestedInterruptTplLib.h, branch master

OvmfPkg: Replace include guards with #pragma once

OvmfPkg: Add library to handle TPL from within nested interrupt handlers