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| -rw-r--r-- | qemu-doc.texi | 34 | ||||
| -rw-r--r-- | qemu-tech.texi | 71 |
2 files changed, 34 insertions, 71 deletions
diff --git a/qemu-doc.texi b/qemu-doc.texi index e60c46b5c9..227c2b0b45 100644 --- a/qemu-doc.texi +++ b/qemu-doc.texi @@ -2629,6 +2629,7 @@ so should only be used with trusted guest OS. @menu * Supported Operating Systems :: +* Features:: * Linux User space emulator:: * BSD User space emulator :: @end menu @@ -2645,6 +2646,39 @@ Linux (referred as qemu-linux-user) BSD (referred as qemu-bsd-user) @end itemize +@node Features +@section Features + +QEMU user space emulation has the following notable features: + +@table @strong +@item System call translation: +QEMU includes a generic system call translator. This means that +the parameters of the system calls can be converted to fix +endianness and 32/64-bit mismatches between hosts and targets. +IOCTLs can be converted too. + +@item POSIX signal handling: +QEMU can redirect to the running program all signals coming from +the host (such as @code{SIGALRM}), as well as synthesize signals from +virtual CPU exceptions (for example @code{SIGFPE} when the program +executes a division by zero). + +QEMU relies on the host kernel to emulate most signal system +calls, for example to emulate the signal mask. On Linux, QEMU +supports both normal and real-time signals. + +@item Threading: +On Linux, QEMU can emulate the @code{clone} syscall and create a real +host thread (with a separate virtual CPU) for each emulated thread. +Note that not all targets currently emulate atomic operations correctly. +x86 and ARM use a global lock in order to preserve their semantics. +@end table + +QEMU was conceived so that ultimately it can emulate itself. Although +it is not very useful, it is an important test to show the power of the +emulator. + @node Linux User space emulator @section Linux User space emulator diff --git a/qemu-tech.texi b/qemu-tech.texi index 75ceea408c..16780a1503 100644 --- a/qemu-tech.texi +++ b/qemu-tech.texi @@ -221,8 +221,6 @@ SH4 * Exception support:: * MMU emulation:: * Device emulation:: -* Hardware interrupts:: -* User emulation specific details:: * Bibliography:: @end menu @@ -410,75 +408,6 @@ Usually the devices implement a reset method and register support for saving and loading of the device state. The devices can also use timers, especially together with the use of bottom halves (BHs). -@node Hardware interrupts -@section Hardware interrupts - -In order to be faster, QEMU does not check at every basic block if a -hardware interrupt is pending. Instead, the user must asynchronously -call a specific function to tell that an interrupt is pending. This -function resets the chaining of the currently executing basic -block. It ensures that the execution will return soon in the main loop -of the CPU emulator. Then the main loop can test if the interrupt is -pending and handle it. - -@node User emulation specific details -@section User emulation specific details - -@subsection Linux system call translation - -QEMU includes a generic system call translator for Linux. It means that -the parameters of the system calls can be converted to fix the -endianness and 32/64 bit issues. The IOCTLs are converted with a generic -type description system (see @file{ioctls.h} and @file{thunk.c}). - -QEMU supports host CPUs which have pages bigger than 4KB. It records all -the mappings the process does and try to emulated the @code{mmap()} -system calls in cases where the host @code{mmap()} call would fail -because of bad page alignment. - -@subsection Linux signals - -Normal and real-time signals are queued along with their information -(@code{siginfo_t}) as it is done in the Linux kernel. Then an interrupt -request is done to the virtual CPU. When it is interrupted, one queued -signal is handled by generating a stack frame in the virtual CPU as the -Linux kernel does. The @code{sigreturn()} system call is emulated to return -from the virtual signal handler. - -Some signals (such as SIGALRM) directly come from the host. Other -signals are synthesized from the virtual CPU exceptions such as SIGFPE -when a division by zero is done (see @code{main.c:cpu_loop()}). - -The blocked signal mask is still handled by the host Linux kernel so -that most signal system calls can be redirected directly to the host -Linux kernel. Only the @code{sigaction()} and @code{sigreturn()} system -calls need to be fully emulated (see @file{signal.c}). - -@subsection clone() system call and threads - -The Linux clone() system call is usually used to create a thread. QEMU -uses the host clone() system call so that real host threads are created -for each emulated thread. One virtual CPU instance is created for each -thread. - -The virtual x86 CPU atomic operations are emulated with a global lock so -that their semantic is preserved. - -Note that currently there are still some locking issues in QEMU. In -particular, the translated cache flush is not protected yet against -reentrancy. - -@subsection Self-virtualization - -QEMU was conceived so that ultimately it can emulate itself. Although -it is not very useful, it is an important test to show the power of the -emulator. - -Achieving self-virtualization is not easy because there may be address -space conflicts. QEMU user emulators solve this problem by being an -executable ELF shared object as the ld-linux.so ELF interpreter. That -way, it can be relocated at load time. - @node Bibliography @section Bibliography |